Article

Flue Gas Desulfurization (FGD) Wastewater Pilot Test Results

Photo comparison of FGD wastewater, one container is brown, murky and the second is clear and colorless water.

FlexEDR Selective FGD Wastewater Pilot Test Results

Mar 19th 2019

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Project Summary

Saltworks Technologies Inc. (Saltworks) completed an off-site FlexEDR Selective pilot test to treat flue gas desulfurization (FGD) wastewater from a coal fired power plant in China. The objective was to reduce chlorides such that the FGD wastewater could be internally recycled and final treatment costs reduced notably. FGD wastewater is generated and released primarily due to chloride content that inhibits sulfur absorption in the stack and can cause corrosion problems. If chlorides can be removed, the FGD wastewater can be recycled.

The results showed that Saltworks FlexEDR Selective achieved:

  • Reliable treatment built from the second most common membrane desalination technology – electrodialysis reversal (EDR) – with modernized membranes and process controls.
  • 90% recovery on a highly scaling calcium sulfate FGD wastewater without the need for expensive soda ash softening. The system produced a predominantly calcium chloride brine with 127,000 mg/L total dissolved solids (TDS) concentration. The brine could be directly solidified with fly ash and other solidification agents for zero liquid discharge, eliminating the need for a crystallizer.
  • Removed 78% of the chlorides with ease: treated water from ~6,900 mg/L chlorides to less than 1,500 mg/L, such that it could be recycled back to the FGD system.

For the complete results of the pilot including detailed water chemistry and cost, download the free case study below.

Download the free FGD wastewater pilot results

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About Saltworks

Saltworks Technologies is a leader in the development and delivery of solutions for industrial wastewater treatment and lithium refining. By working with customers to understand their unique challenges and focusing on continuous innovation, Saltworks’ solutions provide best-in-class performance and reliability. From its headquarters in Richmond, BC, Canada, Saltworks’ team designs, builds, and operates full-scale plants, and offers comprehensive onsite and offsite testing services with its fleet of mobile pilots.

Related Resources

A photo of a wastewater disposal truck used in brine management
Article

How to Manage Brine Disposal & Treatment

The many options for managing brine, a term for saline wastewater from industrial processes, fall under two categories: brine treatment and brine disposal. Brine treatment involves desalinating the brine for reuse and producing a concentrated brine (lower liquid waste volume), or residual solids (zero liquid discharge).

A process flow diagram showing the cost-effective treatment and safe discharge of sulfates
Article

Sulfate Discharge: Measurement and Cost-Optimized Removal

There are many sulfate treatments available, with different advantages and disadvantages. Factors for consideration include capital and operational costs, solid vs. liquid brine reject for disposal, if the need is seasonal or year-round, and suitability for adverse operating conditions.

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Applying Ultra-High Pressure Reverse Osmosis in Brine Management

Process flow diagram of a high pressure recirculation pump used to minimize energy and increase membrane cross flow

Applying Ultra-High Pressure Reverse Osmosis in Brine Management

Mar 21st 2023

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Key Takeaways

  • New ultra-high pressure reverse osmosis technology for minimal liquid discharge (MLD) can reduce brine management costs by three times relative to evaporators.
  • Now rated for 1,740 psi, new UHP RO spiral wound membranes achieve 1.6x brine volume reduction over previous 1,200 psi seawater (SWRO) RO membranes, as long as membrane scaling and fouling are managed.
  • Modernized chemical softening technology is available to prevent scaling and enable recovery up to the osmotic pressure limit at 1,200 or 1,740 psi.
  • Learn to compare spiral wound vs disk tube (DTRO) systems for ultra-high pressure operation to select the best option for your system.

New ultra-high pressure reverse osmosis (UHP RO) membrane elements are entering the market, rated for 50% higher pressures than previously available. These 1,740 psi (120 bar) membranes raise the practical osmotic pressure and brine concentration limit to 130,000 mg/L total dissolved solids (TDS). This is a 1.6x increase relative to conventional “seawater” RO membranes rated for 1,200 psi (80 bar), which tap out at roughly 80,000 mg/L TDS. However, there are important design and technical considerations, which we review in this article.

 

Saltworks is one vendor that offers these new membrane systems. Our product, XtremeRO, delivers the latest UHP RO membrane technology in a reliable, low cost, modularized package. It incorporates all of the important design considerations below, in addition to proprietary enabling features, and expert knowledge.

UHP RO as a Brine Concentrator

Reverse osmosis is the most widely commoditized, cost effective, and lowest energy desalination technology; however, it has limits. These limits can include sensitivity to organics, oxidants, scaling ions, and declining productivity with increasing salinity (TDS). As the brine concentration increases, flux through the membrane and permeate quality decrease. This is shown below in  Figure 1. The data in Figure 1 was gathered on a pilot plant developed by Saltworks, based on 4” membrane elements, shown in Figure 2. Two leading manufacturers’ membrane products were tested. Similar relationships in flux were observed but one company produced high-quality permeate in a membrane element with more reliable and consistent performance. Saltworks builds this knowledge into our XtremeRO reverse osmosis systems for our customers.

Chart showing UHP RO flux and permeate quality with reject brine TDS
Figure 1: UHP RO flux and permeate quality with reject brine TDS. See text for explanations.

The increase in permeate salinity with brine concentration is expected. The RO membrane surface rejects a percentage of salt, for example 99.8%. This means roughly 0.2% of salt permeates through the membrane with the water. Naturally, at higher brine concentration more salt gets through the membrane. Also, operation at lower flux results in lower rejection. The slightly higher salinity permeate can be blended with other lower salinity permeates, using as flush source for upstream ROs, or further refined in a low-pressure polishing RO process. The primary objective and cost driver when applying UHP RO should be brine concentration and volume reduction.

 

Figure 1 also shows the flux declining at higher salinity. Flux values in liters per m2 per hour (LMH) represent proprietary knowledge available only to Saltworks’ customers and partners. Nevertheless, the lower flux trend in Figure 1 is clear and translates into the need for either higher pressure, more membrane area, or both. With the advent of new 1,740 psi UHP RO membranes, designers can apply higher pressures to improve flux at higher TDS, and ultimately concentrate a sodium chloride solution to 130,000 mg/L TDS. If sulfates are present as an appreciable mass fraction, the brine concentration limit increases up to 160,000 mg/L TDS. At these high TDS ranges, flux decreased by three times relative to RO systems operating at 30-60K mg/L TDS. This means more membrane elements, pressure vessels, and pipework in addition to the higher pressure rated equipment.

 

Ultimately, capital cost of UHP RO systems is notably higher than the cost of brackish or seawater RO systems (SWRO). Although more expensive than SWRO, UHP RO still has a much lower cost than thermal evaporators. For this reason, UHP RO can be applied upstream of evaporators, to reduce capacity and energy of more expensive evaporation, or reduce volumes sent to disposal or evaporation ponds. It is important to keep in mind that evaporators can achieve higher brine concentrations and produce lower volumes than UHP RO. For larger flow rates, a combination of technologies, each operating at an optimum capacity, may be the most economical. Typical brine concentration limits and volume reduction ratios are summarized in Table 1.

Table 1: Typical brine concentration limits and volume reduction ratios

Technology TDS Brine Limit (mg/L) Brine Volume Reduction Relative to SWRO
SWRO (1,200 psi) 80,000 1.0x
UHP RO (1,800 psi) 130,000 1.6x
Conventional Evaporator (thermal or MVR) 220,000 2.8x
SaltMaker Evaporator (thermal) 450,000 or solids 5.6x

UHP RO vs DTRO

Reverse osmosis systems have been capable of 1,740 psi operation for a number of years as disk tube RO (DTRO) technology. DTRO employs the same membrane material as SWRO, with the membranes arranged as a series of vertically stacked disks in specialty pressure vessels. The primary benefit of UHP RO is that the membranes are spiral wound—the most widely applied RO technology included in every seawater RO desalination plant worldwide. DTRO is a specialty niche manufactured product, while spiral wound RO membranes are widely produced, available and interchangeable from multiple manufacturers. 

 

Figures 2 to 5 compare spiral wound and DTRO membrane construction.

Image showing a spiral wound reverse osmosis membrane
Figure 2: Lateral flow over spiral wound membranes
Graphic showing the inner workings of DTRO membranes
Figure 3: DTRO membranes (radial flow over membrane disks)
Photo of a reverse osmosis membrane system
Figure 4: Spiral wound membrane system (common)
Photo of a DTRO reverse osmosis membrane system
Figure 5: DTRO membrane system (niche)

Spiral wound membranes have captured over 99% of the global RO membrane market share. Their production has been perfected over the years, resulting in lower cost, high quality, and broad availability. In addition, spiral wound membranes make use of the most common 4” or 8” pressure vessels used in RO, versus a specialty product. Put simply, the end user deciding between either spiral wound or disk tube RO should consider if they prefer commonplace or specialty products. Spiral wound membranes are employed in over 95% of all global desalination plants. DTRO offers some claimed shear benefits and the ability to operate on more turbid waters; however, a well built spiral wound system with high membrane cross flow can achieve the same. Saltworks builds our XtremeRO systems with spiral wound membranes to assure the customer a widely available product that is not dependant on a single manufacturer. We also build in chemical, process, and mechanical considerations that are required to maintain membrane longevity.

Realizing UHP RO's Full Potential

When reaching for ultra-high recovery, scaling ions and organics are concentrated to very high levels. Combined with the ultra-high pressure, they can impinge on the membrane surface at a high force. One must be extremely cautious to manage any membrane scaling or fouling risk. Organics may require a combination of pre-treatment, or a Saltworks continuous-removal approach that is optionally built into XtremeRO. As for removing scaling ions that can block the membrane surface, a variety of both mechanical and chemical methods are available. First, one must know the scaling ion concentration and its solubility. The solubility of scaling ions can be reviewed on our Periodic Table of Scaling Elements. If scaling ions can exceed four times their solubility in the RO brine, even with anti-scalants, they should be reduced to a safe level.

One method of removing scaling ions is to apply a chemical softening technology, such as BrineRefine, to remove or reduce ions such as silica and calcium. When chemical softening is applied before RO, it is important to:

 

  • Adjust dosages to only remove the “right” amount of scaling ions; increased dosages may not increase recovery but will translate into higher chemical cost and increased generation of filter cake waste.
  • Avoid use of coagulants, since they can foul RO membranes.
  • Filter out any precipitant to maintain the RO silt density index specification, and lower pH during RO operation to prevent carbonate scale issues.
  • Consider if the upstream chemistry or flow rate could vary, and how the chemical softening will adjust—via automation or human intervention—with reliability of the latter occasionally being questionable.

BrineRefine technology manages all of the above. It was specifically developed to be paired with ultra-high recovery RO systems, as described in this article. In addition to chemical matters, hydraulics and energy are also important considerations. Hydraulically, designers should aim for high cross flows, which provide high brine velocity to wash away any boundary layers of stagnant water next to the membrane surface where scale and fouling can occur. Steps can be taken to reduce energy.

 

Although energy recovery devices (ERDs) rated for 1,740 psi do not exist yet, an ERD can be avoided and additional benefits realized by including a high-pressure circulation pump as shown below. The high-pressure recirculation pump recycles and upgrades the pressure of a portion of the RO brine. This prevents the breaking of all of the brine’s high-pressure energy before recirculation, lowers feed pump energy, and also beneficially improves cross flow velocity across the membrane surface. Saltworks’ XtremeRO incorporates all of these considerations. If the reader would like to learn more about state-of-the-art, technological advancements in RO design, they can read this accompanying article. 

High-pressure recirculation pump to minimize energy and increase membrane cross flow.

Important engineering considerations also include:

 

  • Pressure vessels: products are emerging that are capable of 1,800 psi operation, with an ASME-level safety factor, yet the ASME code stops at 1,500 psi.
  • Reciprocating pumps for 1,800 psi operation: these exist on the market, but one needs to be conscious of pump metallurgy to avoid corrosion in the ultra-high chloride environment of UHP RO.
  • Fouling and membrane compaction: this should be considered when determining pump sizing.
  • Actual pressure limits that are influenced by temperature: feedwater temperatures above 30 °C will result in lower pressure limits.
  • All high-pressure pipework: this must be designed and certified for use.
  • Membrane cleaning and servicing: think about this ahead of time, including consideration of automated flush and chemical cleans in place (CIP).

Saltworks considers all of the above and more when designing an XtremeRO system for our clients. We welcome the opportunity to work with partners, including integrating with an upstream lower-pressure RO that may release a scaling brine. The figure below shows an example system where an existing RO-1 is in place, but additional recovery of brine volume is desired. This is accomplished by the integration of BrineRefine and a second RO-2 optionally employing UHP RO technology. This system has built-in intelligence to continuously adjust operation to prevent scale formation and ensure peak performance, while also communicating between upstream and downstream treatment assets to deliver value to your entire treatment train. As a result, minimal liquid discharge (MLD) and peak RO brine concentrations of 130,000 mg/L TDS are achieved.

XtremeRO enabled by BrineRefine

Contact Saltworks to review options for your project. All we need is your chemistry and capacity, or a live water sample for testing at our lab.

About Saltworks

Saltworks Technologies is a leader in the development and delivery of solutions for industrial wastewater treatment and lithium refining. By working with customers to understand their unique challenges and focusing on continuous innovation, Saltworks’ solutions provide best-in-class performance and reliability. From its headquarters in Richmond, BC, Canada, Saltworks’ team designs, builds, and operates full-scale plants, and offers comprehensive onsite and offsite testing services with its fleet of mobile pilots.

Related Resources

A photo of a wastewater disposal truck used in brine management
Article

How to Manage Brine Disposal & Treatment

The many options for managing brine, a term for saline wastewater from industrial processes, fall under two categories: brine treatment and brine disposal. Brine treatment involves desalinating the brine for reuse and producing a concentrated brine (lower liquid waste volume), or residual solids (zero liquid discharge).

Render of the vessel of a Saltworks XtremeRO reverse osmosis brine concentrator
News

First Commercial Order of Next Gen UHP RO

Saltworks is thrilled to announce the first full-scale order for an industrial Ultra-High Pressure Reverse Osmosis (UHP RO) system with Nitto high performing HYDRANAUTICSTM PRO-XP1 spiral wound membranes rated to 1,800 psi (124 bar).

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Reverse Osmosis Brine Treatment: Tech Advancements to Minimize Volume & Cost

Photo of a reverse osmosis (RO) system with an array of RO vessels

Reverse Osmosis Brine Treatment: Tech Advancements to Minimize Volume & Cost

Jan 8th 2019

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Key Takeaways

  • Reverse osmosis (RO) is considered to be the workhorse of desalination. Applied correctly, RO brine treatment can be highly effective and less costly than thermal alternatives.
  • RO freshwater recovery and RO brine concentration are limited by osmotic pressures or membrane scaling; both limits can be increased by new technology.
  • New ultra-high pressure RO membranes can achieve pressures of 1,800 psi, 50% higher than previous, enabling 50% brine volume reduction if membrane scaling can be managed. These next-generation membranes are available in systems such as XtremeRO.
  • A series of techniques described in this document can be used to delay or mitigate scale, but in many cases, only chemical softening truly removes the risk.
  • A modernized, compact chemical softening technology—BrineRefine—developed for RO brine treatment can be used to entirely remove membrane scaling risk and realize RO’s full potential in brine volume reduction.
  • Fully integrated RO and chemical softening solutions with central optimization and control can further maximize overall economics and recovery.

How does Reverse Osmosis Work?

Reverse osmosis (RO) is the workhorse of desalination. High pressure is used to drive water through specially engineered semi-permeable membranes that reject salt ions. Recovery increases with higher brine concentration relative to inlet salinity, squeezing more freshwater from the salt water. Osmotic pressure also increases with brine concentration, which means higher driving pressures are required and freshwater permeate flux is reduced, causing a need for a larger membrane area.

Photo of an array of reverse osmosis vessels
An array of conventional reverse osmosis vessels

Historically, there have been three pressure classes for RO membranes: 300 psi, 600 psi and 1,200 psi. The higher the pressure class, the higher the potential for brine volume reduction on a non-scaling fluid. RO membrane vendors are innovating ultra-high pressure reverse osmosis (UHP RO) spiral wound membranes that are capable of 1,800 psi. UHP RO enables brine concentrations of up to 130,000 mg/L of total dissolved solids (TDS), limiting downstream brine disposal or brine treatment costs. UHP RO membranes can be packaged into turn-key systems. One such example is XtremeRO.

Reverse Osmosis Limitations

RO brine treatment will be limited by either osmotic pressure that increases with salinity, which decays permeate flux to an unsuitable level, or scaling ions or organic fouling that can block the membrane. Most industrial RO applications are scale-limited, for example by silica, calcium sulfate, phosphate, fluoride, iron or barium salts. Organic fouling can be managed by pre-treatment, a biocide program, automated high-pH washes, or a “kidney organic removal loop.”

 

Ionic scale can affect end users in three ways:

  1. Reliability challenges, leading to frequent cleaning or shortened membrane life.
  2. Recovery left on the table, generating more brine than required.
  3. RO membrane fouling, caused by indirect effects such as coagulants intended to help remove precipitated scale upstream.

These problems are compounded in industrial wastewater, where the feed chemistry varies and requires constant monitoring. The BrineRefine technology introduced below solves these challenges by automatically adjusting and preventing use of membrane fouling coagulants.

Advanced Innovations in Reverse Osmosis Brine Treatment

A series of techniques, as presented below, could be used to delay or mitigate scale, but they do not entirely remove the risk.

Advancements

Process Description

Anti-scalants

  • Chemicals developed to delay precipitation of scaling ions, roughly doubling their solubility, so that brine can be further concentrated.

Operational

  • Increase crossflow through the membrane element (fluid velocity) to reduce the boundary layer and “concentration polarization” at the membrane surface, thereby decreasing scale deposition potential.
  • Automated permeate flushes and chemical cleans to maintain membrane cleanliness, including consideration of trigger points such as decline of permeate flux or increase in concentrate differential pressure.

Flow reversal

  • Switch the RO inlet flow path on the RO vessel with the RO brine outlet flow path.
  • The last element in a vessel frequently scales first; therefore, the final membrane element alternates operation in supersaturated conditions with undersaturated conditions.

Batch or semi-batch operation

  • RO permeate is continuously produced while brine circulates in a semi-closed loop.
  • Brine should be bled in small volumes and then batch discharged in larger slugs and replaced with feedwater.
  • This allows the entire system to alternate between supersaturated conditions and undersaturated conditions, thereby “shocking” scale formation and disrupting biological growth through frequent salinity changes.

Hardness removal and high pH (for high-silica waters)

  • Operate at high pH to increase both silica solubility and brine concentration in silica-limited waters.
  • This requires effective hardness removal through techniques such as ion exchange (IX) to avoid producing carbonate scale at high pH.
  • IX is less effective at higher salinities, so this method is limited to low salinity feedwaters of <5,000 mg/L TDS.
  • IX also requires chemical regenerations, resulting in a secondary regeneration waste byproduct.

Saturation relief

  • Allow for continuous precipitation of scale outside the RO circuit by relieving saturation in large seeded columns, including shifting pH to relieve the effectiveness of any antiscalants.
  • After scale is precipitated, fresh antiscalant can be added and a secondary RO process applied.
  • This technique requires large contact areas and vessels to allow sufficient residence time, as well as filtration of the precipitants upstream of the secondary RO. 

Disc-tube RO and/or vibratory shear process

  • Larger spacers between membranes and a nonspiral wound membrane allow for higher flow and turbulence through the equipment, as well as acceptance of higher turbidity and service deionization (SDI) on the inlet (less pretreatment).
  • Specialty vendors innovated “vibratory shear” at the membrane surface, aiming to keep the membrane clean.

Although the above-mentioned methods mitigate scaling risks, recovery may still be below osmotic pressure limits with brine concentration potential left on the table. Operators may also still be walking a tightrope because scaling compounds are circulating in a sensitive RO brine treatment system.

Chemical Softening

Chemical softening is a hybrid solution that removes the tightrope entirely, as shown in the process flow diagram below. First, achieve initial recovery through a primary reverse osmosis (RO-1) step, effectively reducing the volume for downstream processes. The techniques explained above are applicable, but do not need to be pushed to their limit. After primary RO-1 recovery, chemically soften the brine to extract the scaling compounds before another secondary RO (RO-2) step that boosts recovery to the osmotic pressure limit of RO. Saltworks has developed an advanced chemical softening system called BrineRefine, of which the pilot unit is shown below.

Integration of RO and advanced chemical systems
Photo of a Saltworks engineer inspecting a BrineRefine module used for chemical softening
BrineRefine Pilot Unit

BrineRefine is a smart and compact chemical softening system that applies modern automation and separation processes to remove scaling compounds. Innovations include:

  • Reduced footprint by replacing the reaction tanks and clarifier with an inline processing system.
  • Precision dosing by modern automation to prevent overdosing (wasted chemicals and added sludge) or underdosing (scale risk), including the ability to adjust with changing upstream chemistry.
  • Elimination of coagulants and floc, which can foul downstream ROs by forming a gel on the membrane that would require frequent chemical cleans.
  • Replacement of manually intensive sludge management techniques with semi-automated solids management technology, borrowed from our crystallizer technology—the SaltMaker.

The controls communicate with any upstream and downstream RO unit to optimize total system performance. Wastewater treatment plants should not be designed or controlled as a linear train of independent unit operations that pass water to each other. Instead, they should be considered as an integrated system, with each unit operation adjusting to its ‘sweet spot’ as upstream conditions change. The systems view of operation enables optimization of total system economics, reliability, energy, chemical consumption, recovery and capacity.

 

RO performance and economics can be fully maximized by tightly integrating RO, UHP RO, and chemical softening under central control and optimization. Integrating the management of residual solids that are produced by the chemical softening further improves overall performance. 

 

Innovation is driving down the cost of treating industrial wastewater. Membrane systems typically cost 5–10 times less than thermal brine concentration evaporators; thus, maximizing membrane recovery is important. Contact an expert at Saltworks today to maximize your membrane recovery and prevent scale formation.

About Saltworks

Saltworks Technologies is a leader in the development and delivery of solutions for industrial wastewater treatment and lithium refining. By working with customers to understand their unique challenges and focusing on continuous innovation, Saltworks’ solutions provide best-in-class performance and reliability. From its headquarters in Richmond, BC, Canada, Saltworks’ team designs, builds, and operates full-scale plants, and offers comprehensive onsite and offsite testing services with its fleet of mobile pilots.

Related Resources

A photo of a wastewater disposal truck used in brine management
Article

How to Manage Brine Disposal & Treatment

The many options for managing brine, a term for saline wastewater from industrial processes, fall under two categories: brine treatment and brine disposal. Brine treatment involves desalinating the brine for reuse and producing a concentrated brine (lower liquid waste volume), or residual solids (zero liquid discharge).

Render of the vessel of a Saltworks XtremeRO reverse osmosis brine concentrator
News

First Commercial Order of Next Gen UHP RO

Saltworks is thrilled to announce the first full-scale order for an industrial Ultra-High Pressure Reverse Osmosis (UHP RO) system with Nitto high performing HYDRANAUTICSTM PRO-XP1 spiral wound membranes rated to 1,800 psi (124 bar).

Contact Saltworks
Sign up for Updates

Modern Chemical Softening to Maximize RO Recovery: Scale Removal

Photo of a Saltworks engineer inspecting a BrineRefine module used for chemical softening

Modern Chemical Softening to Maximize RO Recovery: Scale Removal in Smart, Compact, Modular Systems

Nov 5th 2018

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Key Takeaways

  • With the advent of ultra-high-pressure reverse osmosis and the growing importance of brine management, modernized chemical softening systems can enable economic ultra-high recovery reverse osmosis, minimizing RO brine volume, disposal costs, and reliability risks.
  • Chemical softening systems (conventional and advanced) are described, including chemical dosing and tips on how to remove scaling risk.
  • Conventional chemical softening settling times are reviewed as well as the risks posed by coagulant/flocculants that can foul downstream ROs.
  • BrineRefine is introduced: an advanced chemical softening system that addresses many of the challenges faced by conventional chemical softening; there are no coagulants used or foulants introduced (reduce RO fouling risk); it is compact (no clarifiers), modular (minimal site installation); intelligently automated (precise dosing and recovery tuning); and includes a simplified solids management system to remove sludge management concerns.

Why Care About Scale?

As higher recoveries are pushed on RO systems, scale becomes the primary bottleneck to recovery improvements. As discussed in this RO blog, there have been many innovations within the RO field that seek to manage scale through operational ‘tweaks’ in order to achieve higher recoveries. Saltworks builds such RO systems; we understand that operational tweaks and anti-scalants do not remove the underlying risk, but rather delay the symptoms. Operating at or beyond saturation limits means that any misstep could result in membrane fouling, decreased capacity, higher energy costs, plant downtime, and more repairs. RO systems may also not be operated at their peak performance, reducing membrane recovery and wasting money on expensive brine treatment downstream of the process.

 

Before spending money to remove ions that cause scale, consider which of the three categories you may fit into:

 

1. Basic RO: Desired recovery can be achieved with basic RO and a sound anti-scalant program (lowest cost).

 

2. Advanced RO: Applies operational changes, such as cycling concentrations while draining some brine, high cross-flow, automated flushes and clean-in-place cycles (CIPs), each of which may push an RO to its recovery goal. Alternatively, a scaling risk may limit the brine concentration and prevent the maximum achievable recovery, which can add system costs and complexity.

 

Knowledge tip: Maximum RO recovery is defined by osmotic pressure limits (the pressure at which water stops permeating through the membranes). New generation RO membranes can operate up to 1,800 psi, or concentrate non-scaling fluids to 130,000 mg/L (NaCl) and 150,000 mg/L (Na2SO4). 

 

3. Chemical Softening + RO: If done correctly, chemical softening can now maximize an RO system’s recovery to reach osmotic pressure limits. Scale causing compounds are removed by chemical softening, as reviewed below, which also reduces the operational risk of membrane damage. As a note of caution, only the correct amount of scaling ions should be removed; excessive dosing will result in higher chemical costs and harmful sludge generation. Chemical softening typically adds between $2 and $5/m3 to capital and operating costs, so it is only a worthwhile investment if the added costs of chemical softening and a secondary RO are lower than the alternative brine disposal or thermal brine concentration costs (typically a minimum of $20/m3).

 

Design tip: Assess the RO brine and only remove the right amount of scale. We aim for 85% scaling potential of the downstream RO brine (with 100% representing the onset of precipitation).

 

Correctly applying chemical softening can remove scale and will eliminate/mitigate the fundamental risk of precipitation on a membrane surface, allowing downstream systems to operate at high recoveries and greater reliability. Scale removal is most commonly carried out via chemical softening.

 

It is important to acknowledge that as water is concentrated, organics that can foul an RO will also concentrate. In more severe cases, solvents concentrate to where they become insoluble and damage the RO membrane. Consideration of an organic removal ‘kidney loop’ to treat out organics as they concentrate may be warranted. Nevertheless, do not fret too greatly about the organics, as assessments can be completed. Contact Saltworks for more details.

Scale Management vs. Scale Removal

The first and most important step is to understand your water chemistry—the scale causing compounds the water contains and the concentration factor at which they will precipitate. Scale comprises low solubility salts that precipitate as water is concentrated. Precipitated salt, if uncontrolled, will plate out on membranes. This impedes performance and decreases membrane life. Depending on water chemistry, different scale will pose different challenges. Figure 1 below shows the solubility of some of the most common scaling compounds in industrial wastewater. Readers can use the figure to check the solubilities against their brine water chemistry.

Periodic table of scaling compounds
Figure 1. Periodic Table of Scaling Compounds (Click image to download PDF)

Calculation Tip: Concentrated brine causes scaling, not the feed. So, concentrate the individual ions in your water chemistry by the same factor of volume reduction. For example, if operating at 75% recovery, that is 4x volume reduction, meaning that all the ions in your water will be concentrated by 4x. Multiply your raw chemistry data by 4 and compare to the solubility limits in the Periodic Table of Scaling Compounds above. If two scaling ion pairs are both higher than the concentration shown above, you could have scale forming. Typically, anti-scalants can delay the formation of scaling by 2x above the theoretical concentrations.

 

The most common scale encountered is typically silica and calcium-based salts, and metals (such as aluminum and iron). Table 1 below discloses chemical methods to remove specific scaling ions.

Table 1: Chemical Methods to Remove Scaling Ions

Scalant Chemical Removal Solution Concentration (Post-Softening)
SiO2 pH 11 + magnesium if not sufficiently present < 5 mg/L
Mg pH 11 (not a critical scalant but will increase base consumption) 10–300 mg/L (heavily dependent on Mg levels)
Al pH 11 Case-specific
Ca pH 9–11 + soda ash if required 20–80 mg/L
Ba pH 9–11 + soda ash if required < 1 mg/L (depends on initial levels)
Sr pH 9–11 + soda ash if required < 5 mg/L (depends on initial levels)
Mn and Fe pH 9–11/oxidation/greensand
F pH 9–11 < 2 mg/L
CO32- pH 5

Conventional Chemical Softening 101 and its Challenges

Conventional chemical softening systems have over 100 years of history. They are used throughout water treatment plants, ranging from municipal to industrial wastewater. The process consists of the following:

 

1. Addition of lime to increase pH to 11 to precipitate out silica and heavy metals (aluminum and iron). Some calcium may also precipitate.

 

2. Addition of soda ash to precipitate out hardness ions (calcium, barium, strontium, etc.) if the high-pH step does not reach the calcium goal.

Steps 1 & 2 occur in large reaction vessels, often with a suspended agitator. Be cautious of mechanical forces on the agitator and ensure the metallurgy of the tanks and impellers will not corrode in your brine.

 

3. Clarification + coagulants/flocculants to separate the precipitated solids and water (beware this step if RO is downstream).

Step 3 occurs in a clarifier, which may be a vertical laminar plate type for smaller flows, or a large circular type (see Figure 5 below). A higher-solids brine settles to the bottom, which is then directed to a filter press. The clarified fluid leaving the “top” clarifier is often directed to micro- or ultrafiltration before an RO system. However, dissolve residual coagulants and flocculant byproducts will not be filtered and could foul the downstream RO. 

 

4. Solids management to handle the precipitated solids for disposal, etc.

Step 4 occurs in centrifuges and/or filter presses, with the solids sent to landfill. Metallurgy and operability is extremely important, as is making sure the solids pass a paint filter test for landfill disposal (i.e. no free water droplets). If normally occurring radioactive materials (NORMs) are present in the raw water, they may concentrate in the filter press solids and should be checked for radioactivity.

Conventional chemical softening, though effective, has some challenges when applied to modern RO systems.

 

  • Fouling coagulant chemicals are added: Due to the poor settling nature of chemically softened solids, large clarifiers are required. The addition of flocculants/coagulants is often used to help decrease the size of clarifiers needed. See Figure 2 for settling times of chemical softening solids, with and without the aid of flocculants/coagulants. These specialty chemicals improve the settling times of the solids by approximately 3x, reducing clarifier size by roughly 3x. However, iron and aluminum-based coagulants, as well as added polymers, pose a fouling risk to downstream ROs by forming a gel on the membrane surface and requiring almost daily chemical clean-in-place (CIP) cycles. This common occurrence adds downtime, operator frustration, and increased chemical cost. One should not assume that 20-year-old chemical softening textbooks and design guidelines can be applied to RO systems, as these older systems were not designed for utilization with RO.
Table of photos showing differences in settling of solids in test tubes
Figure 2. Conventional Chemical Softening Settling Time with and without Coagulant/Flocculant addition, by Saltworks
  • Large clarifiers: installed to enable settling and downstream solids management. In higher hydraulic capacities, these need to be built at site, incurring higher installation costs and space requirements.
  • Imprecise chemical dosing: the manual steady state nature of operating a conventional chemical softening plant means that there is higher risk of over-dosing chemicals (waste of chemicals) or under-dosing (scaling risk for RO as the scaling ions will not be adequately removed). If inlet water chemistry changes, so should the chemical dosing set points.
  • Solids and sludge management: low-flux filter presses are commonly used, resulting again in a large equipment footprint and more frequent operator attention.

Tips:

  • Determine the most economic method/chemical for removal. Example: If there are high levels of sulfates and magnesium in the wastewater, the use of lime would be a lower cost option. However, if there are low levels of sulfates and high levels of calcium, sodium hydroxide may be more cost effective if followed by soda ash softening. This is because sodium hydroxide does not add calcium, whereas lime will, resulting in increased usage of more expensive soda ash.
  • Understand your solids disposal costs. Solid waste from the chemical softening process will also need to be disposed. The more chemicals that are added, the more solid wastes are required for disposal.

Advanced Chemical Softening: Introducing BrineRefine

Recent innovations have been developed to focus on addressing the chemical softening challenges discussed above. BrineRefine, an example of advanced chemical softening, offers a safer, more compact, and smarter system for removing scaling ions at the optimal cost.

  • No coagulants or flocculants: No chemicals are added that could foul a downstream RO. Rather than use gravity and time to settle, BrineRefine includes a robust, high-flux mechanical separation step, producing a filtered non-scaling brine that is suitable for direct feed into an RO system.
  • Compact: BrineRefine eliminates the need for large reaction vessels and clarifiers. See Figure 3 below for BrineRefine separation of solids from liquid without the use of clarifiers or coagulants/flocculants.
Table comparing chemical softening settling in test tubes
Figure 3. BrineRefine Solids-Liquid Separation without Clarifier and without use of Flocculants/Coagulants
  • Modular: BrineRefine consists of pre-built ISO container-sized blocks and does not need clarifiers. Higher capacity plants simply add more blocks. The modular and factory tested skids minimize site installation, ensure quality, and provide economies of scale across a standardized factory-built fleet, rather than higher cost project-by-project custom designs.
  • Intelligent: The controls are integrated with downstream and upstream unit operations to communicate changes in process conditions and allow the entire system to adjust to allow for maximum reliability. BrineRefine senses and reacts to changes in the feed chemistry, optimizing operation costs and downstream RO recovery while providing the operator with remote control and a simple human machine interface (HMI). Figure 4 is an example of how BrineRefine integrates controls with an RO system.
Process flow diagram showing how BrineRefine enhances reverse osmosis freshwater recovery
Figure 4. Integration of BrineRefine Controls with Upstream and Downstream RO

Single package: BrineRefine receives inlet feedwater, and outputs high quality filtrate that meets RO’s SDI requirement, and filter cakes.

Photo showing the use of a clarifier in a treatment facility as used in conventional chemical softening
Figure 5. Conventional chemical softening, with large settling clarifiers.
brinerefine-full-scale-2
Figure 6. BrineRefine ISO-based design, without large reaction vessels or clarifiers.

Pilot test units are available for BrineRefine, including both up and downstream RO systems, as shown in Figure 7. 

Photo of a Saltworks engineer inspecting a BrineRefine module used for chemical softening
Figure 7. BrineRefine Pilot Unit

A case study is included below from a mine water treatment project. A primary RO could be used and was recommended by Vendor A; however, the client still sought further volume reduction. The primary RO could concentrate the brine to 50-55,000 mg/L total dissolved solids (TDS) with anti-scalants, but without chemical softening. At ~55K TDS, calcium sulfate or gypsum scale could initiate. If, according to Figure 4 above, the primary RO can be followed by BrineRefine and a secondary RO, brine volume in a membrane system can be further reduced by 2x (50% recovery = 50% less brine).

 

The secondary chemical softening and RO systems will be higher cost than the primary RO, but will be at 4x lower cost than a thermal evaporation system. The chemistry resulting from BrineRefine and the secondary RO brine is shown in the table below. Although calcium can be reduced to ~20 mg/L in BrineRefine, this target was not necessary. A lesser calcium reduction to ~136 mg/L was sufficient to ensure that downstream RO does not suffer gypsum fouling when concentrated to within 85% of the gypsum scale potential (i.e. calcium concentrating beyond 400 mg/L). The result is use of fewer chemicals and reduced sludge generation, while still maximizing recovery and protecting the downstream RO.

A table of chemistry data for chemical softening showing primary brine, filtrate, and reject brine

Every industrial water treatment project, chemistry, and goal may differ. It is important to understand the economics of brine management and the cost of each option. Do not spend more money concentrating brine than the savings that would be achieved from reduced disposal. For example, if ultra-high recovery can be achieved with an advanced chemical softening and RO system for $5/m3, that should only be done if the brine disposal costs are greater than $5/m3. Thermal systems are at least 4x more costly than $5/m3, so advanced membrane systems make a lot of sense to pre-concentrate before an evaporator.

 

In addition to understanding water chemistry, think about variability. A good way to do this is to take water samples at periods of both high and low flow and send them to a lab for a detailed chemical analysis, such as the assay shown above. 

 

Finally, although many vendors have options on how to package both chemical softening and reverse osmosis, look for a company that does this frequently. Engineers can read online design guides and advise on different mechanical design options, but lessons learned from those with past implementation experience can be invaluable and save your project from repeating the mistakes of the past. Vendors who have modular designs that were developed for repeat dispatch may have a more mature and tested product line. These vendors are available to help you understand your total cost of ownership (capital cost plus operating cost) and assess if membrane brine concentration is worth the investment.

 

Please feel free to contact Saltworks for a detailed review of your project, risk and opportunities, as well as options to limit your brine management costs.

About Saltworks

Saltworks Technologies is a leader in the development and delivery of solutions for industrial wastewater treatment and lithium refining. By working with customers to understand their unique challenges and focusing on continuous innovation, Saltworks’ solutions provide best-in-class performance and reliability. From its headquarters in Richmond, BC, Canada, Saltworks’ team designs, builds, and operates full-scale plants, and offers comprehensive onsite and offsite testing services with its fleet of mobile pilots.

Related Resources

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Optimize Existing Water Plant Assets With ScaleSense

Saltworks announces ScaleSense: our real-time, ion-specific sensor that works on saline waters i.e. brines. By measuring scaling species live, it enables users to optimize processes in real time as conditions change—without the need for human intervention, lab work, or guesswork.

Photo of a full-scale, 2-module, Saltworks BrineRefine plant
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Periodic Table of Scaling Compounds
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Periodic Table of Scaling Compounds

Scale is a crust that forms on membrane and evaporator surfaces, blocking performance. Scaling occurs when ion pairs precipitate out of solution. Know your scaling potential with this free periodic table of scaling compounds and the conditions that cause them to precipitate.

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Introducing AirBreather: A Lower Cost Evaporator

Rendered image of a SaltMaker AirBreather evaporator crystallizer

Introducing the AirBreather: Lower Cost Evaporator Crystallizer

Oct 15th 2018

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Key Takeaways

  • A lower cost evaporator crystallizer has emerged—the SaltMaker AirBreather. It is based on the robust backbone of its closest relative—the SaltMaker MultiEffect.
  • It offers four times the capacity, at four times higher thermal energy load vs the MultiEffect; it is best suited where thermal energy costs are < $5/GJ (or $5/MMBTU).
  • The AirBreather optionally reduces volume with either clean water return, or volume reduction without a liquid water by-product.
  • Wastewaters never contact atmosphere, so volatile organic compounds (VOCs) are not released, unlike conventional open-to- atmosphere evaporators that boil water directly to atmosphere, placing air emissions at risk and raising site concerns.
  • The AirBreather decreases trucks on roads and reduces produced water volumes for offsite disposal.
  • It can concentrate to any point: concentrate heavy brine or make solids and achieve true zero liquid discharge.
  • It cleans itself while it operates, and is built from non-corroding, non-scaling, modular components, well suited for remote dispatch.

Rendered image of a SaltMaker AirBreather evaporator crystallizer
The SaltMaker AirBreather

The Origins of the AirBreather

Saltworks originally developed the SaltMaker MultiEffect—the AirBreathers’ older ‘cousin’—in partnership with Canadian oil sands companies. They were seeking to use waste heat thermal energy to treat challenging heavy oil blowdown water. The industrial end users set out the following criteria:

  1. Build the most reliable and cost effective evaporative-crystallizer, re-engineering from the ground-up to be suited for oil and gas.
  2. Remove boiling on heat transfer surfaces, which is the origin of most scale.
  3. Develop a new solids management system, removing the challenges of centrifuges and driers, while producing automated bagged solids suitable for landfill disposal
  4. Deliver a modular, expandable plant, that can be serviced without confined spaces.
  5. Remove single point of failures, such as the vapor compressor in MVR systems.
  6. Employ 60–80 °C waste heat, which is abundant in oil sands.

Saltworks answered this challenge with the SaltMaker MultiEffect. It replaced steam and scaling heat transfer surfaces with an air humidification-dehumidification cycle, which evaporates and condenses water in successive effects. Clean water is produced by each effect, with the final effect open to atmosphere to cool the plant. The machine is designed to remain scale-free.

A photo of a SaltMaker evaporator crystallizer at Saltworks HQ
The SaltMaker MultiEffect

After having completed shale field pilots of the SaltMaker MultiEffect, the team realized that a better configuration existed for shale: leveraging waste thermal energy with an open to atmosphere evaporator that can manage volatile risk. Capacity improved four times per unit of equipment. However, thermal energy also increased four times. As engine jacket cooling water or low-cost gas may be available, this is less of a barrier in shale.

What Do I Need to Know About Open Evaporators?

Open evaporators release water vapor to atmosphere, so there is no condensed water to manage. However, evaporating water requires a lot of energy: 2400 MJ per tonne. In addition, produced water includes more than just water. It includes salt that can scale and corrode the plant, and toxic volatiles such as benzene or ammonia that can pollute the atmosphere or cause health problems. The AirBreather overcomes both challenges through innovation.

Up until recently, most open evaporators were of the submerged combustion type. Combustible gas and compressed air are injected into a large “kettle boiler.” Combustion occurs underwater and heat is transferred directly to the salty water. Water is concentrated, and vapor is released, often resulting in a tall plume rising through the sky. These large kettles must be metallic to withstand combustion temperatures, while also made of exotic materials to reduce corrosion risk related to high salinity. Emissions must also be managed since combustion is involved. Other open types may heat the water making use of direct contact with exhaust gas, or heating via a heat exchanger. Regardless, volatile emissions can still emerge.

The AirBreather overcomes this avoiding any contact of the wastewater with air. The evaporation chambers are 100% sealed from the atmosphere. We provide customers with two options: return freshwater fit for surface discharge, or reduce volume by sending only clean water to atmosphere. How we do this is a proprietary secret that we will release to customers under NDA.  

When developing the AirBreather, we aimed to pack extremely high evaporation capacity into a small repeatable module. Every AirBreather AB-100 consists of 4 evaporation modules, packaged into ISO container frames. The entire plant is built around ISO container frame modules, for ease of delivery, installation, and expansion to suit project needs. The “100” in AB-100 stands for 100 tonnes/day of produced water volume reduction (600 barrels per day or 26K GPD). Larger plants can be built by simply adding AB-100s, allowing customers to grow their volume reduction capacity over time.

Photo of a full 20" effect for a SaltMaker evaporator crystallizer
Effect Module: Built for modular dispatch to minimize site work
Photo of a SaltMaker Franklin evaporator module
Franklin Evaporator Module: The 'lungs' of the AirBreather

Evaporating water is easy; however, managing volatiles and achieving extremely high brine concentration or solids production to realize zero liquid discharge presents new challenges. 

Volatiles:

Wastewaters can contain substances with low boiling points that will evaporate with water. Examples include ammonia, or volatile organic compounds (VOCs) such as methanol, BTEX, and others. Odor may also impact neighbours. The AirBreather’s proprietary “Volatile Management System” prevents volatiles from atmosphere contact so that only safe, clean, low-temperature water vapor is released. Our pilot plants are outfitted with this same system, so we can prove the operations at your site, or ours on shipped water.

Process flow diagram of a SaltMaker AirBreather evaporator crystallizer
Process flow diagram of a SaltMaker AirBreather evaporator crystallizer

Zero Liquid Discharge (ZLD)

As saltwater is concentrated, scale can precipitate, solid salt plugs can form, and high chloride levels will corrode metallic parts. The SaltMaker AirBreather borrows SaltMaker MultiEffect technology to overcome these challenges, resulting in the first open-to-atmosphere evaporator that squeezes every last drop of liquid waste down to a solid by-product or achieves any desired brine concentration along the way. This is accomplished by:

  • Corrosion, Plugging, and Scaling Resistance: High circulation rates, constantly changing saturation gradients, and non-corroding, non-stick wetted surfaces eliminate reliability challenges that plague conventional crystallizers.
  • Reliable Solids Production or Slurry Brine: A circulating slurry continuously forms and grows crystals. Solid salt is discharged to an automated bagging or binning system. Alternatively, one may choose to extract the slurry brine at any pre-determined concentration.
  • Intelligent Automation and Self-Cleaning: The plant has automated start, stop, and hibernate for immediate ramping from 0 to 25% capacity in one step. It operates at any capacity between 25% to 100% in dynamic capacity control mode and will detect and initiate cleaning cycles.
  • One Step Treatment: No pre-treatment is required. For ZLD applications, solids are produced without the need for extra process equipment, such as centrifuges or filter presses.

Photo of a bag of solids as produced by a SaltMaker evaporator crystallizer
Photo of zero liquid discharge solids produced by a SaltMaker evaporator crystallizer

Samples of solids as produced and discharged to an automated bagging system

Want to know if the AirBreather is right for your project? Saltworks hosts a fleet of pilots, ready to test your water for feasibility. Pilots can help test water quality, by-products, and scale issues as well as site performance. Contact us. 
Photo of a mobile, containerized SaltMaker AirBreather pilot
Mobile Containerized AirBreather Pilot Plant

About Saltworks

Saltworks Technologies is a leader in the development and delivery of solutions for industrial wastewater treatment and lithium refining. By working with customers to understand their unique challenges and focusing on continuous innovation, Saltworks’ solutions provide best-in-class performance and reliability. From its headquarters in Richmond, BC, Canada, Saltworks’ team designs, builds, and operates full-scale plants, and offers comprehensive onsite and offsite testing services with its fleet of mobile pilots.

Related Resources

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How to Manage Brine Disposal & Treatment

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What Is Electrodialysis Reversal and What Are its New Innovations?

Diagram of monovalent electrodialysis reversal (mEDR) using selective membranes and FlexEDR technology

What Is Electrodialysis Reversal and What Are its New Innovations?

Aug 10th 2018

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Key Takeaways

Electrodialysis reversal (EDR) technology and its specific application fits are explained.

 

Innovations in EDR enable:

  • Treatment of highly scaling flows without expensive chemical treatment,
  • Selective extraction of ions, and
  • Treatment of highly contaminated organic flows.

EDR is not generally a competitor to reverse osmosis, but rather each has its specific fits. In some applications, such as FGD or produced water, EDR can provide a compelling cost advantage.

How does Electrodialysis Reversal Work?

Electrodialysis (ED) technology is the second most widely used membrane desalination technology and has been developed since the 1960s for a wide range of industrial applications. It involves applying a direct current (DC) electric field to flux positive ions across cation exchange membranes (CEM) in one direction, and negative ions through anion exchange membranes (AEM) in the opposite direction. The two types of membranes alternate within a stack (Figure 1).

Photo of a FlexEDR E150 stack with a transparent background
Figure 1. A single complete electrodialysis stack

As the process feedwater (or wastewater) enters the ‘product’ chamber, ions get pulled out of the product water as it travels up the length of the stack, parallel to the membranes. These ions get concentrated up in the concentrate chamber, also flowing parallel to the product chamber, see Figure 2 below. The ‘reversal’ term in EDR comes from recent innovation that allows the polarity of electrodes and hydraulic channels to ‘reverse’, which helps keep the membranes clean.

A technical diagram showing the operating principle of electrodialysis reversal
Figure 2. Illustration of a functioning electrodialysis system

Typical electrodialysis systems are composed of stacks of cation and anion exchange membranes. However, due to recent advancements in membrane manufacturing, it is increasingly possible to selectively pull out monovalent ions using ion exchange membranes that have high divalent ion rejection (such as Saltworks’ IonFlux products with 98% divalent ion rejection). This monovalent electrodialysis reversal (mEDR) can be used for a number of treatment or reuse applications, including the following:

 

  • Removing chlorides to reduce corrosion in water circulating loops that result in high blowdown. A prime example of where this is particularly useful is in flue gas desulfurization wastewater, where the 90% recovered water can be recycled, while the final 10% residuals can be mixed with combustion ash or fly ash.
  • Removing scale-causing gypsum from cooling tower blowdown to enable higher cooling tower cycling, provided the tower is designed to handle the higher salinity, or if the corrosion-causing chlorides are removed.
  • Selectively removing sodium to reduce the sodium adsorption ratio (SAR) in agricultural or vertical farming wastewater to allow recycling of nutrients or multivalent fertilizer by-products.
Diagram of monovalent electrodialysis reversal (mEDR) using selective membranes and FlexEDR technology
Figure 3. mEDR process flow diagram

Comparing Electrodialysis Reversal and Reverse Osmosis: The Workhorses of Desalination

Reverse osmosis (RO) and EDR are the top two membrane desalination technologies and have their own unique fit for a variety of applications. They should not be seen as competing processes. However, relative economics of either system will depend largely on factors related to water chemistry, process design and site requirements. Below is a quick comparison of EDR and RO technology.

Inorganic Scaling

RO’s main operating principle is the use of high pressure to force water through pico- to nano-scale pores of a membrane and reject salt ions. To mitigate scaling with RO systems, anti-scalants are used. For higher scaling potential waters, chemical pre-treatment will be required to remove scaling compounds.

 

This is contrasted with EDR, which uses a voltage difference, instead of water pressure, to drive ions through the membranes; there is no pressurized impingement on the membrane surface. This means EDR is much more tolerant of inorganic scaling and organic fouling and requires less pre-treatment. Additionally, the EDR process is configured to further mitigate scaling risk with easy clean-in-place design, and the ability to reverse polarity of electrodes and hydraulic channels to flux ions in the opposite direction. This reversal action allows the concentrate chamber to be cleaned with lower salinity product water, further mitigating scaling risk.

Organic Fouling

Typically, membranes do not fare well in the presence of wastewater with high organics. The membranes are susceptible to damage due to the solvent-like properties of organics. To remove organics, oxidants (such as bleach or chlorine), which can also damage RO membranes, are required, but must be removed prior to the membrane stage. Thus, both RO and EDR systems with conventional membranes are susceptible to membrane damage in the presence of organics. However, Saltworks’ FlexEDR Organix system leverages cross-linked EDR membranes that are highly resistant to organics. Furthermore, the membranes can resist bleach and chlorine dioxide, which can be used to clean the membranes after operating on highly fouling or organic wastewater.

Brine and Treated Water

RO systems concentrate up all contaminants in the water into a single brine stream, with no selectivity. This also means that the treated water produced by an RO system is typically very low in salinity and dissolved ions. The brine concentrations achievable are dependent on the amount of pressure that is being applied. Typical RO systems can concentrate up to 80,000 mg/L (1,200 psi) or 130,000 mg/L (1,800 psi), assuming all scalants are removed. However, concentrating brine any further is challenging because RO membranes can withstand only certain amounts of pressure. This results in relatively larger brine volumes.

 

Since electrodialysis does not rely on pressure and is more tolerant to scale formation, it can concentrate the brine up to 180,000 mg/L TDS. Due to flexibility in different ion exchange membrane arrangements, the brine from an EDR system can be tuned to selectively concentrate or extract certain ions. This also allows users to tune the salinity of their treated water outlets to any TDS concentration.

The Economics of Desalinating with EDR: The Importance of ΔTDS

The economics of EDR technology depend most strongly on the starting and final concentrations of the feed stream; this is the ΔTDS (change in concentration of total dissolved solids). With increasing ΔTDS, or the more the EDR system has to desalt, the EDR system will require greater membrane area and more stacks (capital cost), as well as more power (operating cost).

 

EDR systems are sized based on current density and current efficiency. Current density is the amount of current that can be applied per unit area of membrane (typically in A/m2). Current efficiency is a measure of how effective the applied current is in moving ions across the membrane. The higher the current density and current efficiency, the more ions can be moved across the membrane with less membrane area and power. Figure 4 below illustrates the relationship between current density and how much desalination occurs in one pass of a full-scale stack (FlexEDR E200), assuming 80% current efficiency. Two different types of brine are shown: NaCl brine and CaCl2 brine—typically, most wastewater will fall between the two brine lines shown. Depending on the starting TDS of the wastewater feed, a typical EDR product water output of 1,500 mg/L TDS offers the best economics. Treating much lower TDS concentrations will increase the ΔTDS, and subsequently, the cost.

Graph describing the change in total dissolved solids vs. energy required for an electrodialysis reversal process
Figure 4. TDS change compared to energy requirements for a FlexEDR E200 stack

Note that the maximum current density that can be applied is subject to the effects of current limiting density, also known as current limit. Driving EDR at currents higher than this limit will result in the splitting of water molecules at the boundary layers of membranes, which wastes energy to produce H+ and OH–, and reduces current efficiency. Our FlexEDR systems can be driven at higher current limits than conventional systems due to our IonFlux membranes that offer low resistance, small boundary layers, and smooth membrane surface areas.

 

The current limit decreases with decreasing TDS, so the best economics may sometimes be obtained by arranging stacks in series that operate at different currents. An example might be where a high-TDS wastewater would require one stack that operates at 200 A/m2, which must then be sent for final polishing with a second stack at 60 A/m2 to avoid splitting water as the TDS decreases and pushes down the current limit with it.

Comparing the Costs of an RO vs. EDR System

Comparing an RO system against EDR technology requires an in-depth examination of your project needs and water chemistry. In both cases, a simple bench test can show a great deal about the best approach to your water treatment problem.

 

An important factor to consider when evaluating the cost of RO or EDR systems is efficiency. Due to the pressure applied to RO systems, they are much more likely to have their performance reduced by water chemistry that causes scale formation, fouling or organics that damage membranes. This reduction in performance will not only reduce the efficiency of your treatment system but will also drive up your operational and maintenance costs because labour and parts are required to provide fixes. EDR is much more resistant to these performance-decreasing factors, as mentioned earlier, reducing the operational overhead when operating on challenging wastewater, compared to RO.

 

In both RO and EDR systems, the energy required to concentrate brine is dependent on the TDS. The more dissolved salts present in your water, the more expensive your water treatment operations become. However, this cost will scale much more rapidly in EDR systems, due to the impact that ΔTDS has on capital and operating costs. For this reason, RO tends to be more cost-effective when significant reductions in TDS are required, and EDR may be more cost-effective when selective ion removal is required, or smaller TDS reductions are necessary.

The Future of EDR Technology

Homogeneous vs. Cross-linked Membranes

Modern membranes are manufactured from a continuous cast polymer, which, unlike RO and NF membranes, cannot delaminate. The next stage in membrane technology is having membranes with extreme chemical durability. Saltworks’ IonFlux membranes are one example of such membranes: their highly cross-linked polymers enable chemical durability as well as ductility and smoothness.

Modular Design

Having the option of scaling up wastewater treatment systems and changing system capacity according to desired needs is beneficial to companies that own treatment systems. Systems such as FlexEDR arrive as complete, packaged skids with the ability for modular implementation, meaning capacity expansions are easy.

 

At Saltworks, we offer three stack sizes to scale up during project testing: our benchtop E5 stack, a pilot E100 stack, and the E200 stack, which have respective capacities of 5 m3/day, 100 m3/day and 200 m3/day (Figure 5). Our standard skid combines six E200 stacks into a plant, for a capacity of 1200 m3/day, although stacks can be removed or added to adapt to different project needs.

Three electrodialysis stacks ordered from smallest to largest
Figure 5. Three FlexEDR Stacks, from left to right. E5 benchtop stack, E100 pilot stack, full-scale E200 stack.

Tests show that mEDR can achieve over 90% recovery and remove more than 90% of chlorides. The brine reject produced consisted mainly of calcium, magnesium, and sodium chloride, and greater than 150,000 mg/L TDS.

Reduced Need for Pre-Treatment

EDR technology finds itself advantageous over other treatment technologies due to its reduced requirement for pre-treatment. Advances in EDR membrane technology, such as the IonFlux ion exchange membranes used in FlexEDR systems, further reduce the need for pre-treatment, with its resilience to organics and rugged design that are capable of treating demanding oilfield waters. Reducing the need for pre-treatment also provides significant monetary benefits to treatment system owners.

Learning More

Modern EDR may provide certain projects with a real cost advantage. Readers do not need to learn how to size and quote an EDR system. Simply contact us today to get started on your project.  

About Saltworks

Saltworks Technologies is a leader in the development and delivery of solutions for industrial wastewater treatment and lithium refining. By working with customers to understand their unique challenges and focusing on continuous innovation, Saltworks’ solutions provide best-in-class performance and reliability. From its headquarters in Richmond, BC, Canada, Saltworks’ team designs, builds, and operates full-scale plants, and offers comprehensive onsite and offsite testing services with its fleet of mobile pilots.

Related Resources

photo of FlexEDR
Product

FlexEDR Electrodialysis Reversal

FlexEDR is a next-gen electrodialysis reversal (EDR) system for industrial wastewater desalination, solving scaling issues & boosting recovery.

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How to Improve FGD Economics with Chloride Removal using Selective EDR

Photo of a coal-fired power station an FGD plant

How to Improve FGD Economics with Chloride Removal using Selective EDR

Jul 23rd 2018

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Key Takeaways

  • As regulations on FGD wastewater tighten, additional treatment is required. Often, this is chemically intense and at high cost. The best means to lower treatment costs is to reduce the volume of wastewater generated, usually by increasing internal recycle.
  • Internal recycle of FGD wastewater is limited by high chloride concentrations that inhibit sulfur dioxide absorption and can cause corrosion issues as chlorides are cycled up—this can be solved by the solution below.
  • Chlorides can be selectively removed from FGD wastewater by industrially available electrodialysis reversal (EDR) with monovalent selective membranes (mEDR). mEDR selectively transports chlorides under an electric field through monovalent anion exchange membranes while blocking sulfates. This reduces the chloride load to enable internal FGD recycle while producing a non-scaling brine of sodium/calcium chloride at greater than 90% recovery (or 10% brine waste volume).
  • 100% recycle of the low-chloride treated water will not be possible, due to cycling up of organics that are not removed by mEDR; however, even partial recycle will reduce the cost of expensive infrastructure for FGD wastewater treatment.
  • Highly robust monovalent ion exchange membranes with >98% selectivity should be used, such as Saltworks’ Ionflux, which prevents scaling by blocking almost all sulfates and can be cleaned with strong oxidants such as bleach.
  • mEDR can be integrated into existing FGD wastewater treatment trains, and eliminates the need for costly soda ash softening while producing a brine concentration almost equivalent to evaporators.
  • Although chlorides can be removed to less than 200 mg/L, reducing them to between 1,200 and 1,500 mg/L is more economical. Lower chloride levels can be attained at the expense of higher capital and higher energy due to reduced membrane flux below 1,200–1,500 mg/L Cl.
  • For more information on how EDR works, check out this blog. 

Photo of smoke rising from coal power plants that require FGD systems

Background: FGD Wastewater

Flue gas desulfurization (FGD) systems in coal-fired power plants are used to remove sulfur dioxide (SO2) air emissions. FGD systems create wastewater that is often saturated with calcium sulfate while containing both metals and chlorides. FGD water is recycled internally and then purged out of the system when chloride concentrations exceed a set level. High chloride concentrations inhibit SO2 absorption from the flue gas and create corrosion concerns with wetted equipment. Chloride blowdown levels range with operations from 10,000 mg/L to as high as 30,000 mg/L.

Photo of cooling towers in a power plant facility

Most FGD installations already include some wastewater treatment, typically referred to as ‘triple box’, wherein heavy metals and fluorides are removed via moderate pH (~pH 9) precipitation, combined with polymer and coagulation, and followed by a filter press. Historically, the filtrate is released; however, chloride, selenium, and other constituents that make up total dissolved solids (TDS) are not removed. The industry is facing new regulations that force TDS removal.

 

Saltworks has reviewed and tested multiple options in order to inform an appropriate path for future development. The top three contending options, summarized below, are based on industrially practiced technology. However, leading innovation is applied to options 1 and 3. The results show that monovalent electrodialysis reversal (mEDR) holds the greatest promise to provide a step change in reducing costs of FGD wastewater treatment.

  1. UHP RO: Chemical Softening → Seawater 80 bar Reverse Osmosis (SWRO) → Ultra-High Pressure 120 bar Reverse Osmosis (UHP RO)
  2. EVAP: Chemical Softening → Seawater Reverse Osmosis (SWRO) → Evaporator
  3. mEDR: Monovalent Electrodialysis (mEDR), without Chemical Softening: a) Desalt down to 1,500 mg/L chlorides; b) Desalt down to 500 mg/L chlorides

All options assume an upstream ‘triple box’ treatment step is already in place. All options produce a final brine reject that is either combined with fly ash for solidification and landfill disposal or sent to a ZLD system. The recovery and brine reject volume for each option is included in the analysis; however, the final disposal costs of said brine is excluded and assumed to be roughly equivalent, or at least not impact the final conclusions drawn for next steps.

FGD Wastewater Treatment Options

Options 1 (UHP RO) and 2 (EVAP):

Simplified process flow diagrams for FGD wastewater treatment options 1 and 2 are shown in Figures 1 and 2 below. They differ in their final concentration step: Option 1 includes ultra-high pressure reverse osmosis (UHP RO), which can produce a brine reject at 130,000 mg/L TDS; Option 2 includes an evaporator, which produces a more concentrated brine reject at 180,000 mg/L TDS, but at a higher cost than UHP RO.

Simplified process flow diagram of chemical softening and reverse osmosis for FGD wastewater
Figure 1. Simplified process flow diagram for Option 1: Chemical softening–SWRO–UHPRO.
Simplified process flow diagram of a chemical softening and evaporator treatment chain used for FGD wastewater
Figure 2. Simplified process flow diagram for Option 2: Chemical softening–SWRO–Evap.

Both options produce treated water that is suitable for environmental discharge and leverage an upstream seawater reverse osmosis (SWRO) step, which is low cost and widely available. Based on the FGD waters tested by Saltworks, the chemical softening soda ash must be employed with RO and evaporators. Its cost accounts for almost 50% of the treatment total cost of ownership (capital plus operating cost; see Table 2 below).

 

Option 3 (mEDR):

Monovalent electrodialysis (mEDR) selectively pulls out chlorides to increase internal recycle rate and decrease wastewater volume. See Figure 3.

Simplified process flow diagram of a monovalent electrodialysis reversal mEDR system
Figure 3. Simplified process flow diagram for Option 3: mEDR.

mEDR builds upon traditional electrodialysis technology, the world’s second-most practiced membrane desalination technology, and is enabled by recent advances in monovalent ion exchange membranes. These are manufactured from a ductile and highly conductive ion exchange polymer. Under an electrical field, these membranes selectively allow monovalent anions, such as chloride, to pass through the membrane and concentrate up in the brine reject stream while blocking multivalent ions, such as sulfate (see Figure 4). Similar to how kidneys remove waste from the human body, mEDR removes chloride in the wastewater and recycles the low chloride water back to the FGD system for reuse. 

Diagram of monovalent electrodialysis reversal (mEDR) using selective membranes and FlexEDR technology
Figure 4. Monovalent electrodialysis stack.

Since mEDR only moves chlorides and calcium to the brine reject, it produces a non-scaling brine comprising primarily sodium and calcium chloride. Since sulfates are prevented from entering the brine, scaling products do not form and high membrane system brine concentrations can be achieved without the need for expensive soda ash softening.

 

mEDR Tests on Real FGD Wastewater

The mEDR process has been tested on a micro-pilot (see Figure 5) and Saltworks’ micro-stack with real FGD wastewater from a power plant to prove feasibility and provide initial performance data. Full-scale stacks are available in two sizes, also shown in Figure 5, and results scale-up linearly based on a series of past projects.

Photo of a fully automated micro pilot of FlexEDR technology
Micro-pilot: A fully automated and complete process
Photo of a FlexEDR micro-stack
Micro-stack
Photo of an E100 FlexEDR stack
E100 Stack: 100 m3/day
Photo of an E200 FlexEDR stack
E200 Stack: 200 m3/day

Figure 5. Micro-pilot and full-scale EDR stacks.

Tests show that mEDR can achieve over 90% recovery and remove more than 90% of the chlorides. The brine reject produced consisted mainly of calcium, magnesium, and sodium chloride, and greater than 150,000 mg/L TDS. The analytical results of the inlet FGD wastewater, processed water and brine reject are shown in Table 1 below. Figure 6 shows the relative removal of various ions, including the extremely high rate of chloride removal vs sulfate.

Table 1. Water chemistry data for FGD wastewater, processed water and reject brine.

Table providing FGD water chemistry data
Chart providing a comparison of major constituent concentrations in FGD wastewater and mEDR processed water
Figure 6. Comparison of major constituent concentrations in FGD wastewater and mEDR processed water.

The test plant operated reliably without the need for chemical softening. The membranes demonstrated excellent monovalent anion selectivity—chlorides were reduced by more than 90%, while 94% of sulfates remained in the FGD water. On a molar basis, this means for every 200 chloride ions that were removed from the FGD wastewater, only one sulfate ion passed through the monovalent anion exchange membrane. This high monovalent selectivity is critical for realizing chloride removal from FGD wastewater and concentrating calcium/magnesium/sodium chloride in the brine reject without scaling. No irreversible organic or inorganic fouling occurred, and preventive oxidant cleaning followed by a sodium chloride wash every 30 days will maintain performance. 

FGD Wastewater Treatment Costs

Table 2 below compares capital and operating costs of all three options, based on real FGD water, test data, and vendor prices, assuming 300 m3/day capacity (12.5 m3/hr). Costing is based on test data and water chemistry, as shown in Table 1. The total cost of ownership is calculated, assuming capital costs depreciate over a 20-year lifespan at 8% while adding in operating costs such as energy, chemicals, and membrane replacements. Installation, operating labour, and taxes are excluded. The mEDR installation desalting to 1,500 mg/L chlorides requires six Saltworks E200 stacks, while desalting to 500 mg/L requires twelve stacks. Flow rates higher than 300 m3/day are readily achievable by adding more stacks.

Table providing a comparison of flue gas desulfurization water treatment costs

*Costs assume pre-filtration and balance of plant built in China to Saltworks’ specifications; Saltworks to supply membranes, stacks, process engineering (P&ID), and control PLC with program embedded

*Costs do not include installation, labour, VAT; assume equal impact to all options

*Costs assume economies of scale in orders and production

Table 2. Comparison of FGD wastewater treatment costs.

The results show potential, where:

  • mEDR can save up to 50% in capital (no need for chemical softening and thermal system) and operating costs for FGD wastewater treatment, compared to options 1 and 2.
  • mEDR can remove chlorides to very low levels; however, that may not be the most economically practical. Once chlorides are reduced below 1,200 to 1,500 mg/L, the membrane flux is reduced and electrical resistance increases. This increases membrane area and power to reach lower chloride levels. Results show that although mEDR can readily desalt to 500 mg/L chlorides or lower, capital cost and energy increase by 50%. Since the treated fluid is being blended with higher chloride water inside the FGD system, and mEDR pre-treatment costs are low, it may not make economic sense to reduce chlorides much lower than 1,200mg/L to 1,500 mg/L.

Full-Scale mEDR Implementation

Full-scale plants can be implemented as the foundation technology (electrodialysis); this is not new, and production systems are in placed as shown in Figure 7 below.

Collage of photos showing Saltworks employees manufacturing a FlexEDR stack
Figure 7. Full-scale production of electrodialysis stacks.

Standard mEDR skids are produced consisting of six FlexEDR E200 stacks, each with a hydraulic treatment capacity of 200 m3/day per stack. Each stack will remove roughly 4,000 mg/L TDS per pass and multiple passes are required for higher removal. The monovalent ion exchange membranes are essential to the solution and Saltworks Ionflux membranes are recommended due to their high monovalent selectivity, robustness, and oxidant tolerance, balanced with their lower cost.

 

Saltworks owns a series of mobile pilot plants that are available to demonstrate any of the three options on site: RO, EVAP, or mEDR. The pilots are containerized (Figure 8) and re-create full-scale processes that include automation and controls.

Collage of photos of FlexEDR stacks with Saltworks employees and pilot plant delivery
Figure 8. Electrodialysis pilot plant.

Conclusion

mEDR technology, based on industrially available electrodialysis, shows much promise and compelling economics for FGD wastewater treatment at up to 50% cost savings. Field pilots in specific applications are recommended to determine the following:

  • Optimum chloride reduction level for the process;
  • Characterization of purge/blowdown to prevent accumulation of deleterious matter such as organics or other ions;
  • Solidification requirements and recipe for the mEDR brine reject.

After a field pilot, full-scale plants can be rapidly delivered as production is in place and electrodialysis has a long heritage of implementation. This article is intended as general guidance. Specific project needs, water chemistry, and site requirements will change economics. Contact us for further details.

About Saltworks

Saltworks Technologies is a leader in the development and delivery of solutions for industrial wastewater treatment and lithium refining. By working with customers to understand their unique challenges and focusing on continuous innovation, Saltworks’ solutions provide best-in-class performance and reliability. From its headquarters in Richmond, BC, Canada, Saltworks’ team designs, builds, and operates full-scale plants, and offers comprehensive onsite and offsite testing services with its fleet of mobile pilots.

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Frac & Shale Water Management, Treatment Costs & Options

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Frac & Shale Produced Water Management, Treatment Costs & Options

Jun 14th 2018

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Key Takeaways

  • Economic strategies for managing shale produced water require you to explore treatment options, treatment costs compared to disposal costs, and methods to manage risk.
  • Open-to-atmosphere evaporators offer the best economics for shale volume reduction, although it is important to ensure that 1) your emissions of volatile organic compounds (VOCs) are managed, 2) a low-cost heat source is available, 3) your permit will allow it, and 4) sufficient water volume removal can be achieved for minimal liquid discharge (MLD) or zero liquid discharge (ZLD).
  • New advanced membrane systems may be economic for reducing shale produced water volume when the TDS is lower than 80,000 mg/L.

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Periodic table of scaling compounds
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Source Water and Disposal Costs in Shale

Although many water management options are available for shale operators, there is no one-size-fits-all solution. It is important to understand the costs, alternatives, and technical limitations of each option and develop a blended water management strategy to balance costs and risks. Start with identifying the costs of nearby frac/produced water disposal and source water costs. Read this overview of the different types of shale water. These options should then be compared to the costs of any treatment solution. For example:

  • Disposal: $6 to $60/m3 ($1 to $10/BBL)
  • Freshwater: $0.5 to $6/m3 ($0.1 to $1/BBL)
  • Re-use: many operators reuse flow back and produced water, and the cost is largely linked to storage, transport, and any treatment to reduce particulate load (microfiltration) and scalants (chemical softening).

In some cases, logistics or water hauling can dominate the cost equation; therefore, treatment at the source to reduce volume may make sense.

Shale Water Treatment Options

Photo of a shale gas site with wastewater treatment needs

In general, treatment methods fall under three categories, as follows. 

1) Particulate & Hardness Removal: ($)

Technology:

  • Water hardness is removed by chemical softening, and particulates are removed by bag filters. New developments in chemical softening system design remove pains of the past, such as over- or underdosing, poor control, large physical footprint and lack of modularity.

Considerations:

  • Dosing: Conventional chemical softening systems use set dosing rates, which result in poor precision on constantly changing shale waters. This can lead to underdosing, which may cause scale, or overdosing, which results in wasted chemicals and increased operating costs. Modern chemical softening systems that use sensor-driven precision dosing avoid these problems by reducing waste and maintaining treatment system performance.
  • Filter Quality: Some bag filter systems are treated as disposable, resulting in higher waste, higher manual handling, and greater disposal costs. Opting for re-usable, highly robust filters with a semi-automated solids handling system can reduce these costs and improve both the operability and environmental footprint of your particulate removal program.
  • Intervention: Whether dealing with bag filters or chemical softening, conventional systems can require high operator intervention. New technologies, such as our BrineRefine platform, come as a packaged, automated system that reduces intervention and improves the economics of this water treatment process.

Rendered image of a SaltMaker AirBreather evaporator crystallizer
SaltMaker AirBreather

2) Volume Reduction: ($$)

Technology:

  • Open-to-Atmosphere Evaporators: Evaporation to atmosphere will reduce produced water volumes at a lower cost than closed evaporators (discussed later in this article). However, their fit with respect to thermal needs, air emissions, reject concentration, and permitting must be confirmed. Total cost of ownership (capital cost + operating costs) may range from $12-$24/m3 ($2-$4/BBL).

Considerations:

  • Air Emissions: Although water vapour is harmless to the environment, produced water may include volatile organic compounds (VOC) that evaporate with the water. Benzene is the most common VOC in produced water and is a regulated carcinogen. There are also volatile forms of arsenic and radium that exist as a part of organic complexes. Make sure you plan ahead for VOC management, since regulators and stakeholders will expect it. Open to Atmosphere Evaporators have been procured and then rapidly shut down due to stakeholder concerns. Invest in risk management and possibly a pilot project prior to making a large capital purchase. Saltworks’ open-to-atmosphere evaporator, AirBreather, includes a novel VOC management system that removes VOCs from the exhausted water vapour. Pilot plants are available to prove this and can be complemented with air dispersion modeling to support permitting discussions.

Process flow diagram of a SaltMaker Airbreather evaporator
Process flow diagram of a SaltMaker Airbreather evaporator
  • Energy: One cubic meter (6.3 BBL) of water requires 3.3 GJ (2.2 million BTUs) of energy to evaporate. However, the value of energy, known as ‘exergy’, depends on its temperature. It may only make sense to spend this energy if a waste heat source or a low-temperature heat source is available, such as waste heat from reciprocating engine jacket cooling, exhaust, or waste gas that is flared. Water boils at 100 °C (212 °F), and most engine waste heat sources are 85–95 °C, which is not sufficient to evaporate water. However, the Saltworks’ AirBreather does not involve boiling water; instead, it humidifies air. This enables the use of a much lower temperature heat source, whereas other open-to-atmosphere evaporators use submerged combustion with direct-fired gas sources, such as natural gas. There is a trade-off in that humidifying air requires larger chambers, but they operate at a lower temperature and can be constructed from engineered plastics to withstand corrosion and scaling issues.
  • Pre-treatment: Some evaporators cannot tolerate scale-causing compounds, so be sure to complete a water analysis and check with the technology vendor. The AirBreather was developed to accept any fluid without pre-treatment, and remove scale by self-cleaning before it becomes irreversible.
  • Concentration limits: Most open evaporators are limited to an upper TDS concentration of 150,000 to 250,000 mg/L, where they may start plugging with accumulated low-solubility solids. It is worth determining these concentration limits before investing, since they directly impact the plant capacity. If you start with a TDS of 200,000 mg/L and can only concentrate to 250,000 mg/L, this means a volume reduction of 20% will be achieved. Contact us for help with making these calculations for your project. The AirBreather has no TDS limit, and can make solids due to its built-in self-cleaning and corrosion-proof construction. This means you can squeeze almost all the produced water, reducing your volume to any desired level. However, recall that rejected residual TDS waste must be managed.
  • Corrosion: After scale, corrosion is the second greatest killer of evaporators. Stainless steel will rapidly corrode when exposed to high chloride concentrations in produced waters. Super duplex stainless steel variants offer increased resistance, but they can cost more than exotic metals, such as titanium and Hastelloy, which do not corrode. The AirBreather’s wetted parts are 95% gel-coated fiberglass and engineered plastic to entirely remove the corrosion risk. Heat exchangers are constructed with titanium but no boiling occurs on any metal surfaces, limiting scale potential. The AirBreather’s intelligent controls monitor heat exchanger performance and clean them in an automated manner before any irreversible performance degradation occurs.

Photo of scaling found on the interior surface of pipes

3) Fresh Water Production: ($$ to $$$)

Technology:

  • Membranes ($): Reverse osmosis (RO) and electrodialysis reversal (EDR) are the most widely used membrane desalination technologies. However, these methods offer limited economic fit to water with mid-range TDS concentrations (less than 40,000 mg/L). New advancements in membrane systems, such as ultra-high pressure reverse osmosis, can now be economic with TDS up to 80,000 mg/L. Our XtremeRO systems can concentrate produced water up to 140,000 mg/L TDS, reducing disposal volumes for minimal liquid discharge (MLD). Membrane system total cost of ownership (capital cost + operating costs) may range from $3-$9/m3 ($0.5-$1.5/BBL); however, pre-treatment, such as BrineRefine, could change this cost equation. 

Photo of a reverse osmosis system used for brine volume reduction
  • Closed Evaporative Crystallizers ($): Closed evaporative crystallizers can offer applicability across a wide range of TDS concentrations, but they are also the most expensive treatment option due to their size and complexity. Closed systems condense water vapor and employ different methods to recycle a portion of the thermal energy or heat of condensation. This lowers their energy consumption relative to open to atmosphere evaporators but increases their relative cost. 

Photo of a humidification-dehumidification evaporator
  • When considering a closed evaporative crystallizer, you should also factor in pre-treatment for scaling, concentration limits of conventional evaporators, and corrosion risk. In addition, if freshwater is produced, it must either be stored, re-used, or released to the environment. One advantage of freshwater storage and transportation over produced water storage is that it requires less containment. Although you should check your local regulations, in many cases, freshwater may be stored in ponds, industrial water bags, or tanks and transported via a lower cost lay flat hose. Freshwater may be used by a neighboring agriculture facility or can also be discharged to the environment in some jurisdictions, noting that permitting for environmental discharge in the US may take up to a year and the permit is typically valid for only a single site. These added dimensions speak to why open-to-atmosphere evaporators can be a better option if air emissions are managed and thermal energy is available.
  • The total cost of ownership for a closed evaporative crystallizer (capital cost + operating cost) may range from $24-$48/m3 ($4-$8/BBL), making it the most expensive treatment option.

Logistics and Residual Reject Disposal

A photo of a wastewater disposal truck used in brine management

Logistics: Logistics and water hauling can dominate shale water management costs if a disposal outlet is not nearby. Keep an understanding of logistics cost in mind when assessing treatment and disposal options, including wait times for trucks to load and unload. As a rule of thumb, transport may cost $15/m3 ($94/BBL) per hour, once loading and unloading times are factored in. Costs also vary depending on the quality of roads in the area. Reviewing pre-concentration can make sense prior to transport, which lowers the volumes of water being hauled. In many cases, there will be an economic optimum that combines re-use, storage, treatment, and transport for final reject waste disposal.

 

For example, if transport and disposal is $30/m3, and volumes can be halved for $10/m3, and solids produced afterwards for $45/m3, then it may make the most sense to pre-concentrate and halve the volumes for $10/m3 followed by transport and disposal for $30/m3. The net blended cost will be $20/m3. Preferably, the reject waste is as concentrated as possible until it reaches a cost that is just below the transport-disposal costs. It is important to note that as produced water is concentrated and its volume reduced, it can become denser, with more scaling potential. Higher density waters can be beneficial for disposal wells; however, scaling waters may plug them. Technologies, such as BrineRefine, are available to reduce the scaling potential of highly concentrated brines prior to disposal, and thereby protect the disposal well asset from scaling and plugging while maintaining the beneficially high density.

Photo of a full-scale, 2-module, Saltworks BrineRefine plant
Saltworks' BrineRefine Chemical Reactor System

Residual Reject Disposal: Although relatively pure water can be separated from produced waters, reject residual waste is always left behind. This will include organics (petroleum byproducts) and inorganics (mixed salt). Planning for residual waste in advance is important. One advantage of disposal wells is that they dispose of all residuals, and as noted above, disposal costs and volume can be limited through treatments that pre-concentrate. However, it is also possible to (a) produce a mixed solid waste for landfill disposal, and (b) separate out the organic phase and produce refined salts for industrial re-use. This includes a combination of chemical pretreatment and staged crystallization.

 

Be sure to study and assess the lifetime of disposal options if solids are going to be produced. Landfill waste must pass paint filter, leaching (TCLP) and radioactivity tests. Saltworks can help assess if your produced water may pass these tests through bench testing. Saltworks can also review your water’s potential to produce beneficial industrial salt for re-use—although this is unlikely to offer a secondary revenue stream through salt sales. Most salts are of low value and the costs of producing, handling and transport barely offset any revenue generated. However, industrial re-use offsets costs by avoiding the need to pay for landfill disposal.

Summary

Shale gas and oil production presents a leading energy source moving forward, yet its future and production is tightly linked to water management. Every water type, job site, and economic case is different. Contact us to review your specific situation, benefit from our expertise, and assess if your water management costs or risks can be lowered.

About Saltworks

Saltworks Technologies is a leader in the development and delivery of solutions for industrial wastewater treatment and lithium refining. By working with customers to understand their unique challenges and focusing on continuous innovation, Saltworks’ solutions provide best-in-class performance and reliability. From its headquarters in Richmond, BC, Canada, Saltworks’ team designs, builds, and operates full-scale plants, and offers comprehensive onsite and offsite testing services with its fleet of mobile pilots.

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Managing Shale Water and NORM

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Shale Water and NORM

Jun 14th 2018, Updated Sep 29th 2021

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Summary

  • There are four types of shale waters, each with unique properties, uses, and treatment approaches.
  • If your frac or produced water contains NORM (naturally occurring radioactive material), plan to manage them by keeping them in solution, precipitating them for safe handling, or diluting them followed by water disposal.
  • Many factors should be considered in assessing petrolithium extraction projects: concentration of lithium, quality of the water, disposal availability, cost of power, location, flow rate, and more. In the past, concentrations lower than 500 mg/L would have been considered non-viable. With otherwise favourable conditions, wastewaters with lithium >70 mg/L and sustained flow rates >1,000 m3/day might now be considered viable.

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Periodic table of scaling compounds
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Shale water management starts with understanding the distinct types of water, their uses, and their volumes. This will enable better management of the site’s water balance to ensure that the right amount of water is available when needed and excess water does not exceed your storage capacity. Practitioners also need to consider the chemistry, which may include scalants, total dissolved solids (TDS), and NORM (naturally occurring radioactive material). The water chemistry significantly impacts shale produced water treatment strategy, as well as informing end-of-life options for the waste by-products that are left behind once clean water is removed. These by-products are often referred to as reject or residuals.

 

The Different Types of Waters Used in Shale Gas Operations

Four primary types of water are used in shale gas operations.

 

Source water is drawn from nearby water sources, such as surface waters or groundwater, and is typically used for hydraulic fracturing (also known as ‘fracking’).

 

Saline re-use water is the water that returns after the fracking process, with increased salinity, but can sometimes be re-used as source water. It may require mild treatment before being used for another fracking process.

 

Frac flowback is the water that returns from the ground, following a fracking process. Most of it returns rapidly after the fracking process and will include chemicals employed in fracking that can change the treatment process. The flowback flow rate slows over the first week(s) while TDS concentrations increases. Some of this flowback may become saline re-used water, if needed for future fracking applications.

 

Produced water also returns to the surface, like flowback, but produced water largely originates in the formation. It tends to flow more steadily over longer periods of time and will have a higher TDS.

 

See the table below for additional details about each water type.

Water Type Utilization Characteristics Treatment Flow (m3/day)
Source water Fracking Usually locally sourced freshwater, such as surface water or groundwater with little to no TDS Chemicals and sand enhancements may be added High during fracking process, then tapers to zero
Saline re-used water Fracking (re-used) TDS: 10,000 to 200,000 mg/L and scaling ions can be present If re-used in a fracking process, the water is often filtered and occasionally softened (to remove barium & calcium) Best maximized to reduce future management volumes
Frac flowback Re-used if source water needed, otherwise disposed of or treated TDS increases over the first week of flowback See our shale water treatment options High immediately post fracking (~70% of injected water returns), flow rate tapers down over the first week
Produced water Re-used if source water needed, otherwise disposed of or treated TDS varies but often as high as 100,000 to 200,000 mg/L See our shale water treatment options Ranges from 10-1,000 m3/day (63–6,300 BBL/day) per well

Safety Considerations

NORM: NORM are naturally occurring radioactive materials, with radium and its many forms being the most common. Not all produced water contains NORM, but they are occasionally encountered in North American shale.

 

  • It is important to understand the major risks associated with handling water that contains NORM since these risks can be managed. First, ingestion of radioactive material either through inhalation or swallowing is the primary hazard. Always wear gloves and wash your hands and clothes whenever working around potentially radioactive material. Never eat food near NORM and do not bring gloves used to handle NORM into a food zone. Second, gamma rays given off by NORM can be harmful; however, water is an effective insulator. Putting this into context, humans are exposed to more radiation on a 2-hour flight, than standing next to NORM containing produced water for an extended period.

Photo of a fracking site with wastewater treatment needs
  • There can be some risk if NORM precipitate and become dried out, removing the insulating properties of water. NORM can be precipitated alongside barium, which can be achieved by adding sulfates (sodium sulfate) or carbonates (sodium carbonate) at an elevated pH (pH > 9). NORM may also precipitate as a sludge on the bottom of tanks and filter bags, and they should be checked with a radioactive test before handling for safe disposal by a certified party. Diluting NORM sludge with water can improve safety for the reasons mentioned above; however, this will create more liquid waste. The best strategy is to measure the presence of NORM in your water and develop a plan to manage them, either through precipitation removal and safe handling or water disposal.
  • Chlorine dioxide treatment and removal: Chlorine dioxide is used in shale waters to precipitate iron with possible NORM co-precipitation. As a benchmark, the cost of removing iron using chloride dioxide varies widely from $3–$50/m3 ($0.5–$8/BBL), depending on the volume of water that needs to be treated. Chlorine dioxide will damage membrane treatment systems, so be sure to remove the chlorine dioxide upstream of a membrane system. There are many options for this, including activated carbon (expensive) or sulfites addition (more common).

Lithium: Some oil field brines contain lithium in the 60–100 mg/L range (0.006–0.01%) and there is excitement for the potential of harvesting lithium from oil field brines (overview of lithium brine extraction technologies here). This is a new and rapidly developing space so concluding that these resources could be economic at the time of writing would be premature.

 

Saltworks holds patents on lithium extraction, has built machines for lithium companies, and has technology to selectively extract lithium. While the best economics for produced water management are typically achieved through sound water management and treatment, options that incorporate lithium extraction from brine may be worthy of study.

Conclusion

Shale gas and oil production presents a leading energy source moving forward, yet its future and production is tightly linked to water management. Every water type, job site, and economic case is different. Contact us to review your specific situation, benefit from our expertise, and assess if your water management costs or risks can be lowered.

About Saltworks

Saltworks Technologies is a leader in the development and delivery of solutions for industrial wastewater treatment and lithium refining. By working with customers to understand their unique challenges and focusing on continuous innovation, Saltworks’ solutions provide best-in-class performance and reliability. From its headquarters in Richmond, BC, Canada, Saltworks’ team designs, builds, and operates full-scale plants, and offers comprehensive onsite and offsite testing services with its fleet of mobile pilots.

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Lithium Brine Extraction Technologies & Approaches

Photo of the Salar de Uyuni, Bolivia, lithium salt lake

Lithium Brine Extraction Technologies & Approaches

Jun 8th 2018

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Key Takeaways

  • Brines from salars and salt lakes, as well as spodumene ores, are the primary sources of lithium, while geothermal and other brines represent secondary sources.
  • Produced water from oil & gas operations is an untapped source of lithium that may be more important in the future.
  • Chemical precipitation, adsorption with inorganic ion exchange sorbents, solvent extraction and concentration with membrane technologies are the primary means of lithium recovery from brines.
  • Each lithium extraction and recovery process has unique advantages and challenges that need to be considered when determining the best fit for any project.
  • New advances in water processing offer exciting improvements on the economics of using membrane technologies for lithium recovery.

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A simple process flow diagram for lithium processing and refining by Saltworks Technologies
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Summary of Major Lithium Brine Resources and Dominant Recovery Processes

Resource Lithium (mg/L) Dominant Process Challenges Opportunities
Salars (Lake Brines) 200-7,000 Staged evaporation to atmosphere, concentrating and producing lithium. Large land areas and significant quantities of water used to extract lithium from lake beds.

Minimum 18 months from pond start-up to first production due to slow evaporation. 		Massive resource with available natural evaporation energy.

Opportunity to hybridize evaporation with concentration and purification technologies.
Groundwater Brines 20-200 Lithium absorption-desorption on a metal oxide, following by refining. Tend to be richer in hardness than salars, making processing more challenging. Vast resources in USA, close to major lithium utilization plays.
Oil & Gas Brines 50-100 No dominant process established. Low concentration and extremely large volumes needed, while most produced waters are spread out and smaller volume. Attractiveness of oil & gas wastewater adding value.

Roughly half of the world’s commercial lithium is recovered by concentrating naturally occurring lithium brines in evaporation ponds. This practice is low cost and provides ~50% recovery, but is only feasible in arid climates. New technologies are enabling higher recovery of lithium from saline brines without the need for an evaporation pond, opening opportunities in non-desert geographies.

What are the Primary Sources of Lithium?

Photo of the Salar de Uyuni, Bolivia, lithium salt lake
Salars in Bolivia

Due to continuing advancements in mobile devices and electric cars, the demand for lithium is outpacing the rate at which lithium is being mined from brines. Lithium is an abundant element, but there are very few commercial resources where lithium is found in concentrations sufficient for producing useful lithium compounds.

 

The primary sources of lithium are in brines from salars and salt lakes, and lithium-bearing spodumene ores, while geothermal brines represent the second-most productive sources of lithium. Lastly, produced waters from oil & gas fields are an untapped source of lithium that may grow in importance in the future. To ensure the productivity of these lithium resources, it is essential to have lithium recovery technology and processes that are optimized to the characteristics of each individual resource, such as the concentration of lithium, the ratio of lithium to magnesium and calcium ions, and relative concentrations of other ions.

Lithium Recovery via Chemical Precipitation

Lithium recovery via conventional chemical precipitation normally starts by subjecting lithium-rich brine to a series of solar pond evaporations. This will precipitate other salts, such as sodium chloride and potassium chloride, while concentrating the lithium. Lime (calcium hydroxide) is then added to the concentrated lithium brine to further remove magnesium as magnesium hydroxide, and sulfate as calcium sulfate. Any calcium in the concentrated brine is removed as calcium carbonate by adding sodium carbonate. The brine that results from these chemical precipitations is then subjected to a carbonation process, where the lithium reacts with sodium carbonate at 80–90°C to produce technical-grade lithium carbonate. This can be further purified to produce battery-grade lithium by re-dissolving the lithium carbonate, and then using an ion exchange process to remove impurities.

 

To reduce the time that is required for solar-evaporation concentration, lithium will sometimes be precipitated as lithium phosphate, which precipitates more quickly than lithium carbonate due to its roughly 30-fold lower solubility. Lithium phosphate is then converted into battery-grade lithium hydroxide through an electrochemical process.

Lithium Recovery via Adsorption

Lithium-selective ion-exchange sorbents are a promising alternative for extracting lithium from brines. Inorganic ion-exchange sorbents, such as lithium manganese oxides, spinel lithium titanium oxides, and lithium aluminum layered double hydroxide chloride, have been shown to have high capacity for selective lithium uptake. However, the recovery process requires the lithium to be in contact with these sorbents for long periods of time. Additionally, sorbents can be very expensive; they are mostly available as powders that require energy-intensive processes for lithium recovery and can degrade during the acid-driven desorption process.

 

A novel technique based on an electrolytic cell that contains LiFePO4/FePO4 as an electrode material has been studied to selectively recover lithium. Under an electrochemical process, lithium ions from a lithium-bearing brine are selectively intercalated into a cathode made from FePO4 to form a lithium-saturated LiFePO4. Then, the current is reversed, turning the LiFePO4 into an anode that can be used to recover lithium.

Lithium Recovery via Solvent Extraction

One approach that has been tested to selectively recover lithium from brine involves using an organic phase that comprises kerosene and an extractant, such as tributyl phosphate, trioctylphosphine oxide (TOPO), and beta-diketone compounds. Although these organic phases show very high selectivity toward lithium over sodium and magnesium ions under optimized conditions, the lithium stripping phase uses solvent extraction that can result in costly equipment corrosion. In addition, the residual brine that remains after lithium extraction may require post-treatment to remove the leached solvent before it can safely be sent for disposal.

A photo of a Saltworks XtremeRO reverse osmosis plant
Saltworks' XtremeRO reverse osmosis plant

Lithium Recovery Using Membrane Technologies

Reverse osmosis (RO) and nanofiltration (NF) processes have been studied for pre-concentrating or separating lithium from a lithium-bearing brine. A typical lithium brine usually contains high concentrations (e.g. > 5.0 wt%) of salt ions. The maximum salt concentration that an RO/NF process can reach is linked to the osmotic pressure, as well as the membrane’s selectivity and the mechanical stability of any associated equipment. Automated chemical softening systems, such as our BrineRefine system, can help membrane treatment systems reliably reach their treatment limits and improve yield. Conventional NF processes cannot efficiently separate lithium without heavy pre-treatment of the brine, such as diluting the brine with a large amount of fresh water.

Electrodialysis systems, such as our FlexEDR Selective, should be viewed primarily as concentrators and not as refining technology. This is because today’s monovalent EDR systems cannot separate sodium from lithium, and although monovalent electrodialysis may separate monovalent ions from divalent ions, the separation is less effective than chemical methods in the case of lithium, resulting in higher yield losses.

About Saltworks

Saltworks Technologies is a leader in the development and delivery of solutions for industrial wastewater treatment and lithium refining. By working with customers to understand their unique challenges and focusing on continuous innovation, Saltworks’ solutions provide best-in-class performance and reliability. From its headquarters in Richmond, BC, Canada, Saltworks’ team designs, builds, and operates full-scale plants, and offers comprehensive onsite and offsite testing services with its fleet of mobile pilots.

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