Article

Enhanced Oil Recovery (EOR) Produced Water Desalination

enhanced oil recovery pilot oil and gas

Enhanced Oil Recovery (EOR) Produced Water Desalination

October 7th 2019

Saltworks completed two successful live oil field pilots, desalinating enhanced oil recovery (EOR) produced water. The objectives were to lower the clients’ polymer consumption costs and improve the quality of injection water, in order to improve hydrocarbon recovery and lower operating cost. These objectives were met, with over 97% up-time. A video walk through of the pilot can be viewed here.

For further background, some EOR practitioners add polymer to increase the viscosity (“thickness”) of injection water in order to recover more oil. Water returns to the surface as produced water, often more saline. Operators add expensive polymer back to this water to meet their injection viscosity goal. However, polymer consumption and costs increase dramatically with salinity. Polymer costs alone can be over $4-5/m3 injected. By desalinating the produced water prior to polymer addition, the following benefits can be realized:

  1. Reduced polymer consumption to meet the injection viscosity goal.
  2. Re-activate and recycle residual polymer in the produced water.
  3. Deliver an injection water with lower hardness, multivalent ions, and suspended solids which can improve well performance to recover more hydrocarbon.
  4. Increased water recycling, resulting in less produced water disposal and freshwater withdrawal.

The technology and products employed equally apply to other types of produced water desalination, where operators are seeking to treat produced water for discharge and/or to reduce disposal costs. Sign-up to download a presentation report, and/or contact Saltworks with your produced water challenge!

Download the free Enhanced Oil Recovery (EOR) Pilot Results

Get Your Project Assessment

Our Expertise Applied to Your Water Treatment Needs.

Article

Treating Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) Contaminated Wastewater and Landfill Leachate

drinking water pfas

Treating Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) Contaminated Wastewater and Landfill Leachate

October 4th 2019

Key Takeaways: ​

  • PFAS chemicals are often referred to as “forever chemicals” since they do not naturally degrade. They have made their way into some water supplies. Adverse health impacts range from cancer to liver disease and fertility disruption.

  • PFAS are detected in wastewaters and landfill leachate due to their widespread uses in consumer and industrial products.
  • Three existing options for removing PFAS from wastewaters: granular activated carbon (GAC), ion-exchange (IX) resins, and high-pressure membrane filtration of nanofiltration and reverse osmosis (RO). The treatment system needs to be engineered carefully with the consideration of specific wastewater chemistry, co-contaminant removals, and the pros and the cons of these treatment options.
  • The disposal of PFAS-contaminated GAC, IX resins or PFAS-concentrated brine may pose secondary risks and should be considered.
  • New advances in desalination technologies can help reduce PFAS treatment and disposal costs: ultra-high pressure reverse osmosis, minimal liquid discharge (MLD) and zero liquid discharge (ZLD).

drinking water pfas

PFAS the “Forever Chemicals”

Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) are a group of man-made carbon-fluorine chemicals produced since the 1940s. They were widely used in non-stick household products, stain-repellants, food paper packaging (e.g., compostable coffee cups and pizza boxes), lubricants, aviation firefighting foams, and many more. PFAS are comprised of a water-liking “head” group (making them soluble in water) and a long perfluoroalkyl or polyfluoroalkyl “tail” group that is made up of carbon-fluorine bonds.

PFAS chemical structure

The carbon-fluorine bond is one of the strongest chemical bonds ever created, which results in PFAS not degrading naturally or easily. As such, PFAS are often called the “forever chemicals”. PFAS have been found in surface water, groundwater, drinking water sources, wastewater treatment plant effluent and landfill leachates. People may be exposed to PFAS by consuming PFAS-contaminated water or food. PFAS can be harmful to human health causing cancer, liver damage, and a depressed immune system to name a few. The U.S. EPA is taking action by proposing regulations to protect drinking water and to cleanup PFAS-contaminated water sources.

Existing Treatment Options for PFAS Contaminated Waters

Treating PFAS contaminated water before discharge to aquatic receiving sources will reduce its accumulation in water systems. Currently industrialized methods for removing PFAS from contaminated waters are based on (1) physical adsorption technologies, such as granular activated carbon (GAC) and ion-exchange (IX) resins; and (2) high-pressure membrane filtrations, such as nanofiltration (NF) or reverse osmosis (RO). Although work is being done on advanced oxidation techniques, these are not yet commercial and could come with a very high energy price tag. 


The selection of an appropriate treatment method requires careful considerations based on the specific water chemistry, contaminant removals and the required quality of the treated water. In industrial wastewater treatment, the water composition is more complex than that of the “clean” drinking water and comprises co-contaminants besides PFAS. The presence of co-contaminants will impact the method selection, the treatment system sizing and the eventual costs. For example, landfill leachate has co-contaminants of organics, inorganics and volatiles, in addition to PFAS, requiring removal.

The pros and cons for the three industrialized PFAS removal methods are summarized in the below table.

Granular activated carbon (GAC)

Pros


• Reduce PFAS to ng/L level for drinking water.


• Effective for long-chain PFAS removal.
Cons


• Quick PFAS (short-chain PFAS in particular) breakthrough and frequent filter replacement due to weak interactions between PFAS and carbon.


• Not cost effective for waters containing other organic compounds since GAC is non-selective and will be over-loaded by other organics.


• Does not remove inorganics.


• GAC is a very expensive consumable. It can be manual intensive GAC to replace, or energy intensive regeneration (often off-site via extreme temperature vaporization).

Ion-exchange resin

Pros


• Effective for anionic and long-chain PFAS removal to ng/L level.


• Higher adsorption capacity and significantly faster reaction kinetics compared to GAC.
Cons


• Not effective for wastewater containing high levels of inorganic ions (i.e. TDS) and/or natural organic matter (NOM).


• Less affinity for short-chain PFAS.


• Incineration or regeneration of ion exchange resin required.

Nanofiltration or reverse osmosis

Pros


• Effective for both short-chain and long-chain PFAS.


• Capable of handling co-contaminants and treating all types of PFAS-contaminated water.


• High loading flow rate.


• Can be partnered with a disposal well (common in North America) to permanently dispose of the PFAS brine.
Cons


• Possible membrane fouling by scaling inorganic compounds.


• Concentrated brine management, which can be solved through high recovery performance to minimize brine produced and disposed (concentrate the PFAS to the maximum extent in ultra-high recovery RO while avoiding scaling of RO system).

A PFAS removal process may integrate multiple technologies, for example, an upstream reverse osmosis process with a high loading flow rate followed by a downstream GAC or IX-resin polishing step to meet stringent water quality requirements. Refer to our article for an overview of the importance of understanding the water chemistry, especially for nanofiltration and reverse osmosis processes. An experienced wastewater treatment team can engineer and price a solution including initial desk study for the PFAS-removal system, site investigations, and risk assessments.

Technologies to permanently and economically treating PFAS wastewater

Spring leaves are reflected in a flowing stream.

Physical separation technologies (GAC, IX resin, NF, or RO) do not destroy PFAS but only remove PFAS from contaminated water onto adsorbents or into a concentrated brine. The disposal of PFAS contaminated absorbents or PFAS-concentrated brine may pose secondary pollution risks. Technologies for permanently degrading PFAS are based on high-energy incineration or advanced oxidations including electrochemical oxidation, microwave thermal treatment, photolytic degradation, pyrolysis, and sonochemistry. These extreme PFAS degradation pathways are very costly, especially when the volume and the flowrate of PFAS wastewater are large. It is thus ideal to use other relatively cost-effective technologies to first reduce PFAS wastewater volume and concentrate PFAS into its highest allowable concentration together with co-contaminate removals. The highly concentrated PFAS wastewater can then be transported to either a disposal well for permanent disposal deep underground, or a PFAS-specialized degradation site for final destruction.

 

New advances in desalination technologies (ultra-high pressure reverse osmosis, minimal liquid discharge (MLD) and zero liquid discharge (ZLD), such as our modular BrineRefine, XtremeRO/NF, and our SaltMaker family of evaporator crystallizers) can help economically reduce PFAS wastewater volume and concentrate PFAS to a level that was previously unreachable. These modular mobile water treatment units can also be deployed to a PFAS wastewater site for onsite treatment. Our article on how to manage brine disposal & treatment provides a summary of management options.

 

Please feel free to contact Saltworks for a detailed review of your PFAS project, risk and opportunities, as well as options to manage the result brine residuals.

Related Resources

Get Your Project Assessment

Get More Information on Saltworks Solutions & Products
Article

Achieving 70x Cooling Tower Blowdown Volume Reduction

Cooling tower steam water blowdown

Achieving 70x Cooling Tower Blowdown Volume Reduction

September 13th 2019

Key Takeaways:

  • Recent RO improvements enable extreme recoveries of up to 99% for treating cooling tower blowdown (CTBD) for minimal liquid discharge (MLD) while reducing capacities for zero liquid discharge (ZLD) systems.
  • Costs and complexity increase with each added process step to boost recovery. The costs and processes are covered herein.
  • Know your brine disposal costs to determine where to stop in the treatment process. Each incremental process can achieve greater volume reduction and recovery but only take the next step when the treatment cost is less than the disposal cost.
  • BrineRefine chemical softening systems enable higher RO recoveries and reduce scaling/fouling.
  • Ultra-high-pressure spiral wound membrane systems can achieve brine concentrations near that of evaporators, 130,000 mg/L total dissolved solids (TDS), so long as scaling and fouling are controlled.

Cooling tower steam water blowdown

Background

Cooling towers are used by industrial plants to reject waste heat to atmosphere. Evaporation of the water to remove the plant’s process heat results in concentration of ions and metals in the cooling water. A portion of the cooling water is blown down after a number of cycles of concentration, before the ions and metals reach their scaling limits. This blowdown requires management. Makeup water, typically from a freshwater source, replaces the lost water from the blowdown as well as from evaporation and drift.

Options for managing cooling tower blowdown (CTBD) requires management with options consisting of:


  • Direct discharge to nearby surface water if regulations permit;
  • Storage and volume reduction in an evaporation pond if climatic conditions are favorable;
  • Disposal via injection wells if located near the site;
  • Discharge to a local wastewater treatment facility if they accept; or
  • Treatment for discharge or reuse.

The focus of this article is on the last option: CTBD treatment.

Cooling Tower Blowdown Treatment

To treat CTBD, a water treatment practitioner would need to understand some key project information:

  1. CTBD water chemistry and its scaling potential. Our article on RO & Evaporator Scale Control discusses how scale forms, its implication on water treatment systems, and how to avoid scaling. Alternatively, contact Saltworks with your chemistry and we can help you.
  2. The required water quality for the treated water for its intended final use, whether it is reused in the plant or discharged, will need to be considered. Any water treatment system will need to meet this water quality criterion.
  3. What to do with the brine? CTBD consists of inorganic constituents and any industrial desalination technology to treat the water will produce a concentrated brine. Our article How to Manage Brine Disposal & Treatment describes several options for managing this brine.

Combining the above information will inform the appropriate level of treatment, which could be a relatively simple pre-filtration and high recovery membrane system or a more advanced full treatment train of membrane and thermal systems to achieve minimal liquid discharge (MLD) or zero liquid discharge (ZLD). The total cost of treatment compared to other available means to manage the brine will determine how extensive a treatment process is required, as demonstrated in the following CTBD treatment case study.

Pilot Case Study

A North American power plant was sending their CTBD to evaporation ponds. However, the ponds were reaching capacity and offsite disposal was an expensive option. The power plant sought a treatment option to reduce offsite disposal volumes in order, to lower costs. Water chemistry is summarized in Table 1. The treated water needed to meet utility water reuse requirements required TDS < 500 mg/L.

Table 1: Power Plant Raw Water Chemistry and at Each Successive Recovery Increase
Power Plant Raw Water Chemistry Cooling Tower Blowdown

The water chemistry, with a TDS of 1,750 mg/L, is suitable for treatment by reverse osmosis (RO). For lowest cost, it is beneficial to achieve the highest RO recovery possible to minimize more expensive further brine volume reduction. An overview of RO and techniques to achieve maximum recovery are discussed in Reverse Osmosis Brine Treatment: Tech Advancements to Minimize Volume & Cost. 80% recovery is achievable with this primary RO, reducing CTBD volume by a factor of 5.


After primary RO, other technologies can further reduce volume and increase recovery by 10x (90%), 20x (95%), 40x (97.5%), and 70x (99%). These technologies are further described in the articles Modern Chemical Softening to Maximize RO Recovery and Applying Ultra-High Pressure Reverse Osmosis in Brine Management. The incremental process steps and costs required to achieve each are explored below. Volume reduction factors are presented as the primary metric, nothing that small recovery changes can be misleading. For example, boosting recovery from 95% to 97.5% may seem like gaining “only 2.5%”; however, this gain represents halving brine volume. This means 50% fewer trucks sent to disposal or a 50% smaller evaporation pond or a 50% smaller downstream evaporator. The savings to a project or operator can be enormous.


A flexible pilot plant was used to test the incremental CTBD volume reduction for the power plant. Figure 1 shows a simplified process flow diagram showing the water treatment plant’s process units. Table 2 shows each recovery stage (volume reduction), the technology to achieve it, and the cost guidance. The water chemistry emerging from each step is also included in Table 1.

Figure 1: Process Flow Diagram (PFD) showing Successive Recovery Additions
PFD Process Flow Cooling Tower
Table 2: Cooling Tower Blowdown Successive Recovery Increases
State Point Volume Reduction Recovery Technology Cost Guide: OpEx + CapEx

A

5X

80%

RO-I with anti-scalants, concentration polarization management, and flushes

$1–2 /m3

B

10X

90%

Above + high pH, UF & RO-II

$2–3 /m3

C

20X

95%

Above + some soda ash

$3–3.5 /m3

D

40X

97.5%

Above + more soda ash

$3.5–5.8 /m3

E

70X

99%

Above + UHP-RO

$4–8 /m3

Although each step can be viewed as a unit operation, it should be treated as part of an integrated plant with unified and integrated process controls. This is recommended for the following critical reasons:

  1. As feedwater chemistry and flow rates change upstream, an integrated plant can better react and adjust each unit operation accordingly.
  2. Enabling performance monitoring algorithms to be applied. This is done at both the plant and unit operation level, whereby upstream and downstream systems can communicate their performance and status to one another. Adjustments can then be made to achieve “best system efficiency.” A unified dash board is included to assist plant operators and owners in monitoring performance.
  3. Coordinate all process control design methods, control system design components, and programming style and documentation for both capital cost and operational cost efficiency (e.g. spares and maintenance).

Brine concentration and composition changes with each incremental step in recovery improvement, shown in Table 1. It is possible to vary the quantity of soda ash (sodium bicarbonate) dosing to achieve the desired recovery: if higher recovery is desired then more soda ash can be added; if lower recovery is sufficient then less soda ash is needed. Regardless, it is advisable to stay below 80% calcium sulfate saturation in the brine to prevent irreversible scaling. Soda ash chemical cost can be one of the higher operational cost inputs into a high recovery plant; therefore, it should be controlled carefully. Saltworks has technology to help with this.

Economic Guidance

Readers are offered the following reminders and guidance when considering brine treatment economics:

 

  • Sum the costs of chemical treatment and secondary RO, since the secondary RO would require chemical treatment to operate. For example, the net cost of a secondary RO may be $8/m3 ($4/m3 chemical treatment + $4/m3 RO).
  • Thermal system costs are typically >$20/m3, so although the advanced membrane brine system costs may seem high to traditional potable water RO practitioners, these costs are still much lower than thermal brine concentration methods.
  • Know where to stop: For example, if a brine disposal outlet is available for $5/m3, a primary RO system may offer economic advantages for concentrating brine but a secondary RO may not.
  • Capacity matters: For smaller capacity plants, adding unit operations can add process and operational complexities. For example, if the brine flow rate from the primary RO is 100 m3/day and a thermal system is economic i.e., disposal costs >$10/m3, it may make more sense to skip the secondary RO and proceed directly to the thermal system. This could be especially true if chemical treatment is avoided through use of a SaltMaker evaporator crystallizer that does not require upstream pre-treatment. At higher brine flow rates, such as 500 m3/day, a secondary membrane concentrator can be highly cost advantageous.
  • Simple bench or pilot tests can considerably de-risk investments and offer pay back periods of weeks to months by enabling economic and process optimization of the overall system.
  • Project owners do not need to become experts in advanced brine treatment or economic optimization. Help and guidance is available on completing these calculations by contacting Saltworks.

Cooling Tower Water Treatment Related Resources

Get Your Project Assessment

Our Expertise Applied to Your Water Treatment Needs.

Article

Landfill Leachate Treatment: High Recovery and ZLD Results

Samples of water going from dark brown to clear

Landfill Leachate Treatment: High Recovery and ZLD Results

May 22th 2019

Project Summary

Saltworks Technologies Inc. (Saltworks) completed an end-to-end zero liquid discharge (ZLD) and zero air emission off-site pilot to treat concentrated reverse osmosis leachate brine from a municipal landfill in China.

The site presently treats raw leachate with biological treatment, conventional RO and disc tube RO (DTRO) systems. The DTRO brine reject is sent back to the landfill. However, the TDS of leachate is getting higher. The client is preparing for new regulations that could forbid this practice. The project objective was therefore to eliminate the wastewater volume by producing both clean water and solids at the lowest total cost of ownership.

For the complete results of the pilot including detailed water chemistry, sign-up below to download the free case study.

Download the free landfill Wastewater Pilot Results

Related Resources

Get Your Project Assessment

Our Expertise Applied to Your Water Treatment Needs.

Article

Flue Gas Desulfurization (FGD) Wastewater Pilot Test Results

Comparison of FGD wastewater, one container is brown, murky and the second is clear water.

FlexEDR Selective FGD Wastewater Pilot Test Results

March 19th 2019

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 reverse (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, sign-up below to download the free case study.

Download the free FGD Wastewater Pilot Results

Related Resources

Get Your Project Assessment

Our Expertise Applied to Your Water Treatment Needs.

Article

Applying Ultra-High Pressure Reverse Osmosis in Brine Management

High Pressure Recirculation Pump to Minimize Energy and Increase Membrane Cross Flow

Applying Ultra-High Pressure Reverse Osmosis in Brine Management

March 1st 2019

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, so 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 the curve of Figure 1. The data in Figure 1 was gathered on a Saltworks developed pilot plant, based on 4” membrane elements shown in Figure 2. Two leading manufacturers’ membrane products were tested. Similar relationships in flux were observed, however one company produced high quality permeate in a membrane element with more reliable and consistent performance. Saltworks builds this knowledge into our Xtreme Reverse Osmosis systems for our customers.

UHP RO flux and permeate quality with reject brine TDS
Figure 1: UHP RO flux and permeate quality with reject brine TDS

The permeate salinity increase 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 decline at higher salinity. Flux numbers in liters per m2 per hour represent proprietary knowledge only available 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 is still 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 than UHP RO, meaning they will produce a lower volume. For larger flow rates, a combination of technologies each operating in at an optimum capacity may be most economic. Typical brine concentration limits and volume reduction ratios are summarized in Table 1 below.

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

Table 1: Typical brine concentration limits and volume reduction ratios

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 compares spiral wound and DTRO membrane construction.

Spiral Wound RO Membrane
Figure 2: Spiral wound membranes (lateral flow over membrane sheets)
Inner workings of a DTRO Membranes
Figure 3: DTRO membranes (radial flow over membrane disks)
reverse osmosis system
Figure 4: Spiral Wound Membrane System (common)
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 Xtreme RO 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 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 Xtreme RO. When it comes to scaling ions that can block the membrane surface, there are a variety of both mechanical and chemical methods. First, one must know the scaling ion concentration and its solubility. The solubility of scaling ions can be discovered 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 to remove 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 filter cake waste generation.
  • 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 in Figure 6 below. The high-pressure recirculation pump recycles and upgrades the pressure of a portion of the RO brine. This prevents breaking 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’ Xtreme RO incorporates all of these considerations. If the reader would like to learn more about RO design state-of-the-art technology advancements, they can in this accompanying article

High Pressure Recirculation Pump to Minimize Energy and Increase Membrane Cross Flow
Figure 6: High Pressure Recirculation Pump to Minimize Energy and Increase Membrane Cross Flow

Important engineering considerations also include:


  • Pressure vessels: products are emerging capable of 1800 psi operation with an ASME level safety factor, yet the ASME code stops at 1500 psi.
  • Reciprocating pumps for 1800 psi operation exist in the market place, 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 should be considered when sizing the pump sizing.
  • Actual pressure limits are influenced by temperature.  Feedwater temperatures above 30 °C will result in lower pressure limits.
  • All high-pressure pipework must be designed and certified for use.
  • Think about membrane cleaning and servicing 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 Xtreme RO 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. Figure 2 shows an example system where an existing RO-1 is in place, but additional brine volume recovery 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.

brinerefine reverse osmosis
Figure 7: XRO enabled by BrineRefine

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

Related Resources

Get Your Project Assessment

Our Expertise Applied to Your Water Treatment Needs.

Article

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

Reverse Osmosis System

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

January 8th 2019

Key Takeaways:

  • Reverse Osmosis is considered the workhorse of desalination. Applied correctly, Reverse Osmosis Brine Treatment can be highly effective and lower cost than thermal alternatives.
  • RO recovery and RO brine concentration is limited by osmotic pressures or membrane scaling; both limits have been 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 second 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 brine volume reduction potential.
  • Fully integrated RO and chemical softening solutions with central optimization and control can further maximize overall economics and recovery. BrineGo is one example of such a unified system.

How does Reverse Osmosis Work?

Reverse osmosis (RO) is the workhorse of desalination. High pressure is used to drive water through specially-engineered semipermeable 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 requires higher driving pressures and reduces freshwater permeate flux requiring larger membrane area.

 

Reverse Osmosis Unit
Reverse Osmosis Unit

Historically, there are three pressure classes for RO membranes: 300 psi, 600 psi and 1,200 psi. The higher the pressure class, the higher the brine volume reduction potential on a nonscaling fluid. RO membrane vendors are innovating ultra-high-pressure reverse osmosis (UHP RO) spiral wound membranes capable of 1800 psi. UHP RO enables brine concentrations up to 130,000 mg/L 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 increase 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 pretreatment, 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.

The problems are compounded in industrial wastewater where the feed chemistry varies, requiring 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

Antiscalants

Chemicals developed to delay precipitation of scaling ions, roughly doubling their solubility, so 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 clean 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 semibatch operation

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

Hardness removal and high pH (for high silica waters)

Operate at high pH to increase silica solubility to increase 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 <5000 mg/L TDS. IX also requires chemical regenerations, resulting in a secondary regeneration waste byproduct.

Saturation relief

Continuous precipitation of scale outside the RO circuit by relieving saturation in large seeded columns, including shifting pH to relieve any antiscalants’ effectiveness. 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 Figure 1. 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, shown below.

brinerefine reverse osmosis
Integration of RO and advanced chemical softening systems to increase RO recovery reliably
Engineer inspects BRAD module chemical softening brinerefine
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 — 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 a crystallizer technology – the SaltMaker.

The controls communicate with any upstream and downstream RO to optimize total system performance. Wastewater treatment plants should not be designed or controlled as a linear train of independent unit operations passing water to each other. They should be considered as an integrated system, with each unit operation adjusting to its ‘sweet spot’ as upstream conditions change. The systems’ view 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 produced by the chemical softening further improves overall performance. BrineGo is an example of such an integrated system.

 

Innovation is driving down the cost of treating industrial wastewater. Membrane systems typically cost 5-10 times lower than thermal brine concentration evaporators and so it is important to maximize membrane recoveries. Contact an expert today to maximize your membrane recovery and prevent scale formation.

Related Resources

Get Your Project Assessment

Our Expertise Applied to Your Water Treatment Needs.

Article

Modern Chemical Softening to Maximize RO Recovery: Scale Removal

Engineer inspects BRAD module chemical softening brinerefine

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

November 5th 2018

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. The authors build such RO systems; they 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 scale causing ions, consider which of the three categories you may fit in:

 

1. Basic RO: can achieve the desired recovery 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 CIPs; 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 1800 psi, or concentrate non-scaling fluids to 130,000 mg/L (NaCl) and 150,000 mg/L (Na2SO4). 

 

3Chemical Softening + RO: If done correctly, chemical softening can now maximize an RO system’s recovery to reach the 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 will also concentrate which can foul an RO. In more severe cases, solvents concentrate to where they become insoluble and damage the RO membrane. This article focuses on scale removal to achieve ultra-high recoveries, but concentrated organics also need to be checked. 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 the authors for more details.

Scale Management vs. Scale Removal:

The most important and first step is to understand your water chemistry: the scale causing compounds it contains and 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 is a “Periodic Table of Scaling Compounds” that shows the solubility of some of the most common scale compounds in industrial wastewater. Readers can use it 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 your water chemistry individual ions by the same factor of volume reduction. For example, if operating at 75% recovery, that is 4X volume reduction, meaning 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 in the table above, you could have scale form. 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). The table 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:

 

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 vertical laminar plate type for smaller flows, or large circular type shown below in Figure 5. 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 (no free water droplets). If normally occurring radioactive material (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 chemical 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 timeline photos of chemical softening solids settling without and with the aid of flocculants/coagulants. These specialty chemicals improve the settling 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: 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.
Settling differences shown 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 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 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 added, the more solid waste is required for disposal.

Advanced Chemical Softening: 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.

 

BrineRefine is:

  • 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 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 solids liquid separation without the use of clarifiers or coagulants/flocculants.
Chemical Softening Settling in test tubes
Figure 3: BrineRefine Solids-Liquid Separation without Clarifier and without use of Flocculants/Coagulants
  • Modular: Without the need for clarifiers, BrineRefine consists of pre-built ISO container-sized blocks. 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 simple human machine interface (HMI). Figure 4 is an example of how BrineRefine integrates controls with an RO system.
brinerefine reverse osmosis
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.

Chemical softening clarifier plant
Figure 5: Conventional chemical softening and the 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. 

Engineer inspects BRAD module chemical softening brinerefine
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 the ~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, further reducing brine volume in a membrane system 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 four times lower cost than a thermal evaporation system. The chemistry resulting from BrineRefine and the secondary RO brine is also shown below.  Although calcium can be reduced to ~20 mg/L in BrineRefine, this target was not necessary. A lesser calcium reduction to ~135 mg/L was sufficient to ensure the 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 less chemical use and sludge generation, while still maximizing recovery and protecting the downstream RO.

Chemical softening chemistry table

Every industrial water treatment project, chemistry, and goals may differ. It is important to understand the economics of brine management and cost of each option. Do not spend more money concentrating brine than the savings that would be achieved from reduced disposal. For example, if it costs $5/m3 to achieve ultra high recovery with an advanced chemical softening and RO system, 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 into a lab for a detailed chemistry analysis such as the one above. 

 

Finally, although there many vendors and options on how to package both chemical softening and reverse osmosis, look for a company who does it 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 repeating mistakes of the past. Vendors with modular designs 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 plus operating cost) and assess if membrane brine concentration is worth it.

 

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.

Related Resources

BrineRefine modern chemical softening and treatment

BrineRefine Chemical Softening

Chemical softening system for scaling ion removal Request More Information Download Spec Sheet BrineRefine is a smart, compact, and modular chemical softening system. It reduces chemical softening costs with precision

More ...
Periodic Table of Scaling Compounds

Periodic Table of Scaling Compounds

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

More ...

Get Your Project Assessment

Our Expertise Applied to Your Water Treatment Needs.

Article

Introducing the AirBreather: Lower Cost Evaporator Crystallizer

lower cost evaporator crystallizer model

Introducing the AirBreather: Lower Cost Evaporator Crystallizer

October 15th 2018

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 site raising 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.

lower cost evaporator crystallizer model
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.

SaltMaker-Evaporator-Crystallizer-at-Saltworks-Technologies-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 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.

Full 20" Effect for SaltMaker Evaporator Crystallizer
Effect Module: Built for modular dispatch to minimize site work
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 low boiling point substances that will evaporate with water. Examples include ammonia or volatile organic compounds (VOCs) including 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.

SaltMaker AirBreather Evaporator Crystallizer
AirBreather PFD

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 achieve any desired brine concentration along the way. This is achieved 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.

SaltMaker - Bag of Solids
Zero liquid discharge zld solids produced

Samples of solids produced and discharged to 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

airbreather mobile containerized pilot
Mobile Containerized AirBreather Pilot Plant

Related Resources

Truck carrying brine

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).

More ...

Get Your Project Assessment

Our Expertise Applied to Your Water Treatment Needs.

Article

What is Electrodialysis Reversal and its New Innovations?

Diagram of monovalent electrodialysis (mEDR) using FlexEDR technology

What is Electrodialysis Reversal and its New Innovations?

August 10th 2018

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 a competitor to reverse osmosis, but rather each have a specific fit. 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).

FlexEDR stack
Figure 1. 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 comes from recent innovation that allows the polarity of electrodes and hydraulic channels to ‘reverse’, which helps keep the membranes clean.

FlexEDR
Figure 2. Diagram of How Electrodialysis Works

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

 

  • Remove chlorides to reduce corrosion in water circulating loops that result in high blowdown. This is particularly useful for flue gas desulfurization wastewater, where 90% of the recovery can be recycled, while the final 10% residuals can be mixed with combustion ash or fly ash.
  • Remove scale-causing gypsum from cooling tower blowdown to enable higher cooling tower cycling, provided the tower is designed to handle the higher salinity or the corrosion-causing chlorides are removed.
  • Selectively remove sodium to reduce the sodium adsorption ratio (SAR) in agricultural or vertical farming wastewater to allow recycling of the nutrients or multivalent fertilizer by-products.
Diagram of monovalent electrodialysis (mEDR) using FlexEDR technology
Figure 3. mEDR Process Flow Diagram

Comparing Electrodialysis Reversal and Reverse Osmosis: The Workhorses of Desalination

Reverse Osmosis 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 and rejecting salt ions. To mitigate scaling with RO systems, antiscalants 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 to drive ions through the membranes instead of water; there is no pressurized impingement on the membrane surface. This means EDR is much more tolerant to 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 causes the ions to flux in the opposite direction, and for 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 high organics wastewater. They 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. 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 or chlorine dioxide, which can be used to clean them 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 to 80,000 mg/L (1200 psi) or 130,000 mg/L (1800 psi), assuming all scalants are removed. However, concentrating brine any further is challenging since RO membranes can withstand only certain amounts of pressure. This is 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, resulting in almost half the brine volume compared to a typical RO system. Due the 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 electrodialysis reversal technology depend most strongly on the starting and final concentrations of the feed stream; this is the ΔTDS (change in total dissolved solids concentration). 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 ‘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 (E200), assuming 80% current efficiency. Two different types of brine are shown: NaCl brine and CaCl2 brine – typically, most wastewater will fall in 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 Total Dissolved Solids change
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 reducing 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.

 

Current limit decreases with decreasing TDS, so the best economics may sometimes be obtained by arranging stacks in series operating at different currents. An example might be that a high TDS wastewater would require one stack operating at 200 A/m2, which must then be sent for final polishing with a second stack at 60A/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

Considering an RO system against Electrodialysis Reversal 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 system 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 also drive up your operational and maintenance costs as 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 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: its highly cross-linked polymers enable its 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, our pilot E100 stack, and the E200 stack, which have 5, 100 m3/day and 200 m3/day capacities. Our standard skid combines six E200 stacks into a plant with a 1200 m3/day capacity, although stacks can be removed or added to adapt to different project needs.

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

The 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.

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, 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 a real cost advantage. Readers do not need to learn how to size and quote an EDR system. Contact us today to get started on your project.  

Related Resources

FlexEDR stack

FlexEDR Electrodialysis Reversal System

Request More Information Download Spec Sheet FlexEDR is an advanced electrodialysis reversal (EDR) system, leveraging our next generation ion exchange membranes. It requires less pre-treatment, tolerates oils and organics, selectively removes ions and uses fewer chemicals. ADVANCED ELECTRODIALYSIS REVERSAL WASTEWATER  REUSE SELECTIVE ION REMOVAL REDUCE BRINE VOLUME For the Most Rugged Applications Built with our

More ...

Get Your Project Assessment

Our Expertise Applied to Your Water Treatment Needs.