Article

RO & Evaporator Scale Control: The Guide to Better Performance

Scaling found on the interior surface of pipes

RO & Evaporator Scale Control: The Guide to Better Performance

June 27th 2018

Scale is a crust that forms on membranes, heat transfer surfaces, and on the inside of pipes as salts precipitate out of solution. It blocks flow, disrupts heat transfer, and increases energy requirements for water treatment systems. Scale is bad news: it limits system performance and increases maintenance costs. You can protect your plant’s productivity from scale armed with an understanding of scaling water chemistry and the right technology. You can also push and maximize performance of your plant, if you understand the scaling ‘danger zone’. Download our periodic table, which includes an easy to use guide and example. Keep reading to learn more. 

How do Scaling Ions Precipitate?

Scaling occurs when ions pairs form salts as they reach their solubility limits. Ion pairs are comprised of positive cations and negative anions, and most scale is caused by ions that are multivalent pairs. Multivalent ions, such as Calcium (Ca2+) and Sulfate (SO42-), are more likely to cause scale than monovalent ions since they have lower solubilities and will precipitate earlier. Watch out, however, for one particular mono-multi pair, Calcium (Ca2+) and Fluoride (F), which can also cause scale. Our engineers use the above scaling periodic table of elements to easily check the concentrations where ions in water might precipitate and affect evaporator or membrane system performance.

 

The solubility of an individual ion pair is the most essential information to use when designing a scale management strategy. However, scaling concentration limits can be affected by the temperature, pH, and mixed ion chemistry of the water. Ions in mixed solutions tend to have higher solubilities than pure solutions, which can be difficult to predict, even with some of the software models that are available. We treat mixed ion effects as an extra buffer that prevents scale.

Scaling found on the interior surface of pipes
Scaling found on the inside of pipes

How Does Scaling Impact Evaporators & Membrane Systems?

Any heat transfer surface where scaling occurs will observe decreased efficiency and capacity. Although scaling is typically shown on metal surfaces, it can also form on membranes used in reverse osmosis systems and reduce membrane performance. In severe cases, scale can mechanically damage or rupture the membrane.

 

A plant that ignores scaling limits can experience equipment plugging and surface crusting, or be operating sub-optimally leaving room to increase freshwater recovery. Time and money are wasted on either low performance, or efforts to recover from a scaling event. Although carbonate scaling is easy to remove with acid, other scales take much more effort such as expensive chemical cleans or mechanical removal. It is best to know where you stand and prevent scaling, rather than try to deal with it after it forms.

How to Avoid Scaling in Your Industrial Water Treatment Process

  • Get a complete analysis of your water chemistry to understand the concentrations of your potential scalant ions. For a few hundred dollars, you will receive analytical data that will help you understand low and high concentrations for your water. Ensure you sample during periods of both low and high concentration for better representation of your complete picture.
  • Know the scaling potential of any scaling ions in your water using our Periodic Table of Scaling Compounds, or find a software package if you wish to get more advanced.
  • Design and operate your process to push recovery, but avoid exceeding scaling ion solubility limits.
  • Consider automated chemical softening that uses precision dosing to minimize the risk of scale formation, while also reducing wasted chemicals that may result from manual chemical softening.
  • Consider adding anti-scalants that may boost your scaling ion solubilities as much as 3-4x, but be sure to use the correct anti-scalant and consider testing. There are many companies that will sell you anti-scalants and their performance may vary.
  • Contact an expert today to optimize your process and prevent scale formation.

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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).

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How to Manage Brine Disposal & Treatment

Truck carrying brine

How to Manage Brine Disposal & Treatment

December 15th 2017

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). Brine disposal includes discharging brine to sewers, surface water, injection wells, or sending it to environmental service providers.

 

The cost and environmental impact of each option varies significantly based on many factors. Choosing management options for the waste brine requires careful consideration of applicable discharge regulations, availability of disposal methods, and the economic feasibility to treat the brine.

Understanding Your Brine Water Chemistry

Water Science Team at Saltworks Technologies Analyzes SampleBefore deciding on how to manage waste brine, you should consider completing a water chemistry analysis to understand essential indicators, such as the salinity level (e.g. total dissolved solids), metals contaminants, and the scaling potential of the water (e.g. calcium and sulfate). This will assist in evaluating regulatory requirements as well as determining available options and their associated costs.

 

Water chemistry data provides the most value if you end up deciding to treat your brine. The chemical makeup of the water identifies the technologies that will best fit a specific brine treatment process, for example, whether you should choose thermal or membrane systems. This data enables early assessments of project feasibility and economics, as well as any pretreatment requirements or scaling and fouling risks.

 

Another advantage of brine chemical characterization is that it allows you to identify opportunities for beneficial resource recovery. For example, it is possible to recover ‘fertilizer water’ from a waste brine. If a brine contains a mixture of sodium and hardness, electrodialysis reversal (EDR) with certain monovalent ion selective membranes could produce a water high in plant-nourishing hardness with low concentrations of the pollutant sodium. This water would have a low soil adsorption ratio (SAR) that would be valuable to the agricultural industry.

 

Alternatively, if a brine consists mostly of sodium and chloride, it can be treated with a crystallizer to produce solids that can be used as road de-icing salts. Consider working with experts who can help you determine the most economic options for managing your brine.

Brine Treatment

Brine treatment is usually considered if discharge options are not available, brine disposal is expensive, or freshwater recovery is important. There are many technology options to concentrate brine, reduce its volume and disposal costs, or to produce solids for zero liquid discharge. Regardless of the treatment strategy you choose, it will beneficially produce freshwater.

Membrane Treatment Systems

Reverse Osmosis Membrane Treatment SystemReverse osmosis (RO) is the membrane system most widely used to desalt brine waters. RO produces freshwater and more concentrated brine often referred to as RO brine, reject, or concentrate. This brine concentrate will usually reach concentrations of dissolved salts and chemicals that will be near scaling limits. This requires treatment to relieve the scaling potential if you will use a thermal system to further concentrate the brine or to produce solids. Alternatively, you could consider thermal systems that can operate under scaling conditions, such as seeded slurry evaporators or a SaltMaker, to eliminate the thermal pretreatment step.

 

Conventional RO can concentrate brine to a theoretical maximum of 80K mg/L. This is based on the technology’s inherent osmotic pressure limit. However, the achievable output brine concentration will usually be less due to the input brine’s scaling potential. New Ultra-high Pressure RO (UHP RO) membranes that operate at up to 1800 psi compared to conventional RO’s 1200 psi can reduce brine volume to half that of RO, however scaling must be even more carefully managed due to the higher pressure. Saltworks’ XtremeRO is an example of an RO/UHP RO system.

 

Chemical softening can be used to manage scaling; however, cost, physical footprint, and the ability to deal with varying feedwater chemistry must be considered. Technologies such as Saltworks’ automated BrineRefine provide an economic, compact, and flexible chemical softening solution for maximizing RO and UHP RO brine concentration. Saltworks’ BrineGo is an example of a fully integrated solution that combines RO or UHP RO, BrineRefine, and central control to provide a membrane based solution that concentrates brine to levels only previously attainable by more costly thermal systems.

 

If your brine contains hydrocarbons or organics, electrodialysis reversal (EDR) may be a better fit than RO due to its lower pretreatment requirements. EDR is a low-pressure system that fluxes salts through ion exchange membranes using an applied electrical charge. There are EDR systems that use anti-fouling ion exchange membranes, such as Saltworks’ FlexEDR Organix, that can operate with hydrocarbons and organics present in the brine.

 

If a thermal system will be used for further concentration or to produce solids then scaling management is still important. Alternatively, you could consider thermal systems that can operate under scaling conditions, such as seeded slurry evaporators or a SaltMaker, to eliminate the thermal pretreatment step.

Thermal Treatment Systems

Industrial EvaporatorIf you are considering thermal evaporative systems, maximizing freshwater recovery from lower cost membrane systems before using expensive thermal systems will deliver the best project economics. In general, there are two types of thermal systems based on their residual outputs: (1) evaporators that produce concentrated, low volume brine but do not precipitate solids; and (2) crystallizers that exceed salt saturation and produce solids. For high flow rate zero liquid discharge applications, evaporators are used to preconcentrate the brine prior to the crystallizer for final solids production. At lower flows, the waste brine can be sent directly to the crystallizer after treating with a membrane system.

 

The final disposal of residuals is important in determining whether additional process steps are required. If you have options for disposing of concentrated brine, it will usually not require further treatment. Evaporators are only reducing the volume of brine for final disposal, ensuring you need fewer trucks to move the brine or less capacity in disposal wells or ponds. However, depending on the treatment technology you use, additional treatment may be required for solid residuals before a landfill will accept them for disposal. Almost all landfills require solids to pass a paint filter test, while some also require analysis of pH and leachable metals. To pass a paint filter test, the solids should be dewatered until they have no free water present. Centrifuges, filter presses, and/or dryers are required to further process solids produced by conventional crystallizers to pass the paint filter test. Other crystallizers, such as the SaltMaker MultiEffect, have their own solids management systems that produce dewatered solids in sacks without the need for centrifuges, filter presses, or dryers.

 

Treatment costs increase the further you concentrate brine towards solids, which is why it is important to carefully consider all disposal and reuse options before implementing a technological solution.

Brine Disposal

Discharging Brine into Surface Bodies of Water or Sewer Systems

Effluent Pipe Discharging Brine into Surface WaterIf your brine meets regulatory requirements, brine discharge into the nearest body of water or to sanitary sewers is usually the lowest cost option for disposal. Discharge regulations or guidelines vary widely from region to region, or are sometimes determined on a project-specific basis. Regulations may prohibit discharge based on any of the following:
  • Concentrations of certain constituents of concern (e.g., maximum limits for metals, salinity, or compounds)
  • Total mass per day of certain constituents of concern
  • Specific properties, such as temperature and pH
  • Volumetric flow rates
  • Discharges only during certain time of day
One option to comply with regulatory discharge requirements may be to dilute the brine stream with other waters requiring discharge. With sufficient dilution, this may reduce the controlled constituents to below the allowable concentration limits. If the brine stream has only one or two constituents of concern that exceed the discharge limits, you should consider selective treatment or removal of those constituents. There are low cost solutions available for removing certain constituents, such as using green sand for iron removal. While discharging brine directly into surface water systems or sewers is often the most cost-effective solution, your organization should consider how it will impact the local environment. If regulations do not exist, studying the potential impacts of discharging the brine on local flora and fauna will help identify the benefits of treatment to protect the ecosystem or prepare for impending regulations.

Brine Disposal in the Ocean

Brine Discharge Pipe to the Pacific Ocean from Desalination PlantLike discharging brine into surface bodies of water, ocean discharge is another brine disposal method that tends to be very cost effective. In southern California, there is a ‘Brine Line’ that allows inland plants to discharge their brine to the ocean rather than to sewer or surface waters. Due to the ocean’s naturally high salinity, there are lower environmental risks of brine discharge. If you are considering installing a brine discharge line, you will need to acquire a permit. As part of the permit application, the regulatory body may ask for environmental studies that address the impact on local marine ecology of the brine temperature, pH, salt density, and other property differences between the brine and seawater.

Deep Well Injection of Waste Brine

Waste brine can be disposed by injecting it into deep wells. These injection wells are installed thousands of feet deep into the ground, away from the upper aquifers that feed drinking water sources. The availability of injection wells is geology-dependent, so they are not available in all regions. In the oil and gas industry, abandoned oil wells are often converted into disposal wells. Recently, there have been studies that correlate deep disposal wells with increased seismic activity, as evidenced by earthquakes in Oklahoma. Deep well capacities have also reduced as regulations are requiring lower injection pressures to minimize the risk of contaminating the upper water aquifers. Moreover, securing a functioning deep well is similar to drilling for oil – you take a risk and invest capital before knowing if the underground geology will meet your expectations. It is possible that deep wells once drilled will accept very small volumes, or exceed expectations and accept more. 

Brine Evaporation Ponds

Evaporation ponds are the artificial solution to inland surface water discharge of waste brine. Under the right climatic conditions, the water evaporates, allowing you to discharge more brine to the ponds. One limitation of ponds is that they require large areas of land to increase the surface area where the water can evaporate, and can represent a future environmental liability due to either animal entry or future decommissioning. If you need to recover solids for disposal or reuse, then multiple evaporation ponds may be necessary to rotate between brine evaporation and solids extraction. Evaporation also happens more quickly in warmer, arid climates. You should consider installing proper liners, preventing waterfowl poisoning from brine that contains metals, and develop an end of life closure plan if your project will be using evaporation ponds.

Brine Incineration

Waste brine can be sent to an incinerator facility, where it is typically mixed with other solid wastes for processing. Incineration evaporates the water, while the salts in the brine become part of the residual ash that requires further management. Incineration is popular in countries with limited availability of land for landfills.

Brine Management from Environmental Service Providers

There are companies that provide environmental services to accept waste brine. These companies will typically take ownership of the brine and charge on a dollars-per-gallon basis. This is an option you should consider if there are facilities nearby, although distance and transportation costs may reduce its cost effectiveness. Once the service provider takes ownership, they will use their own assets to either treat the brine or dispose of it.

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What is Zero Liquid Discharge & Why is it Important?

Zero Liquid Discharge Flow Chart

What is Zero Liquid Discharge & Why is it Important?

January 15th 2018

Zero liquid discharge (ZLD) is an engineering approach to water treatment where all water is recovered and contaminants are reduced to solid waste. While many water treatment processes attempt to maximize recovery of freshwater and minimize waste, ZLD is the most demanding target since the cost and challenges of recovery increase as the wastewater gets more concentrated. Salinity, scaling compounds, and organics all increase in concentration, which adds costs associated with managing these increases. ZLD is achieved by stringing together water treatment technology that can treat wastewater as the contaminants are concentrated.

There are a number of benefits to targeting zero liquid discharge for an industrial process or facility:

 

  • Lowered waste volumes decrease the cost associated with waste management.
  • Recycle water on site, lowering water acquisition costs and risk. Recycling on-site can also result in less treatment needs, versus treating to meet stringent environmental discharge standards.
  • Reduce trucks associated with off-site waste water disposal, and their associated greenhouse gas impact and community road incident risk.
  • Improved environmental performance, and regulatory risk profile for future permitting.
  • Some processes may recover valuable resources, for example ammonium sulfate fertilizer or sodium chloride salt for ice melting.

Several methods of waste management are classified as zero liquid discharge, despite using different boundaries to define the point where discharge occurs. Usually, a facility or site property line that houses the industrial process is considered the border or ‘boundary condition’ where wastewater must be treated, recycled, and converted to solids for disposal to achieve zero liquid discharge.

 

Certain facilities send their liquid waste off-site for treatment, deep well disposal, or incineration and they consider this to qualify as zero liquid discharge. This approach to zero liquid discharge eliminates continuous discharge of liquids to surface waters or sewers, but can significantly increase cost.

Zero liquid discharge zld solids produced

Some engineers describe their designs as near-zero liquid discharge or minimal liquid discharge to highlight that they discharge low levels of wastewater, but do not eliminate liquid in their waste. For some facilities, it may be more economic to approach but not achieve complete ZLD by concentrating brine to lower volumes. Furthermore, it may be possible to avoid the creation of liquid waste on-site through careful water conservation or by treating contaminants at their source before they can enter the main flow of water.

Download our ZLD infographic for detailed information on costs.

Why is Zero Liquid Discharge Important?

In a world where freshwater is an increasingly valuable resource, industrial processes threaten its availability on two fronts, unless the water is treated. Many industrial processes require water, and then reduce the availability of water for the environment or other processes, or alternately contaminate and release water that damages the local environment.

 

Although the history of tighter regulations on wastewater discharge can be traced back to the US Government’s Clean Water Act of 1972, India and China have been leading the drive for zero liquid discharge regulations in the last decade. Due to heavy contamination of numerous important rivers by industrial wastewater, both countries have created regulations that require zero liquid discharge. They identified that the best means to ensure safe water supplies for the future is to protect rivers and lakes from pollution. In Europe and North America, the drive towards zero liquid discharge has been pushed by high costs of wastewater disposal at inland facilities. These costs are driven both by regulations that limit disposal options and factors influencing the costs of disposal technologies. Tong and Elimelech suggested that, “as the severe consequences of water pollution are increasingly recognized and attract more public attention, stricter environmental regulations on wastewater discharge are expected, which will push more high-polluting industries toward ZLD.”

 

Another important reason to consider zero liquid discharge is the potential for recovering resources that are present in wastewater. Some organizations target ZLD for their waste because they can sell the solids that are produced or reuse them as a part of their industrial process. For example, lithium has been found in USA oil field brines at almost the same level as South American salars. In another example, gypsum can be recovered from mine water and flue gas desalinization (FGD) wastewater, which can then be sold to use in drywall manufacturing.

 

Regardless of an organization’s motivations to target zero liquid discharge, achieving it demonstrates good economics, corporate responsibility and environmental stewardship. By operating an in-house ZLD plant, disposal costs can be reduced, more water is re-used, and fewer greenhouse gases are produced by off-site trucking, which minimizes impact on local ecosystems and the climate.

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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.