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 vary significantly due to 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.
Before deciding on how to manage waste brine, you should consider 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 decide to treat your brine. The chemical makeup identifies the technologies that will best fit a specific brine treatment process, for example, whether to choose thermal or membrane systems. This data enables early assessments of project feasibility and economics, as well as any pre-treatment requirements and scaling and fouling risks.
Another advantage of brine chemical characterization is that it allows you to identify opportunities for beneficial resource recovery. For example, recovering ‘fertilizer water’ from a waste brine is possible. If a brine contains a mixture of sodium and hardness, electrodialysis reversal (EDR) with certain monovalent ion selective membranes could produce a water that is 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 is usually considered if discharge options are not available, brine disposal is expensive, or freshwater recovery is important. Many technology options are available to concentrate brine, reduce its volume and disposal costs, or produce solids for zero liquid discharge. Regardless of the treatment strategy you choose, it will beneficially produce freshwater.
Reverse osmosis (RO) is the membrane system most widely used to desalt brine waters. RO produces freshwater and more concentrated brine that is 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 pre-treatment step.
Conventional RO can concentrate brine to a theoretical maximum of 80,000 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 1,800 psi, compared to conventional RO’s 1,200 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 system provide an economical, compact, and flexible chemical softening solution for maximizing RO and UHP RO brine concentration. Saltworks provides fully integrated solutions that combine RO or UHP RO with BrineRefine and central controls 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 lower pre-treatment 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 that are present in the brine.
If you are considering thermal evaporative systems, then 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:
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 flow rates, 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 that you will use fewer trucks to move the brine or need 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 landfills 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 with each step that you concentrate brine toward solids, which is why it is important to carefully consider all disposal and reuse options before implementing a technological solution.
If 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:
One option for complying with regulatory discharge requirements may be to dilute the brine stream with other waters that require discharge. Sufficient dilution 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. Low-cost solutions are 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 discharge 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.
Like discharging brine into surface bodies of water, ocean discharge is another brine disposal method that tends to be very cost-effective. In southern California, a ‘Brine Line’ 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, the environmental risks of brine discharge are lower.
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.
Waste brine can be disposed of by injecting it into deep wells. These injection wells are installed thousands of feet underground, 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, studies have shown a correlation between deep disposal wells and increased seismic activity, as evidenced by earthquakes in Oklahoma.
Deep well capacities have also reduced, as regulations require 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.
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. This 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 developing an end-of-life closure plan if your project will be using evaporation ponds.
Waste brine can be sent to an incinerator facility, where the brine 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.
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 cost-effectiveness. Once the service provider takes ownership, they will use their own assets to either treat the brine or dispose of it.
Disposal wells are an established method for disposing of hazardous fluids by injecting them deep underground. Commingling (mixing) incompatible fluids in a disposal well may inadvertently cause solids to precipitate, which risks plugging the well. Plugging is disruptive and costly to fix, but operators can prevent it with advanced sensors, controls, and targeted wastewater treatment.
New ultra-high pressure reverse osmosis technology for minimal liquid discharge (MLD) can reduce brine management costs by three times relative to evaporators. 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.
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
Saltworks’ innovative brine treatment solutions include RO concentrators, industrial evaporators & crystallizers, and electrodialysis treatment systems. Our custom solutions minimize volume, reduce your disposal costs, and maximize freshwater recovery.