Brines are liquid concentrates of salts produced as waste from industrial production processes, oil and gas fracturing or desalination of saline groundwater, seawater or wastewater recycling. Brine concentrate management presents a challenge because of the waste product’s composition, the mass of liquids that need to be managed and the solids that are generated. Disposal options are limited depending on the origin of the brine, its composition, location and potentially substantial costs. To avoid or minimize the disposal challenge, recovery opportunities include producing marketable products such as road salt or feed for electrolytic production of chlorine and caustic soda, as well as the possible extraction of valuable metals.
The Southern California Regional Brine Concentrate Management Study Report (U.S. Bureau of Reclamation, 2009) provides reasonably detailed discussions of numerous technologies for brine management. It includes: descriptions of the technologies; advantages and disadvantages; and estimated capital and operations and maintenance (O&M) costs for the technologies at that time.
Some major volume-reduction technologies for brine concentrate management that were evaluated include: mechanical and thermal evaporation, electrodialysis/electrodialysis reversal, vibratory shear-enhanced processing, precipitative softening and reverse osmosis (RO), enhanced membrane system brine concentrator and natural treatment systems.
Other technologies being evaluated or under development include: two pass nanofiltration, forward osmosis, membrane distillation, slurry precipitation and reverse osmosis, advanced reject recovery of water, and capacitive deionization.
“This discussion describes the elements of several brine concentrate management technologies.”
The following discussion describes the elements of several brine concentrate management technologies. The descriptions are based upon pilot, bench and full-scale data and information obtained from vendors. Cost information was obtained from equipment manufacturers and implementation experiences. The cost estimates are described as conceptual cost estimates or Class 5 estimates and are usually order-of-magnitude costs without detailed engineering data.
Concentration by evaporation: A natural treatment method
Some of the oldest and simplest passive approaches to brine concentrate management involve the use of lined evaporation ponds in areas where climate, soil conditions and location make it feasible. Impermeable linings are essential to prevent contamination of groundwater by percolation of the salt-laden liquids. Past practices of unmanaged evaporation ponds are unacceptable and have led to expensive regulatory and public-driven groundwater cleanup demands.
Technologies are also available for active concentration by precipitation before using membranes, ion exchange or thermal evaporative processes. Both active and passive approaches are beneficial by substantially reducing the volume of product that needs to be managed; both will likely require additional needs to manage the super concentrates or solids that are generated. Possibilities include transport and deep well injection or hazardous material landfilling; both are regulated by federal and state Resource Conservation and Recovery Act (RCRA) regulations or Underground Injection Control (UIC) requirements. Hydraulic fracturing operations predominantly use deep well injection for disposal of contaminated hydraulic fluids.
Other natural treatment methods for brine concentrate management
Some natural treatment systems are established for polishing and treatment of municipal wastewater but have not been generally used for RO concentrate disposal. Two pilot studies involve the use of halophytes (salt-tolerant plants in a closed system) or open wetlands to uptake the concentrate prior to final disposal. These approaches might be difficult to apply in most circumstances and are subject to numerous reliability concerns.
Mechanical and thermal evaporation
These approaches to brine concentrate management are energy-intensive processes that reduce the volume of concentrate by boiling the liquid and recovering distillate. Heat is added to the concentrate by a mechanical adiabatic heating process, or steam is added to heat the concentrate, causing accelerated evaporation. The vapor is condensed, becoming distillate for reuse. Reduced pressure facilitates vaporization. Because of the energy intensiveness of distillation approaches or pressurized membrane approaches, these are costly technologies.
Seawater and groundwater salt waters
Waste from desalination plants include concentrated brines, backwash liquids that contain scale and corrosion salts and antifouling chemicals and pretreatment chemicals in filter waste sludges. Similar issues would be encountered in sewage-based potable and nonpotable reuse applications of the same technologies. Depending upon the location and other factors including access to the sea, presence of sensitive aquifers, concentrations of toxic substances and other considerations, waste could be discharged to the sea, mixed with other wastes before discharge, discharged to sewers or treated at a sewage treatment plant, placed in lagoons, injected into deep wells, or dried and disposed of in landfills. Additional pretreatments may be required. Sewer discharges are subject to National Pollution Discharge Elimination System (NPDES) permit requirements to not disrupt sewage treatment plant performance. Seawater discharges will often require long pipes and diffusers.
Electrodialysis and electrodialysis reversal
Electrodialysis (ED) uses an electrical current to remove salt ions from a solution. Salts in the solution are dissociated into positively and negatively charged ions. A semipermeable membrane barrier allows passage of either positively charged ions (cations) or negatively charged ions (anions) but excludes passage of ions of the opposite charge. These semipermeable barriers are commonly known as ion exchange (IX), ion-selective or electrodialysis membranes.
Electrodialysis reversal (EDR) is effective for feedwater with total dissolved solids (TDS) up to 8,000 parts per million (ppm), less than a 1 percent TDS solution, which is fairly limiting. It has been used for potable water and for wastewater applications but has not been proven for dealing with brine concentrates.
Advantages of EDR include:
- Potentially higher recovery than other membrane processes.
- Lower fouling potential because, unlike RO, nonionic contaminants (particulates) are not driven to the membrane surface.
- Inability to remove all constituents (such as boron, silica and uncharged micropollutants); however, more neutral nonhighly ionized species such as boric acid and arsenites are also not well-removed by RO.
- Effectiveness is achieved only when the TDS concentration in the feedwater must be less than about 8,000 ppm; multiple stages are required for treatment of high TDS feedwater.
Vibratory shear-enhanced processing (VSEP)
To reduce membrane fouling by colloids, VSEP was developed by New Logic Research to reduce polarization of colloids on the membrane surface by introducing vibrational shear. The shear waves produced on the membrane surface keep the colloidal material in suspension and minimize fouling. The VSEP torsional oscillation at a rate of 50 times per second (50 hertz) inhibits diffusion polarization of suspended colloids, which are washed away by a tangential cross flow.
- Potentially high recovery rates.
- Water quality is similar to conventional RO.
- Potentially limited pretreatment chemicals, e.g., antiscalant and pH adjustment.
- Performance needs evaluation through pilot testing.
- Potentially susceptible to fouling with aluminum, iron and manganese oxide deposits.
- Higher clean-in-place frequencies than conventional RO.
- Changing all membrane elements in a stack is required if one membrane plate needs replacement.
- Lacks experience in municipal applications.
- Sound attenuation is likely required.
- Proprietary technology from a single vendor.
- Higher capital and O&M costs than traditional RO.
Precipitative softening and reverse osmosis
Precipitative softening (PS) is a conventional pretreatment integrated with the RO system to increase recovery of concentrate as a volume-reduction process. PS increases the recovery rate of the RO process by precipitation and removal of sparingly soluble inorganic salts. The process includes chemical addition and clarification for softening (alkalinity and hardness removal) and pH adjustment for silica removal.
PS is effective in removing scale-forming calcium, barium and strontium. Silica removal is achieved by pH elevation — adding magnesium and/or sodium hydroxide to increase the pH to 10.3 or higher. Pellet softening is an alternative where hardness can be removed by growth of calcium carbonate crystals in a fluidized bed reactor, or pellet reactor, producing solid calcite grains, which have economic value. The process is proven for municipal and industrial applications and can be installed in existing chemical- and sludge-handling facilities.
- Proven technology with many installations with RO following PS or lime softening.
- Applicable to concentrate with high silica content.
- Regulatory issues similar to RO.
- Large footprint.
- Space required for chemical facilities and sludge recovery.
- High chemical usage depending on feedwater quality.
- Sludge disposal is required.
- Overall recovery is limited by RO system osmotic pressure constraints.
Enhanced membrane systems
Enhanced membrane systems (EMS) reduce the volume of reject concentrate by increasing the recovery of the RO process. One type of EMS is the patented High-Efficiency Reverse Osmosis (HERO) process that involves: IX softening of reject from a first-phase membrane system to reduce the scaling potential of the concentrate fed to the HERO system; a degasification step to remove carbon dioxide; and addition of a caustic that would increase pH (to about 11) to retard silica scaling and biofouling. The process combines a two-phase RO process with chemical pretreatment of primary RO concentrate and high pH operation of secondary RO, resulting in a higher recovery than standard RO systems.
- Applicable to concentrate flows with high silica content.
- Relatively small footprint.
- Higher recovery than conventional RO.
- Small aesthetic profile (no tall stacks).
- Inefficiency due to TDS limitations.
- High capital and O&M costs.
- Skilled operations staff is required.
- Complex process control system for IX, pH adjustment and RO systems.
- Two concentrated waste streams are produced, which form voluminous precipitate when combined.
Recovery of commercial components
Recovery of elements from brines has been practiced for many years. The viability of the extractions is a function of their economics. Almost all types of brines contain metals with commercial interest. The greatest portions are usually sodium, potassium, magnesium and calcium, but there are ppm, ppb and ppt concentrations of numerous trace components; e.g., lithium, precious metals and rare earths may be found in seawater. Literature is available on the subject, but technologies are commercially viable in only certain circumstances. Recovered sodium chloride can be used for several processes including road salting and electrolytic chlorine and caustic soda production. Regulatory requirements and economics drive and limit many situations.
- Cotruvo, J.A. (2004). Desalination Guidelines Development for Drinking
Water. http://www.who.int/water_sanitation_health/dwq/nutrientschap2.pdf http://www.who.int/water_sanitation_health/dwq/nutdesalination.pdf.
- USBR (2001). Zero Discharge Waste Brine Management for Desalination Plants https://www.usbr.gov/research/dwpr/reportpdfs/report089.pdf.
- USBR (2009). Brine-Concentrate Treatment and Disposal Options Report. https://usbr.gov/lc/socal/reports/brineconcentrate/6TreatmentandDisposal_part1.pdf.
- Wall, A. (2016). Mineral Recovery from Geothermal Brines: Resources, Technologies, and Economics. https://geothermal.org/PDFs/California_Geothermal_Forum/Session_4_1_Wall.pdf.
Joseph Cotruvo, Ph.D., BCES, is president of Joseph Cotruvo and Associates LLC, water, environment and public health consultants, and technical editor of Water Technology. He is a former director of both the EPA Drinking Water Standards and the Risk Assessment Divisions.