BWRO opens previously unusable groundwater reserves
Whether for seawater, saline groundwater, or brackish groundwater, reverse osmosis (RO) desalination uses membranes with microscopic pores to filter out salt. It produces a permeate, fresh water, that can be used for drinking or virtually any other application. Reverse osmosis desalination was often thought to be too costly, but today, brackish water reverse osmosis (BWRO) desalination is much more popular.
There are vast reserves of brackish water throughout the nation and the world, even far inland in arid regions that need water the most. The cost of reverse osmosis desalination has dropped precipitously in the past decade as the cost of fresh water from natural sources has skyrocketed. Brackish water is much easier and less costly to desalinate than seawater; it appears that BWRO’s time has come.
Brackish Reserves
How much brackish water is there? According to the United States Geological Survey, 800 times more brackish water lies in U.S. aquifers than the amount of fresh water the nation uses every year. It might be water from prehistoric seas trapped far inland, intrusion of coastal seawater, water from saline soils that leach into groundwater, water contaminated by road salt, produced water from the oil and gas industry, or from other sources of human activity.
Coastal brackish aquifers such as the bountiful ones in Florida are well known, but brackish water can also be found in some surprising locations. In the ocean off the Eastern Seaboard, a vast brackish aquifer has been discovered under the seabed. Throughout the parched West, in the grip of aridification from climate change, and in the industrial Midwest, vast aquifers exist at depths of 500 to 1,000 feet.
Desalination Technologies
The two main types of desalination are membrane and thermal. Thermal distillation essentially evaporates water, leaving salts behind. Membranes filter out salt by forcing pressurized water through them.
Particularly in the past decade, thermal distillation methods have fallen out of favor mostly because they require a whopping 10 times more energy. BWRO requires even less energy and fewer chemicals than the desalination of saltier water.
Reverse osmosis is and will remain an energy-intensive process. The advanced membranes must be maintained to prevent fouling, and replacement costs are significant. Care must be taken to responsibly manage the highly saline discharges from desalination plants as well as the chemicals used to clean membranes.
Environmental and energy footprints can be minimized by maximizing brine concentration, recycling, crystallization, and solidification, increasing recovery rates, utilizing energy recovery devices, employing batch operation, and optimizing operating conditions. But while best practices are important, reverse osmosis still stands above thermal alternatives.
Understanding Osmosis and Reverse Osmosis
Osmosis is a natural process in which solvent molecules, usually water, move without an external energy source from an area of low solute concentration to high solute concentration through a semipermeable membrane until equilibrium of the solute concentrations is reached.
Reverse osmosis, conversely, uses compression to overcome the natural osmotic pressure and force a high-concentration solution through a semipermeable membrane to an area of low solute concentration. In essence, the membrane rejects salts, minerals, and other impurities as the solution passes through under pressure, and a high-purity permeate comes out the other side.
Brackish Water Reverse Osmosis
Brackish water reverse osmosis systems generally use thin-film composite membranes because of their high rejection rates and efficiency. They consist of a thin, dense polyamide layer on top of a porous support layer, which provides mechanical strength and durability. Other types of membranes that might support BWRO systems include nanofiltration and ultrafiltration membranes with larger pore sizes.
A typical brackish water reverse osmosis plant pretreatment stage involves removing suspended solids, chlorine, and other contaminants that could foul the membranes. Common methods include filtration, sedimentation, and chemical dosing. High-pressure pumps then increase the pressure of the feedwater to the required level for reverse osmosis, typically between 200 to 600 psi. The pressurized feedwater passes through the semipermeable reverse osmosis membranes, which reject salts and other impurities and allow pure water to pass through.
After filtration, the permeate or filtered water may undergo further treatment to adjust pH, remineralize, or disinfect before it is considered potable. A polishing stage may be used to ensure the water meets all quality standards, including the removal of any remaining trace contaminants.
Economic Benefits of BWRO
This BWRO plant in Alice, Texas proves BWRO’s potential to provide reliable, sustainable water to communities in need.
The economic benefits of BWRO vary, but in a region that struggles to source enough water, they can be dramatic. Ample water can attract business, industry, and new residents, leading to a boom in development. Communities dependent on regional utilities and outside entities can realize water independence and unburden ratepayers of high water costs.
Consider the Seven Seas BWRO plant in Alice, Texas, the first BWRO plant in the state delivered under a public-private partnership agreement. Seven Seas completed construction of the plant at no upfront cost and lowered the existing cost of water that the city was paying. As part of a Water-as-a-Service® agreement, Seven Seas will operate and maintain the plant for 15 years, handling all compliance issues and brine management responsibilities. The city only pays a bill for the water used.
The Alice project demonstrates how BWRO can deliver a reliable and sustainable water supply for water-stressed communities. Many communities have a potential source of water independence and security waiting underfoot. Seven Seas is proving that BWRO is a sustainable, real-world solution for water scarcity, jumpstarting economies and improving lives as only fresh, clean water can.
Is your community facing water scarcity?
Seven Seas can help you unlock the potential of brackish water with our proven BWRO desalination solutions. Contact our water experts to discover how we can turn your water challenges into a sustainable future.
Image Credit: calyptra/123RF
David Charles is a highly skilled Environmental Engineer with a Bachelor of Science in Environmental Engineering from the University of Cincinnati. Based in Florida, David has accumulated extensive experience through various internships, including roles at Kiewit Corporation in Omaha and Atlanta, and AVCON Inc. in Orlando. He has also served as an Operations Intelligence Analyst in the United States Air Force. David is certified in Environmental Inspections (FSESCI) and is proficient in English and Spanish. His technical skills encompass environmental permitting, groundwater testing, soil sampling, AutoCAD, Bluebeam Revu, and Stormwater Management Model (SWMM). David excels in managing environmental compliance programs, obtaining permits, and coordinating project-wide environmental strategies.