Reuse to the Rescue – From Toilet to Tap Combats Drought
Globally, more than 80 percent of wastewater generated flows back into the ecosystem without being treated.1
As the demand for water grows worldwide, so does the need for us to conserve, reuse and recycle water. Advanced reverse osmosis technology can help turn wastewater into a valuable resource in a circular economy and can contribute to a safe and plentiful water supply in water-stressed areas.
DOW FILMTEC™ Reverse Osmosis (RO) Elements helped purify treated wastewater in drought-stricken California, turning it into high-quality drinking water.
By 2015, the California drought caused an estimated 2,400 wells to dry up while reservoir levels hit historic lows2 – forcing some local regions to step up imports of water, which is an expensive and energy-intensive endeavor.
But for years, some areas of the state, notably Orange County, have treated wastewater to stock underground drinking water supplies. The Orange County Water District (OCWD) has long been an innovative leader in recovering municipal secondary-treated effluent to create reusable, potable water. An integral component of its process is the Groundwater Replenishment System (GWRS) – an advanced water purification facility that uses reverse osmosis (RO) membrane technology as the workhorse of the treatment system.
At full operation, the OCWD facility is the largest “toilet-to-tap” system in the world and purifies more than 100 million gallons of treated wastewater a day3 – enough for 850,000 Orange County residents. Due to the stringent regulations on the quality of reclaimed water, the state-of-the-art facility uses a multiple-barrier water treatment process. To create potable water, the facility first implements a microfiltration pretreatment to remove microorganisms and large, suspended particles. The water then goes through an advanced RO treatment system, removing dissolved chemicals, viruses and pharmaceuticals in the water. Finally, advanced oxidation (UV and hydrogen peroxide) disinfects the water and destroys remaining low-molecular-weight compounds, including those that must be removed to parts-per-trillion levels. Most of the purified water then goes to spreading basins to replenish groundwater aquifers, injected underground near the coast to protect aquifers from seawater intrusion, and provide the county with an ongoing supply of highly purified drinking water that meets or exceeds all state and federal standards.
The OCWD sought a long-term strategy to further increase efficiency and productivity in the treatment of wastewater for reuse with the new RO membrane technologies that have higher permeability and fouling resistance. This is one reason why they chose to work with Dow Water & Process Solutions, filling their recent 30 mgd RO system expansion with DOW FILMTEC™ Reverse Osmosis Elements.
In facilities like the GWRS, the RO system is the most energy-intensive process. In 2012, nearly 50 percent of all energy usage was tied to the RO process. Adoption of Dow’s membranes in RO operation, as seen with the 30 mgd expansion in early 2015, lowered the energy required to treat the same amount of water by 13 percent when compared to the status quo performance of the existing membranes used in the original 70 mgd facility. Not only does reducing the energy it takes to purify wastewater translate into reduced operating costs for the plant, but it also lowers the carbon footprint of the facility.
As population grows and urbanization rises, treating municipal wastewater for reuse presents a reliable and safe option to help mitigate drought and provide clean, potable water to residents. By working together, Dow and OCWD research and development teams hope to create technologies that can be implemented across the globe, making wastewater reuse an even more attainable reality for water-stressed communities.
Learn more about how wastewater reuse can address global water scarcity.
1 United Nations
2 California Weekly Drought Update, Sept. 23, 2015
3 The OC Register