Even as the Southwest grapples with acute water shortage, the question of driving greater performance out of existing water treatment infrastructure has never been more pertinent. Operators and utilities around the globe are striving to get a higher return on their operating assets. Yet, in spite of all the recent advances in membrane technologies, the most common question we encounter from our customers hasn’t changed in the past decade.
“Why can’t reliability and higher recovery both be achievable over a long period? Why do we have to sacrifice one for the other?”
It was the same question that brought key stakeholders at the Orange County Water District (OCWD) to evaluate the DesaliTec™ Closed Circuit Reverse Osmosis (CCRO) technology. As an internationally recognized leader in the water industry and a long-term customer of DuPont’s multi-technology portfolio, OCWD also operates the world’s largest indirect potable reuse plant. The Ground Water Replenishment System, or GWRS, currently employs three-step advanced treatment technologies such as microfiltration and reverse osmosis to generate potable water to standards exceeding both state and national drinking water quality standards.
The facility currently treats 100% of the secondary effluent available from a wastewater treatment facility using a 3-stage Reverse Osmosis (RO) system, treating 118 MGD (million gallons per day) flow at an 85% recovery. If there was a way to add a fourth-stage, the plant could not only potentially recover additional 9MGD of clean water, but also lower brine disposal volumes by approximately 40%. However, operating a fourth-stage RO reliably over a long period of time is no child's play! As the recovery is driven higher, the concentration of mineral salts goes above their solubility limits, causing their precipitation on to the membrane surface– leading to several well documented scaling problems and limiting membrane life.
In order to better define the new boundaries of achieving consistently higher recovery, OCWD ran a pilot using the DesaliTec™ SOAR™ Max (previously called Reflex™ Max) from 2017 to 2019 on feedwater sources ranging from the primary RO feed, the 3rd stage RO concentrate and a diluted 3rd stage RO concentrate as summarized in Table 1, found below.
The comprehensive two years of pilot testing demonstrated the sustainable use of CCRO technology for RO concentrate treatment, driving recoveries up to 91%, without compromising CIP frequencies of 2 months or greater.
According to a spokesperson from OCWD, “A comprehensive two-year pilot-scale study was done in collaboration with Dupont/Desalitech, Jacobs and Carollo Engineers that demonstrated the sustainable use of CCRO for RO concentrate treatment. Water recovery from concentrate is becoming more feasible as the cost of membrane treatment technologies has dropped and the value of water has increased. OCWD is proud to be a part of this cutting-edge research project which will provide critical data to support advancements in water reuse and treatment.”
Similar sentiments were shared by Jacobs, the technical advisor on this pilot project.
“The pilot testing of CCRO at GWRS was a great example of collaborative innovation between Desalitech, Orange County Water District and Jacobs. Through this testing, CCRO was able to sustainably demonstrate increased recovery of the GWRS RO system using a PLC-based adaptive control strategy that automatically adjusted system operations to changes in feed water quality thereby mitigating the impacts of fouling. Jacobs appreciates the opportunity to have served as a technical advisor on a project that advances the sustainability of potable reuse in meeting our water resource needs.”
Water recovery by further concentrating existing reject streams is becoming both relevant and practical in the current times. Increased value on resource recovery, combined with lowering cost of treatment is helping guide this change. Add to it a more robust technology such as DesaliTec CCRO and the future may be nearer than what we think!