Field validation of self-regenerating reversible ion exchange-membrane (RIX-M) process to prevent sulfate and silica fouling

Abstract

Desalination of brackish water and municipal wastewater will be integral to water resource resiliency during uncertain climate conditions. Higher efficiency and higher recovery than conventional desalination is achievable if biofouling and inorganic scaling can be avoided on membranes or heating surfaces. Temporary hardness is well addressed through acid and antiscalant dosing, but permanent sulfate hardness lacks selective removal techniques that do not require external chemicals or produce large volumes of sludge. Self-regenerating reversible ion exchange-membrane (RIX-M) processes have been proposed using a tunable anion exchange blend to remove silica and sulfate selectively from influent water with efficient regeneration via brine reject. A 2.5GPM RIX-M process was tested at the US Bureau of Reclamation (USBR) Brackish Groundwater National Desalination Research Facility (BGNDRF, Alamogordo, NM). High sulfate-containing brackish groundwater was desalinated at high recovery (80%) without membrane fouling through selective sulfate removal and regeneration via desalination brine reject, without external chemical addition. Ten treatment-regeneration cycles were performed without degradation in system performance. High efficiency silica removal from complex groundwater backgrounds at BGNDRF was also achieved across varying water chemistries. RIX-M offers a new pre-treatment opportunity to protect RO membranes from sulfate and silica fouling without dosing anti-scalants, while attaining high recovery.