(666c) RO Treatment of Small Community Wellhead Water for Contaminant Removal and Salinity Reduction

The rising salinity and nitrate levels in groundwater water supplies in agricultural regions pose a threat to potable water supplies of many rural communities who are without suitable and immediate alternative water supplies. Salinity and nitrate reduction can be effectively achieved via RO membrane treatment of such impaired water supplies. The challenge in small remote communities, however, is in (a) attaining high recovery while avoiding mineral scaling, (b) providing effective nitrate monitoring to comply with regulatory requirements, (c) effective low-cost operation, affordable by the communities, and (d) community septic system capable of handling the combined volume of discharged domestic wastewater and RO concentrate stream. Accordingly, the present study reports on the technical, operational and economic feasibility of a water treatment system, based on RO treatment train (i.e., RO, MF, media filtration, activated carbon adsorption, and remineralization), designed, constructed and deployed in a small agricultural community in Northern California. RO system operation was implemented at high recovery (up to ~90%) allowing a sufficient retention time in the septic tank, while ensuring the target nitrate removal and salinity reduction. The RO system featured a unique approach to recovery enhancement via partial concentrate recycle and product water quality monitoring (with respect to nitrate and salinity) via online nitrate and conductivity sensors, in addition to establishment of a correlation between membrane salt and nitrate passage. Field tests demonstrated the potential for deployment of a novel RO system, integrated with a pressure intensifier, in which the RO feed pump outlet pressure requirement was significantly reduced, thereby enabling utilization of renewable energy sources (e.g., solar or wind). Field studies have demonstrated the ability to mitigate mineral scaling with the combination of periodic triggering a freshwater flush and optimal antiscalant dosing based on the direct membrane surface monitoring. It was also shown that operating costs could be significantly reduced by implementing a unique remote supervisory control and decision support system.