(212b) RO Denitrification and Desalting of Impaired Brackish Water in Remote Communities

Groundwater nitrate contamination poses a threat to public health for community water systems especially in agricultural areas and in rural communities that cannot afford and/or capable of operating and maintaining the necessary small water treatment systems. In recent years, RO has been promoted as a technical solution to providing such communities with safe drinking water. However, the challenge to RO application in distributed remote communities is that the operation must be flexible with respect to water demand and quality. It is also critical to establish a cost-effective approach to assess the adequacy of deployed RO water treatment process for nitrate removal (real-time nitrate monitoring might still be costly for a number of distributed small treatment systems) as well as to provide an economical solution to handle the nitrate-laden residual stream locally in a robust and environmentally manner. In order to address the above challenges, the technical feasibility of RO water treatment in remote communities was evaluated based systematic analysis of process simulation for pilot communities’ water treatment system based on site-specific information (e.g., water consumption, water quality). RO system design was evaluated for operation with concentrate recycle, over a wide range of external variables (e.g., water use demand, feed nitrate, and salinity levels), for target nitrate removal at water recovery effective for reducing system foot print and suitable for deployment in remote communities. The correlation between nitrate and salt passage was established via computer simulation as well in a series of laboratory experiments using a pilot-scale brackish water RO unit (developed by UCLA) integrated with the portable online nitrate monitoring system. In addition, the feasibility of utilizing existing septic tanks in remote communities for handling nitrate containing RO concentrate was evaluated with respect to technical and environmental viewpoints given. Results demonstrated that system operation at the optimal concentrate recycle ratio enabled recovery up to ~90%, while producing permeate product water at nitrate levels well below the regulatory established MCL for nitrate. Through establishing a correlation between nitrate passage and salt passage, small water system owners/operators, and regulatory agencies can assess the performance of the distributed small water treatment systems in an economical manner in order to gain confidence in the reliability of treatment system to handle nitrate removal. The current study suggests that local RO treatment of community groundwater and handling RO residual stream in a septic tank would have a minimal environmental impact while providing a significant beneficial use of safe drinking water.