Evaluation of Advanced Water Treatment for Indirect Potable Reuse

The City of San Diego (City) and MWH recently completed a 18-month pilot testing program to determine the effectiveness of a three-step Advanced Water Treatment (AWT) process to produce water suitable for indirect potable reuse from tertiary water produced at the North City Water Reclamation Plant (NCWRP). This testing program was conducted as part of the City's Water Reuse Study, which was initiated in 2004 to explore all options for utilizing recycled water which can be produced by the City's existing water reclamation facilities. The option of using AWT for indirect potable reuse is only one of several options the City has identified to meet water recycling goals. The AWT process consisted of three steps: ultrafiltration (UF); reverse osmosis (RO); and ultraviolet (UV) light + hydrogen peroxide. The main objectives of this testing program were to assess the water quality performance of the AWT process and evaluate the long term operational performance of new generation RO membranes currently offered for water reuse applications. In addition, the study aimed to assess the ability of UV + hydrogen peroxide to remove a diverse group of endocrine disrupting compounds (EDC) and pharmaceuticals and personal care products (PPCP). Results from the study showed the product water from the AWT pilot system met all federal and State of California drinking water standards. In addition, 21 contaminants of concern measured in the RO permeate and UV peroxide effluent including NDMA, 1,4 dioxane and perchlorate were all below current notification levels established by California Department of Health Services (CDHS). RO performance testing showed no decrease in specific flux occurred for a runtime of 1,250 hours at flux of 12 gfd and feedwater 75% recovery. Lastly, UV applied at an equivalent dose to achieve 1-log destruction of NDMA with 5 ppm hydrogen peroxide achieved greater than 98% removal of all EDC/PPCP, with the exception of TCEP, spiked upstream of the UV process.