Pilot Study of Advanced Treatment Processes to Recycle JWPCP Secondary Effluent

A collaborative project between the Sanitation Districts of Los Angeles County and the Metropolitan Water District of Southern California was initiated to evaluate the feasibility of purifying secondary effluent from the Districts' Joint Water Pollution Control Plant for a regional indirect potable reuse program.The study tested two separate advanced water treatment process trains to determine the capability of meeting the groundwater recharge water quality criteria specified in Title 22 of the California Code of Regulations and the California Department of Public Health notification levels. One process train consisted of ultrafiltration (UF), followed by reverse osmosis (RO), with advanced oxidation process (AOP) consisting of UV oxidation and hydrogen peroxide. The second process train consisted of a membrane bioreactor (MBR) followed by RO and AOP. This paper discusses the operations of the UF, MBR, and RO systems and the water quality results of the product water and concentrate.The sampling results show that both treatment trains produced high quality recycled water for parameters relevant to groundwater recharge projects, such as nitrogen, TOC, trace organic compounds including volatile organic compounds, pesticides, herbicides, pathogens indicators, and contaminants of emerging concern. Both trains treated these compounds to levels either below the laboratory reporting limits or relevant regulatory limits; the only exceptions were nitrosamines and boron. The nitrosamines can be removed by AOP (UV plus hydrogen peroxide) to meet the Title 22 Draft Groundwater Recharge Regulations. Boron levels in the RO permeate were slightly above the Basin Plan limit of 0.5 mg/L. Source control may be required to reduce the boron levels to meet this limit.