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A demonstration pilot study was conducted in Lake Arrowhead, Calif., to determine the feasibility of reclaiming municipal secondary effluent for indirect potable reuse and stabilizing the lake level during periods of extended drought. The lake, which is the sole drinking water source for the community, was severely affected during the long drought from 1985 to 1991. A 12 000-L/d pilot plant was constructed and tested for nearly 3 years. The pilot plant included denitrification followed by alum coagulation/flocculation/sedimentation, sand filtration, primary ozonation, granular activated carbon (GAC) filtration, ultrafiltration (UF)/nanofiltration (NF), reverse osmosis (RO), and final ozone disinfection. A comprehensive analytical testing program was devised to monitor product water quality as well as to compare it with the lake water. Phosphorus and turbidity in the product water were consistently below detection limits (0.02 mg/L and 0.1 nephelometric turbidity unit [NTU], respectively). Product water total organic carbon (TOC) and conductivity levels were 1-2 mg/L and 20-40 μMho/ cm, respectively, which were approximately 25%-50% and 30%-50% of the lake concentration. Challenge testing revealed nearly complete removal of pathogenic material (an approximate 21-22 log removal of bacteriophage and 8-10 log removal of Giardia and Cryptosporidium). Trace organic chemical analysis of volatile and base neutral organic compounds indicated that it is possible to produce reclaimed water that is superior to the lake water. Only nitrogen (N) removal did not meet expectations for the entire period. It is anticipated that better process control will ensure meeting the nitrogen product water goals for full-scale treatment. |
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