WASTE-WATER RECLAMATION AT LAKE ARROWHEAD, CALIFORNIA - AN OVERVIEW

A demonstration pilot study was conducted in Lake Arrowhead, Calif., t o determine the feasibility of reclaiming municipal secondary effluent for indirect potable reuse and stabilizing the lake level during peri ods of extended drought. The lake, which is the sole drinking water so urce for the community, was severely affected during the long drought from 1985 to 1991. A 12000-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, prima ry ozonation, granular activated carbon (GAG) filtration, ultrafiltrat ion (UF)/nanofiltration (NF), reverse osmosis (RO), and final ozone di sinfection. A comprehensive analytical testing program was devised to monitor product water quality as well as to compare it with the lake w ater. 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 co nductivity levels were 1-2 mg/L and 20-40 mu Mho/cm, respectively, whi ch were approximately 25%-50% and 30%-50% of the lake concentration. C hallenge testing revealed nearly complete removal of pathogenic materi al (an approximate 21-22 log removal of bacteriophage and 8-10 log rem oval of Giardia and Cryptosporidium). Trace organic chemical analysis of volatile and base neutral organic compounds indicated that it is po ssible to produce reclaimed water that is superior to the lake water. Only nitrogen (N) removal did not meet expectations for the entire per iod. It is anticipated that better process control will ensure meeting the nitrogen product water goals for full-scale treatment.