Control of Pond Algae Utilizing Peracetic Acid

Peracetic acid (PAA) was evaluated as an algae control agent at the City of Modesto, CA Publicly Owned Treatment Works (POTW), during the period of June 2–4, 2003. Algae have been a problem at the POTW for many years and have become an increasing problem as the POTW attempts to increase its treatment capacity. High algae levels entering the chlorine contactor cause high chlorine demand, high TSS, and high pH in the chlorine contactor (CC) effluent. PAA was added to the storage reservoir effluent at a dose of 3 to 6 ppm. Reservoir effluent flow was 7.5 to 15 MGD and passed through two flow equalization ponds with a combined capacity of 3.5 MG. The PAA was fed for a period of 48 hours while measurements of water quality were taken. Measured parameters included BOD, TSS, total coliform, conductivity and pH. Algae were observed for bleaching. A dose of 6 ppm of PAA was required to kill the entrained algae. Some of the dead algae settled in the equalization ponds and lowered the CC influent TSS by 45%. 3 ppm of PAA did not appear to have any effect on the algae but did lower the chlorine demand in the CC by 50%. A dose of 6 ppm PAA reduced total coliforms by 97% over contact times of 1 to 11 hours. A dose of 3 ppm PAA lowered total coliforms by 91% after one hour but re-growth of coliforms was noted after 5 hours. Lab tests revealed no statistically significant increase in COD, BOD, TDS, or acetate.