No abstract

No abstract

To preserve the parklike appearance of an open finished water reservoir and meet a state mandate for increased protection of stored finished water, the Pittsburgh Water and Sewer Authority investigated postreservoir treatment options. Faced with a state mandate to cover a 125‐mil‐gal‐ (0.4 × 106–m3‐) capacity finished water reservoir and with public opposition to using a floating cover, the Pittsburgh Water and Sewer Authority explored the possibility of postreservoir treatment options. The regulatory agency indicated that any acceptable posttreatment must ensure 4‐log reduction of viruses, 3‐log reduction of Giardia, and 2‐log reduction of Cryptosporidium. The authority studied ozonation and membrane filtration for this application. Ozone inactivation trials resulted in a 1.0‐ to 1.2‐log inactivation of Cryptosporidium oocysts at bench scale and 0.1‐ to 0.5‐log inactivation at pilot scale. Membrane filter challenge studies demonstrated a 5‐log removal of Giardia cysts and 6‐log removal of Cryptosporidium oocysts. Based on the results of pilot testing and additional considerations, the authority is constructing a 20‐mgd (0.07 × 106–m3/d) microfiltration plant to treat water leaving the finished water reservoir.