AWWA JAW52064

Faced with a state mandate to cover a 125-mil-gal- (0.4 x 10 (6)-m3-) capacityfinished 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 0.2- 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 x 10(6)-m3/d) microfiltration plant to treat water leaving the finished water reservoir. Includes 17 references, tables, figures.