CRYPTOSPORIDIUM AND WASTEWATER REUSE THE CITY OF FRISCO, TX EXPERIENCE

The Stewart Creek Regional wastewater treatment plant (WWTP), operated by North Texas Municipal Water District (NTMWD), consists of two separate treatment trains, the east plant and the west plant. The treatment trains consist of a conventional activated sludge process, secondary clarification, chlorination, and filtration. During peak flows, each treatment train can handle more than 5.0 mgd. Currently, the treated effluent is either released through the creek outfall or pumped to a nearby golf course for use as irrigation water. Recently the plant was upgraded by adding a UV disinfection system and a reuse effluent pumping station.To comply with TNRCC requirements, a study was conducted to validate the effectiveness of the UV system in inactivating CRYPTOSPORIDIUM. Results of this study indicated that CRYPTOSPORIDIUM in wastewater can be inactivated using significantly lower doses of UV than required to inactivate fecal coliforms: the system can achieve a 10-log removal of fecal coliforms at the design dose of 45 mJ/cm2 and can meet the requirements for Type I reuse water specified in 30 TAC 210.33(2)(B). The results of this study further indicate that the UV system can achieve 3.23-log inactivation of MS-2 as well as more than 10-log removal of CRYPTOSPORIDIUM. At the flow rate of 1.74 mgd that was used during this test, the system would have been capable of better than 5-log removal of MS-2 at a UV dose of 79 mJ/cm2, which meets NWRI guidelines. At the 79 mJ/cm2 dose, the system can achieve better than 10-log inactivation of Cryptosporidium.