Black & Veatch

Class a biosolids production at eastern municipal water district using heat pasteurization

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Courtesy of Black & Veatch

Since 1998, the Eastern Municipal Water District (District) has developed and successfully operated a heat pasteurization facility to treat extended aeration waste activated sludge (WAS) from the Perris Valley Regional Water Reclamation Facility (PVRWRF). The treatment train uses hot water to sludge spiral heat exchangers and a patented continuous-feed, complete mix pasteurization vessel (heated sludge holding tank). Treated biosolids are dewatered on belt filter presses and applied to farmland either within 8 hours of pasteurization or after air drying to 75 percent total solids on sludge drying beds.

The pasteurization process has proven to be reliable and cost effective. Tests for fecal coliforms have consistently demonstrated that the pasteurization system produces Class A biosolids when operated at 158 degrees F in accordance with the Part 503 requirements. Based on fecal coliform monitoring, Class A biosolids could possibly be produced at temperatures below 158 degrees F. However, additional monitoring of parasites and viruses should be conducted to establish the minimum required temperature for complete pathogen inactivation Pasteurization does not adversely impact the downstream dewatering process or appreciably change the nutrient quality of the biosolids.

From a national perspective, the pasteurization offers several potential advantages for POTWs with aerobic digesters which can not meet Class B biosolids standards: (1) cost effective production of Class A biosolids, (2) potential use of waste heat generated from engine driven blowers and pumps, (3) elimination of dust, odor and vector problems of composting and other open air processes, and (4) compact facility design with minimal land requirements and minimal manpower requirements.

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