Correlating Fecal Coliform Measurements and Odors in Biosolids Cake to Digester Performance Parameters

Abstract

The Philadelphia Water Department (PWD) is uniquely situated to place the recent findings of two major WERF-sponsored biosolids studies into the context of detailed performance of a single wastewater facility. That is because Philadelphia's Southwest Water Pollution Control Plant (SW WPCP) stands alone as the one facility used in both WERF reports as a case study for linking performance of single-stage mesophilic anaerobic digesters with characteristics of biosolids odor generation and of fecal coliform reactivation and regrowth. Philadelphia has a monitoring program for the operation of its digesters and dewatering equipment that goes well beyond minimum requirements; for example, it has continuously monitored its digested and dewatered biosolids for fecal coliform since 1994, even though Philadelphia demonstrates compliance for pathogen reduction through time-temperature record keeping, as required for this Process to Significantly Reduce Pathogens. What is more, PWD has maintained a comprehensive record of operational parameters for its digesters, including volatile solids loading rates, volatile acids, alkalinity, and pH, in addition to digester temperature, sludge retention time, and volatile solids reduction based on intensive daily monitoring that mirrors the intensive "snap shot" created for each of the 11 WWTP plants in the WERF odor study and the 7 WWTP plants in the fecal coliform study, so that a direct correspondence to the WERF research can be observed. Additionally, the procedure used in the WERF odor study to characterize odorant emissions from biosolids cake --the headspace chemical analysis for odorous compounds --has been applied to monthly samples of biosolids cake from the SW WPCP for the period May 2004 to the present, the only such long-term odor characterization database of its kind. This paper reports on the statistical treatment of the operational records of the digesters and centrifuges at its SW WPCP and the adjoining centralized dewatering facility, the Biosolids Recycling Center (BRC), against the corresponding fecal coliform and odor databases to test for associations between digester and dewatering equipment performance and these parameters. This review first shows that the WERF studies engaged in sampling events at the SW WPCP that were representative of typical operations at the SW WPCP, and that the consequent fecal coliform densities and odorant intensities were within levels measured as part of Philadelphia's long-term monitoring for fecal coliform and odors, which for both parameters exhibited a wide variation, typically two orders of magnitude over the 2 ½ year monitoring period. The broad findings of this review confirm the WERF study report conclusions. That is: 1) no apparent correlation 1082 WEF/AWWA Joint Residuals and Biosolids Management Conference 2007 Date of Daily Calculated V.S. Destruction Percent V.S. Destruction % V.S. Destruction