Solids Handling Improvements Pays Back! Results from an Anaerobic Digester Upgrade Project

The City of Clearwater, Florida maintains and operates three wastewater treatment plants. The 5 mgd East Advanced Pollution Control Facility (APCF), the 13.5 mgd Northeast APCF, and the 10 mgd Marshall Street APCF. Both Northeast APCF and Marshall APCF use anaerobic digesters for biosolids handling. The biosolids from East APCF is hauled and processed at Northeast APCF. During the early 2000’s the city experienced poor results from their digesters, due to deteriorated heating and mixing equipment. Consequently the City embarked on an initiative to invest in a rehabilitation program for all their digester facilities. The purpose of this paper is to provide data on increased gas production and reduced hauling cost savings after the digesters were rehabilitated in late 2006. The data from the Northeast APCF is presented. The intent of the Clearwater Anaerobic Digester Improvements Project is to improve biosolids treatment processes at the APCFs, to enhance and improve disposal options and operational flexibility, to promote biosolids reuse and energy recovery, and to reduce operating costs as feasible at the facility. Placing the anaerobic digesters back into service reduced approximately 40 percent of the residuals volume. By rehabilitating and utilizing the anaerobic digesters over the past five years WPC has generated O&M savings of $1,711,000. If nothing had been accomplished to reduce the volume of biosolids hauled, the present day annual cost would be $1,424,700. Another added benefit is the reduction in fossil fuel not hauling 14,210 wet tons per year. This equates to 63 truckloads annually. It is also rare to be able to have the opportunity to roll back and reduce costs to a rate lower than they were six years ago while dealing with an increase in unit cost. Source: WEFTEC 2009 Proceedings