CHARTING THE FUTURE FOR BIOSOLIDS MANAGEMENT USING LIFECYCLE COST

The City of Rocky Mount, North Carolina operates the 21-million gallon per day pure oxygen activated sludge Tar River Regional Wastewater Treatment Plant (TTRWWPT). Residuals resulting from the activated sludge treatment process are currently thickened by dissolved air floatation and aerobically digested for stabilization to 40 CFR 503 “Class B” levels prior to liquid land application under a state issued non-discharge residuals application permit.Future land application permit modifications are expected to bring about significant changes in the day-to-day operation of the liquid land application program by further restricting liquid biosolids land application on currently permitted sites. These restrictions are anticipated to include more stringent limits on sites with high seasonal groundwater tables, incorporate seasonal restrictions based on crop coverage and active growing season, and include potentially lower allowable plant available nitrogen (PAN) loading rates. These restrictions, individually or in combination, will severely limit land application during the November to March period based on the currently permitted application sites. To accommodate these contingencies, if the Class B liquid land application program were continued, additional liquid sludge storage volume would be required at the treatment facility to handle extended seasonal application restrictions.Due to the capital and operating costs associated with the additional long-term aerated storage volume the City of Rocky Mount initiated a study to examine the lifecycle costs associated with other long-term biosolids management approaches and to develop a step-wise approach to systematically address the potential regulatory changes. Detailed results of the lifecycle cost analysis and long-term biosolids management study are shared in this case study comparing a wide range of biosolids management alternatives. Furthermore, this case study clearly demonstrates the methodology used to incorporate lifecycle cost analysis into both short-term and long-term biosolids management process decision making for a municipal wastewater treatment utility.