Quantifying Sludge Production in Municipal Treatment Plants

This paper addresses the issue of sludge production in plants treating municipal wastewater. The historical understanding and quantification of sludge production in activated sludge systems is reviewed briefly. An important factor is the selection of three parameters used in the estimation of sludge production (and carbonaceous oxygen requirements). These are the yield coefficient (Y), the endogenous decay rate (b), and the endogenous residue fraction (f). A method is presented for estimating sludge production, and the composition of the sludge, based on the WERF (2003) influent wastewater COD characterization and inorganic settleable solids (ISS) content. The method can be applied to systems treating either raw influent wastewater or primary effluent, based on a mass balance across the primary settling tank and an assumed percent solids removal. Predictions of sludge production by simulation models are discussed, and an issue is identified regarding the heterotroph decay rate parameter in the ASM 2d model (Henze et al., 2000).