Coprocessing Water Treatment Residuals and Biosolids for Control of Water Soluble Phosphorus in Biosolids

Evolving phosphorus (P) nutrient management policies represent a major challenge for land-based biosolids recycling. Research indicates that release of P from land-applied biosolids into runoff and subsurface drainage is directly related to the water extractable P (WEP) content of the biosolids. Biological P removal processes, increasingly used for nutrient control, produce biosolids exceptionally high in WEP. Thus, strategies that reduce biosolids WEP are needed to sustain land application programs. This study evaluated conditions under which blending alum-based water treatment residuals (WTR) with digested wastewater sludge prior to dewatering reduces WEP and P-loss susceptibility of land-applied biosolids. Laboratory experiments showed that coprocessing WTR and biosolids at a 1:1 ratio (dry mass basis) resulted in the following: (1) substantial (>75%) reduction in WEP of the resulting biosolids; (2) soluble P in mechanical dewatering filtrate was reduced by > 50 %; and (3) the polymer dose required for conditioning was lowered by ∼15 %. While results will vary with WTR / biosolids characteristics and system operational conditions, coprocessing is one strategy for managing municipal by-products as new P-based nutrient regulations are deployed.