A large fraction of the biosolids produced in the U.S. are placed in landfills or incinerated to avoid potential water quality problems associated with non-point source phosphorus (P) runoff. The objective of this study was to determine the effect of various chemical amendments on soluble P in biosolids and P runoff from biosolids. Laboratory studies showed that alum-based water treatment residuals (WTRs) could reduce P solubility in biosolids as well as alum or ferric chloride. Likewise, rainfall simulation studies showed P runoff from biosolids was reduced with WTRs. During year 1, soluble P loads were reduced by 48% when WTRs were mixed with biosolids at a rate of 20% (wt/wt) and were not significantly different from P runoff using chemical amendments. In year 2, when WTR/biosolid mixtures of 15% and 30% (wt/wt) were allowed to incubate for three weeks prior to land application, soluble P loads in runoff were 78% and 85% lower than untreated biosolids, respectively. The improved reductions in P runoff observed in year 2 indicate that longer incubation times may allow for greater P adsorption which is limited by the rate of P diffusion onto WTRs. Treating biosolids with WTRs results in an environmentally friendly fertilizer and allows for the agronomic use of these important resources.