Reducing Phosphorus Runoff From Biosolids with Water Treatment Residuals.

A large portion of the biosolids (sewage sludge) produced in the U.S. are incinerated or placed in landfills because of potential water quality problems, such as phosphorus (P) runoff.  The objective of this study was to evaluate the effects of chemical amendments, including water treatment residuals (WTRs), on P runoff from biosolids.  Rainfall simulations were conducted in 2006 on small plots fertilized with biosolids that had been treated with alum, ferric chloride or an alum-based WTR.  The WTR was added a rate of 20% by weight.  In 2007 rainfall simulations were conducted using WTR/biosolid blends of 15 and 30% by weight, which were allowed to incubate for three weeks prior to application.  During year 1, soluble P loads in runoff with the 20% WTR treatment were not significantly different from alum or ferric chloride and resulted in a 48% reduction in soluble P runoff.  Soluble P runoff loads in year 2 were reduced by 78% and 85%, respectively, with the 15 and 30% mixtures of WTRs.  Greater reductions in P runoff found in the second year indicate that longer storage times may allow for greater P adsorption, most likely caused by P diffusion into micropores.  Mixing biosolids with WTRs will allow for greater land application of biosolids and WTRs, which will greatly reduce the costs associated with landfilling and incineration of these two resources, while protecting the environment.