Reducing Phosphorus Runoff from Biosolids with Water Treatment Residuals.

Phosphorus (P) runoff from fields fertilized with biosolids has been shown to be highly correlated to the biosolids soluble P content. The objective of this study was to measure P runoff from land fertilized with biosolids and to determine the effect of various chemical amendments, including water treatment residuals (WTRs), on P runoff. Rainfall simulations were conducted on small plots cropped to tall fescue in 2006 and 2007.  Simulations were conducted on the day of biosolids application, then at 1, 2, 4 and 6 weeks after application.  When WTRs were mixed with biosolids at a rate of 20% (wet basis) three days prior to land application it decreased soluble P runoff by 45% and total P runoff by 41%.  We hypothesized that WTRs would decrease P runoff better if the reaction time with biosolids was increased, since P diffusion is probably limiting P adsorption. Hence, in year 2 the WTRs were mixed with biosolids three weeks prior to application.  The addition of WTRs to biosolids decreased soluble P loads in runoff by 93% and total P loads by 89%.  This practice would save cities money since both biosolids and WTRs are currently being landfilled in NW Arkansas. Rough calculations indicate that there should be enough WTRs to treat the entire amount of biosolids produced in the U.S. each year. This should create an environmentally friendlier fertilizer, since P runoff could be greatly decreased.