Co‐Application Effects of Water Treatment Residuals and Biosolids on Two Range Grasses

Abstract

AbstractAlum [Al2(SO4)314H2O] is commonly used in the municipal water treatment process to destabilize colloids for subsequent flocculation and water clarification. Water treatment residuals (WTR) can be classified as a waste material from these treatment plants. Concerns over land application of WTR are due to its postulated reduction of plant available P and potential plant Al toxicity with increasing WTR rates. Co‐application of WTR with biosolids may benefit municipalities with biosolids inherently high in P concentrations and in terms of a cost savings by landfill avoidance. In a greenhouse study, we investigated the efficacy of co‐application of WTR and biosolids to the native shortgrass prairie species blue grama (Bouteloua gracilis H.B.K. Lag) and western wheatgrass [Pascopyrum smithii (Rydb.) A. Love]. Our objectives were to quantify co‐application effects on plant P and Al concentrations and uptake, biomass production, and WTR P adsorbing capacity. With blue grama, we observed a positive linear relationship between increasing WTR rate and yield and a negative linear relationship with increasing WTR rate and shoot P and Al concentration (P < 0.10). With western wheatgrass, increasing WTR rate produced a negative quadratic effect on shoot Al concentration (P < 0.10). Some investigators have observed P deficiency symptoms associated with WTR application; however, we did not. Our adsorption study indicated that co‐mixing of the City of Fort Collins, CO, WTR and biosolids at ratios of 8:1 will adsorb all soluble biosolids P. Beyond this ratio the WTR could adsorb all biosolids available P and possibly some soil‐borne P.