Coprocessing water treatment residuals and biosolids for phosphorus management in wastewater treatment

The purpose of this research was to investigate coprocessing as an additional strategy for managing residuals produced in water and wastewater treatment under evolving nutrient management policies. The effects on sludge dewaterability and P concentrations in water generated during dewatering (reject water) were investigated. A unique aspect of this effort was a quantitative evaluation of how coprocessing influences the environmental lability of P in biosolids land application. Laboratory experiments were conducted to evaluate the effects of coprocessing on: (1) biosolids dewaterability and polymer dose, (2) the water extractable P (WEP) concentration in dewatered biosolids, and (3) the total P concentration in reject water from dewatering operations. Results were then validated through a case study involving full-scale water and wastewater treatment facilities.;Laboratory studies investigated dewaterability (using capillary suction time, CST) of combined alum residuals (Al-WTR) and anaerobically digested biosolids at various blending ratios (BR), defined as the mass ratio of WTR to biosolids on a dry solids basis. Without polymer addition, the CST was 160 s for a BR of 0.75 compared to 355 s for the biosolids alone. The operational polymer dose (OPD), defined as the polymer dose yielding CST of 20 s, was reduced from 20.6 g kg-1 dry solids for the biosolids alone to 16.3 and 12.6 g kg-1 when BR was 0.75 and 1.5, respectively. Precipitated Al hydrous oxides in the WTR likely caused flocculation of the biosolids particles through heterocoagulation or charge neutralization. The solids contents of the blended materials and biosolids at their respective OPDs were not statistically different (α = 0.05) following dewatering by a belt-filter press (BFP). It was concluded that coprocessing with Al- WTR improved biosolids dewaterability and reduced polymer dosage.;The impact of coprocessing on the partitioning of P during dewatering and the environmental lability of biosolids-P as measured by water extractable P (WEP) were also evaluated in lab-scale studies. The reject water total P (TP) content from dewatering biosolids alone (250 mg L-1) was progressively reduced with increasing BR reaching 60 mg L-1 for a BR = 1.5. The dewatered cake (∼20% solids) WEP varied inversely with BR, dropping from 7.6 g kg-1 (biosolids only) to ∼0.2 g kg-1 for BR = 1.5. Polymer addition resulted in lower reject liquid TP for all conditions tested, indicating the cationic polyelectrolyte contributed to P binding.;A case study was completed at the Media, PA, wastewater treatment plant in an attempt to validate findings from the laboratory experiments. Al-WTR were coprocessed with digested anaerobic biosolids at BR = 1.3. Because the filtrate is recycled to the headworks, coprocessing results in a net reduction in P loading to the WWTP. Phytoavailable P (measured as Mehlich-3 P) was not reduced by application of the coprocessed material. Trace element content in the WTR is comparable to, or less than, the trace element content in the biosolids, therefore coprocessing will not prohibit land application or beneficial use with respect to trace metal concentrations. Aluminum (Al) in coprocessed cake was shown to be highly insoluble, therefore land application should not induce Al phytotoxicity or enhance Al movement to surface or ground waters. For this facility, coprocessing was established as a viable method for processing WTR and biosolids with several distinct benefits.;The potential for using WTR for P control applications appears promising and the demand for a product with this capability is steadily increasing as concerns about surface water degradation and P-based nutrient management continue to receive intense focus. In practice, the extent of these benefits may be limited by factors such as: variability in the chemical and physical properties of WTR and biosolids, (2) infrastructure and economic considerations, and (3) quantities of WTR produced relative to the amount of biosolids generated by a municipality. Nonetheless the results of this study indicate that coprocessing provides an additional strategy for managing residuals produced in water and wastewater treatment under evolving nutrient management policies. (Abstract shortened by UMI.).