SOLIDS AND NUTRIENT REMOVAL FROM FLUSHED SWINE MANURE USING POLYACRYLAMIDES

Abstract

Most of the organic nutrients and reduced carbon (C) materials in liquid swine manure are contained in finesuspended particles that are not separated by available mechanical separators. Treatment with polyacrylamide (PAM)polymers prior to mechanical removal or gravity settling has the potential for enhancing solids-liquid separation, thusconcentrating nitrogen (N), phosphorous (P), and organic C. In this work, we determined PAM charge and densitycharacteristics most desirable for swine wastewater applications and established the optimum chemical requirement.Treatments were applied to flushed manure from two swine operations in North Carolina. Cationic PAMs significantlyincreased solids separation while performance of neutral and anionic types was not different from a control. CationicPAMs with moderate-charge density (20%) were more effective than polymers with higher charge density. Flocs werelarge and effectively retained with a 1-mm screen. Optimum PAM rate varied with the amount of total suspended solids(TSS) in the liquid manure; 26 and 79 mg PAM/L for samples containing 1.5 and 4.1 g TSS/L, respectively. CorrespondingTSS removal efficiencies were 90 to 94%. In contrast, screening without PAM treatment captured only 5 to 14% of thesuspended solids. Polymer usage rate was consistent and averaged 2.0% based on weight of dry solids produced. Volatilesuspended solids (VSS) were highly correlated with TSS and comprised 79.5% of TSS. Chemical oxygen demand (COD)and organic nutrient concentrations in the effluent were also significantly decreased by PAM treatment. The decrease ofCOD concentration, an important consideration for odor control, was linearly related with removal of suspended solids,at a rate of 2.0 g COD/g TSS and 2.6 g COD/g VSS. Removal efficiency of organic N and P followed approximately a 1:1relationship with removal efficiency of TSS. Chemical cost to capture 90% of the suspended solids was estimated to be$0.026 per hog per day ($2.79 per finished hog). Results obtained indicate that PAM treatment is very effective forremoval of manure solids, COD, and organic nutrients from flushed swine effluents. The technology provides an attractivealternative to existing liquid manure handling methods for conserving nutrients and avoiding excessive nutrientapplication in areas where swine production is concentrated.