PARTICLE DESTABILIZATION AND REMOVAL FROM CONCENTRATED DAIRY MANURE SUSPENSIONS

Large-scale animal feeding operations generates substantial volume of excreta, urine, spilled feed, and bedding materials often together as solid or liquid manure mixtures. That manure often contains elevated concentrations of macronutrients and minerals, in particular phosphorus (P) because livestock rations are often formulated with excess nutrients when compared to basal metabolic requirements. Nutrient emissions and nutrient-laden runoff from livestock pens, manure storage structures, and fields where manure was repeatedly applied presents potential risks of eutrophication to nearby surface waters and major estuaries. Post-excretion treatments of animal manure to remove suspended solids and chemically remove dissolved-reactive phosphorus (DRP) before manure is applied to fields has become a focus issue in national strategies for managing animal residuals. Many agricultural soils in the United States contain excessive levels of nutrients, especially P upon repeated manure applications. A promising management and processing technology to sequester manure P and other organic nutrients is the separation of concentrated liquid manure into particulate and liquid fractions. However, theinefficiency of mechanical separators or screening has led to the rapid loss of capacity in storage ponds or lagoons that require frequent cleaning. Drinking water treatment coagulants may enhance the removal of organic and mineral matter and P from concentrated manure slurries to alleviate manure storage and land-application constraints.Mechanisms of particle destabilization in wastewater suspensions include surface charge neutralization, interparticle bridging, and particle diffuse-layer compression. Combinations of these mechanisms were operational in our optimization approach to enhancing solid-liquid separation in concentrated dairy manure suspensions. Water treatment polymers and mineral Pimmobilizing chemicals [Al2 (SO4)3.18 H2O, FeCl3.6 H2O, and coal-combustion ash] were coapplied to determine particle destabilization efficiency and DRP reduction mechanisms in high total suspended solid (TSS) dairy manure. In the TSS range between 30 and 100 g L−1, coapplication exceeded the level of aggregation achieved with individual manure additives. Solution chemistry was the overriding considerations in enhancing particle destabilization with organic polymers-hydrolyzing metal salt combinations. Surface reactivity of the coalcombustion ash played more of a key role in the particle destabilization and P recovery processes. The experimental results suggest that the synergistic effect that exists between chemical aggregation aid chemicals can be optimized to achieve reduction in coagulant inputs, while the knowledge of key manure slurry characteristics and controlling mechanisms for particle destabilization and P recovery improve manure treatment efficacy.