Study of Metal Distribution in Raw and Screened Swine Manure

The growth of industrial swine production over the last few years has led to a growth in concern over effluents generated by the activity. Several elements, mainly toxic metals, can be present in swine wastewater and can have a serious environmental impact. It is important, therefore, to know the metal concentration before the discharge of wastewater. In this work the temporal metal distribution in swine manure and its potential reduction using coarse (2 mm) and fine (<0.45 mu m) liquid-solid separation techniques were investigated. In order to do this, different swine manure sample preparation methods for Al, Ba, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Sr and Zn determination by Inductively Coupled Plasma Optical Emission Spectrometry (ICP OES) were tested. The acid mixtures used to digest the manure sample significantly affected the metal recovery. Good analyte recoveries were observed with nitric acid/hydrogen peroxide mixtures or nitric acid/perchloric acid mixtures. Sulfuric acid/hydrogen peroxide mixtures produced inconsistent results and poor recoveries, mainly for Ba and Pb. It was observed that metal concentrations in swine manure varied greatly with time, tip to one order of magnitude, due to changes in swine production Such as feed and animal numbers. Metals concentrations observed in the raw wastewater exceeded Brazilian limits for discharge into water bodies and recommendations for agricultural use. Results obtained from the liquid-solid separation study showed that metals in the raw swine manure were not removed with coarse screening. However, the major fraction of metals were removed by filtration (0.45 mu m), with the exception of Na, K and Sr. Thus, the use of liquid-solid separation techniques that capture the fine solid fractions (and associated metals) from raw manure can have a favorable impact on the environment and contribute to swine production wastewater treatment.