Abstract
Cu and Zn are known to be abundant in swine feces; hence, concentrations of these metals need to be lowered before swine feces are applied to land in order to prevent potential environmental problems. The main objective of this study was to develop an appropriate chemical process to remove Cu and Zn from swine feces using acid extractions. The removal efficiencies of Cu and Zn decreased in the order of H2SO4 > HNO3 > organic acids (citric and oxalic acids). Owing to the highest removal efficiencies of Cu and Zn by using H2SO4, it was selected for further elimination of Cu and Zn from swine feces. By using H2SO4, the optimal concentration, solid-to-liquid ratio, and reaction time were 2%, 1:50, and 8 h, respectively. At the optimum conditions, Cu concentration was decreased from 198 mg/kg to 40.1 mg/kg and Zn concentration from 474 mg/kg to 80.0 mg/kg, with removal rates of 79.7% and 83.1%, respectively. The low Cu removal efficiency, resulting from the strong complexation between Cu and organic matter of swine feces, was improved by the increase in the reaction time and H2SO4 solution concentrations. However, about half of the total nitrogen (TN) was also removed by using H2SO4, indicating that the swine feces treated with H2SO4 may have poor value as fertilizer. Additional studies are required to find an optimal method to maintain TN concentrations while simultaneously removing Cu and Zn.
Highlights
Owing to the economic profitability and low environmental pollution, swine feces have been frequently used as an alternative to chemical fertilizers [1,2]
Land application of swine manure as a fertilizer can lead to the accumulation of heavy metals (e.g., Cu and Zn) in soil [6,11,13,14]; soil and groundwater qualities possibly deteriorate, and the metals accumulated in soil can be transferred to plants in excessive amounts, which affect the health of animals and humans through the food chain [15]
Our results revealed that inorganic acids are better than organic acids for the removal of heavy metals
Summary
Owing to the economic profitability and low environmental pollution, swine feces have been frequently used as an alternative to chemical fertilizers [1,2]. Most of Cu and Zn (up to ~95%) are excreted in swine feces, and concentrations of Cu and Zn in swine feces are greater than those in cattle and horse feces [7,9,10]. Cu and Zn concentrations in swine manure were greater than those in cattle, sheep, and poultry manure in England, Wales, and China [11,12]. Land application of swine manure as a fertilizer can lead to the accumulation of heavy metals (e.g., Cu and Zn) in soil [6,11,13,14]; soil and groundwater qualities possibly deteriorate, and the metals accumulated in soil can be transferred to plants in excessive amounts, which affect the health of animals and humans through the food chain [15]
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