Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 30, 2011
Publication Date: July 19, 2012
Citation: Uchimiya, M., Cantrell, K.B., Hunt, P.G., Novak, J.M., Chang, S. 2012. Retention of heavy metals in a Typic Kandiudult amended with different manure-based biochars. Journal of Environmental Quality. 41:1138-1149. Interpretive Summary: Biochar is one of the products formed during thermochemical waste-to-energy conversion processes from a variety of agricultural wastes including manures. Manure-derived biochars are nutrient-rich and are expected to be beneficial for both agricultural and contaminated soils. The local availability of manure type varies and their influence on the biochar property must be systematically investigated for on-farm production and application. In this study, biochars were produced from five manure varieties (dairy, paved feedlot, swine solids, poultry litter, and turkey litter) under controlled slow pyrolysis conditions and were examined for their ability to stabilize selected heavy metals in weathered acidic sandy loam soil. The results suggest that specific measurable properties of biochars, most importantly the organic carbon and exchangeable cation contents and basicity, directly impact their heavy metal retention ability in soil.
Technical Abstract: Although nutrient-rich manure biochars are expected to be a cost-effective heavy metal stabilizer in both agricultural and contaminated soils, systematic studies are lacking to predict the influence of manure variety and pyrolysis temperature on metal binding potentials. In this study, biochars were produced from five manure varieties (dairy, paved feedlot, swine solids, poultry litter, and turkey litter) at two pyrolytic temperatures (350 and 700°C under N2 flow) and were examined for the stabilization of Pb, Cu, Ni, and Cd in a weathered, acidic Norfolk loamy sand (Fine-loamy, kaolinitic, thermic, Typic Kandiudult) having low organic carbon content. Equilibrium concentrations in the aqueous phase were determined for heavy metals (Cu, Ni, Cd, and Pb) and additional selected elements (Na, P, S, Ca, Mg, Al, and K); these were analyzed by positive matrix factorization to quantitatively fingerprint the principal components responsible for the biochar ability to bind the select heavy metals in soil. The results indicate that manure type and pyrolysis temperature directly impact the ability of biochar to stabilize heavy metals by modifying both soil pH, quantity and quality of dissolved and particulate organic carbon and exchangeable cations as well as providing aromatic and chelating sites for binding metal ions. Concurrent with the greatest increase in aqueous pH and greatest release of Na, S, and K, poultry litter, turkey litter and feedlot 700°C biochar treatments to the soil exhibited the greatest heavy metal retention capacity. In contrast, manure varieties with disproportionately high (swine) and low (dairy) ash, P and other elemental composition were least effective sorbents for these biochar-soil systems. Proton NMR analyses indicated increasing aromatization of volatile matter as a function of pyrolysis temperature, and strong influence of volatile matter composition especially on the fate of Cu.