Removal of Cu, Pb and Zn from stormwater using an industrially manufactured sawdust and paddy husk derived biochar

Direct flow of untreated stormwater containing Cu, Pb and Zn is of immediate concern to aquatic life in waterways. To date, most biochar used has been synthesized under controlled laboratory conditions using furnaces purged with inert gasses. In this study, the removal of Cu, Pb and Zn using biochar synthesized using paddy husk and sawdust feedstocks has used an industrial scale double chamber downdraft pyrolysis reactor. The effect of pyrolysis temperature and the effect of feedstock in the removal of Cu, Pb and Zn was evaluated by conducting batch adsorption experiments. Synthesized adsorbent materials were characterized using proximate analysis, zero-point charge, scanning electron microscopy, X-ray diffraction and Fourier Transform infrared spectroscopy. The biochar yield was in a lower range compared with the literature attributed to the higher heating rate (50 degrees C/min) in the pyrolizer. Maximum removal efficiencies were observed when the initial pH was at the value closest, when below the solubility limit for the heavy metals. The paddy husk biochar and sawdust biochar synthesized in the temperature range 350-450 degrees C and 450-550 degrees C performed best in the removal of the three heavy metals. Chemisorption was the main mechanism for the removal of the three heavy metals. The maximum adsorption capacities of Cu and Zn were 10.27 and 6.48 mg/g was achieved with paddy husk biochar and a maximum Pb adsorption capacity of 17.57 mg/g was achieved by sawdust biochar. Surface complexation, co-precipitation, p-electron interactions, physical adsorption and surface precipitation were the main mechanisms of removal of the three heavy metals.