Evaluation of Soil Amendment with Biochar from Sewage Sludge on Heavy Metal Concentrations in Leachates of Applied Industrial Effluent: A Leaching Column Study

Abstract

Industrial global production of heavy metals as a result of anthropogenic activities, are considered the main sources of heavy metal pollution both in the developed and developing countries with possible toxic effects to the environment and poses a threat to human life with possible cumulative heavy metal production. The objective of this study was to investigate the effectiveness of sewage sludge 350°C biochar as sorbents in immobilization of industrial effluent heavy metals using batch leaching study as a model testing program. This pragmatic laboratory experiment was conducted concomitant to determination of hydraulic conductivities of clean and contaminated industrial effluent. To achieve this objective, soil and soil biochars mixtures were put into the columns and then leached with clean water parallel to industrial effluent for the period of ten weeks. Leachates at end of experiment samples were analysed for; pH, electrical conductivity, chromium, copper and zinc. Effluent pH remained constant during the experiment where clean water was used, while leaching with effluent resulted in decreasing trends as experiment duration increased. Leachate electrical conductivity was highest in the highest biochar rate when leached with effluent. Leachate zinc was below detection in the first three pore volumes and increased thereafter for all treatments while copper remained low for biochar treated soil. The findings of this study imply that high application of sewage sludge biochar reduces leaching of copper and zinc but not chromium from neutral loam soils.