Biological Remediation of Polychlorinated Biphenyl (PCB)-Contaminated Soil Using the Vermicomposting Technology for the Management of Sewage Sludge Containing Eisenia fetida Earthworms

Abstract

ABSTRACT Biological vermicomposting is an economic and eco-friendly method to remove PCBs from contaminated soils. This study aimed to investigate the effects of biological sewage sludge on contaminated soil in the presence of Eisenia fetida earthworms for the removal of PCBs. For this purpose, different mixtures of contaminated soil and biological sludge were prepared at various mixing ratios in sample containers, followed by the addition of earthworms. The degradation period was 80 days. During the degradation process, the PCBs concentrations, C/N ratio, temperature, and number of earthworms were measured. The highest reduction in PCBs (47.4%) was found in vermicompost pilot D at a contaminated soil-to-biological sludge volume ratio of 1:4, where the PCBs concentration decreased from 18 mg/kg to 9.5 mg/kg. In the control pilot D, which was identical to the vermicompost pilot D, but lacked the earthworms, the removal rate was 34%. This means that earthworms have played an effective role in increasing the removal rate. Degradation mainly occurred by microorganisms; the earthworms increased the degradation efficiency by increasing contact between microorganisms and contaminants. Overall, the vermicomposting process, in which biological sewage sludge is used for feeding E. fetida earthworms to reduce the amount of PCBs in contaminated soil, can be introduced as an innovative approach. The present study proposed a practical method to manage soil PCB contamination, using available and cost-effective raw materials that can be used in a large scale in situ. The present results indicated that the use of biological sludge, in the presence of E. fetida earthworms, could reduce highly chlorinated PCB contamination in soils.