Toxic hydrocarbon removal of contaminated soil using Eisenia fetida with response surface methodology

Petroleum sludge is typically caused by petroleum contaminants, effluents, and wastes from various stages of hydrocarbon separation. In this study, samples of oily sludge were collected from heavy fuel storage tanks in Sirjan Petrochemical Company in order to investigate the bioremediation of oily sludge by Eisenia fetida earthworms. The effects of oily sludge content, soil ratio, and sawdust weight percentage on total petroleum hydrocarbon (TPH) removal and reproduction of earthworms were evaluated. According to the design of the experiment (DOE), 17 samples with different combinations of petroleum sludge, soil, cow manure, and sawdust were selected to be tested. Also, to determine the effectiveness of the bioremediation process, some properties of samples including pH, total organic carbon (TOC), total Kjeldahl nitrogen (TKN), carbon to nitrogen ratio (C/N), and electrical conductivity (EC) were measured. The results showed that all properties, except for the electrical conductivity, decreased. Besides, in the presence of worms, the TPH could reduce by 66% after 90 days for samples containing up to 40 g oily sludge. Moreover, a statistical model was proposed using the response surface methodology (RSM) to predict the TPH removal and earthworm population as the targeted responses. Keywords: oily sludge; earthworm Eisenia fetida; Vermiremediation; response surface methodology.