Biodegradation assessment of biological oil sludge from a petroleum refinery

Sludge with high concentration of hydrocarbons 470 mg/g was studied for 14 months of storage. the biodegradation was evaluated during the decomposition time by physicochemical analyses,hydrocarbons content,humic substances and phytotoxicity test. the final products showed a high degree of biodegradation as illustrated by a decrease of c/n and nh4 +/no3 - ratios,from 18.05 to 15.6 and from 26 to 2.25,respectively. organic matter and total petroleum hydrocarbons exhibited a significant abatement rate of about 50.5% and 62% respectively. the evolution of humic substances showed a high degree of polymerization,1.2%,which provides information on maturity of final product. the storage process led to reduction of phytotoxicity by the partial removal of toxic compounds such as low molecular-weight hydrocarbons and polycyclic aromatic hydrocarbons. this was also supported by the germination index,which exceeded 124% for alfalfa seeds after 14 months.