Oil sludge contaminated soil bioremediation via composting using refinery treatment plant sludge and different bulking agents

In bioremediation, oil degrading microorganisms are applied to remediate contaminated soil. Air is an essential factor for activation of degrading microorganisms. Adding some bulky wastes or by-products which enhance the air circulation in the system is one of the economical approaches for aeration. In this study, co-composting of oil sludge contaminated soil from a local refinery plant was studied using dry yard waste (CI) and nonrecyclable paper (CII) as bulking agents. Initially 16 L cubic composters were made using plexiglass. Composters were opened at the top and had number of holes at the bottom and sides. The soil was spiked with petroleum refinery sludge (20%, dry weight basis) and the ratio of contaminated soil to bulking agents and seeding materials was 1:1 (v/v) and 1:0.5 (w/w), respectively. The seeding materials as source of microorganisms was brought from the same refinery plant wastewater treatment facility. The total volume of each mixture was approximately 4.3 kg. The composters were cultivated weekly and water was added occasionally to maintain moisture content. Results show the temperature profile for both composters were built up after initial weeks. Moisture content reached to steady conditions (50% to 60%) in second week and was maintained within the range till the end of experiments. pH showed more fluctuation in CII compared to CI. The maximum reduction of total petroleum hydrocarbon (TPH) was 55% and 56% for CI and CII, respectively over the 14-week study duration. The composting degradation rate kinetics indicates that the TPH concentrations will reach less than 100 mg/kg after 23 weeks of degradation.