Biodegradation of total petroleum hydrocarbons from acidic sludge producedby re-refinery industries of waste oil using in-vessel composting

Background: In Iran, re-refinery industry has been developed many years ago based on the acid- clay treatment. Acidic sludge with high concentration of total petroleum hydrocarbon (TPH) is the final products of some facilities. In this study removal of TPH by aerated in-vessel composting was investigated. Methods: In order to microorganisms seeding and nutrient providing, urban immature compost was added as an amendment to acidic sludge. The ratios of acidic sludge (AS) to compost were, 1:0 (as control), 1:5, 1:8, 1:10, 1:15, 1:20, 1:30, 1:40, 1:50, 1:75 and 1:100 (as dry basis) at a C: N: P ratio of 100:5:1 and 45–65% moisture content for 70 days. Results: The removal efficiency in all reactors was more than 48%. The highest and lowest TPH removal was observed in 1:5 (71.56%) and 1:100 (48.53%) mixing ratios, respectively. The results of the control reactors showed that biological treatment was the main mechanism for TPH removal. Experimental data was fitted second order kinetic model (R2 0. 8006). Degradation of TPH in 1:5 mixing ratio (k2 = 0.0038 gmg^ −1 d^−1; half-life = 3.08d) was nearly three times faster than 1: 100 mixing ratio (k2 = 0.0238; half-life = 8.96d). The results of the control reactors showed that biological treatment was the main mechanism for TPH removal. Conclusion: The results of this study revealed in-vessel composting with immature urban compost as the amendment maybe recommended as an effective method for TPH remediation.