Biodegradation of total petroleum hydrocarbons from acidic sludge produced by 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 (R (2) > 0.8006). Degradation of TPH in 1:5 mixing ratio (k(2) = 0.0038 gmg (−1)d(−1); half-life = 3.08d) was nearly three times faster than 1:100 mixing ratio (k(2) = 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.