Enhanced refinery oil sludge biodegradation in the presence of sewage sludge

The present study focuses on the feasibility of cocomposting
petroleum refinery oil sludge with sewage sludge to enhance biodegradation of the former. Six laboratory scale composters, each containing 5 kg soil spiked with 10% oil sludge (mass basis) were used for the bioremediation study. Shredded grass was used as bulking agent at a soil:grass ratio of 1:0.5 (v/v). The C/N and C/P ratios of the composting mixtures were adjusted to 20:1 and 800:1 using urea (H2NCONH2) and potassium dihydrogen phosphate
(KH2PO4) respectively. The ratio of contaminated soil to sewage sludge was varied as 1:0 (control), 1:0.1, 1:0.3, 1:0.5, 1:0.7 and 1:1. The moisture content was adjusted to 20% and the experiment was conducted at room temperature for a nine week period. The results showed enhanced oil biodegradation due to sewage sludge addition. The optimum contaminated soil:sewage sludge ratio was 1:0.5 at which the oil removal was 65.6% and the reaction rate constant was
0.0139 per day (10% higher than that of the control composter). The remaining 34.4% oil and grease was considered recalcitrant and not available to micro-organisms. The experiment also demonstrated the
feasibility of composting at low temperatures (23-25 °C).