Biodegradation of Hydrocarbon-Contaminated Drill Mud Waste with Compost and Cow Bile

Bioremediation of hydrocarbon-contaminated drill mud waste (HCDMW) presents a major challenge to environmental scientists worldwide, particularly in relation to the low bioavailability of the hydrocarbons and lack of reliable nitrogen source. In this study, the effects of cow bile and compost on the degradation of HCDMW were investigated to determine their potentials as sources of biosurfactant and nitrogen, respectively, for bioremediation. The HCDMW, with an initial total petroleum hydrocarbon (TPH) content of 165 g/kg was amended with varying amounts of cow bile solution (0 mL, 10 mL, 20 mL and 30 mL), compost (0% N, 1.4% N, 2% N and 2.6% N), and their mixtures giving 16 treatments. TPH, interfacial tension and C:N ratio, among other variables, were monitored as indicators of hydrocarbon degradation over a six-week period. Results indicated at least 90% TPH reduction across the various amendments compared with 3.7% for the control. The treated HCDMW also had lower residual interfacial tension (17.5–32.5 mN/m) relative to the control (32.4–35.9 mN/m). Multiple linear regression analysis revealed strong effects of interfacial tension, pH, electrical conductivity and C:N ratio on TPH degradation. The combination treatment of compost and cow bile solution resulting in 1.4% nitrogen and 20 mL cow bile was the most effective for TPH reduction (99.9% or 0.14 g/kg). These findings suggest a strong interactive effect of compost and cow bile on degradation of HCDMW, demonstrating their potentials for bioremediation as nitrogen source and biosurfactants, respectively.