Abstract

The petroleum-based drilling fluids constitute major environmental pollutants due to their persistence and toxic effects on aquatic ecosystems. This study monitored the biodegradation potential of freshwater bacterial species on oil-based drilling fluid (OBDF) and water-based drilling fluid (WBDF), with the aim of determining their degradability and the microbial species involved in the process. The findings revealed that indigenous bacterial genera including Micrococcus, Pseudomonas, Bacillus, Corynebacterium, and Proteus were actively involved in the degradation of the drilling fluids, demonstrating their capacity to utilize hydrocarbon compounds as sources of carbon and energy. Marked reductions in Biological Oxygen Demand (BOD) and Chemical Oxygen Demand [COD] were observed throughout the biodegradation period, indicating progressive microbial degradation of organic pollutants present in the drilling fluids. COD ranged from 79.40 - 193.10 mg/L for OBDF and 78.10 - 298.60 mg/L for WBDF, while BOD from 16.10 - 65.70 mg/L and 11.70 - 68.60 mg/L for the OBDF and WBDF respectively. The study further revealed that WBDF showed a higher biodegradation percentage [79.90%] when compared to 60.00% recorded for OBDF after 20 days. Although WBDF showed the highest biodegradation percentage, the difference among treatments was not statistically significant at [p≤0.05]. These findings show the ecological importance of indigenous freshwater bacteria in the natural remediation of drilling fluid contamination.