Toxicity of raw and bio slurry treated oily sludge on Nitrobacter species and Tilapia guineensis

Toxicity of raw and bio-slurry treated oily sludge (OS) on Nitrobacter species was determined using standard analytical procedures. The total petroleum content of the OS was 116.44 ± 3.57 g/kg. The TPH was rich with Saturate (40.46 ± 0.73 %). This was followed by Aromatics (27.94 ± 0.50 %) and Asphaltenes (26.58 ± 0.90 %), while NSO fraction had the least proportion (5.75 ± 0.47 %). Contamination of coastal soil with the OS increased the residual TPH concentration in the soil from 5.0561 ppm to 24.2305 ppm. The OS-ladened soil were subjected to biodegradation using 1.5-litter borosilicate glass bioreactors bioaugmented with single population of known OS utilizer (Pseudomonas aeruginosa) and consortium of known OS utilizer and biosurfactant producing bacterial species (Bacillus subtilis). Findings revealed that he bioslurry augmented with the bacterial consortium reduced the concentration of the residual TPH in the soil to 6.313 ppm (73.95% reduction) while 11.5751 ppm (52.23%) was recorded for the single bacterial population. Findings also revealed that the consortium were able to remarkable reduce the toxicity of the raw OS (LC50 = 20.94 ppt) on Nitrobacter species. The LC50 for the consortium treated OS was 104.64 ppt while that of single bacterial population treatment was 36.25 ppt. The reduction in the toxicity of the OS treated with the bacterial consortium indicates the potentials of the synergistic action between the biosurfactant producer and OS utilizer to reduce OS toxicity. The findings of this study can be explored as a cost-effective method for oily sludge waste management in the Oil and Gas industry.