Enhanced Bioremediation of Commercial Diesel Contamination by Mixed Culture of Newly Isolated Providencia vermicola IITG20 and Pseudomonas aeruginosa IITG21 from Local Refinery Waste

Two bacteria Providencia vermicola IITG20 and Pseudomonas aeruginosa IITG21 were isolated from the local refinery waste sludge and contaminated soil. They were found to be able to utilise different hydrocarbons such as diesel, petrol, kerosene and engine oil for their growth. The effect of process parameters was studied and most suitable conditions for degradation by the selected strains and their mixed culture were found to be 4% v/v initial diesel concentration, 37 °C temperature, pH 7, and 1% v/v initial inoculum concentration. The highest growth was observed for mixed culture. The lowest growth was observed for the pure culture of Pseudomonas aeruginosa IITG21. The degradation of 4% v/v diesel at 37 °C in 15 days was found to be 70 and 76% by the pure culture of Pseudomonas aeruginosa IITG21 and Providencia vermicola IITG20, respectively. Their mixed culture gave 85% degradation. The rate of degradation for diesel was highest for mixed culture compared to pure cultures. The rate constant for first order degradation was 0.154 day⁻¹ for mixed culture. It was higher compared to that of the pure culture of Providencia vermicola IITG20 (0.098 day⁻¹) and Pseudomonas aeruginosa IITG21 (0.83 day⁻¹). Accordingly, the half-life for mixed culture was lower (4.5 days) than that for pure cultures of both bacteria (7.1 and 8.3 days). These findings highlight the potential of mixed bacterial culture of Providencia vermicola IITG20 and Pseudomonas aeruginosa IITG21 for more efficient hydrocarbon degradation in petroleum hydrocarbon contaminated environments, offering promising implications for bioremediation strategies.