Bioaugmentation and biostimulation of crude oil contaminated soil: Process parameters influence

•Crude oil-contaminated soil bioaugmentation and biostimulation were studied.•Biostimulation was significant on the percentage of TPH biodegraded.•Degradation efficiency of 93.75% was obtained.•Model developed was effective for future prediction.•Bacteria isolates from native polluted site were effective for the process. In this study, investigation of bioaugmentation and biostimulation process parameters’ influence on biodegradation effectiveness of bacteria isolates in a crude oil polluted soil for 60 days was conducted. A native environment of crude oil polluted site was considered for bacteria isolation. Dilution plate technique was used for bacteria culturing under laboratory conditions. Central composite design embedded in design expert software was used for the design of experiment and optimum point prediction. The influence of nitrogen:phosphorus nutrient ratio and bacteria concentration at varying crude oil concentration and soil pH on percentage of total petroleum hydrocarbons (TPH) biodegraded was investigated. Biostimulation was highly significant on the percentage of TPH biodegraded as revealed by experimental results. Degradation efficiency of 93.75% was obtained for a soil pH of 10 contaminated with 100 g/Kg of crude oil using 600 cell/g of bacteria supplemented with 8 g/g of nitrogen-phosphorus ratio. The model developed was effective for future prediction with better correlation between experimental and predicted values. A biodegradation efficiency of 77.42% was achievable at the optimum predicted point by central composite design. Hydrocarbons biodegradation in the crude oil contaminated soil via the action of supplemented bacteria isolates was revealed. Conclusively, bacteria isolates from native polluted site could be applied as effective scavenger for hydrocarbons in crude oil contaminated soil.