Factorial design study of total petroleum contaminated soil treatment using land farming technique

Land farming technique was used to treat hydrocarbon contaminated soil collected from a crude oil spill sites in Edo State, Nigeria. Calibrated standard auger was used to collect soil samples from the site at depth below 30 cm. The samples were characterized and classified. Cow dung and NPK fertilizer were added as additives to complement the nutriments of the soil samples before total petroleum hydrocarbon (TPH) quantification and remediation procedures. Factorial design was applied to vary the input parameters such as pH, mass of substrate, moisture content and turning times of land farming so to ascertain the optimal conditions for the procedure. The result revealed that the in-situ TPH value was 5000 mg kg^{− 1} on the average and after 90 d of treatment, TPH reduced to 646 mg kg^{− 1}. The turning rate, pH, moisture content and mass of substrate hade 83, 4.36, 0.48 and 0.046% contribution, respectively, for the degradation process using land farming treatment. Numerical optimization techniques applied in the optimum point for land farming input parameters to achieve predicted maximum removal of 99% were evaluated as pH, mass of substrate, moisture content and turning rate to be 6.01, 1 kg, 10% and 5 times in a week, respectively. TPH removed at this optimum point was 98% reducing from 5000 to 636 mg kg^{− 1}. The high coefficient of determination (r² = 0.9865) as observed in the closeness of predicted and experimental values reflects the reliability of the model and hence, land farming practice with close attention on turning rate as revealed by this study, is recommended for TPH contaminated soil remediation.