Kinetic Modelling Of Enhanced Bioremediation Of Hydrocarbon Polluted Soil

ABSTRACT 

Remediation of hydrocarbon polluted soil applying all existing techniques can be slow, expensive and requires close monitoring. Bioremediation and phytoremediation augmented bioremediation have been used to treat petroleum contaminated soil and even the difficult poly aromatic hydrocarbon polluted soil which takes longer time. What has not been studied was the effect of heavy metals present in petroleum which slows down the substrate degradation by microorganisms.  After the primary and secondary recovery method for petroleum contaminated site, Phyto-remediation augmented bioremediation using locoweed was selected amongst twenty species as most suitable for hyper-accumulation of heavy metals in contaminated soil into the rhizosphere of the plant tissues. Application of the augmented technique was carried out after the microorganism can no longer degrade substrate contaminant any further during the stationary phase. The results obtained for the six different models based on biomass growth and enhanced remediation showed that the logistic model was the most fitting models. The results revealed that bioremediation and phytoremediation augmented bioremediation are based on the same mechanism. During both processes the biomass grows according to the logistic model (with inhibition as the amount of substrate is depleted) and the rate of production of biomass per unit substrate consumed can be considered constant. Bioremediation and phytoremediation are first order processes whose rates are directly proportional to the substrate concentration driving force. Phytoremediation enhances the rate of the bioremediation process by reducing the ultimate substrate concentration achievable through bioremediation alone, though the first order rate constant is reduced in the process. The method employed reduces the contaminant concentration by about 65%, while when augmented with Phytoremediation, the contaminant concentration was reduced by 69% and 88% for Sunflower and Locoweed respectively. With respect to time savings of achieving 60% contaminant removal from 1 (100%) mol to 0.4 (40%) mol concentrations, the results gave total required time of 9.7055 weeks, 7.5652 weeks and 8.1014 weeks for bioremediation, phytoremediation (locoweed) and phytoremediation (Sunflower) respectively. Also, in terms of cost savings, phytoremediation (Locoweed) showed the lowest average total cost savings of $6,597.32 for locoweed and $7,119.0 for Sunflower when compared to $13,344.09 for bioremediation or 49.44% and 45.86% respectively. Locoweed showed higher effectiveness in enhancing the remediation process in comparison to Sunflower. Phytoremediation augmented with bioremediation is therefore recommended as a viable means for remediation of polluted soil and should be backed by legislative and regulatory frameworks. 

Keywords: polluted soil, bioremediation, model, phytoremediation, substrate  concentration and total petroleum hydrocarbon.