Remediation of hydrocarbons contaminated groundwater by silica encapsulation technique

Abstract

Silica encapsulation technique was investigated for effectiveness as a green remediation technology for the cleanup and restoration of hydrocarbons contaminated groundwater. Optimum conditions of pH, contact time, and the concentration of the treatment solution for each of the contaminants were known. After testing different kinetics models, the pseudo-first-order kinetics gave the best result in each case with the regression coefficient in the range of 0.9964–0.9988. Rate constants of 2.56 × 102, 2.70 × 102 and 1.23 × 102 mg−1 L h−1 were obtained from the kinetics plots for crude oil, diesel and domestic purpose kerosene in that order. The 82.34%, 86.24% and 97.58% reduction in chemical oxygen demand (COD) for crude oil, diesel and domestic purpose kerosene contaminated samples respectively at the end of the residence time of 144 h depicts that remediation occurs significantly. Percentage reduction in total petroleum hydrocarbon was in the range of 51.97–90.68%. The material data sheet of the reagents used indicates low toxicity. The encapsulated hydrocarbon in the silica coating is stable even in extreme acidic and basic states. At the end of the remediation only dissolved oxygen, biochemical oxygen demand, nitrates and ammonia as physicochemical parameters were within the safe permissible levels set by the Federal Minstry of Environment, Guideline and Standards for Environmental Pollution Control in Nigeria while others were not and therefore the need for post-treatment in order to make the treated contaminated groundwater safe for drinking and agricultural use.