Photocatalytic remediation of organics in groundwater.

May S M Chan, Cambridge University
Geotechnical Engineering Group


The aim of this research is to investigate the remediation of Methyl Tertiary Butyl Ether (MTBE) and other organics in groundwater by applying photocatalysis as an in-situ process. Photocatalysis is a chemical process in which organics are decomposed into carbon dioxide, water and inorganic compounds in the presence of catalyst (TiO2), ultra-violet light and oxygen. Five bench-scale reactors was designed and evaluated by photocatalytic degradation of MTBE. Photocatalytic degradations of MTBE and some other organic pollutants were proved to be possible. Experimental results suggest that photocatalytic degradation is accurately described by first order kinetics. The efficiency of photocatalytic degradation was expressed as the rate constant or the quantum yield. It was found that complete photocatalytic degradation of MTBE was only possible under aerobic conditions. Intermediates, such as Tertiary Butyl Formate (TBF) and acetone were found in oxygen-limiting photocatalytic degradation of MTBE. It was experimentally deduced that the rate constant of photocatalytic degradation was linearly proportional to the light irradiance and illuminated catalyst surface and inversely proportional to the reactor volume. The quantum yields of photocatalytic degradation of 100 mg/L MTBE solution in the five reactors were measured as 0.23% to 0.71%. The equilibrium adsorption of MTBE on TiO2 was found to be a linear isotherm. Flow experiments were conducted by circulating MTBE solution between one of the designed reactors and a reservoir. It was found that the reduction of pollutant was a function of the circulation rate, reactor volume and the batch rate constant of photocatalytic degradation in the reactor. Some soil experiments were conducted using one of the designed reactors, which was an underground reactor and some corresponding modelling was done to simulate the transport of MTBE under different flow regimes. It was found that pumping and regional flow facilitated the exchange of water between the reactor and the surrounding soil.