Photo-Fenton oxidation of pesticides

The photo-Fenton process is becoming a practical treatment option for waters contaminated with pesticides and other organic compounds that are poorly biodegradable. This process can potentially be integrated into an existing water treatment process to enhance organic compound removal. It can operate at low concentrations of contaminant and can often completely mineralise the compound or convert it into a less toxic form. The process is most efficient at around pH 2.8; however, it has been found that with the addition of suitable complexing agents for Fe(III), the process can be operated at close to neutral pH. This study used citric acid as a complexing agent, 2,4-dichlorophenol (DCP) as a model contaminant and investigated the extension of the feasible pH range of the process from pH 5 to pH 8. The study involved synthetic solutions and light from a mercury arc lamp, with a bandpass filter used to isolate the emission band at around 360 nm. Low concentrations of DCP (12 μM) and Fe(II) (10 mM) were used to simulate conditions possible in the environment. In this work, no H2O2 was added, however, a relatively high concentration of citrate (100 μM) was used. Citrate is itself degraded in the process, and since it is highly biodegradable any excess could be consumed in a subsequent biological treatment process. The extent of degradation of DCP after 2 hours was found to be 91% at pH 5, 73% at pH 6, 74% at pH 7, and 59% at pH 8.