Solar heterogeneous and homogeneous photocatalysis as a pretreatment option for biotreatment

In this paper, we present pilot-scale solar Photo-Fenton and TiO2 treatment of a model compound (α-methylphenylglycine) dissolved in 500 mg/l concentration in water. Not only contaminant disappearance and mineralisation were evaluated, but also enhancement of biodegradability. The solar photoreactors, composed of 4.16 m2 of compound parabolic collectors, had a total volume of 82 l (44.6 l illuminated). Treatment was successful with both Advanced Oxidation Processes (AOPs) tested, but photo-Fenton was shown to be by far more efficient from the kinetic and practical point of view. To find out the conditions for biocompatibility using the AOPs as a pre-treatment, waste water after certain degradation time, unacclimated municipal sludge and mineral nutrients were placed together and evaluated by the Zahn-Wellens (Z-W) test. Biodegradability was enhanced (70% biodegradable) by both AOPs, but photo-Fenton was demonstrated to be more efficient, requiring a treatment time one order of magnitude shorter than TiO2. Hydrogen peroxide management for reduced consumption and elimination prior to discharging water to the biotreatment step is also discussed in detail.