Light-enhanced chemical oxidation for tertiary treatment of municipal landfill leachate

Three advanced oxidation processes involving hydrogen peroxide, ozone, and ultraviolet (UV)/visible light were investigated for their relative effectiveness in removing refractory organics from biotreated leachate collected at the municipal landfill site of the city of Stuttgart, Germany. The efficiency of each system was compared with respect to the total reduction and the rate of degradation observed in chemical oxygen demand (COD), total dissolved organic carbon (TOC/DOC), and total organic halogens (TOX/AOX) during eight hours of treatment at acidic pHs. The effect of irradiation was investigated. by operation of the systems under two different light sources, namely a low-pressure mercury UV lamp with a maximum emission at 253.7 nm, and a high-pressure mercury UV-visible lamp, emitting light from 200 nm to 470 nm, respectively. Hydrogen peroxide- (H2O2) added systems with or without ozone (O-3) and used with high-pressure lamps were found adequate for reducing the TOX of the tested leachate to desirable limits. The greatest COD reduction was obtained with the H2O2-O-3 system irradiated by low-pressure lamps. Ozonation without the addition of H2O2 proved inadequate for the tested leachate even under high irradiation intensity.