Photocatalytic treatment of humic substances in drinking water

Currently drinking water from the Mourne Mountains in Northern Ireland is treated by the traditional process of coagulation and filtration. Semiconductor photocatalysis was investigated as an alternative. Aldrich humic acid solutions (100 mg dm−3, filtered through 0.22 μm Millipore filters) were photolysed in a 0.1% suspension of Degussa P25 titanium dioxide using a mercury lamp. Degradation of humic acid was followed over time by measuring colour in Hazen units, 254/400 nm absorbance, fluorescence (excitation 237 nm; emission 400 nm) and size exclusion high performance chromatography. The extent of complete oxidation was determined by measuring dissolved organic carbon, chemical oxygen demand and carbon dioxide released. It took approximately 12 min to reduce the humic acid concentration by half; however 50% complete mineralization took 60 min. Some of the intermediates of reaction were highly fluorescent. In the absence of oxygen, light or titanium dioxide no significant degradation occurred.