Destructive removal of humic acids in aqueous media by photocatalytic oxidation with illuminated titanium dioxide

This paper is concerned with the application of photocatalytic oxidation process for the destructive removal of humic acids. According to the bench scale experiments, humic acids could be degraded in the presence of semiconductor powders (TiO2) upon irradiation with a Black Light Fluorescent Lamp (320-440 nm). The degradation was followed in terms of UV-VIS spectra and TOC. After 1h of irradiation 40% of TOC and 75% Color(400) were removed for 50 mg/L humic acid solution with TiO2 concentration of 1.0 mg/L. The effect of initial concentration of humic acid and the effect titanium dioxide loadings were investigated. The optimum concentration of TiO2 was found to be 1.0 mg/mL. Photodegradation rate was accelerated in acidic medium (pH: 3.0) and a retardation factor of 0.5 was attained when the reaction was carried out in alkaline medium with respect to the natural pH of the humic acid solutions (pH: 6.0). Apparent primary quantum yield (APQY) was reported as 0.221 for 50 mg/L humic acid solution and 1.0 mg TiO2/mL. Increasing titanium dioxide loadings caused an increase in APQY values but increasing the humic acid concentration reflected as a decrease in APQY values for a fixed TiO2 concentration. The biodegradability (BOD5/COD) for humic acid solution (50 mg/L and 1.0 mg TiO2/mL) was determined as 0.66 after 2 hours of irradiation. It was concluded that photocatalytic degradation process might be an alternative technique for the removal of humic acids in water.