Removal of Humic Acid by Photocatalytic Process: Effect of Light Intensity

Abstract

Humic acid is commonly found in natural water as it is one of the by-products from decomposition of plants and animal residues. In a conventional water treatment process, which chlorine is common used as a disinfectant, the presence of humic acid could lead to the formation of carcinogenic substances, such as trihalomethanes and haloacetic acids. Thus, removal of humic acid from raw water before disinfection process is necessary. Photocatalytic reaction using Titanium Dioxide (TiO 2 ) as a catalyst is one of the most effective techniques for degrading humic acid. The efficiency of this process depends on several factors; and, one of these factors is light intensity. This research investigated the effect of light intensity (35, 225 and 435 µW/cm 2 ) and studied kinetic of photocatalytic degradation of humic acid, using commercial TiO 2 Degussa P25 as a photocatalyst. Concentration of humic acid in water was monitored using UV254 absorbance and concentration of total organic compound was measured using a Total Organic Carbon Analyzer (TOC) every 30 min. The results showed that the removal efficiency of humic acid increased with increasing light intensity and then becoming asymptotic. At light intensity of 435 µW/cm 2 and initial humic acid concentration of 4 mg/L with TiO 2 loading of 100 mg/L was found to have highest removal efficiency, nearly 95% of humic acid measured by UV254; however, the removal efficiency of total organic compound was found only 20%. The photocatalytic degradation rate of humic acid was followed by Langmuir – Hinshelwood (L–H) kinetic models, and the reactivity constant kL–H values for the light intensity of 35, 225 and 435 µW/cm 2 were found as 0.049, 0.152 and 0.178 mg L -1 min -1 , respectively.