Journal of Engineering, Computers & Applied Sciences (JEC&AS ISSN No: 2319-5606 Volume 1, No.1, October 2012 _________________________________________________________________________________ 61 www.borjournals.com Blue Ocean Research Journals 61 Degradation of Humic Acid by Titanium Dioxide Catalyst RIUNGU N. J., Department of Biomechanical and Environmental Engineering, J. K. U. A. T., P.O. Box 62,000-00200, Nairobi, Kenya HOME P. G., Department of Biomechanical and Environmental Engineering, J. K. U. A. T., P.O. Box 62,000-00200, Nairobi, Kenya NDEGWA G. M., Department of Biomechanical and Environmental Engineering, J. K. U. A. T., P.O. Box 62,000-00200, Nairobi, Kenya Abstract The presence of humic acid (HA) in water has for long posed a challenge for treatment. Its presence in water during treatment such as disinfection by chlorination leads to formation of disinfection by-products (DBPs) that may be carcinogenic. It forms complexes with heavy metals present in water and also causes membrane fouling during membrane application for water treatment. HA should hence be removed from water before chlorination or membrane filtration as this would lead to longer membrane life with minimum operational cost and also reduce the health hazards associated with DBPs. This paper compares the efficiency of two forms of Titanium dioxide (TiO 2 ) catalysts; TiO 2, solution form (TiO 2 , s) and TiO 2 , powder form (TiO 2 , p). Of major interest was their ability to degrade humic acid both in presence and absence of UV radiation. TiO 2 , s showed higher degradation efficiency than TiO 2 , p both in presence and absence of UV radiation, an observation that was attributed to the differences in surface area between the two catalyst when at same concentration. Degradation efficiency was seen to be affected by initial catalyst loading and type of catalyst. It was seen that use of TiO 2 is a promising method degradation of organic contaminants. 1.0 INTRODUCTION Humic substances make up a large portion of organic matter found in natural environments with a typical concentration in the range of 0.1 to 200 mg/L dissolved organic carbon (Kinniburrgh et al., 1996). Humic acid (HA) is a key component of humic substances (Stevenson, 1994) and they are a complex mixture of organic compounds. The removal of humic substances from water has been a challenge. In many countries, the HA is eliminated from water before chlorination by coagulation with aluminium sulphateand filtration. However, coagulation presents two main disadvantages which are maintenance of residual sludge with high aluminium concentration and treated water needs high quality monitoring of aluminium. The recommended aluminium concentration is 0.2 g/L (Wiszniowski et al., 2002). The conventional treatment process can remove only 10–50% of the TOC (Wiszniowski et al., 2002). Photocatalysis using semiconductor catalysts such as TiO 2 is a promising method for removing humic substances and other organic compounds from water. The process can degrade the majority of the organic molecules, without additional chemicals except the photocatalyst (e.g. titanium dioxide). The basic process of photocatalysis consists of ejecting an electron from the valence band (VB) to the conduction band (CB) of the TiO 2 semiconductor creating a h+ hole in the VB (Wiszniowski et al., 2002) that occur due to the UV irradiation of TiO 2 with an energy equal or superior to the band gap (>3.2 eV). The photocatalyst absorbs efficient photons from UV light, producing strong oxidants including OH - radicals that decompose organic compounds adsorbed on the catalyst surface. Numerous organic contaminants including herbicides, pesticides, and halophenols have been reported to be efficiently removed from polluted water using this method (Bertelli and Selli, 2006; Toepfer et al., 2006; Parra et al., 2004; Hoffmann et al., 1995). Recently, TiO 2 -based photocatalysis has been reported to effectively remove humic acid (Fang et al., 2005; Li et al., 2002; Tay et al., 2001) and NOM (Fu et al., 2006; Le-Clech et al., 2006; Doll and Frimmel, 2005). No studies have been made to compare the effectiveness of the solution and powder form of the TiO 2 catalyst.