The Research Of Controlling Disinfection By-products By Adding TiO₂ In UV-chlorination Integrated Process

Biotreated water contains variety of pathogenic microorganisms, trace toxic and hazardous chemical contaminants and plant nutrients. For the sake of safe use of recycled water, disinfection process is of great necessity. However, disinfection byproducts will be produced through the reaction between dissolve organic matters in water and chemical disinfectant which restricts the reuse water recycling. In this study, TiO2 was added in UV process as a photocatalyst. The purpose of this research is to investigate the inhibition effects of photocatalysis on THMs formation which were produced in sequential chlorination. Three different water samples (secondary urban sewage treatment plant effluent, simulated MBR effluent, municipal MBR effluent) were selected to investigate. XAD-8 resin separation,3-D fluorescence spectroscopy, FTIR and GPC chromatography were used in this study to carify the DOM properties and photodegration mechanism. The main conclusions of this paper are as follows:(1) The addition of TiO2 in UV process has a good effect on inhibiting the formation of THMs in chlorination. Removal rate of THMs changes with photocatalysis conditions. The dosage of photocatalyst plays the most import role in removing THMs. In this study, the removal of THMs increased with the increasing dosage. The main fluorescent matter in secondary effluent is aromatic protein and humic acid-like matter (about 70%). UV process could decrease aromatic protein but increase fuvic acid-like and humic acid-like matter. The addition of TiO2 removes more aromatic protein. UV process breaks some function groups in the raw water and the addition of TiO2 intensifys this effect. GPC results show that UV irradiation could degrade high molecular weight organic matters into low molecular weight ones. The addition of TiO2 degrades more completely.(2) The combination of MBR and photocatalysis improves the quality of MBR effluent significantly. THM precusors decrease greatly after photocatalysis. However, though photocatalysis could decrease the concentration and THMs formation potential of hydrophibic acid matter, the yields of total THMs did not change much The chlorination kinetic experiment shows that THMs formation in both MBR effluent and MBR-photocatalysis effluent increases with disinfection time increasing. The increasing rate decreases after 48 h and keeps stable after 72 h. Compared with MBR effluent, MBR-photocatalysis effluent contains less fluorescent matter, in which the aromatic proteins decrease most signigicantly.(3) Photocatalysis could significantly decreases THM precusors in municipal MBR effluent and removes most of HO A. However, photocatalysis shows little effects on removing HOB, HON and HIS. The main fluorescent matter in municipal MBR effluent and municipal MBR-photocatalysis effluent are humic acid-like matter. Compared with municipal MBR-photocatalysis effluent, municipal MBR effluent contains more aromatic proteins. Photocatalysis could degrade most functions groups of DOMs and has a great effect on removing phenol, alcohol and aromatic substances. The molecular weights of most DOMs in municipal MBR effluent and municipal MBR-photocatalysis effluent are over 20 kDa. Photocatalysis could degarade high molecular weight compounds into low molecular weight compounds.