Study On Characteristics Of Formation And Removal Of Haloacetic Acids In Water

At present, chlorine was used as the primary disinfectant in our country, and could be reacted with organic matter(NOM) to generate disinfection by-products (DBPs). Haloacetic acids as an indicator of the total carcinogentic risk of disinfection by-products(DBPs).For the micro-contaminated source water of the HuangPu river, the thesis focus on studying characteristics of formation and removal of haloacetic acids(HAAs) in water.In the thesis, aimed at the raw water of the Huangpu river and effluent of different conventional treatment units, and investigated the rule of formation and variation with seasons of HAAs after prechlorination and secondary dosing chlorine into filtered water for disinfection. Simultanous, combine with the treatment process of pilot-scale experiment of the national 863 program, the removal effect of HAAFP by ozonation-biological activated carbon(O₃/BAC) process was investigated. Comparing with the disinfection effects of chlorine,chloramine, chlorine dioxide and their combination processes, the influence factor of HAAs formation was studied in order to select safe and appropriate disinfectant. Furthermore, the removing methods of HAAs were researched through the bench-scale experiments, such as granular activated carbon(GAC) adsorption, UV, O₃, H₂O₂, UV/H₂O₂ and UV/H₂O₂/O₃,etc, to control the HAAs formed in different water treatment units..The results indicated that: the HAAs quantity formed after conventional water treatment processes in summer is larger than in winter. The sequence of HAAs concemtration is that settleing water > finished water > filtered water. When measuring the haloacetic acids formation potential(HAAFP) of Huangpu raw water, the adoptable dosage of chlorine is 13.52mg/L, and the largest react time is 6 days. The removal efficiency of HAAFP by O₃/ BAC advanced treatment process is about 60%. The low dosage of ozone(2.0mg/L) can make sure the removal effect of HAAFP in water, and the removal efficiency will be improved as increasing of the dosage of ozone. Using the chloramine and chlorine dioxide as disinfectant can decrease the formation quantity of HAAs. The disinfect effect of combination technique of chloramine and chlorinedioxide is better than using them alone.GAC were adopted to study and contrast the adsorption characteristics of two kinds of HAAs in drinking water. It has to mentioned that the adsoption isotherm of HAAs is best according with the amendatory Freundlich equation under single component system . At the concentration below 200ug/L. When the quantity of GAC is 1600mg/L,the removal efficiency for trichloroacetic acid (TCAA) and dichloroacetic acid (DCAA) can arrive at 98.49% and 98.01% respectively. The adsorption capacity for trichloroacetic acid (TCAA) is larger than dichloroacetic acid (DCAA), the mol adsorption capacity for TCAA is 1.17 times as much as for DCAA at the mol equation concentration of 0.3umol/L.It's better for GAC adsorption of HAAs in the acidic condition.Under multicomponent system, there were competition for adsorption between different kinds of HAAs, compared with the case under monocomponent system the influence on adsorption capacity for TCAA is slighter than DCAA, the above results consist with structure character of different organic compounds.At the same time, the adsorption rate were contrasted to show that the adsorption rate for DCAA is rather high.HAAs is difficult to be oxidated after reacting 2 hours, the removal efficiency of HAAs are both blow 15% by using O3 or H2O2 alone, and the removal efficiency of DCAA and TCAA by UV advanced oxidation technique were increased appreciably. The removal efficiency of DCAA and TCAA are preferable by UV/H2O2 or UV/H2O2/O3. Even more, the affect factors of removing DCAA and TCAA were discussed.