Research On Conversion Mechanism Of Inorganic By-products Disinfected By High Purity Chlorine Dioxide In Water

Chlorine dioxide is a key role for drinking water disinfection in water plant by GB5749-2006. Yet chlorine dioxide disinfection by-products are potential hazards to human health. Ensure enough dosing amount of chlorine dioxide disinfectant, on the basis of disinfection by-products not overweight is the concerns of the waterworks. Water quality affect by numerous factors in network. The purpose of this study is to analyse of relevant influence factors and mechanism to disinfection by-products in drinking water through the pipe network, and help to accurate control the dosing quantity of chlorine dioxide.The detection method of chlorinated compounds in water was assessed. N- N-diethyl-phenylene diamine(DPD) was used as chromogenic agent to detect chlorine dioxide, it is proved that the dynamics distinguish of DPD is best, the response time is 30 s, the standard addition recovery rate is 98.5%. By using ethylenediamine tetraacetic acid(EDTA) as a masking agent to detect chlorine dioxide disinfection by-products, it is proved that the dynamics distinguish of EDTA is best. Analysis of pipe network data based on the detection method, chlorite are mainly by-products by high purity chlorine dioxide disinfection. The concentration of chlorine dioxide and chlorite showed a trend of transformation of different seasons in pipe network, and pipe scale in the network effect the concentration of chlorite. Chlorite in pipe networks water was transformed, the transformation rate was 22.6%.In order to illustrate the transformation mechnism of chlorite disinfected by high purity chlorine dioxide, chlorine dioxide attenuation regularity in network management were discussed. It is proved that the highest attenuation rate of chlorine dioxide is cast iron pipe, the minimum is PVC pipe. Initial concentration of chlorine dioxide showed a trend of negative correlation. Temperature and flow velocity were positively correlated, which fit to pseudo-first-order reaction kinetics.Based on the research of water phase factors to disinfection by-products in pipe network water, shows that chlorite is the main disinfection by-products of chlorine dioxide. It is proved that the residual chlorine dioxide concentration, pipe material, zero-valent iron and ferrous ions concentration in water influent on the transformation of chlorite. Orthogonal experiments were studied, the fit attenuation of 0.05 mg/L ferrous ion, 0.3 mg/L zero-valent iron, 0.5 mg/L residual chlorine dioxide, p H 7.0, 20℃ in water was 1.2%.Further discuss to the solid phase factors of disinfection by-products in network. Analysis of influence factors to disinfection by-products by the pipe scale adsorption in drinking water through the pipe network, proved that pipe scale adsorption are the dominant mode in transformation. The secondary adsorption dynamics model, intra-particle diffusion kinetic model and Freundlich model fit to the adsorption by pipe scale. Thermodynamic equilibrium experiments suggest that the adsorption of pipe scale is spontaneous(Δ(?)<0). Analysis of pipe scale adsorption is chemical adsorption. WDXRF, XRD and XPS spectra of adsorption by pipe scale were analyzed for pipe scale with and without chlorite, and the results show that chlorine(-1 valence) in the pipe scale increased after adsorption, proved the adsorption behavior of disinfection by-products from theory and experimentFinally, the adsorption model of disinfection by-products was built on the above research, and response surface method was used to study the adsorption of pipe scale. The optimal transformation equation of the pipe scale adsorption of chlorite wasη=212.40+37.35C_o-48.23pH+2.75T-6.00C_opH~2-0.07T~2. The attenuation effect of pipe scale for chlorite in optimal environment was 16.8% calculate by transformation equation, the total conversion rate of chlorite was 18.0% in drinking water pipe. The result is close to the data 22.6%. With reference to our country’s "drinking water health standards", according to the theory of conversion rate of 95-98%, the maximum actual dosing of chlorine dioxide were from1.14 mg/L to 1.18 mg/L. Based on high purity chlorine dioxide disinfection in ground water, allowable concentration of chlorite is no more than 0.2 mg/L accordance with most strictly international standard, which think of theory dosing quantity of chlorine dioxide increased by 0.04mg/L still accord with standard. Allowable concentration of chlorite is no more than 0.7 mg/L accordance with our country’s "drinking water health standards", which think of theory dosing quantity of chlorine dioxide increased by 0.18mg/L still accord with standard.To sum up, the thesis research on conversion mechanism of disinfection by-products disinfected by high purity chlorine dioxide, provided the precise control to the actual use of chlorine dioxide dosing amount by theoretical basis, help people to realize water from safe to health.