Study On The Preparation Of Sodium Hypochlorite And Its Decay Simulation In Rural Water Distribution Network

Disinfection is a weak link in rural water supply and the last line of defense for rural drinking water security.It is of great significance to study the appropriate disinfection technology to ensure the safety of rural water supply quality.Sodium hypochlorite is an efficient and broad-spectrum disinfectant with good disinfection effect.Sodium hypochlorite produced by sodium hypochlorite generator has the advantages of convenient purchase of raw materials,low operation cost and high safety,so it is suitable for rural water supply projects.However,the existing sodium hypochlorite generator has some problems,such as low available chlorine concentration,high salt consumption and high power consumption,which restrict its development and application to a certain extent.In recent years,the advantages of membrane electrolysis technology,such as improving available chlorine,reducing salt consumption and power consumption have been paid more and more attention,but the optimization of electrolytic conditions and the effective formation of sodium hypochlorite need to be solved when this technology is applied to the preparation of sodium hypochlorite solution.On the other hand,how to put the obtained sodium hypochlorite solution safely and reasonably to ensure the reasonable residual disinfectant in the whole rural water supply network also needs to be studied.In this paper,sodium hypochlorite used in rural water supply disinfection is taken as the obj ect of study,and the preparation of sodium hypochlorite and its attenuation in rural water supply network are taken as the main research contents.Firstly,the optimization of membrane electrolytic sodium hypochlorite test device was carried out through laboratory test.The effects of different electrolyte flow rate,electrolyte circulation mode,membrane material,chlorine gas separation device and reaction conditions of sodium hypochlorite formation on the operation of the test device were analyzed.In order to verify the operation effect of the optimized sodium hypochlorite electrolysis test device,respectively from the disinfectant quality,impact on water quality,the effect of disinfection and the operating effects of four aspects,the sodium hypochlorite generator proposed in this paper was compared with commercial sodium hypochlorite solution,non-diaphragm electrolysis sodium hypochlorite generator and conventional diaphragm electrolysis sodium hypochlorite generator.Finally,EPANET2.0 software is used to simulate the decay process and dynamic change of residual chlorine in rural water supply network sterilized with sodium hypochlorite.The node residual chlorine is used as the evaluation index of pipe network quality safety,and the fuzzy evaluation method is used to carry out the evaluation.The water quality improvement measures of pipeline network are put forward,which provides scientific and reasonable suggestions for the rational application of sodium hypochlorite disinfection technology in rural water supply proj ects.The main conclusions are as follows:(1)The experimental study on the performance optimization of the membrane electrolytic sodium hypochlorite unit shows that when the electrolyte cycle mode is natural circulation,the membrane material is perfluorosulfonic acid double layer composite membrane,the chlorine separation device is designed with porous plate at the top,and the reaction conditions of sodium hypochlorite formation are porous aeration,the operation effect of the generator is better.When the natural circulation is used,the voltage of the electrolyzer is relatively low.After long-term operation,the current efficiency is about 1.2 times of that of the forced circulation,and the power consumption and salt consumption are 17%and 16%lower than those of the forced circulation,respectively.When the membrane material is perfluorosulfonic acid double layer composite membrane,the cell voltage and power consumption are relatively low.Under the same test conditions,the average cell voltage and power consumption of the composite membrane are 6.5%and 23.5%lower than those of the monolayer film,respectively.When the chlorine separation device with porous plate is added to the electrolyte outlet,a better gas-liquid separation effect is obtained,and when the inlet flow rate is controlled in a certain range,the available chlorine concentration can be significantly increased.When the reaction condition of sodium hypochlorite formation is set to porous aeration,the formation efficiency of sodium hypochlorite can be improved,and the effect is more remarkable when the temperature is properly reduced.The reaction condition is that the effective chlorine concentration of porous aeration cold bath is higher than that of porous aeration,respectively.Single tube aeration cold bath,single tube aeration high 3.4%,15.5%and 20.9%.(2)The sodium hypochlorite solution produced by the optimized membrane electrolysis sodium hypochlorite generator has high quality,little influence on water quality,good disinfection effect,and relatively low operation cost.The available chlorine concentration of sodium hypochlorite solution produced by the optimized membrane electrolytic sodium hypochlorite generator is 10.75 times,4.51 times and 1.41 times higher than that of the non-diaphragm electrolysis,the conventional diaphragm electrolysis and the commercial sodium hypochlorite electrolysis respectively,can achieve the effective inactivation of Escherichia coli.The concentration of impurities chlorate and chlorite in sodium hypochlorite is low,and the influence of sodium hypochlorite on water quality is the smallest,and the concentration of trihalomethane,the disinfection by-product,is the lowest.At the same time,the power consumption and salt consumption of the optimized membrane sodium hypochlorite generator are relatively low,and the operating cost is 46%,56%and 81%lower than that of non-diaphragm method,conventional diaphragm method sodium hypochlorite generator and commercial sodium hypochlorite solution,respectively.(3)The decay model of residual chlorine in the pipeline network was established,and the dynamic simulation of residual chlorine in the node of the pipeline network was realized in the actual rural water supply project using sodium hypochlorite disinfection.The initial residual chlorine concentration was optimized through the model trial calculation,and a good result of water quality fuzzy evaluation was obtained.On the assumption that the decay of residual chlorine accords with the first order reaction kinetics,the dynamic simulation of residual chlorine in the pipe network of a practical rural water plant is realized by adj usting the parameters of EPANET2.0 software and checking the model.With the calibrated residual chlorine decay model as the tool,the variation of residual chlorine decay in the pipe network in different water supply periods was analyzed.The results showed that when the residual chlorine concentration of the factory water was 0.60mg/L,the residual chlorine decay was faster in the low peak period of water consumption,and the residual chlorine in 11%of the pipe network nodes could not meet the hygienic standard for drinking water Taking the actual monitoring value of residual chlorine in the pipeline network as the evaluation index of pipe network water quality safety,the fuzzy evaluation method is used to evaluate and analyze the water quality safety of the pipe network,and the established residual chlorine decay model of the pipe network is used.The initial residual chlorine concentration of factory water was optimized(0.68mg/L),and better water quality evaluation results could be obtained.At this time,the proportion of the pipe network node which did not meet the hygienic standard for drinking water was reduced to 5%.