Disinfection is an indispensable process component in drinking water treatment and an essential measure to ensure the safety of drinking water in rural areas. Among all kinds of drinking water disinfection methods, sodium hypochlorite is an efficient, broad-spectrum disinfectant with good disinfection effect and continuous disinfection ability. In recent years, the application scope of liquid chlorine disinfection and chlorine dioxide disinfection has been limited due to the safety of raw materials and use
The advantage of sodium chlorate disinfection in drinking water treatment in villages and towns has gradually emerged.
At present, there are two main ways to obtain sodium hypochlorite: one is to buy commercial sodium hypochlorite solution; The other is to prepare sodium hypochlorite solution by electrolyzing salt water on site. The commercial sodium hypochlorite solution is dangerous goods, which is not easy to purchase and troublesome to transport, and the high concentration of sodium hypochlorite is easy to decay and cannot be stored for a long time. The method of on-site electrolytic preparation of sodium hypochlorite disinfection may be a better choice of raw materials easy to purchase, because of the use of tap water and food grade salt, to ensure the purity of sodium hypochlorite, and at any time to prepare, use at any time while the generator management operation is simple; BLUEWAV Sodium hypochlorite generator brine electrolysis type is your quality choice. According to whether there is a diaphragm between the anode and the cathode chamber, the generator can be divided into two categories: non-diaphragm electrolytic sodium hypochlorite generator and diaphragm electrolytic sodium hypochlorite generator. The conventional diaphragm method refers to a diaphragm between the anode and the cathode to separate the negative and anode products. The diaphragm materials include traditional materials (such as nylon film) and new materials cation exchange membrane.
Test method
(1) Compare the quality of sodium hypochlorite solution and commercial sodium hypochlorite solution produced by electrolysis of three kinds of sodium hypochlorite generator, and determine the change of the concentration of effective chlorine in the generator with the running time. The disinfectants in the four application modes were added with 2mg/L available chlorine, and the pH value, TDS, Na+ and CI concentrations of the water were measured 30 min later, and the changes in water quality indexes were compared.
(2) Taking Escherichia coli 8099, a commonly used indicator bacterium for faecal pollution, as the representative, the disinfection effect of four different application modes of sodium hypochlorite disinfection was investigated. All the water samples were injected into the same water body at the dosage of 1mg/L, quickly stirred evenly and timed for 1, 3, 5, 7, 10, 20 and 30min, respectively. After neutralization for 10min, two parts of 100, 10 and 1mL were taken, respectively, for filtration and filtration, and incubated at 37℃ for 24h. At the same time, the formation of trihalomethane, dichloroacetic acid and trichloroacetic acid as disinfection by-products were measured after 30min.
(3) The salt consumption and power consumption changes of the three electrolytic devices running continuously for 6h were measured and calculated, and the operating cost of disinfection with commercial sodium hypochlorite was compared and analyzed.
Index measurement and calculation methods
The effective concentration was measured by a portable rapid chlorine meter (0-10mg /L). The effective chlorine concentration of sodium hypochlorite solution in the test was mostly above 10g/L, so it was necessary to measure the sodium hypochlorite solution after dilution. In the test, after the electrolytic device runs stably, sampling is carried out every 1h to determine the effective chlorine concentration. Chlorate and chlorite were detected by ion chromatography, each group of samples were measured 3 times, and the average value of 3 samples was taken as the detection result.
pH and TDS were measured with a pH meter, and the average value of 3 samples in each group was taken as the test result. Na+ and Cl- were measured with an ion meter, and the average value of 3 samples in each group was taken as the test result. The E. coli 8099 strain was derived from the Chinese Center for Disease Control and Prevention, and the test method was based on the Technical Specifications for Disinfection (2002 edition of the Ministry of Health) and the Standard Test Method for Drinking Water (GB/T5750-2006).
The salt consumption per unit time is calculated according to the change of chloride ion concentration in brine before and after electrolysis. The calculation of salt consumption and power consumption per unit of effective chlorine is calculated according to the index calculation method in Sodium hypochlorite Generator (GB12176-1990). The operating cost is calculated according to the market unit price of electricity and salt. The unit is yuan /g. The calculation formula is: operating cost = power consumption x power unit price + salt consumption x salt unit price. Among them, power consumption, kW·h/kg; Salt consumption, kg/kg.
Results and analysis
Disinfectant quality and impact on water quality: the effective chlorine concentration can not only reflect the oxidation capacity of sodium hypochlorite solution, but also compare the performance of the generator. The effective chlorine concentration of sodium hypochlorite solution produced by electrolysis of sodium hypochlorite generator without diaphragm and diaphragm method is relatively stable with the extension of running time, while the concentration of sodium hypochlorite solution produced by electrolysis of sodium hypochlorite generator by ion membrane method increases slowly with the extension of running time, and tends to be stable after 5h. The average effective chlorine concentration of sodium hypochlorite solution produced by ionic membrane electrolysis sodium hypochlorite generator is 80.51g, which is about 10.75 times that of non-diaphragm electrolysis sodium hypochlorite generator (7.51/L), 4.51 times that of diaphragm electrolysis sodium hypochlorite generator (17.86 G/L), and 1.41 times that of commercial sodium hypochlorite solution. The concentration of chlorate in sodium hypochlorite solution produced by electrolysis of three kinds of sodium hypochlorite generator did not change much with the running time. The average concentration of chlorate in sodium hypochlorite solution produced by electrolysis of sodium hypochlorite generator by ion membrane method was only 34.57% of that by diaphragm method, but slightly higher than that by electrolysis of sodium hypochlorite generator without diaphragm method. However, as far as chlorite is concerned, the chlorite content in the three sodium hypochlorite solutions is low. Ionic membrane electrolysis sodium subaerate generator Because the electrolytic cell uses a cation exchange membrane that only allows sodium ions to pass through, preventing chloride ions from migrating to the cathode and hydroxide ions from migrating to the anode, avoiding the side reactions that may occur in the non-diaphragm electrolytic cell, which is the reason why the effective chlorine concentration in the ionic membrane electrolysis method is much higher than that of the non-diaphragm method and the conventional diaphragm method.
Conclusion
(1) When three kinds of electrolytic sodium hypochlorite generators electrolyzed the same saturated salt water, the effective chlorine concentration of the ion-film electrolysis generator was 10.75, 4.51 and 1.41 times that of the non-diaphragm method, the conventional diaphragm method electrolysis generator and commercial sodium hypochlorite, respectively; There was no difference in the concentration of chlorite among the three kinds of sodium hypochlorite solution, but the chlorite concentration of commercial sodium hypochlorite solution was relatively high. When sodium hypochlorite solution was added into water at the same effective chlorine concentration, the sodium hypochlorite solution of ion-membrane electrolysis generator had the least influence on raw water quality.
(2) Taking Escherichia coli as the disinfection capacity index of sodium hypochlorite solution, the bactericidal effect of sodium hypochlorite solution of the three electrolytic generators is equivalent, and the bactericidal rate is superior to that of commercial sodium hypochlorite solution; At the same time, the amount of trihalomethane produced by disinfection byproduct was the least after adding sodium hypochlorite solution of ion-membrane electrolysis generator.
(3) The power consumption and salt consumption of ionic membrane electrolysis sodium hypochlorite generator are relatively low, and the average operating cost is only 0.0078 yuan /m, which is far lower than the other three modes.
(4) Compared with the other three sodium hypochlorite disinfection modes, the ionic membrane sodium hypochlorite generator has the highest effective chlorine concentration, the least impact on raw water quality, good disinfection effect, the least by-product generation and the lowest operating cost, so it is a suitable sodium hypochlorite disinfection technical mode for village and town water supply.
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The article is reproduced from the Journal of China Institute of Water Resources and Hydropower Research, Vol. 17, No. 2