Pilot-scale Study On Removal Of Chlorinated Hydrocarbons In Groundwater Sources For Drinking Water By Aeration Stripping Technology

At present,volatile chlorinated hydrocarbon organics have become a major source of pollution for groundwater safety in China.As a low-cost,easy-to-operate,green and efficient chlorinated hydrocarbon treatment technology,aeration stripping has been successfully applied in the treatment of groundwater sources in the United States and other countries.In China,the current aeration stripping technology research is still in the laboratory experiment stage,further evaluation for the application form and applicability of aeration stripping is needed.It is urgent to develop aeration stripping systems suitable for water supply plants,and carry out pilot-scale study on different aeration stripping systems,providing technical support for the promotion and application of the technology in China's water supply plants.For chloroform,carbon tetrachloride,trichloroethylene and tetrachloroethylene,exceeding national standard limits seriously in groundwater,four different forms of aeration stripping process were used to study the effects of gas-water ratio,influent flow rate,initial concentration and filling ratio on the removal efficiency of each chlorinated hydrocarbon.In the study of removing four chlorinated hydrocarbons from the spray aeration tower,a central combination test was designed for the four chlorinated hydrocarbons by the response surface method,and a mathematical model for predicting the removal rate of each chlorinated hydrocarbon was obtained.According to the significant degree of influence on removal rates of the four chlorinated hydrocarbons,the factors are ranked as follows:influent flow rate>gas-water ratio>initial concentration.The spray aeration tower has better removal effect on the four chlorinated hydrocarbons.Under the test conditions,the removal rate ranges from 77%to 89%for chloroform;over 96%for carbon tetrachloride;and between 79%and 97%for trichloroethylene;for tetrachloroethylene,the removal rate ranges from 87%to 99%.For the unfilled bubbling aeration tower,carbon tetrachloride and tetrachloroethylene are easily treated to within the“Sanitary Standard for Drinking Water”(GB5749-2006)limits under test conditions.For trichloroethylene or chloroform,other measures like increasing gas-water ratio or increasing residence time should be adopted to achieve the standard limits.A combined blade structure blow-off filler was independently invented.The fluid-mechanical simulation of the gas-liquid flow state of pre and after adding the filler unit to the fixed-fill aeration device was carried out by CFD simulation software.The simulation results showed that the distribution of flow lines inside the unit space was more chaotic and concentrated after the filler was added.The ratio of the total bubble area to the total bubble volume(S_Q/V_Q)in the filler unit is increased by 68%compared with the no-filler.The addition of the filler greatly improves the gas-liquid mass transfer effect.For the suspended filler aeration device and the fixed filler aeration device,when the influent flow rate was 5 m~3/h,the gas-liquid mass transfer process in the device reached equilibrium in 15 min or so.Prior to 15 min,the removal of chlorinated hydrocarbons in the plant met the first-order kinetic equation.The larger the gas-water ratio,the smaller the influent flow rate,the better the removal effect of the device on chlorinated hydrocarbons,and the initial concentration has little effect on the removal of chlorinated hydrocarbons.Under the same conditions,the fixed filler aeration device has better removal effect on chlorinated hydrocarbons than the suspended filler aeration device.Under the conditions of a filling ratio of 60%,an influent flow rate of 5 m~3/h,a gas-water ratio of 5,and an initial concentration of 5times the limit set by the“Sanitary Standard for Drinking Water”(GB5749-2006),the average removal rates of chloroform,carbon tetrachloride,trichloroethylene and tetrachloroethylene in the suspended filler aeration device were 50%,90%,69%,83%,respectively;and under the same conditions,the removal rates of the four chlorinated hydrocarbons were 62%,95%,72%,and 93%,respectively in the fixed filler aeration device.For chloroform and trichloroethylene,the removal rates can be increased by increasing the gas-water ratio or increasing the filling ratio.In the technical and economic analysis of the aeration stripping process,it is found that the higher the gas-water ratio is,the higher the cost per ton of water in the aeration stripping process.In engineering applications,the gas-water ratio should not exceed 15.In actual production,factors such as gas-water ratio,influent flow rate,and filling ratio should be comprehensively considered,and appropriate aeration stripping process or combination process should be selected according to the type of pollutants and newly built water plants or rebuilt water plants.