Application Research On The Removal Of THMs In Tap Water By Activated Carbon Adsorption Technology

Tap water generally contains chlorine disinfection by-products such as THMs which affect human health during long-term drinking.Activated carbon adsorption technology can effectively remove THMs.However,there is a great variety of activated carbon on the market.Appropriate kinds of activated carbon need to be chosen to remove THMs.Water quality of tap water and chlorine disinfection by-products THMs from 40 cities in our country were investigated in this study.15 kinds of activated carbon were evaluated from angles of safety performance,structure properties and adsorption ability to investigate correlation and effectiveness of each analytical method.At the same time,four kinds of activated carbon which presented better performance and conformed to the standard,were chosen to remove low concentration THMs in tap water.Adsorption speed and equilibrium time were analyzed from the aspects of static adsorption kinetics and dynamic penetration.The adsorption capacity of CHCl3,CHCl2Br,CHClBr2,CHBr3 was fitted according to Freundlich isothermal adsorption equation.the speed,equilibrium time,capacity of adsorption as well as the influence of initial concentration,temperature,the types of activated carbon on adsorption process were studied.The initial concentration of THMs,temperature,and the influence on absorption process caused by types of activated carbon were investigated.Dynamic penetration experiment was carried out to analyze influence on practical operation caused by speed,initial concentration and carbon bed height.The first,second and third activated carbon water purifier filter element absorption device of 200L/h with the size of 10 inch were designed.The results are as follows:(1)In the 40 China’s cities samples,the pH of tap water is in the range of 7～8,which conformed the standard of 6.5～8.5 in "Sanitary standard for drinking water"(GB 5749-2006).The TDS is below 150mg/L from East,Southern,Southwest and Northeast China except for some cities,which is higher relatively in Central,North and Northwest China.Besides,THMs in tap water were mainly CHCl3 which occupied more than 60%.In term of the ratio between the detection value and the limit value stipulated in "Sanitary standard for drinking water"(GB 5749-2006),HD10 and HD11 exceeded 1,HD14,HD17,HN1,HN2 and XB1 were close to 1,and the rest of the samples conformed to the limit requirements.(2)Among the 15 kinds of activated carbon,moisture content(MC)of 1-3#,2-1#,3-2#,5-1#,5-2#and 8#were less than 5%,MC of 1-4#and 3-1#were more than 7%;pH was in the range of 4-11,1-4#,7-2#were acidic and the remaining were alkaline.Chloride content of activated carbon was below 0.5%.The content of zinc,lead and cadmium were far less than the limitation in "Activated carbon drinking water purifier"(CJ 3023-1993).1-3#,2-1#,3-2#,5-1#,5-2#and 8#were more appropriate to be used for drinking water purification referring to CJ 3023-1993.1-4#and 7-2#were made from wood whose microporous charcoal were most developed,the surface area reached 1600m2/g and helpful for the adsorption of small organic molecules;1-1#,2-1#3-1#,5-1#,7-1#and 8#were coconut shell charcoal,the surface area was more than 800m2/g.Adsorption rate of 7-1#and 7-2#for small molecule organic was the fastest,and 1-3#,2-2#,3-1#4#,7-1#took the second place.The pore volume and the specific surface area of activated carbons were positively correlated to some extent.From the perspective of pore size,1-1#2-1#,5-1#and 8#had the best adsorption effect on small organic compounds.From iodine adsorption value,methylene blue adsorption and phenol adsorption,the results of the evaluation were basically consistent with the structural analysis of activated carbon.(3)In terms of the adsorption rate on THMs,5-1#was the best and 7-1#took the second place.Equilibrium time of 4 kinds of activated carbons was basically one hour,the adsorption between 1h～4h was slow and after then THMs were no longer adsorbed.The Freundlich fitting showed that THMs adsorption process by activated carbon belonged to non-uniform surface adsorption.According to K and 1/n,5-1#was more appropriate for the adsorption of THMs,which was in agreement with the fifth chapter.The adsorption rate of activated carbon was faster when the initial concentration of THMs was higher.In the experimental conditions,the adsorption rate of THMs by activated carbon increased slightly with temperature increasing.The adsorption effect of 5-1#on THMs was CHBr3>CHClBr2>CHClh>BrCHCl3.(4)Under the experimental conditions,with the water flow augmented,the THMs concentration higher,activated carbon penetrated faster,adsorption capacity and capacity utilization rate of activated carbon increased slightly.While absorbed layer increasing,the activated carbon penetration was slower,but there is no influence on adsorption capacity and capacity utilization rate of activated carbon.(5)Set the influent concentration of trichloromethane as 120ug/L for preliminary design,quantity of flow was set to 200L/h,effluent concentration was 20ug/L,designing in accordance with the 10 inch water purifier filter.The utilization rate of activated carbon was 68.4%.The carbon filter should be changed every 4 months with the first-order adsorption,and it should be changed every 9 months with the second-order adsorption,then every 15 months with the third-order adsorption.This study provided a theoretical basis for the rapid and effective selection of activated carbon,and some references for the practical application of activated carbon to remove THMs in tap water.