Study On The Adsorption Properties Of Activated Carbon For GSM And 2-MIB

With the rapid development of economy in China,the water pollution and the water eutrophication caused by it are also increasingly prominent.One of the characteristics of water quality deterioration is causing taste and odor.The removal efficiency of odor substances are limited in the conventional coagulation,sedimentation,sand filtration and disinfection purification process due to their low content in the water source and belonging to the nanogram level.The activated carbons adsorption have many advantages of flexible dosing mode,deodorization and decoloration effect in the existing water strengthening purification technology,which are widely used.But the activated carbons have various kinds and different removal properties for the odorous substances.In this study,the common seven kinds of activated carbons in the market are selected to evaluate their adsorption characteristics for Geosmin?GSM?and2-methylisoborneol?2-MIB?which are two representative odor substances.And combined with the carbon surface morphology,pore structure and functional group characterization of type,the adsorption sites types on GSM and 2-MIB are put forward.The main conclusions are as follows:?1?The removal efficiency of GSM and 2-MIB are low in conventional coagulation,precipitation and filtration process.When the PACl coagulation was used?pH=7.0,t=15,PACl=20.0,mg/L?,the removal rate of GSM and 2-MIB were 20.3%and 23.1%in the filtered effluent,respectively.Under the same conditions,the removal rate of GSM and2-MIB were reduced to 14.3%and 16.5%,when the coagulant was changed from PACl to chitosan or FeCl₃.Because PACl is a positively charged inorganic macromolecule comparing with chitosan and FeCl₃,which has stronger adsorption properties on GSM and 2-MIB and can remove a small amount of odor substances by the effect of net capture-sweep and coprecipitation.However,due to the limitation of the specific surface area and active sites number of the coagulant hydrolyzate,it is difficult to meet the requirements of water quality purification by the deodorization ability of coagulation process.?2?They are obvious differences for removal effect of GSM and 2-MIB by activated carbons with larger specific surface area and active adsorption sites.Such as kemi'ou coal carbons?C₁?,Tianli coal carbon?C₂?,walnut shell carbon?C₃?,jujube shell carbon?C₄?,coconut shell carbon?C₅?,asphalt carbon?C₆?and shell carbon?C₇?.C₅has higher removal efficiency than other activated carbons on GSM and 2-MIB.In the neutral environment,the removal rate of GSM and 2-MIB in adsorption equilibrium?GAC=3.0,g/L?was 90.2%and 81.3%,respectively.Under the same conditions,the removal rate of C₂ to GSM was the lowest?1.3%?,and the removal rate of 2-MIB was only 24.9%.C₁ and C₂ belonged to coal carbon,but the removal rate of C₁ was significantly higher than that of C₂ on GSM and 2-MIB,93%and 61.1%,respectively.?3?The removal efficiency of activated carbon on GSM and 2-MIB is mainly related to the number of pore channels,the pore size ratio and the active site type of carbon surface.The larger the specific surface area of the activated carbon is,the greater the adsorption capacity of the odor substances is.In the similar specific surface area,the more the ratio of pore volume?pore size<2 nm?to total pore volume is,the more favorable the adsorption of GSM and 2-MIB is.At the same time,the more the number of oxygen functional groups of alcohol hydroxyl groups,phenolic hydroxyl groups and carboxyl groups on the carbon surface are,the stronger Chemical adsorption ability on GSM and 2-MIB is.Using chemical oxidation method to remove C₅ surface alcohol hydroxyl groups,phenolic hydroxyl groups and other active sites,the adsorption capacity on GSM and 2-MIB of C₅ decreases obviously,which further confirmed the above conclusions.?4?C₅ adsorption processes of GSM and 2-MIB follow the pseudo second-order netics model and Freundlich isotherm model.In the presence of coexisting substances,the adsorption rate and the amount of equilibrium adsorption will be affected.Na⁺has virtually no effect on the removal of GSM and 2-MIB,because of its poor competitive adsorption on the active sites.Similar to Na⁺,low concentration of Ca²⁺?<1.0 mmol/L?also has little effect.When Ca²⁺>1.0 mmol/L or Kaolin?turbidity?matter is coexisted,the activated carbon will appeare pores clogging phenomenon,which make it significantly decrease to adsorption capacity on GSM and 2-MIB.Comparing with Kaolin?turbidity?matter,HA will form a wrapping effect on activated carbon,which blocking the migration of GSM and 2-MIB into the carbon.The activated carbon type?coconut shell charcoal?have good adsorption and removal properties for common odor substances such as GSM and 2-MIB in natural water,which was certified in this paper,which will provide theoretical support for the selection of activated carbon in tap water plants and the emergency treatment of sudden water pollution accidents.Meanwhile,based on the principle of interaction between activated carbon and odor substances,it also points out the direction for the optimization and modification of activated carbon and the development and utilization of new adsorption materials,which have important theoretical significance and application value.