Research On The Optimization Of Adsorption Process Of Malodorous Gas Produced By Aerobic Fermentation Of Sludge From Municipal Sewage Treatment Plant

There are some problems in adsorption process of malodorous gas of a sewage treatment plant in Zhengzhou,such as low emission rate,short service life of adsorbent.The result is that the adsorption process of malodorous gas is not effective.The main objective of this research is to optimize the malodorous gas adsorption process in the plant,taking dimethyl sulfide and dimethyl disulfide as test objects,a kind of adsorbent which is more suitable for practical engineering operation is screened out from activated coke and activated carbon.In addition,in order to solve the problem that water molecules can seriously affect the adsorption of dimethyl sulfide on adsorbent,a kind of desiccant is selected from silica gel,calcium chloride and calcium oxide.Finally,the optimum design and calculation of the adsorption process are carried out.The main results are as follows.(1)Selection of adsorbents:(a)The activated coke and activated carbon are characterized by BET with whole pore structure and FTIR methods,respectively.The results show that the activated coke has more developed mesoporous structure and higher specific surface area than the activated carbon,and the total pore volume is about 2 times of that of the activated carbon,and the activated coke surface has more functional groups,stronger polarity,easier to absorb some of the polar substances.(b)Adsorption of dimethyl sulfide and dimethyl disulfide on single-component gas:the adsorption equilibrium time of dimethyl sulfide on activated coke and activated carbon is about 12 h.The presence of water molecules can seriously affect the adsorption of dimethyl sulfide on activated coke and activated carbon,and the effect on activated carbon is greater.The adsorption equilibrium time of dimethyl disulfide on activated coke and activated carbon is about 32 h and 12 h respectively.The influence of water molecules on the adsorption of dimethyl disulfide on activated coke and activated carbon is small.Langmuir adsorption isotherm model can better describe the adsorption process of dimethyl sulfide and dimethyl disulfide on activated coke and activated carbon.(c)Adsorption of mixed gas of dimethyl sulfide and dimethyl disulfide by adsorbent:when dimethyl sulfide and dimethyl disulfide coexist,dimethyl disulfide preferentially adsorbs on the adsorbent.When dimethyl sulfide,dimethyl disulfide and water molecules coexist,dimethyl disulfide and water molecules have the same competitive ability to the adsorption sites,and preempt the adsorption sites.Active coke is more tolerant to water molecules and can adsorb more mixed gas of dimethyl sulfide and dimethyl disulfide than active carbon in the presence of water molecules.(d)Dynamic experimental on adsorption of dimethyl sulfide by adsorbent:as the competition of dimethyl sulfide to the adsorption site is the least,the dimethyl sulfide is chosen as the dynamic test object.The results showed that the activated coke could adsorb more dimethyl sulfide in the practical applications.(2)Selection of desiccant:in the process of adsorption,it is found that the presence of water molecules can seriously affect the adsorption of dimethyl sulfide,so it is necessary to dehumidify the malodorous gas before adsorption.A desiccant suitable for drying actual malodorous gas is selected from silica gel,calcium chloride and calcium oxide in this thesis.The water absorption of calcium oxide is 0.372 g/g,which is between silica gel and calcium chloride.Calcium oxide is cheap,and after absorbing water,it is a powder calcium hydroxide,so it is easy to clean and replace,and the calcium hydroxide can be used as a construction filler,chemical raw material and other secondary use.Therefore,calcium oxide is more suitable to be used as a desiccant for malodorous gas in the plant.(3)In the process of optimization design and calculation of adsorption process,the pre-dehumidification column is added before the adsorption column,and calcium oxide is selected as desiccant in the pre-dehumidification column,and active coke is selected as adsorbent in the adsorption column.The designed pre-dehumidification column can reduce the humidity of malodorous gas from 18.82 g/m3to 2.27 g/m3,thus effectively extending the service life of the adsorbent.In addition,the designed adsorption column occupies an area of 177.5 m~2less than that of the original,and only occupies 41%of the original area,but the treatment gas volume remains the same,and the operation time can be extended about 1 week.The concentration of dimethyl sulfide can be reduced from 0.4069 mg/m~3to 0.07 mg/m~3,which can meet the"emission standard for odor pollutants"(GB 14554-93).