Study On The Purification Of Volatile Organic Compounds From P-Cyanobenzyl Chloride Waste-Water By Denitrification

A variety of volatile organic compounds(VOCs)are contained in the wastewater produced in the production process of p-cyanobenzyl chloride.These VOCs are usually toxic,harmful and irritating.During the treatment of such wastewater,these substances volatilize from the waste water into the atmosphere because of the disturbance of water which not only pollutes the natural environment seriously,but also do great harm to human health.In this dissertation,volatile organic compounds generating from p-cyanobenzyl chloride waste water are treated by denitrification method and common biological method.An effective technical method for volatile organic compounds generating from chemical wastewater is provided by contrastively studying the treatment efficiencies of the two methods.Meanwhile,the changes of volatile organic compounds in the reaction process and the mechanism of purification of volatile organic compounds are studied and discussed.A kinetic model of reaction is established to achieve a prediction of the purification process and provide a basic theory for the engineering design.The results show that:(1)The denitrifying biological purification unit(No.1 column)has a better purification effeciency on the volatile organic compounds generating from p-cyanobenzyl chloride wastewater than the common biological purification unit(No.2 column).When the inlet concentration increases from 350mg/m3 to 820mg/m3,the outlet concentration of No.1 column which is added in nitrate increases from 0.9mg/m3 to 5.8mg/m3 and the removal rate keeps above 99%that the outlet has no obvious odor.The outlet concentration of No.2 column is higher than that of No.1 column.The outlet concentration of No.2 column increases from 15mg/m3 to 230mg/m3 and the removal rate decreases from 95.6%to 72.0%that the outlet changes from no obvious odor to a strong headache odor.Under all inlet concentrations,COD in No.1 column is lower than that in No.2 column and the accumulation of organic pollutants in liquid phase is relatively small,indicating that No.1 column has better degradation capacity for these organic pollutants.(2)There are hydrocarbons,acids,aldehydes,phenols,esters,ketones,hormones and other 126 kinds of volatile organic compounds in the organic waste gas generating from p-cyanobenzyl chloride wastewater of which most are toxic,harmful and irritating.After 45 days of stripping,kinds of substances in wastewater is reduced by 84.Concentration is significantly reduced and the peak area decreased by 99.93%.The removal of these substances makes the smell of the wastewater lighter and the colour more shallow.There are hydrocarbon,hormones,acids,alcohols,aldehydes and other 102 kinds of substances in the 1st day inlet.Compared with the 1st day inlet,the kinds of volatile organic compounds in the outlet of NO.1 column and NO.2 column are reduced by 84 and 73 respectively,the peak area are reduced by 98.23%and 96.52%respectively.There are only 30 kinds of volatile organic compounds in the 45th day inlet.Compared with the 45th day inlet,the kinds of volatile organic compounds in the outlet of NO.1 column and NO.2 column are reduced by 14 and 10 respectively,the peak area are reduced by 89.63%and 76.84%respectively.During the reaction process,the organic pollutants in the inlet are degraded after entering the reactor rather than accumulate in the liquid.The kinds of volatile organic compounds in the NO.1 column and NO.2 column are similar,but the concentration of volatile organic compounds in the NO.1 column is relatively lower.(3)The purification of volatile organic compounds generating from p-cyanobenzyl chloride wastewater in the NO.1 column is mainly dependent on aerobic degradation and anoxic denitrification degradation.The system is macroscopically aerobic,but an anoxic microenvironment can exist in the biofilm which provides conditions that aerobic denitrification needs.Some refractory volatile organic compounds can be degradated by denitrification so that NO.1 column has a better effect on treating the volatile organic compounds from p-cyanobenzyl chloride wastewater.(4)On the basis of "adsorption-biofilm" theory,a kinetic model describing the biological purification process of the volatile organic compounds generating from p-cyanobenzyl chloride wastewater is established by using biochemical reaction principle and chemical reactionengineering.The kinetic equation is (?) The biochemical degradation reaction rate constant b= 32.258(mg/L · h),the adsorption coefficient? =0.00074697.The NO.1 column experimental data is used to validate the kinetic model.The result shows that there is a good relevance between the calculation values and the experimental values and the correlation coefficients are r=0.9799 and r=0.9377.It shows that the model is suitable to describe the actual operation process and predict the treatment effect.