Biopurification Of Waste Gas Containing Mixed Chlorinated Hydrocarbons And The Community Structure

The majority of organic chlorinated hydrocarbons have been listed as priority pollutants by the United States Environmental Protection Agency(EPA)because of their teratogenicity,carcinogenicity and mutagenicity.Chlorinated hydrocarbons are important raw materials,organic solvents and intermediates,and are widely used in the chemical,pharmaceutical,leather and other industries,which may cause over-discharge of the chlorinated hydrocarbons in the waste gas from these industries.However,the conventional biological treatment process may not effective enough in treating chlorinated hydrocarbons-containing waste gas because of the low water solubility and biodegradability of chlorinated hydrocarbons.Therefore,it is of great significance to develop biological treatment process to treat chlorinated hydrocarbons-containing waste gas.This research created a method to detect the bacteria Methylobacterium rhodesianum H13 and Starkeya sp.T-2,which were isolated by our research group from activated sludge to treat dichloromethane(DCM)and dichloroethane(1,2-DCA)respectively,by real-time PCR(RT-PCR)method based on TaqMan probe.According to 16S rRNA sequences of these strains,we designed specific primers and probes,amplified fragment,prepared positive standard plasmid and got the best reaction conditions and reaction systems.H13 and T-2 were used to strengthen the performance of bio-trickling filter(BTF)for the purification of mixed gas of dichloromethane and dichloroethane.The results showed that the start-up period of BTF was 14 days.The best removal efficiency of DCM and 1,2-DCA was achieved when the total inlet loading is 40 g·m-3·h-1,and the removal efficiency would keep stable when the total inlet loading is greater than 50 g·m-3·h-1.There was a linear relationship between the generation load of CO2 and mixed gas removal load,the maximum mineralization rate of mixed gas was 76.9%.After 15 days of starvation,the removal of DCM and 1,2-DCA could reach over 90%(at the 13 day)and 80%(at the 18 day)respectively.The interaction test indicated that DCM and 1.2-DCA would compete with each other.The impact loading test showed that the removal efficiency would decline under high impact load,this may caused by the decrease of the microbial activity,as the oxygen uptaken rate(OUR)droped during this period.In this paper,three kinds of molecular biology methods RT-PCR,molecular cloning and high-throughput sequencing were employed to study the varation of the community structure during the start-up and starvation periods of the BTF.RT-PCR analysis showed that the number of high-degrading bacteria after start-up was about 106 times that of before start-up,the amounts of high-degrading bacteria after 15 days of starvation were equal to the beginning period of the start-up perios.Clone library construction and high-throughput sequencing results showed that many kinds of microbial populations existed in biological trickling filter system,amount which Methylobacterium and Starkeya account for a high and stable proportion,Hyphomicrobium,Rhizomicrobium,Sphingomonas,Pseudomon and Pusillimonas could maintain stable proportion,based on which we may conclude that DCM was mainly removed by Methylobacterium and Hyphomicrobium,1,2-DCA mainly by Starkeya.