The Effect Of Microbial Directed Domestication On The Anaerobic Dechlorination Of 2,4-dichlorophenol

In the study of chlorophenol biodegradation,it is found that monochlorphenol,dichlorophen and trichlorophenol can be degraded effectively by openning ring under aerobic conditions,but tetrachlorophenol or pentachlorophenol can not be degraded directly under aerobic conditions.In the previous study,2-monochlorphenol(2-CP)was easily degraded under anaerobic conditions,but 2,4-dichlorophenol(2,4-DCP)and 4-monochlorphenol(4-CP)were more difficult to degrade.In order to improve the anaerobic biodegradation efficiency of 2,4-DCP,the aim of this study was to develop and domesticate the characteristic dominant bacteria groups for the degradation of the substrate chlorophenol,and to enhance the effect of the removal of the substituent chlorine group,and to obtain the efficient degradation of 2,4-DCP in the anaerobic biological system.With sodium propionate as the main organic matrix,three anaerobic biochemical sludge reaction systems were established respectively.The first group was added to 2-CP,second groups were added to 4-CP,and third groups were added to 2,4-DCP,in order to improve the removal effect of specific chlorine substituents.By constructing microbial communities,the rate of reductive dechlorination of the chlorinated substituents was accelerated,thereby accelerating the overall degradation of 2,4-DCP.Then the different properties of three kinds of enhanced sludge were studied,including the study on the regularities of microbial dechlorination in the sludge and the stability of mixed microbial communities.Finally,the composition and diversity of several microbial communities were analyzed.The results show that:1)in the early stage of stable operation of anaerobic system,microbial community can remove ortho chloro substituents on 2-CP and 2,4-DCP molecules,and the degradation rate of 2-CP is 1.62 μM/h.It can not remove the para chloro substituents on 4-CP and 2,4-DCP molecules.The first group was added 2-CP to acclimatized anaerobic sludge to obtain 2-CP enhanced sludge.It can only remove the ortho chloro substituents on 2-CP molecules.After domestication and stabilization,the degradation rate increased from 1.62 μM/h to 4.3 μM/h,but it could not effectively degrade 2,4-DCP and 4-CP.The second group was added to 4-CP to domesticate anaerobic sludge,and 4-CP enhanced sludge was obtained.It can remove the para chloro substituent on 4-CP molecule,and its degradation rate can reach 2.15 μM/h.It preferentially removed the para chloro substituents on 2,4-DCP molecules and removed the ortho chloro substituents on the molecule.The third group was added to 2,4-DCP to domesticate anaerobic sludge,and 2,4-DCP enhanced sludge was obtained.The preferential removal of ortho chloro substituents on 2,4-DCP molecules and removal of the counter chloro substituents on the molecule can remove the average degradation rate of 2,4-DCP by 3.4μM/h.Thus,the "site directed dechlorination" of anaerobic biodegradation of chlorophenols was achieved.2)based on 4-CP enhanced sludge and 2,4-DCP intensified sludge,a new microbial community was constructed which could remove the chlorinated substituents on the 2,4-DCP molecule of 95μM in 40 h,and the removal rate could reach 100%.The removal rate of the chlorinated substituent from the microbial community increased from 1.1μM/h of 2,4-DCP enhanced sludge to 2μM/h.Thus,the "directional acceleration" of chlorophenol degradation process was achieved.3)4-CP enhanced sludge can reduce the para chloro substituents on chlorophenol molecules.It can restore the structure of chlorophenol substituents instead of restricting the degradation of a substance,such as 4-CP or 2,4-DCP.It is not affected by chlorinated substituents at other positions of chlorophenol molecules,but has no degradation tendency for 2,4-DCP and 4-CP molecules.4)4-CP enhanced microbial communities constructed by strengthening sludge and 2,4-DCP,and treated 2,4-DCP simulated wastewater.The concentration of water distribution in 2,4-DCP was 62μM,and the hydraulic retention time was 72 h.After 10 cycles,the maximum concentrations of 2-CP and 4-CP produced by degradation were all about 20μM.It was concluded that several microbial communities of the microbial community did not deteriorate due to matrix changes or intercommunity interactions and could remain stable for a long time.5)The diversity of three kinds of intensified sludge is analyzed.We find that the species composition of 4-CP intensified sludge is the most abundant,including 1022 microorganism types,and the lowest overlap degree of the other two kinds of intensified sludge.It is possible to speculate that the microbial community has certain particularity,which may be related to the removal of the counterpart chlorine.