Effects Of Iron Elements And Mediators On Pentachlorophenol Degradation And Its Microbial Community Structure By ASBR

In recent years, the surface water pollution problems were increasingly prominent, especially organic halogen contamination, such as pentachlorophenol(PCP), hexchlorobenzene(HCB) and polychlorinated biphenyls(PCBs) etc. Research on treatment of this kind of waters had become a hot and difficult point in water treatment field. Based on simulated anaerobic sequencing batch reactor(ASBR), the optimum operating condition was as follows: temperature of 35℃, pH of 7.2, glucose dose of 1800 mg/L and stirring rate of 130 r/min, under which the influences of redox mediators and iron elements on PCP degradation by ASBR and its microbial community structure changes were studied, especially riboflavin(Rib) and nanoscale iron(n ZVI). The degradation pathways, mechanisms and microbial community structure changes of PCP in different systems were investigated as well. The results were as follows:(1)Various iron elements and redox mediators had obvious influences on the degradation efficiency of PCP, of which nZVI and Rib could significantly improve the removal efficiency of PCP with the optimum doses of 2.0 g/L and 100.0 μM. The degradation efficiencies of PCP by AAS(anaerobic granular sludge), AAS+Rib, AAS+n ZVI and AAS+Rib+nZVI were gradually enhanced, and its complete degradation times of PCP were 10, 8, 7 and 6 days, respectively.(2)Using GC-MS and HPLC for the qualitative and quantitative analysis of PCP degradation mesostates, it was found that the degradation of PCP prevailingly included two pathways: â‘  PCPâ†'2,3,4,6-TeCPâ†'2,4,6-TCPâ†'2,4-DCPâ†'4-CPâ†' phenol; â‘¡ PCPâ†'2,3,4,5-TeCPâ†'2,3,5-TCPâ†'2,5-DCPâ†'3-CPâ†'phenol. Different degradation systems had different degradation pathways; the PCP degradation of AAS was only pathway â‘ , and others included both â‘  and â‘¡ pathways. The main degradation pathways of AAS+Rib, AAS+nZVI and AAS+Rib+n ZVI were pathway â‘ , pathway â‘¡ and pathway â‘¡, and phenol was completely degraded to CH4 and CO2.(3)The promoting mechanisms of Rib and n ZVI were not the same for the reductive dechlorination of PCP. As redox mediator, Rib improved the transfer rate of electrons from microorganism to PCP, reduced the activation energy of the reaction system, and it was beneficial to the dechlorination of PCP. nZVI could supply enough electrons for the reductive dechlorination of PCP, also served as microelement to promote the growth of microorganisms, and was able to effectively mitigate the pH upheaval of reaction system as well.(4)Compared with the initial anaerobic granular sludge, the microbial community structure of different reaction systems had changed markedly, and most of the bacterias were rods and cocci. The changes of DGGE had something to do with the species succession of activated sludge, especially the growth of anaerobic dechlorination bacterias.(5)Obvious changes had taken place of microbial populations in PCP domesticated sludge with iron elements and redox mediators, bacteria spectrum similarity analyses showed that the domesticated sludge similarity was 32.2 compared with the original sludge, the similarity of Rib, nZVI and Rib+n ZVI systems respectively were 71.8, 56.0 and 51.5 compared with the domesticated sludge.(6)The DNA sequence of DGGE banding analyses results showed that the main bacterias in the reactor were Dehalobacter sp, Methanosarcina, Bacteriodes, Sulfurospirillum sp, Nevskia sp and Betaproteobacterium,and Dehalobacter sp, Bacteriodes, Sulfurospirillum sp and Nevskia sp were related to the degradation of PCP.