Study On The Influence Factors And The Dynamic Changes Of Microbial Community Structure Of Activated Sludge During The Treatment Of Fluoride Wastewater

In recent decades,the fluorine chemical industry has rapidly developed,and the total waste water amounts are increasing.The composition of fluorine chemical wastewater is always complex.This kind of wastewater is very difficult to be degraded and it poses a serious ecological and health risk.Using the functional microbe to degrade the fluorine containing wastewater is an important method.However,little is known about the effects of microorganisms on the treatment of mixed wastewater from a wide range of fluorine chemical compounds.Moreover,there are also some catalyzes such as heavy metals in the wastewaters.Thus,these mixed fluorine chemical wastewaters are toxic,high organic loading,high salinity,high concentration of heavy metal and poor biodegradability.It greatly limits the application of biological method to treat these wastewaters.To study the effects and the changes of microbial community structures of activated sludge during the treatment of organic fluorine wastewater,the activated sludge of a fluorine chemical wastewater treatment unit was used as the experimental object.The adaptability of activated sludge to the mix organic fluorine wastewater and dynamics of microbial community in the sequencing batch reactor coping with different conditions,such as salinity,metal ions,temperature,C/N/P were studied.The main conclusions are as follows:(1)In the raw fluorine chemical wastewater,the concentrations of heavy metals such as Cu,Ni,Pb,Cd,Cr,Mn,As,were analyzed by atomic absorption spectrometry using an AA6300C spectrometer(SHIMADZU)with an air/acetylene flame following mixed-acid digestion.The main fluorine containing organic compounds were identified as bis(4-fluorophenyl)ether,2,4-Difluorophenol and so on through GC-MS and HPLC-MS.The salinity of the wastewater was as high as 53400 mg·L-1.The results showed that the optimal respiration rates of sludge in glucose wastewater were 189.2 ±1.11mg·L-1·h-1.In the raw fluorine chemical wastewater,their optimal respiration rates were only 8.87 ± 0.97 mg·L-1·h-1.It was clearly indicated that harmful substances were toxic to the activated sludge in wastewater.Furthermore,mixed organic fluorine wastewater was purified by the solid-phase-extraction(SPE)method.And the optimal respiration rates of sludge in such kind of purified wastewater were 68.60 ± 0.96 mg·L-1·h-1.The PCR-Denaturing Gradient Gel Electrophoresis(PCR-DGGE)analyses illustrated that the microbe diversities of all these sludge were significant.By cloning and sequencing analyses,6 kinds of dominant functional microorganisms such as Kineococcus gynurae were identified.(2)After 70 days of acclimatization in fluoride chemical organic mixing wastewater,the activated sludge can adapt to the wastewater containing 400 mg·L-1 TOC,and the degradation percentage of TOC was above 80%.After domestication,by the 16S rDNA-based molecular analysis techniques,it was demonstrated that the dominant bacteria in the sludge were Proteobacteria(78%-84%),Chloroflexi(3%?12%),Bacteroidetes(1%?10%).The microbe structures of the sludge after acclimation were significantly different from those before acclimation.Comparing three aeration strategies,under the condition of“on/off =3/3h",it was beneficial for the stable succession of microbial community in the sludge and environmental stress.In all of the experimental groups the mdh2 gene appeared,and the amo gene was appeared in the experimental groups of R1-1 and R1-2.The experimental results showed that the different aeration cycle and aeration amounts can affect the genetics and variations of gene,and then change the structure of microbial community.(3)The increasing of salinity impacted the degradation effects of activated sludge.The normal metabolism of microorganisms was inhibited under high salinity(10000 mg·L-1),and the degradation percentage of TOC was only 50%.Higher salinity reduced the microbial diversities and the community structures.The Shannon index decreased from 3.85 to 2.51.With the increasing of salinity condition,the halophobic bacteria were instead by the halotolerant microbes,such as Xanthobacter.(4)When the concentrations of Cu2+ Zn2+,Mn2+ and Ni2+ were more than 20 mg·L-1,the metal ions can inhibit the microbial activities.Higher concentrations of various metal ions(from 0.5,1,10,to 20 mg·L-1)resulted in reduction of the microbial diversities and change of the community structures.The Shannon index changed from 2.77 to 3.97.With the increasing of the concentration of metal ions,Xanthobacter became the dominant bacteria.Sphingomonas,Desulfovibrio,Cupriavidus,Rhodopseudomonas were only detected in the reactor with metal ions.It was clearly indicated that the biological stimulation by metal ions can lead to the evolution of the internal gene recombination along the direction of the environment.(5)At 25? the degradation effect of fluorinated organic compounds in the reactor was the best,and the removal percentage of TOC was even 90%.In terms of microorganisms,Xanthobacter,unidentified bacteria,Prosthecomicrobium and Prosthecobacter constituted the main microbes in the activated sludge.At 10?,the relative abundance of Xanthobacter was the highest.With the increasing of temperature,the abundance of Xanthobacter decreased gradually in each reactor.It was demonstrated that low temperature was more suitable for the survival of Xanthobacter.(6)Under the different C/N/P conditions,there were no significantly defference among the TOC removal rates.Sphingomonadales,Flaobacterales,Caulobacterales,Desufovibrionales were found in the activated sludges with higher nitrogen concentrations.(7)The quantitatie PCR analyses illustrated that prm,xyl,mdh2,mxaF,tomA3,dcmA genes which were capable of encoding monooxygenase,dioxygenase,or dehydrogenase may play the important roles in the degradation of fluoride wastewater.