The Study On Microorganism Community Structure In Biological Treatment System Of Saline Organic Wastewater

With the shortage of water resources,more and more attention have been paid to wastewater treatment and recycling.Biological treatment is one of the most common used methods of wastewater treatment,due to its economic,efficiency and widely adaptability.Salt concentrations more than 1%can cause bacterial plasmolysis and loss of the metabolic functions,resulting in ineffective wastewater treatment by conventional biological treatment.For this reason,high-salinity wastewater is difficult to treat by biological processes.But microorganisms are capable of surviving in hypersaline environments by regulating their metabolic functions when they are exposed in high salt concentrations for a long period.In this research,the treatment effect of high-salinity wastewater by two-stage A/O filter process has been investigated,the microorganism diversity and structures on the biofilm were analysed by using conventional microbiological methods and molecular biological methods,moreover,the subject of the study include the isolation and identification of halotolerant microorganisms.The conclusions were drawn as follows:1.The salinity in wastewater treatment system fluctuated between 1.9 and 4.5 percent. Under the high-salinity conditions,the removal rate of COD,NH4⁺-N and TN in treatment process could achieve to 96.2%,90.2%and 59.3%respectively,which indicated that two-stage A/O filter process on high-salinity wastewater could satisfy the treatment demands.It suggested that some halotolerant and halophilic microorganisms appeared after a long-term and stable adaptation.2.The results of microscopy of biofilm showed that the microbial community structure in every reactors were different,on account of different DO and nutritional status.Overall,the microorganism diversity in aerobic phase was higher than the anoxic phase.The most common microbes were nematodes,epistylis lacustris and enchytraeidae.A large numbers of enchytraeidae appeared in the biofilm of the second aerobic reactor,and they existed in all seasons and had relation with sludge reducing,which is an interesting phenomenon of concern.3.The results of microbiological counting showed that the heterotrophic bacteria was predominated in biofilm.Their number were greater than other functional microorganisms by4～6orders of magnitude.The number of heterotrophic bacteria in the first anoxic reactor and the first aerobic reactor were the most,as much as 10¹⁰～10¹²cfu/gDW,and the number of nitrifying bacteria and denitrifying bacteria were almost 10⁶～10⁷cfu/gDW.The salt tolerance of nitrifying bacteria is better,coupled with a long-term domesticated,so even in the high-salinity wastewater,the number of nitrifying bacteria maintained higher biomass,which ensured the successful progress of nitrification.In winter the number of bacteria decreased somewhat,however,the treatment efficiency almost not be affected since the process is longer.4.After the isolation and pure culture from the biofilm samples of wastewater treatment system,by determination of flocculation and the degradation of halotolerant bacteria to wastewater,seven bacteria have been selected and sequenced finally.The identification proved that three of them were halomonas,and others are similar to marine bacteria.These bacteria have a widely halotolerant range and strong ability of wastewater degradation. Therefore,for high-salinity wastewater treatment,they may be the potential candidate bacteria to be inoculated.5.The analysis result of the microorganism diversity and similarity in biofilm showed that the microbial diversity in the first aerobic reactor and the first anoxic reactor were relatively higher,the next was second aerobic reactor,the second anoxic reactor was lowest. Microorganism diversity of aerobic reactors were generally higher than the corresponding anoxic reactors.In winter especially in January,microbial diversity was lowest compared with other seasons.The difference of microorganism diversity and similarity in biofilm reactors showed that the microbial community obviously affected by the operating conditions and the parameter of the treatment process.