Evolution Of The Microbial Community In A Full-scale Printing&Dyeing Wastewater Treatment System

For most current industrial wastewater treatment plants, seed sludge was normally collected frommunicipal wastewater treatment plants as inoculums at their establishment stages. This sludge underwentdramatic variation in microbial community structure during adaptation to the new wastewater environmentsthat sometimes resulted in failure of the system start-up. At hypothesis that the dominant microbes play themost important roles in each stage of the system running, clarifying the dominant microbial compositionsin the biological treatment processes and their evolution rules with the system running will be helpful forunderstanding and solving some important mechanism problems. However, reports on microbialcompositions and evolution have been rare, especially in a full-scale printing&dyeing wastewater (PDW)treatment system. In this study, PCR-DGGE and T-RFLP methods were used to trace the evolutionprocesses of three domains of microorganisms, bacteria, fungi and archaea in a full-scale PDW treatmentsystem treating1000tons dyeing wastewater per day during its establishment and commissioning operationstages. The following conclusions were obtained:1. The system consisted of a coagulation-precipitation unit, biological treatment process1(ahydrolytic and acidification unit, an activated sludge treatment unit and a settling tank1) and biologicaltreatment process2(a hydrolytic and acidification unit, a bio-contact oxidation unit and a settling tank2).During more than three months monitoring, the full-scale PDW biological treatment system hadsignificantly COD and color removal efficiencies:85%and84.9%of COD and color removal, respectively.The microbial communities involving bacteria, fungi and archaea were pursued and investigated using boththe culture-dependant and culture-independent methods during the system start-up and its steady runningstages. The microbial enumeration results based on both cultivation and fluorescence quantitative PCR(FQ-PCR) techniques showed that bacteria were the predominant population in the system all the timefollowed by fungi and archaea. With the system operation, the concentration of fungi decreasedsignificantly, which was contrary to the variation trend of archaea. At the last stage of determination (after3months of operation), the ratio of archaea to bacteria was significantly increased to1:0.58, and evenbecame the dominant population, especially in the second stage biochemical treatment process.2. The evolution process of the microbial community in this PDW treatment system was traced byusing PCR-DGGE technique. The results indicated that the microorganisms in the seed sludge from municipal wastewater treatment plant underwent dramatic variation during adaptation to the new PDWenvironments. Bacteria and fungi were easier to be persistent than archaea in the treatment tanks at thestage of the system started up, with57.3%of bacteria,57.6%fungi and only34.8%of archaea persistent inthe system from the seed sludge. With the fluctuation of waste water and pollutants components, themicrobial community changed constantly with a significant increase in archaea and bacteria diversities,ratios of archaea to bacteria but decrease in fungi diversity and concentrations. Biological treatment process2received the effluents of biological treatment process1and thus with a little fluctuation in its composition.Therefore the microbial community in the treatment process1was significantly more stable than thetreatment process2. Almost all the bands were recovered from the DGGE gel and sequenced. Phylogenetictree based on these sequences showed that nine distinct lineages of bacteria were in the samples belongingto Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Bacteroidetes, Clostridia, Bacilli,Caldilineaceae, Nitrospira, Chlorobia, Acidobacteria; fungi were in the samples belonging toChytridiomycetes and Zygomycota were detected from the samples. Archaea were in the samplesbelonging to Euryarchaeota the most were Methanogen,and Crenarchaeota.3. Similar results about the evolution trend of the microbial community were obtained by usingT-RFLP technique. By this method, the ratio relationship of the predominant bacteria was determined asfollowing: Caldilineaceae (4.46%-11.6%), Alpha-proteobacteria (7.51-9.67%), Chloroflexi bacterium(6.02%-7.15%), Rhodobacter sp.(24.32%-28.81%), Thermomonas sp (17.34%-38.95%); Among fungi,only Blastocladiales sp.(2.30%-3.12%) was detected; The dominant archaea as Methanogen.4. During more than three months monitoring, although the microbial communities underwentdramatic variation during the system running and with the influents fluctuation as described above, theefficiencies with no effects on the reactor function. Although bacteria was easier to be persistent thanarchaea and fungi in the treatment tanks, the stability of bacteria in diversity and species was significantlyhigher than fungi and archaea indicating high functional redundancy of bacteria. The phenomenon ofarchaea presence in such large amount in the PDW treatment system, especially in the biological treatmentprocess2suggested that archaea might play important roles in degradation of refractory pollutants.