Study On The Treatment Of Laboratory Sewage And Bacterial Community Succession By Moving Bed Biofilm Reactor

With the increase of research process and teaching tasks in Chinese universities,the environmental pollution of laboratory sewage is also becoming increasingly serious.According to the identity and emission characteristics of laboratory wastewater,the modified moving bed biofilm reactor?MBBR?is applied to treat laboratory wastewater in autumn and winter,and the consequences of Cylinder MBBR treatment in different organic loads,DO,HRT,pH stages are discussed.Scanning electron microscopy?SEM?and high throughput sequencing techniques are used to analyze the dynamics of bacterial community structure in different environmental conditions of MBBR and Cylindrical MBBR.The main results are as follows:?1?MBBR adopts a method called‘aerobic natural biofilm-formation'to generate the biofilm,and DO=2-2.5 mg/L of MBBR-A and DO=5-5.5 mg/L of MBBR-B during biofilm-formation.After 22 days,the COD and NH₄⁺-N removal rates of MBBR-A are stable at 75.26%and 76.08%.The COD removal rate of MBBR-B reach 75.83%,and the corresponding data of NH₄⁺-N is 86.96%.Studies have shown that DO=2-2.5 mg/L can be efficient to culture biofilm successful.Many protozoa and metazoans in biofilm can be seen by microscope.The morphology of the biofilm surface is observed by SEM.In the early stage of biofilm while bacillus takes up the largest propottion in the microorganism.In mature stage,the structure of biofilm is dense with coccus and bacillus growing crosswise,which strengthens the solidity of biofilm.?2?MBBR continuous operation of laboratory wastewater for 106d.The effluent COD and NH₄⁺-N concentrations of MBBR-A and MBBR-B remained at 41.38 mg/L and 1.01 mg/L.The results show that the overall effluent reaches the Class A standard.The reactors can resist different organic load.Bacterial community sequencing of MBBR samples showed that,The dominant bacteria are Proteobacteria,Bacteroidetes and Planctomycetes.The population of Pseudomonas is larger and the relative abundance of Phytophthora decreases significantly in November and December.At the genus level,Zoogloea is the dominant strain of MBBR-A.The relative abundance of Hydrogenophaga is higher in September and October,while the scale of Pseudomonas go up significantly in November and December.The rates of Dechloromonas,Flavobacterium and Aeromonas in MBBR-B are significantly diverse in different months.RDA analysis shows that Tw,DO and pH are indispensable environmental factors which have an impact on the bacterial community succession of those biofilm.?3?The Cylinder MBBR treats different organic load sewage,and the effluent reaches the first-level A standard.With the increase of DO content in the system,the effluent COD removal rate decreased by 15.73%,while the NH₄⁺-N removal rate increased by 41.45%.In different HRT conditions,the effluent quality reached the first-class A standard.When HRT=10h,the effluent COD removal rate and NH4+-N removal rate increased by 13.69%and 19.47%,respectively.From the perspective of various pH conditions,the COD and NH₄⁺-N removal rates peak in weak alkaline environment.?4?The samples of Cylinder MBBR contain abundant bacterial communities in different stages,and the community structure keeps pace with the changes of the environment.Among the samples`community composition of organic load treatments,Proteobacteria dominates at phylum level.the abundance of Flavobacterium and Zoogloea go down on the circumstance of higher organic load.In the diverse DO stage,the relative abundance of Firmicutes remains constant.When DO=5 mg/L,Nitrospirae shares the largest percentage in all bacteria,on the contraty,the figure of Flavobacterium and Zoogloea decrease obviously.In the HRT stage,the relative abundance of Proteobacteria and Bacteroidetes are relatively steady,and the variety of Comamonas and Delftia are distinct.In the pH stage,the proportion of Gemmatimonadetes rise extremely in the neutral pH environment,and Verrucomicrobia climb to the highest level in a weak alkaline treatment.To sum up,the bacterial communities of biofilms are rich in different phases with the community structure changeing dynamically due to diverse environmental conditions.