Research On The Formation Mechanism Of Bacteria-algal Biofilm And The Removal Of Pollutants

The biofilm method is a biological wastewater technology developed in the 1950 s,which is widely used in practical projects.Because it has strong resistance to impact load,no sludge expansion,and convenient management and saving energy.However,It has some problems such as long start-up time of active biomass and poor stability are the current defects.The new wastewater treatment technology represented by the bacterial-algae biofilm technology solves the problem of the traditional biofilm method by establishing a bacterial-algae symbiotic bioreactor.In this study,different fillers were used to study the hanging of bacterial-algae biofilm,and the biofilm was characterized and its film-forming mechanism was explored.The structural characterization of microbial communities in the fillers was also carried out by macrogenetic sequencing technology.On this basis,the effect of environmental factors on the removal of conventional pollutants by the bacterial-algae biofilm system is investigated and the optimal environmental factors for the bacterial-algae biofilm in stable operation are determined.The results are as follows:(1)The microbial community structure of the bacterial-algae biofilm attached to the packing was studied.The distribution and changes of microbial community structure on the filler in the reactor were analyzed by high-throughput techniques,and the differences of microbial species in CK(pure algal species)and A(polyurethane sponge filler),B(cultivated cotton balls),C(shelled cultivated cotton balls),D(large pore size MBBR effluent filler),E(small pore size MBBR effluent filler),and F(threedimensional filler)with biofilm attached after the completion of membrane hanging were compared,respectively.The microbial structure analysis at the phylum level and species level showed that the microorganisms on D were dominated by Candidatus Parcubacteria,Candidatus Nomurabacteria and Candidatus Wolfebacteria;on F were mainly enriched with Chitinophagaceae The main enrichments on F were Chitinophagaceae bacterium,Gammaproteobacteria bacterium,Flavihumibacter sp.CACIAM＿22H1 and Gemmatmonas sp.The PCA(principal component)analysis showed that there were large differences in the microflora between each of the attached fillers.By correlation analysis,the least enriched flora on A were Flavobacterium＿sp.＿FEMGT703F,Methyloversatilis＿discipulorum,Flavobacterium＿sp.,Acidovorax＿temperans,Thauera＿sp F.The most enriched colonies on F were Flavobacteriales＿bacterium,Bacteroidetes＿bacterium,Saprospiraceae＿bacterium,Nocardioides＿sp.＿SLBN-35,Methyloversatilis＿discipulorum,Flavihumibacter＿sp.＿CACIAM＿22H1,Rubrivivax＿albus,Porphyrobacter＿sp.＿SLTP,Chitinophagaceae＿bacterium,Gemmatimonas＿sp.,Gammaproteobacteria＿bacterium,Sphingopyxis＿terrae,Thauera＿sp.This indicates that F is richer for mycorrhizal biofilm species diversity.(2)Physicochemical analysis of the bacterial-algae biofilm.The bacterial-algae biofilm and extracellular polymeric substance(EPS)were characterized and analyzed.The biofilms were characterized by dry weight of biomass,scanning electron microscopy,confocal microscopy,Fourier transform infrared(FTIR),Fourier transform infrared spectroscopy and three-dimensional fluorescence spectroscopy,and the results showed that the polyurethane sponge produced more biofilms and the hanging rate reached 126.57%.The main components of EPS include proteins,polysaccharides,and possibly carboxylic acids.Therefore,the polyurethane sponge filler is most suitable for the growth and reproduction of the biofilm of bacteria and algae,and has the best film formation effect.(3)The factors influencing the removal of pollutants by bacterial-algal biofilms were investigated.The optimal operating parameters of the bacterial-algal symbiotic system were determined by different influencing factors(light intensity,light time,p H,rotational speed)for each index effluent removal rate.The water quality indicators were measured as TN,TP,NO3-N and COD to determine the treatment efficiency of the bacteriophage biofilm system.The study showed that the best performance of the biofilm system in removing nitrogen,phosphorus and COD from wastewater was achieved under the same conditions of influent water,with light intensity of 4000 lux,light time of 12 h,p H of 7 and rotational speed of 120 rpm/min.