| Micro-animals often appear in sewage biological treatment devices,among which bdelloid rotifer are of great concern,because bdelloid rotifer can be used as indicator organism for good biological performance of sewage treatment.However,the role of bdelloid rotifer in sewage biological treatment is still unclear.In this paper,Philodina sp.,which is a common kind of bdelloid rotifer in the wastewater treatment,was used as the research object,and the effects of the secretion of rotifer on the flocculation and growth characteristics of flocculent bacteria isolated from the activated sludge are discussed,and the impact on the biological performance of Sequencing Batch Reactor(SBR)sewage biological treatment and the microbial community structure of activated sludge in the reactor.In order to reveal the role of rotifer in biological treatment systems,and provide a scientific basis for the establishment of new technology characterized by the beneficial effects of micro-animals to improve the activated sludge flocculation activity and sewage treatment performance.The main research contents and research results of this paper are as follows:(1)To isolate and screen bacteria from activated sludge for subsequent experiments.A total of 30 strains of bacteria were isolated,from which 8 strains of bacteria were selected for follow-up experiments based on their growth characteristics and flocculation.After morphological characterization and 16 S r DNA sequencing identification,the 8 strains were identified as Alcaligenes faecalis XJ4,Alcaligenes aquatilis XJ19,Stenotrophomonas koreensis XJ20,Rheinheimera mesophila XJ22,Bacillus thuringiensis XJ23,Bacillus amyloliquefaciens XJ24,Bacillus cereus XJ25 ?Bacillus velezensis XJ26.(2)The effect of rotifer secretion on bacterial growth density and flocculation activity.Since some previous studies have preliminarily clarified that the action of rotifer on bacteria is mainly through their secretion,the focus of related research is on rotifer secretion.Among 8 strains,2 strains have a flocculation activity of 50% to 60%,4 strains have a flocculation activity of 60% to 80%,and 2 strains have a flocculation activity of 80% to 100%.These bacteria can be based on the relative size of their flocculation activity divided into three groups: low,medium and high.The average increase rates of rotifer secretion to the bacterial growth density of the low,medium and high groups were 31.7%,32.5%,29.6%,and the average increase rates of bacterial flocculation activity were 6.4%,17%,and 4.3%,respectively.This result shows that after adding rotifer secretion to the bacterial culture medium,the growth density and flocculation activity of the bacteria have a certain promotion effect,and it is suggested that the promotion effect of the rotifer secretion is more effective for the bacteria with medium flocculation activity.Obviously,this may be because the bacteria with low flocculation activity themselves have lower secretion efficiency and greater restrictions,the bacteria with high flocculation activity have less space for improvement,and the bacteria with medium flocculation activity have smaller restrictions and larger space for improvement.(3)The effect of rotifer secretion on the time for bacteria to reach maximum flocculation activity and maximum growth density.The time to reach the maximum growth density of the strains XJ4 and XJ20 added with rotifer secretion in the medium was 12 hours earlier than that of the control group without rotifer secretion,and the remaining 6 bacteria to reach the maximum growth density was the same as that of the control group;XJ20,XJ23 and XJ24 added secretion reached the maximum flocculation activity time 12 hours earlier than the control group,and the remaining 5 bacteria to reach maximum flocculation activity was the same as the control group.Therefore,it can be seen that the rotifer secretion can shorten the time for some bacteria to reach the maximum growth density and flocculation activity,that is,to promote the growth rate of bacteria and the speed of bacteria to produce flocculated substances.(4)The effect of rotifer and rotifer secretion on the removal performance of bacterial pollutants.The removal efficiency of COD in domestic sewage from 8 strains of bacteria was 33.2% ? 66.2%,and the removal efficiency of TOC was 22.8% ? 53.8%;after the addition of rotifer secretion,the removal efficiency of COD by 8 strains increased by 4% ? 18.2%,an average increase of 11.7%;after adding rotifer secretion,the removal efficiency of TOC by 8 strains of bacteria increased by 0.8% ? 12.7%,an average increase of 5.55%.The experimental results of rotifer secretion can improve the removal efficiency of bacteria to organic matter in different degrees,suggesting that rotifer not only affects the growth of bacteria,but also affects the activity of bacteria.(5)Effect of rotifer and rotifer secretion on the biological treatment performance of SBR wastewater.Three experimental groups were set up: rotifer group(group R)with rotifer added to SBR,rotifer secretion group(RS group)with rotifer secretion added,and control group(group C)with no added rotifer or secretion.In the SBR sewage treatment system,the COD,TOC,NH3-N,TN and TP removal efficiency of the R and RS group were significantly higher than those of the control group at 12 hours of operation,of which the COD removal efficiency of the C,R,and RS group 70.4%,79.1%,and 82.5% respectively;during the entire experiment period(12 h-10 d),the pollutant removal efficiency of the three groups were generally similar,among which the COD removal efficiency of group C,group R,and group RS were 89.8%,92.4%,92.8%.It shows that in the early stage of SBR operation,that is,when the biological treatment performance of the reactor is not at a high level,the presence of rotifer or the addition of rotifer secretion can significantly improve the biological treatment performance;while the biological treatment performance is at a high level,the presence of rotifer or the addition of rotifer secretion has a limited effect on improving the biological treatment performance.The removal effects of pollutants in group R and RS are basically similar,suggesting that the beneficial role of rotifer in biological treatment is mainly in the form of rotifer secretion.(6)The influence of rotifer and rotifer secretion on the microbial community structure.The optimized sequence and coverage analysis results of the microbial sequencing results of the activated sludge samples of groups C,R and RS show that the amount of sequencing data is sufficient to detect enough species,the sequencing depth is high,and the sequencing results can represent the real situation of microbial community structure in activated sludge.The results of dilution curve analysis,abundance grade curve analysis and Venn diagram(VENN)analysis of the samples in groups C,R and RS show that the three groups of samples have similar trends and amplitudes,and the three groups of samples had similar uniformity,and the differences in the types of microorganisms among the three groups of samples were small.The analysis results of Chao index,Ace index and Simpson index in the activated sludge samples all showed that the richness of the microbial communities in the three groups of samples was relatively similar.The Shannon indexes of the samples in groups C,R and RS was 4.83,4.87 and 4.97,respectively,indicating that the three groups had similar biodiversity,and the diversity in group R and RS was slightly better than that in group C.The results of microbial relative abundance analysis of the activated sludge samples of group C,group R and group RS shows that the composition of the dominant species in the three groups at the phylum,class,order,family and genus levels are all similar.The above results generally indicate that at the end of the SBR operation group C,R and RS have similar microbial community structures,and some microbiological indicators of group R and RS are slightly better than group C.Comparing the characteristics of pollutant removal efficiency between the three groups in the late SBR operation and the characteristics of the microbial community structure between the three groups at the end of the operation,it shows that the sewage treatment efficiency and the composition of the microbial community structure are highly consistent. |
PDF Full Text Request