Analysis Of Microbial Diversity In Biogas Slurry Treatment Systems And Cultivation Of Desmodesmus Sp.PW1 In Sewage

China's livestock industry has progress rapidly over the years,the arbitrary discharge of livestock and poultry breeding wastewater without proper treatment has posed serious threats to the environment.The swine wastewater can be cleaned with biogas after anaerobic fermentation,but the fermented biogas slurry still contains a large amount of inorganic salts such as nitrogen and phosphorus as well as organic matter.The microbial community composition and dynamic changes in the biogas slurry treatment systems are great significant for the stable operation of the sewage treatment pond.Biochemical treatment engineering research is usually designed and carried out at a macro level,and the wasteater treatment systems can be regarded as an ecosystem from an ecological point of view.It is of great theoretical and application value to conduct in-depth study at the molecular level through some microbial molecular ecology research methods,which has critical reference significance for understanding the biochemical reaction nature of pollutants and the analysis of various useful microorganisms in the degradation process of pollutants.Therefore,this paper takes samples from five biochemical reaction pools in different seasons,such as summer and winter,and the composition of dominant bacteria in the wastewater treatment pool systems under different seasonal conditions were studied by means of microbial diversity spectrum sequencing analysis.The results showed that the dominant flora of each biochemical treatment reaction pool were detected,as Proteobacteria,Cyanobacteria,Bacteroidete,Chloroflexi,Firmicutes,Actinobacteria and Chlorophyta by establishing 16S rDNA and18S rDNA gene libraries for the samples.Cryptomycota were gradually to be the major bacteria in the aerobic pool 2?hy2?and oxidation pool?yt?during winter sampling.The above studies show that the microbial species of the slurry treatment systems are very rich,and the microbial groups play a major role in a certain reaction stage and change dynamically.At present,there have been lots of researches on the utilization of microalgae to remove nutrients such as nitrogen and phosphate from wastewater and eutrophic water body,and the research content and depth are relatively mature.However,the concentration of pollutants in the biogas slurry is extremely high,and most algae cannot adapt to this harsh system.In this thesis,a strain of algae was isolated and purified from livestock culture wastewater,and it was named as Desmodesmus sp.PW1,which has strong ability to treat sewage wastewater.Desmodesmus sp.PW1 is a large submerged green algae,which can be visibled to the naked eye after the process of aggregation and has strong reproductive ability.Due to the naturally subsidence at the bottom of the culture medium during the growth of this algae.therefore,it is easier to separate the algae cells from the purified water body by simply concentrating the deposited high-density algal cells and the algae slurry containing a part of medium,which greatly reduces the steps and the cost of this algae to be separated from the water body after the treatment of biogas slurry.The Desmodesmus sp.PW1 effects of purifying wastewater under the conditions of laboratory shake flask culture were studied.Furthermore,bioactive substances of Desmodesmus sp.PW1 were harvested from BG-11 medium and biogas slurry medium to evaluate the resource utilization value of this algae in the wastewater treatment.To investigate whether the Desmodesmus sp.PW1 has the possibility of being used for large-scale wastewater treatment,it was inoculated into a plate photobioreactor to study the effect of this algae stain on the removal of nutrients in the sewage.This thesis are from the following aspects and the the main results as follows:1.To study the dynamic changes of microbial community structure and composition in the five biochemical pools of wastewater treatment systems under different seasonal conditions,five biochemical reaction pools in summer and winter were sequenced for the microbial diversity analysis.Results displayed that?1?there were significant differences in microbial community and species abundance in the five wastewater ponds under cold and warm seasons.?2?Under two hot and cold conditions,there are small differences in the dominant species of the five biogas slurry treatment systems in the phylum level;while the difference in the genus classification level was obviously.?3?There are a certain relationship between the operation effect of wastewater treatment systems and the distribution of microbial diversity.2.Under laboratory shake flask culture conditions,the removal efficiencies of pollutant?TN;TP;NH₄⁺-N;COD?of biogas slurry and the growth of algae cells were compared when the wastewater concentration of 25%,50%,75%and 100%.The results demonstrated that?1?Desmodesmus sp.PW1 can adapt well to the above four sewages environment and grow rapidly.?2?Desmodesmus sp.PW1 has significant degradation effects on TN,TP and NH₄⁺-N in different concentration of biogas slurry.After 8 days,the highest degradation rate of total nitrogen and ammonium nitrogen has reached 64.8%and 78.4%at the 100%and 25%wastewater.Total phosphorus removal efficiency was up to 92.8%at the 100%wastewater,which was implied that Desmodesmus sp.PW1 has an ideal removal effect on total phosphorus.?3?The COD degradation rate was merely13.8%,which was manifested that the effect of Desmodesmus sp.PW1 on the removal of organic compounds in wastewater was little and it was need to cooperate with other heterotrophic microorganisms.Further,the nutritional value of the Desmodesmus sp.PW1 powder harvested from normal medium?BG-11?and biogas slurry were analyzed.The protein,polysaccharide,lipid,Chlorophyll and other indicators of the algal powder in the two culture environments were determined to evaluate the resource utilization value of he Desmodesmus sp.PW1.The results revealed that PW1 was more likely to accumlate lipid in the biogas slurry;while it was more easier to produce proteins and chlorophyll when inoculated in normal medium.There was no significant difference in polysaccharide content of PW1 grown in both media.3.To investigate the possibility of using the isolated algae Desmodesmus sp.PW1 in the large-scale treatment of wastewater,the purification effects of this strain in biogas slurry were studied by using plate photobioreactor.It turned out that Desmodesmus sp.PW1 can grow normally in a flat photobioreactor with a maximum biomass of 1.50±0.02g/L.After 14 days,the removal rates of TN,TP and NH₄⁺-N were 73.7%,60.2%and78.4%,respectively.Therefore Desmodesmus sp.PW1 has the potential to treat wastewater under larger scale conditions.The degradation rates of COD in swine wastewater was consistent with that the results of Desmodesmus sp.PW1 in laboratory condition,which confirmed again that this algae strain had litter effect on the removal of organics matter in biogas slurry.