Construction Of Microalgae-bacteria Co-culture System And The Application On The Biogas Slurry Wastewater Treatment

Livestock and poultry farm wastewater brings about huge pressure on the environment due to the high concentration of nitrogen,phosphorus and COD,which has been an important factor restricting the sustainable development of the aquaculture industry.A/O,A²/O and SBR methods are the technologies that are often used in current organic waste water treatment,but these methods have the disadvantages of poor removal efficiency of N and P,especially NH₄⁺-N,and high cost.Microalgae and bacteria have synergistic effects on wastewater detoxification and integrated utilization as resource through combining aerobic microorganisms'ability to degrade organic matter with the ability of algae to rapidly remove nutrients such as N and P from water using photosynthesis.It has become a new way to treat biogas slurry wastewater and it is also a research hotspot of biological wastewater purification in recent years.In this study,based on the screening of Chlorella vulgaris growth-promoting bacteria,a stable microalgae-bacteria co-culture system was constructed.This system was used to investigate the synergistic effect of algae and bacteria on the treatment of biogas slurry wastewater,and the synergistic mechanism was discussed.The biological treatment method of wastewater was established to provide an important reference for wastewater detoxification and integrated utilization as resource.The specific research contents and results are as follows:?1?Isolation and identification of commensal bacteria and screening of microalgae growth-promoting bacteria?AGPB?.6 bacteria were separated by flat-plate separation method from wastewater treated by C.vulgaris for 15²0 d and were identified by 16S rDNA sequencing technology.They were highly similar to Pseudomonas alcaliphila,Exiguobacterium,Bacillus amyloliquefaciens,Bacillus subtilis,Bacillus licheniformis and Bacillus tequilensis.The isolated six strains were inoculated into the sterilized Chlorella vulgaris biogas slurry culture solution respectively.The concentration of chlorophyll-a in algal cells in the microalgae-bacteria co-culture system were measured to screen the microalgae growth promotion bacteria?AGPB?.The results showed that all the six bacteria can promote the growth of C.vulgaris.In the C.vulgaris—Microbacterium,C.vulgaris—Bacillus licheniformis and C.vulgaris—Pseudomonas co-culture system,the bacteria could proliferate stably,and the concentration of chlorophyll-a in algal cells were significantly higher than that in the other three algal—bacteria systems.It showed that these three bacteria have better growth promoting effect on C.vulgaris.These three microalgae-bacteria co-culture systems were used to treat biogas slurry wastewater.The results showed that C.vulgaris—Microbacterium and C.vulgaris—Bacillus licheniformis co-culture systems had better removal effects on nitrogen,phosphorus and COD in biogas slurry,and the removal rates were 64.4%?78.2%?73.3%and 62.1%?83.7%?60.9%respectively.?2?Selective construction of microalgae-bacteria co-culture systemC.vulgaris—Microbacterium co-culture system was selected to investigate the effect of different inoculation proportion of microalgae and bacteria on the treatment of biogas slurry wastewater.The results showed that under the same culture conditions,C.vulgaris had the largest biomass when the inoculation ratio of C.vulgaris to Microbacterium was 1:2.The maximum chlorophyll-a concentration reached 2.373 mg/L on the 6th day,and the algal cell concentration reached 2.36×10⁷cells/mL on the 9th day,which was significantly higher than other proportional combinations.The C.vulgaris—Microbacterium system at this ratio had the best removal efficiency of TN,NH₄⁺-N,TP and COD,and the highest removal rates were53.8%,58.4%,79.6%and 70.1%respectively.The effects of single algae-single bacteria and different combinations of single algae-complex bacteria co-culture system on biogas slurry treatment were investigated.The results showed that C.vulgaris—Microbacterium,C.vulgaris—Bacillus licheniformis and C.vulgaris—Microbacterium/Bacillus licheniformis?the ratio of two bacteria=1:1?co-culture systems had no significant difference in the growth of C.vulgaris and the treatment effect of biogas slurry wastewater.The removal rates of TN,NH4+-N,TP and COD in different co-culture systems were more than 50%,60%,80%and 65%,respectively.?3?The effect of microalgae-bacteria co-culture system on biogas slurry wastewater treatmentC.vulgaris—Microbacterium and C.vulgaris—Microbacterium/Bacillus licheniformis co-culture systems were selected to investigate the photosynthesis activity of C.vulgaris and the treatment effect on biogas slurry wastewater under the aeration and amplifying culture conditions in a column photobioreactor.The results showed that after 6 days of aeration culture,the photosynthesis activities of C.vulgaris in the two co-culture systems were 1.55 times higher than that in the pure culture system of C.vulgaris,and the highest removal rates of TN,NH₄⁺-N,TP and COD in the biogas slurry wastewater were more than 75%,89%,87%and 86%.The treatment effects were obviously better than that of the triangular flask culture and after the removal of ammonia nitrogen and total phosphorus contents reached the livestock and poultry wastewater discharge standards.It was proved again that there was no significant difference in the biogas slurry treatment between the two microalgae-bacteria co-culture systems?P>0.05?.?4?The synergistic mechanism of microalgae-bacteria co-culture system for biogas slurry wastewater treatmentThe C.vulgaris—Microbacterium co-culture system was selected to investigate the transformation of different forms of nitrogen sources and changes of related metabolic enzyme activities in artificial wastewater system.The results showed that compared with the pure culture system of C.vulgaris,the microalgae-bacteria co-culture system significantly improved the absorption of nitrous nitrogen,nitrate nitrogen,ammonia nitrogen and urea nitrogen in wastewater by 44%,47%,61%and74%respectively.It was found that the order of absorption of different nitrogen sources in the wastewater system has some regulations,and ammonia nitrogen and urea nitrogen were preferentially utilized,followed by nitrous nitrogen and nitrate nitrogen.The activities of nitrate reductase?NR?,nitrite reductase?NiR?,glutamine synthetase?GS?,glutamate synthase?GOGAT?and glutamic acid dehydrogenase?GDH?were determined.The results showed that in the process of microalgae-bacteria co-culture system treating biogas slurry wastewater,NiR and NR had the highest enzyme activities on the 12th day of culture,which were 2 times higher than the initial enzyme activities.GS and GOGTA had the highest enzyme enzyme activities.The activities of the four enzymes in the microalgae-bacteria co-culture system were more than 50%higher than the pure culture system of C.vulgaris.There was no significant difference in GDH enzyme activity between two systems and different culture times.In summary,bacteria may achieve a synergistic effect by increasing the activities of nitrogen-related metabolic enzymes in C.vulgaris.