Optimization Of Preparation Technology Of Bacteria And Algae Immobilized Pellets And Research On Their Effect On Biogas Slurry Purification

The booming pig industry has led to the continuous increase in the production of biogas slurry in pig farms,and this poses a serious threat to the surrounding environment.So,biogas slurry recycling is an inevitable choice to realize sustainable development of aquaculture industry.The use of microalgae and bacteria in the treatment of biogas slurry has been widely concerned by researchers,but the free bacteria and algae in the treatment of biogas slurry has the disadvantage of easy loss and difficult to collect,and the application of immobilization technology of bacteria and algae can solve this problem.In this paper,the pig farm biogas slurry was selected as the research object,and Chlorella DTG5,Arthrospore sp.A2-2,Bacillus subtilis Y28,Bacillus licheniformis Y26,and Pseudomonas aeruginosa LG2-2 were selected as test materials.By optimising the preparation conditions of the immobilised pellets,the microalgae and bacteria with better purification effect on the biogas slurry were screened out,the differences in the purification capacity of different bacteria and algae co-culture systems on the biogas slurry were analysed and the effectiveness of the immobilised pellets of bacteria and algae for reuse in the methane was assessed.The main findings are as follows:1.The pelletizing conditions of the immobilized pellets were optimized,and the scavenging effect of ammonia nitrogen（NH₄⁺-N）in the biogas slurry was used as the evaluation index to conduct orthogonal tests and single factor analysis tests,and the optimal parameters of the immobilized pellets were determined as:10%sodium alginate（SA）,3%Ca Cl₂,cross-linked at room temperature for 12 h,the diameter is about 0.45～0.55 cm.2.The microalgae suitable for growing in biogas slurry and their optimum dilution ratio of biogas slurry were determined.The results showed that Chlorella DTG5 had the highest biomass,and its relative growth rate was significantly higher than Chlorella DTG3,Desmodesmus DTY2,Chlorella vulgaris（CV）and Chlorella proteinosa（CP）（P<0.05）.The optimum concentration of biogas slurry dilution of algal strain DTG5,the contents of ammonia nitrogen（NH₄⁺-N）,total nitrogen（TN）,total phosphorus（TP）and chemical oxygen demand（COD）were 123.81±2.09 mg/L and 217.24±2.21 mg/L,9.06±0.15 mg/L,511.03±40.23 mg/L.3.The free DTG5 and immobilized DTG5 were transferred to 4-fold diluted biogas slurry for cultivation.The treatment effect on the biogas slurry showed that the free DTG5 had better removal effect on TN and COD.Immobilized DTG5 had a significant effect on TP,and there was no significant difference in the removal rate of NH₄⁺-N between the two.4.Arthrospore sp.A2-2,Bacillus subtilis Y28,Bacillus licheniformis Y26,and Pseudomonas aeruginosa LG2-2 were freed and immobilized respectively,and then transferred to 4-fold diluted biogas slurry for culture.The results showed that the immobilised bacteria were more effective than the free bacteria in purifying the biogas slurry.The ability of the four bacteria to purify biogas slurry from high to low is A2-2,Y28,Y26,LG2-2.Therefore,A2-2 and Y28 were selected for the next step of co-culture with Chlorella DTG5.5.Two co-culture systems were constructed for Bacillus subtilis A2-2 and Chlorella DTG5（A2-2-D）and Bacillus subtilis Y28 and Chlorella DTG5（Y28-D）.The free bacteria and algae system and the bacteria and algae immobilized pellets were cultured in the biogas slurry respectively.The results showed that the free A2-2-D and Y28-D bacteria and algae systems gradually reduced the nitrogen and phosphorus content in the biogas slurry,the A2-2-D and Y28-D immobilized beads can quickly reduce nitrogen and phosphorus content,which can shorten the culture time by two-thirds.After 6 d of incubation,the removal of NH₄⁺-N,TN and TP was increased by31.36%,39.69%and 62.67%for A2-2-D immobilized pellets compared to the free A2-2-D system,respectively.The immobilised Y28-D pellets increased the removal of NH₄⁺-N,TN and TP by 35.2%,41.8%and 57.5%respectively compared to free Y28-D.10 m L bacterial solution+10 m L algae solution/100 m L biogas slurry is the best embedding volume for immobilized beads.6.The A2-2-D and Y28-D immobilised pellets were collected after use and transferred to new biogas slurry again,and this was repeated several times.The results showed that the bacteria and algae immobilized pellets could be recycled 3 times in the biogas slurry.After the fourth culture,the immobilized pellets softened,ruptured,and the bacteria and algae spilled out,so they could not be recycled again.In summary,the optimal parameters of the immobilized pellets were determined,and the dominant algal strains and strains in the biogas slurry were screened to construct a bacterial-algal co-culture system.The bacteria and algae immobilized pellets could improve the removal rate of NH₄⁺-N,TN and TP in biogas slurry,shorten the treatment period,and can be reused 3 times.The above research results show that the use of bacteria and algae immobilization for resource utilization of biogas slurry in pig farms is of practical significance.