| Livestock and poultry farming,as an important part of my country’s agricultural economy,but a large amount of aquaculture wastewater rich in nitrogen and phosphorus cannot be effectively treated due to high treatment costs and poor results.Emissions have brought serious pressure to the ecological environment and become an important restrictive factor affecting the sustainable development of my country’s livestock and poultry breeding industry.The purpose of this paper is to construct a chlorella-bacteria immobilized biofilm system,and to investigate the removal rates of nitrogen,phosphorus and chemical oxygen demand（COD）in pig wastewater.The inoculation ratio of algae,the initial inoculation amount of algae and the order of adding algae to the purification effect of swine wastewater were optimized to obtain the best algae-bacteria co-cultivation system;Amplify the treatment,optimize the control parameters such as temperature and renewal rate of the semi-continuous treatment process,and explore the algal-bacterial interaction mechanism by changing the microbial community and metabolites in the algal-bacterial biofilm system.The specific research contents and results are as follows:（1）Construction of co-culture system of algal bacteria and optimization of culture conditionsThe effects of inoculation ratio,initial inoculation amount and addition sequence of algae on chlorella growth,p H,total inorganic carbon（TIC）and wastewater pollution index removal in the co-culture system were investigated,and the optimal construction conditions of co-culture system were determined as follows:inoculation ratio of algae is1:1.The inoculation density was 0.792×10~7/m L,and activated sludge bacteria were inoculated first,and chlorella（B1C）was inoculated 24 h later.Under these conditions,the biomass of Chlorella reached 5.5×10~7/m L.The p H of the co-culture system decreased and remained at 7.0 on the 6th day of culture.Compared with the pure algae system,the TIC of the co-culture system could maintain a higher level.Under the optimal culture conditions,the removal rates of TP,COD,NH4+-N and TN in the co-culture system were 81.3%,52.6%,97%and 78.2%,respectively,which were110.0%,93.96%and 41.12%higher than those in the pure algae group,respectively.Compared with pure bacteria group,it increased by 99.3%,95.33%and53.02%.These results indicate that there exists synergistic promoting effect among algal bacteria.（2）Formation and characteristic analysis of immobilized chlorella-bacteria biofilmsHollow fiber membrane was used as the membrane module,the flow rate of wastewater was set at 1.5 L/min,chlorella and activated sludge bacteria could hang the membrane after 6 days of operation.After 18 days,the thickness of biofilm reached 1.5mm,and the dry weight of biomass was up to 5.74mg/cm.Electron microscopic observation showed that the chlorella on the immobilized algal membrane was spherical with clear outline and bacteria adhered to its surface.（3）Influence of semi-continuous culture on wastewater treatment effectIn a self-designed flat-plate immobilized algal biofilm reactor,the effects of the renewal rate of semi-continuous treatment on the growth of chlorella,the operating parameters of the reactor and the effect of wastewater treatment were investigated.（1）The biomass on the large membrane with the renewal rate decreased,so the experimental group with a renewal rate of 10%had the largest algal biomass,reaching3.27 mg/cm ~2,which were 1.16 and 1.22 times that of the 20%and 30%experimental groups,respectively.（2）The effect of the renewal rate on the p H of the co-cultivation system was not significant.The p H of the experimental group with a high renewal rate（30%）was closer to 7.0;the level of dissolved oxygen（DO）in the system shows that the smaller the renewal rate,the higher the dissolved oxygen level.The DO concentration of the experimental group with a renewal rate of 10%is 8.30 mg/L,which is higher than that of the experimental group with a renewal rate of 30%.15.28%.（3）The experimental groups with different renewal rates showed no significant difference in the removal effects of TP,TN and ammonia nitrogen by the algae-bacteria system,The removal rates reach 59.55%,79%and 99.04%.In terms of the removal effect of COD,the 30%renewal rate experiment has the best effect.The removal rate reaches65.67 mg/L/d,which is 6.13 times and 6.13 times higher than that of the 10%and 20%experimental groups.4.46 times,and the final effluent COD concentration reached 367.41mg/L,reaching the national discharge target.Since COD degradation is often the most difficult index to achieve in the process of wastewater treatment,this study selected a 30%update rate as the best update condition.（4）Influence of the operating temperature of the reactor on the wastewater removal effect（1）From the biomass of algal bacteria on the immobilized membrane,the biomass of the low temperature operation（18℃）was significantly higher than that of the high temperature（30℃）operation group.On the 19th day of culture,the dry weight of the algal bacteria on the membrane reached 3.66 mg/cm 2,which was 1.52 times that of the experimental group at 30℃.（2）The effect of culture temperature on the p H of the system is significantly different.The high temperature operation group is conducive to the growth of bacteria,so the system maintains a lower p H.After equilibration,there was little difference between the two operating temperature groups,and both were maintained at around p H-8.0.（3）The effect of operating temperature on the removal of TP and TN showed that the effect of low temperature operation was better.On the 19th day of cultivation,the removal rates of TP and TN at a temperature of 18°C were 90.96%and 82.04%,respectively,which were higher than those of the experimental group operated at 30℃.22.29%and4.10%higher;the removal rate of NH4+-N has no significant difference between the two groups,both of which are around 96.28%;however,in terms of COD removal effect,the removal rate of the 30°C operating group（T30）reached the highest of 81.41%,a high The output of T18 experimental group was 24.27%,and the effluent concentration reached215.98 mg/L.（5）Changes in the microbial community structure of immobilized algal biofilmsAlpha diversity index analysis was performed on bacteria on algal biofilms at different renewal rates and temperatures.Compared with only adding activated sludge,the biofilms with Chlorella addition had higher species biodiversity and uniformity The presence of biofilm effectively increased the microbial community diversity of the reactor.Using high-throughput sequencing technology to compare the similarity and difference of algal biofilm microbial community composition,the results show:（1）Proteobacteria,Bacteroidetes,Actinomycetes,Cyanobacteria and Firmicutes were the main dominant bacterial phyla in the bacterial community composition of algal biofilms.Among them,the richness of Proteobacteria under the 30%renewal rate was63.11%,which was 24.18%and 17.96%higher than that of the 10%and 20%renewal rate systems,respectively,and the richness of Green Bay increased with the increase of the renewal rate.The community analysis of bacteria on algal biofilms at different temperatures showed that the addition of Chlorella in the second stage significantly affected the abundance of Proteobacteria and Bacteroidetes,and the temperature significantly affected the dominant genus of algal biofilms（P<0.05）.（2）The results of bacterial community function prediction show that the relative abundance of metabolic functions is the largest among the primary functions.The secondary metabolic functions show that the functions are mainly concentrated in carbohydrates.Membrane transport in metabolism and amino acid metabolism and environmental information processing.Summary,the synergistic effect between algae and bacteria is used to remove nitrogen and phosphorus from pig wastewater,and convert nitrogen and phosphorus in wastewater into nutrients for microalgae.While the wastewater is discharged up to the standard,the resource utilization of microalgae cells can be realized.To achieve the effect of turning waste into treasure,the research of this paper can provide an important reference for the utilization of synergy between algae and bacteria to treat livestock and poultry wastewater. |
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