| With the rapid promation of many large-scale pig industries,China’s livestock and poultry breeding industry is also advancing,and the environmental problems are inevitable at the same time.Therefore,a large amount of solid waste and aquaculture wastewater pollution generated in the breeding process have become the main obstacles restricting the sustainable development of the modern aquaculture industry.At present,due to the problems of high organic load,high NH4+-N content,low C/N ratio and large impact load,the wastewater quality is difficult to meet the discharge standard.Therefore,in this study,the pig biogas slurry wastewater was used as a culture medium for algal-bacteria symbiosis,which can not only solve the purification problem of the major pollutants in the wastewater and realize the harmless treatment of wastewater,but also save investment cost for the production of high value-added by-products,finally realizing the resource utilization of wastewater.Firstly,the optimum environmental conditions for the dominant algae strains growing in imulated biogas slurry wastewater were studied.Secondly,activated sludge was added to microalgae system to promote the removal of pollutants in wastewater and stimulate the growth of microorganisms by algae-bacteria symbiotic system,and the optimal type and concentration of organic carbon source were explored.On this basis,the two-stage continuous treatment mode（the first-stage by treatment of algae-bacteria symbiotic,the second-stage by single algae reprocessing）was used to study the purification characteristics of the actual biogas slurry wastewater,so as to provide theoretical and technical support for the actual large-scale treatment.The main results are as follows:（1）Determination of dominant algal species and the study on the optimum environmental conditions for the treatment of simulated biogas slurry wastewaterThe effects of Chlorella sorokiniana and Chlorella vulgaris on the removal of pollutants in wastewater and the growth of microalgae under different wastewater dilution ratios and initial inoculated biomass were investigated.The experimental results showed that Chlorella sorokiniana had the best adaptability under the original concentration of simulated biogas slurry wastewater with the highest biomass accumulation（0.41 g/L）at the initial inoculation amount of 0.4 g/L.For the absorption and utilization of pollutants,the removal of NH4+-N,TN,TP and COD was the highest at the end of the culture,which were 174.89 mg/L,171.36 mg/L,32.39 mg/L and516.50 mg/L,respectively,and the removal rate were 39.28%,39.17%,70.51%and52.37%,respectively.The biomass accumulation of Chlorella sorokiniana was almost twice that of Chlorella vulgaris.Therefore,Chlorella sorokiniana was selected for the next stage of the experiment.（2）Study on the optimum environmental conditions for simulated biogas slurry wastewater treatment by algae-bacteria symbiosis systemThe co-culture system of Chlorella sorokiniana and activated sludge were selected to treat the simulated pig biogas slurry wastewater,focusing on the effects of algae-bacteria inoculation ratio and organic carbon sources on the treatment effect of biogas slurry pollutants.The results showed that the addition of activated sludge was more conducive to the growth of microorganisms and the removal of pollutants in wastewater,and when the ratio of algae to bacteria was 1:3,the biomass concentration and biomass productivity reached 0.54 g/L and 0.11 g/L/d,respectively,and the removal efficency of pollutants was also enhanced,but it cannot meet the wastewater discharge standard.Therefore,the effects of different types of organic carbon source（glucose,starch,sodium acetate and citric acid）and diffrent C/N ratios on the treatment effect of biogas slurry pollutants were demonstrated.When the organic carbon source was sodium acetate and C/N ratio was 30:1,the growth of microorganisms and the removal of pollutants in wastewater were significantly improved.The removal rates of NH4+-N,TN,TP and COD reached 99.12%,98.72%,94.11%and 97.18%respectively,reaching the pollutant discharge standard of the livestock and poultry breeding industry.In addition,in terms of resource utilization of biogas slurry,the contents of lipid,protein and total sugar content were 33.60%,48.09%and 17.31%respectively.（3）Study on the treatment of practical biogas slurry wastewater by algae-bacteria symbiosis systemThe algal-bacteria symbiosis+algae reprocessing system was constructed to carry out two-stage continuous treatment of actual pig biogas slurry wastewater.The biomass accumulation in the actual wastewater by the algal-bacteria symbiosis+algae reprocessing system was 0.96 g/L in the first stage,and the final biomass concentration of the algae system in the second stage was 1.67 g/L.It can be seen that the microorganisms in the system grew well,and the pollutants in the wastewater had a certain degree of purification.In the algal-bacterial symbiosis+algae reprocessing system with optimal C/N ratio,the biomass of 3.01 g/L was accumulated in the first stage by adjusting the sodium acetate concentration,and the biomass of 3.64 g/L was accumulated by algae in the second stage.The algal-bacterial symbiosis+algae system with optimal C/N ratio had better removal effect of pollutants in wastewater than the algal-bacteria symbiosis+algae system,and the final concentrations of NH4+-N,TN,TP and COD were 16.98 mg/L,18.72 mg/L,0.48 mg/L and 263.49 mg/L,respectively,all of which have reached the《Emission Standard of Pollutants for Livestock and Poultry Breeding Industry》（GB18596-2001）.In addition,through microbial community analysis,it was concluded that the dominant species in the algal-bacterial symbiosis system was Acinetobacter（genus level）,while the dominant species of the algal-bacterial symbiotic system with optimal C/N was Corynebaterium（genus level）.The lipid,total sugar and protein contents were higher after adjusting C/N,which indicated that the algae-bacteria symbiosis treatment of actual biogas slurry wastewater had a good resource utilization ability. |
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