| Microalgae culture has many problems such as low biomass conversion efficiency,difficult harvest and large capital investment,which seriously hinder the large-scale production of microalgae culture.In recent years,microalgal attached culture and the construction of algae-bacteria cooperative system to improve microalgal biomass and wastewater treatment efficiency have attracted wide attention.The attached culture can solve the problems of high water consumption and difficult harvest of suspended culture,and algae-bacteria collaboration can improve microalgal biomass and effectively absorb nutrients in wastewater,which has good economic benefits.The purpose of this study was to reduce the production cost of microalgae and improve the biomass of microalgae.Beer wastewater was used as the medium to study the effects of different forms of Paenibacillus xylanexedensand Azotobacter beijerinckiion the growth of Chlorella pyrenoidosa and the purification effect of beer wastewater in the attached culture.This study provides a new method for improving microalgae biomass coupled wastewater treatment technology based on algae-bacteria collaboration,which is conducive to the further development of microalgae industry.The main research results are as follows:(1)Effects of different forms of P.xylanexedens and A.beijerinckii on C.pyrenoidosa growth and wastewater treatmentThe effects of different forms of P.xylanexedens,A.beijerinckii(supernatant of bacteria,live bacteria,broken bacteria)on C.pyrenoidosa growth and wastewater treatment were studied.The results showed that the broken P.xylanexedens had the most significant effect on the biomass and protein content of C.pyrenoidosa.Compared with pure culture of C.pyrenoidosa,the biomass and protein content of C.pyrenoidosa increased by 125.67% and 25.04%,respectively.The removal rates of COD,PO43-,NH4+-N in wastewater increased by 23.57%,146.14% and 9.96%,respectively.These results indicated that the intracellular materials of P.xylanexedens were more effective for the biomass improvement and wastewater treatment of C.pyrenoidosa.Similarly,the broken A.beijerinckii had the best growth promotion effect on C.pyrenoidosa.Compared with pure culture,the biomass and protein content of C.pyrenoidosa increased by 71.8% and 28.2%.Different from the P.xylanexedens,the combination of C.pyrenoidosa and living A.beijerinckii had the best effect on improving the wastewater treatment efficiency,and the removal rates of COD,PO43-and NH4+-N were increased by 20.8%,18.5% and 8.9%,respectively,compared with the pure culture of algae.(2)The effects of algae-bacterial collaboration on C.pyrenoidosa growth and wastewater treatment efficiency in different culture modesThe biomass of C.pyrenoidosa in attached culture mode was higher than that in suspended culture mode,and the addition of bacteria enlarged the difference between the two culture modes.The combined biomass of C.pyrenoidosa + P.xylanexedens,C.pyrenoidosa + P.xylanexedens and C.pyrenoidosa + broken P.xylanexedens in attached culture mode was 1.4 times,4.5 times and 2.1 times of that in suspended culture mode,respectively,while the biomass of C.pyrenoidosa pure culture mode was only 1.04 times of that in suspended culture mode.The protein content of algae cells in the attached culture mode was significantly higher than that in the suspensded culture mode,and the protein content of algal + broken P.xylanexedens in the attached culture mode was the highest,reaching 78.4%,which increased by 12.32% compared with the suspended culture mode in the same conditions.The removal rate of wastewater in the attached culture mode is higher than that in the suspended culture mode.The removal rates of COD and PO43-in the attached culture mode are 83.3% and 86.1%,respectively,which are 39.77% and 22.65% higher than that in the suspended culture mode.The above results indicated that the addition of different forms of P.xylanexedensnot only improved the biomass and wastewater treatment efficiency of C.pyrenoidosa,but also expanded the differences between the two culture modes,which indicated that the synergic effect of algae and bacteria in the attached culture mode was stronger than that in the suspended culture mode.(3)Stress tolerance of attached culture modeThe physiological and biochemical indexes of C.pyrenoidosa cells were investigated by increasing the concentration of ammonia nitrogen.When the concentration of ammonia nitrogen reached 500 mg/L in suspended culture mode,the growth of C.pyrenoidosa began to stop,and the contents of lipid,protein and carbohydrate decreased with the increase of ammonia concentration.In the attached culture mode,the growth of C.pyrenoidosa began to slow down when the concentration of ammonia nitrogen reached 2000 mg/L,and the content of biochemical components of C.pyrenoidosa in different ammonia gradients was higher than that in suspended culture.This indicates that C.pyrenoidosa can tolerate higher concentration of ammonia nitrogen in attached culture mode.The broken P.xylanexedens were added to the two culture modes.It was found that in the suspended culture mode,C.pyrenoidosa could grow normally in the wastewater with an ammonia nitrogen concentration of 500 mg/L,and the biomass of C.pyrenoidosa began to decline when the ammonia nitrogen concentration reached 1500 mg/L.In the attached culture mode,C.pyrenoidosa can grow normally in the wastewater with ammonia nitrogen concentration of 2000 mg/L,and the protein content of C.pyrenoidosa is significantly increased to 57.64 mg/L.This indicated that the algae-bacteria collaboration could further improve the stress tolerance of C.pyrenoidosa,and the algae-bacteria collaboration attached culture mode had the highest stress tolerance. |
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