The Research Of Nutrient Recovery And Energy Utilization Mechanism In High-strength Organic Wastewater By Algal-bacteria Symbiosis

Microalgae wastewater treatment can effectively achieve the recovery of nutrients and energy utilization in wastewater,while the co-cultivation of microalgae with bacteria has great promise to replace conventional biological treatment systems that use a single microorganism.Building a reasonable system of algae-bateria symbiosis is the key to achieving enhanced wastewater treatment performance.In this paper,from the nutritional utilization and energy recovery standpoint,the anaerobic fermentation,microalgae cultivation,algae-bateria symbiosis and other techniques were used to explore the treatment performance and mechanism in wastewater treatment.The sequential process of anaerobic fermentation followed by microalgae cultivation for treating high-strength organic wastewater holds efficient wastewater treatment performance.Pre-sludge heat treatment can control the fermentation process for the production of hydrogen-dominating bigas,the volume fraction of hydrogen in hydrogen-dominating bigas was as high as 54.8%.In the sequential process of hydrogen production fermentation process followed by microalgae cultivation,the removal effiencies of COD,NH₄⁺-N and TP in wastewater could reach 100%,98.3%and 64.2%respectively.And the heat value conversion efficiency?HVCE?for the wastewater could reach 41.2%.According to the results of microbial community analysis,the dominant species in water samples after the sequential process were Stenotrophomonas,Chryseobacterium and Exiguobacterium.Under the conditions of simulated high-strength fermentation wastewater,the wastewater treatment performance under different initial inoculation concentration was explored.When the initial inoculum concentration of microalgae was 0.5 g/L,the removal effiencies of total carbon?TC?in wastewater could reach 55.6%,and the biomass concentration?after three-days cultivation?was 1.93 g/L Based on the consideration of organic compounds removal,biomass accumulation and operation cost,0.5 g/L was selected as the optimum initial inoculum of microalgae for the high-strength fermentation wastewater treatment.Exiguobacterium aurantiacum, Stenotrophomon asacidaminiphila and Chryseobacterium scophthalmun were used to construct three co-culture systems for the high-strength fermentation wastewater treatment.The co-culture of Chlorella sorokiniana L3 and Chryseobacterium scophthalmun achieves the best wastewater treatment performance.Compared with the Chlorella sorokiniana L3 system,the removal efficiencies of COD,NH₄⁺-N and TP in wastewater under the co-culture system were increased by 21.7%,17.8%and 22.6%,respectively.At the same time,1.61 g/L COD equivalent,91.5 mg/L NH₄⁺-N and 131.7 mg/L TP were removed from the fermentation wastewater.The results of energy analysis showed that the optimal energy conversion efficiency of was obtained when co-culture Chlorella sorokiniana L3 and Exiguobacterium aurantiacum.The total energy conversion efficiency?TECE?could reach 70.7%.which was significantly higher than 38.8%of the single-algal system.The results of nutrient utilization and energy analysis under the algae-bateria symbiosis showed that the mechanism for the enhanced wastewater treatment performance is the nutrient exchange between carbon dioxide and oxygen.The effects of Chryseobacterium scophthalmun on the accumulation of carbohydrate in Chlorella sorokiniana L3 were also studied.The nitrogen-deficient culture environment promoted the accumulation of the carbohydrate in microalgal cell,and the maximum cell carbohydrate content of Chlorella sorokiniana L3 was increased from 35.3%to 61.9%.It is nitrogen-deficiency culture conditions that result in high-yielding carbohydrate in microalgal cells.The addition of growth-promoting bacteria only promoted the utilization of C,N nutrients and biomass accumulation,but had no significant effect on the accumulation of carbohydrates.