| With the development of biogas engineering in China,a considerable amount of anaerobic fermentation broth was produced,which is a kind of organic wastewater with high ammonia nitrogen content.Biological treatment is the most common method used to treat and reuse this type of wastewater.The symbiotic system of microalgae and nitrifying bacteria community can complement the shortcomings of each other and treat anaerobic fermentation broth efficiently,which has several advantages,including reducing energy consumption,enhancing the recovery and utilization of microalgae,and improving treatment efficiency.The paper aimed to explore the mechanism of wastewater treatment using the symbiotic system of microalgae and nitrifying bacteria community,with the goal of improving efficiency.Firstly,important conditions such as initial algal-bacteria ratio,light time,light intensity,and aeration intensity were investigated to evaluate their impact on the treatment efficiency of the system.Then,under optimized conditions,a bacterial-algal symbiotic SBR biofilm system was constructed,and its treatment efficiency was explored.The mechanism of microbial population change was analyzed to provide theoretical and technical support for the resource and harmless treatment of anaerobic fermentation broth.The specific experiments and conclusions are as follows:(1)After comparing the efficiency of the activated sludge system,pure algae system,and algae-bacteria 1:1 combination system in treating anaerobic fermentation broth,the results showed that the algae-bacteria system exhibited an aggregation and binding phenomenon,promoting the growth of bacteria and algae in the system.This resulted in the best removal efficiency for ammonia nitrogen and total nitrogen,with removal rates of70.80% and 40.12%,respectively.Additionally,the COD removal rate was 92.78%,which was higher than that of the pure algae system.The removal effect of phosphorus was also better than that of the activated sludge system.Three-dimensional fluorescence characterization of the soluble organic compounds in the three systems showed that the EPS(Extracellular Polymeric Substance)was mainly composed of tyrosine proteins,tryptophan proteins,and soluble microbial metabolites.The total EPS and PN/PS values of the algae-bacteria system showed an upward trend in the three stages,indicating that the algae-bacteria binding would promote the production of EPS among microorganisms,and the coagulation performance and system stability between microorganisms continued to improve.(2)The environmental factors of the algae-bacteria system were investigated.The different initial algae-bacteria ratios had little effect on the removal of ammonia nitrogen and COD in the system,while the removal of orthophosphate mainly depended on the assimilation of microalgae;the growth and removal efficiency of the algae-bacteria system increased with the increase of the set lighting time,but there was no significant difference in various indicators between the lighting time of 12 hours and the light time of 16 hours;the growth and removal efficiency of algae-bacteria systems with light intensity between4000 and 6000 Lux are significantly better than those with light intensity of 2000 Lux and without light.When the light intensity is higher than 4000 Lux,there is no significant difference in the growth and removal efficiency of the system.The growth and pollutant removal efficiency of algae-bacteria systems with aeration intensity between 400-600 m L/min are significantly better than those with aeration intensity of 200 m L/min and without aeration,and there is no significant difference between the growth and pollutant removal efficiency of systems with aeration intensity of 400 m L/min and 600 m L/min,with COD removal rates of 98.40% and 95.96%,and ammonia nitrogen removal rates of84.53% and 84.83%,respectively.In combination with the issues of microalgae loss and energy consumption in the SBR system,the optimal conditions provided for subsequent experiments are algae-bacteria ratio of 1:2,daily illumination time of 12 hours,illumination intensity of 4000 Lux,and aeration intensity of 0.4 vvm.(3)Based on the aforementioned conclusions,the algae-bacteria symbiotic SBR biofilm system was constructed to investigate its treatment efficiency.The results demonstrated that the algae-bacterial biofilm system exhibited the most efficient removal of ammonia nitrogen,total nitrogen,and orthophosphate.At the end of the experiment,the removal rate of ammonia nitrogen had reached 99.22%.All systems including the activated sludge system,algae-bacteria suspension system,and algae-bacteria biofilm system had a satisfactory COD removal efficiency,with an average removal rate exceeding 97%.The metagenomic sequencing results at the phylum level indicated that the addition of microalgae and fillers helped maintain the diversity and stability of the microbial community structure.The enrichment of nitrifying bacteria communities was observed,and the algae-bacteria biofilm system was suitable for the growth of various bacterial communities.At the genus level,the genus Alicycliphilus with the highest abundance at the end of the algal-bacteria suspension system experiment could promote microbial flocculation and biofilm formation during stable growth,which is conducive to microalgae sedimentation and algal and bacteria growth.The environment of the algae-bacteria system was more suitable for the growth of Comamonas(AOB),and the relative abundance of Nitrosomonas and Nitrospira increased,indicating that the biofilm was more conducive to the enrichment of nitrifying bacteria(AOB and NOB).The main reason for the accumulation of nitrite nitrogen in the SBR system experiment was the inhibition of NOB.Figure [65] table [6] reference [97]... |
PDF Full Text Request