| In recent years,with the rapid development of industrial and agricultural production,a large number of nitrogen and phosphorus pollutants enter lakes and reservoirs,resulting in eutrophication of water,causing a large number of algae such as cyanobacteria,green algae and diatoms,causing serious damage to the environment.Anaerobic digestion is one of the economic and effective techniques for algae treatment.Anaerobic digestion is one of the economic and effective technologies for algae treatment.However,the application of this technology in algae treatment in China is still insufficient,mainly because one of the main reasons is that the main components of cyanobacteria cell wall are peptidoglycan and colloid,which are difficult to hydrolyze.In addition,the traditional electron transport with hydrogen as the electron carrier is difficult to maintain the acid balance and the stability of methanogenic intertrophic metabolism in the system,resulting in the low anaerobic digestion efficiency.Some studies have shown that the anaerobic digestion of waste water or waste can be promoted in the microbial electrolysis tank.The reason is that the electrode is used as an electron acceptor to enrich the iron-reducing bacteria and promote the decomposition of complex organic matters by anodic oxidation,thus promoting anaerobic digestion.Nano magnetite as a conductor material promotes direct electron transfer between species and improves anaerobic digestion.However,the mechanism of MEC/ nano magnetite anaerobic digestion of microcystis aerulosa by anodizing or accelerating electron transfer between microorganisms has not been elucidated.In this study,an electric field was introduced to investigate the effect of high and low voltage on methane production by anaerobic digestion of microcystis aeruginosa;On this basis,conductor nano magnetite was added to further study the promotion effect and mechanism of nano magnetite on organic decomposition and methanogenesis in anaerobic digestion of microcystis aeruginosa in MEC.The main research results are as follows:(1)In order to explore the promoting effect of high and low voltage on anaerobic digestion of cyanobacteria,carbon brush and carbon rod were placed in the anaerobic digestion reactor as anode and cathode respectively to form a MEC reactor with single chamber methane-producing.The results showed that the cumulative gas production and methane production in group 1.2 V increased by 35.7% and 47.8%respectively compared with the control(no voltage applied),VSS increased by78.95%;The average anode coulombic efficiency of the 1.2 V reactor was increased by 24.9%.Current calculation confirmed that applying voltage to strengthen anodic oxidation decomposes complex organic matters(peptidoglycan and colloid),promotes anaerobic digestion and hydrolysis process,and provides more substrates for methane production.High-throughput analysis revealed that Geobacter was enriched at the anode,and it was confirmed that the electric field could facilitate electron transfer between iron-reducing bacteria and methanogens and promote methanogenesis.2.0 V The cumutive gas production increased by 24.40% and methane production increased by 33.77% compared with the control(1172 m L).VSS removal rate increased by60.71%,which was lower than that of 1.2 V.The reason was that high voltage inhibited anaerobic microorganisms and affected anaerobic digestion effect.(2)The voltage of MEC was set at 1.2 V,and 0 mg/L,20 mg/L,1 g/L and 4 g/L nano magnetite were added respectively to study the effect of nano magnetite on MEC anaerobic digestion of MEC by microcystis aeruginosa.The results showed that the cumulative methane production of the 0 mg/L,20 mg/L,1 g/L and 4 g/L groups were 459.40 m L,579.54 m L,538.41 m L and 419.92 m L,respectively.The cumulative methane production of the 20 mg/L group was 26.15% higher than that of the control group(459.40 m L).The cumulative methane production of the 1 g/L group was 17.20% higher than that of the Control,and the cumulative methane production of the 4 g/L group was inhibited.The effect of methane production was the best in the 20 mg/L,and the average anode coulombic efficiency was increased by11.12% compared with the control group.Current calculation confirmed that nano magnetite enhanced MEC promoted the anaerobic digestion and hydrolysis process,provided a large number of small molecular organic matters for the methane production stage,and promoted methane production.The results of high-throughput microbial sequencing analysis showed that the abundance of suspended sludge Clostridium sensu stricto and Syntrophomona in the 20 mg/L group increased by33.04% and 66.3%,respectively,compared with the control(no nano ganamite);In addition,there are Geobacter and Methanothrix in the sludge on the anode surface,which indicates that the addition of magnet is helpful for direct electron transfer between iron reducing bacteria and methane-producing bacteria,thus promoting decomposition of cyanobacteria organic matter and methane production.The relative abundance of Methanobacterium increased by 12%.Therefore,MEC enhanced by nano magnetite promoted the anaerobic digestion and hydrolysis process as well as the microbial co-trophic metabolic process. |
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