Anaerobic Co-digestion Characteristics And Microbial Regulatory Mechanism Of Wheat Straw And Swine Manure

To reveal the response mechanism of anaerobic digestion system for straw and livestock manure mixture under different fermentation processes,to explore the characteristics of anaerobic digestion and its key functional microorganisms,to elucidate the response of microorganisms to the environmental conditions,and to identify the key driving factors for the change of community structure and its succession in such processes,this study used a mixture of wheat straw and swine manure as the substrate.Different amounts of magnet powder and ammonia were used to pretreat the wheat straw,and the anaerobic digestion system was operated at different temperatures.The characteristics of the fermentation process and its kinetics,C,N,P content and their stoichiometric ratios,key enzyme activity and microbial community structure were thoroughly analyzed.The main conclusions include:?1?The fermentation process has a significant effect on biogas production efficiency,system self-buffering capacity and stability,most obvious at the high temperature of 55°C.Under the single-factor fermentation process,adding 3.0 g of magnet powder effectively improved the system's buffer capacity and stability,and promoted the conversion to methane from the substrate.A high fermentation temperature of 55°C easily led to inhibition due to the intermediates,and the inhibitory factor is VFA.The synergic fermentation process intensified the inhibition of the intermediates,showing high intermediates concentration,low system stability,and low gas production efficiency.The inhibitory factors were ammonia nitrogen and VFA.The influence of the fermentation process manifested itself in the final production of gas by directly affecting the microbial ecological environment of the fermentation system.?2?The kinetic parameters of the fermentation process can be used to predict the potential of biogas and the fermentation cycle time,so that the fermentation process can be better controlled.The addition of 3.0g of magnet powder significantly increased the gas production potential,promoted the start of the fermentation system and shortened the fermentation period;while 10%ammonia pretreated wheat straw helped to increase the gas production,but extended the fermentation period.A high fermentation temperature of 55°C easily led to irreversible inhibition of the fermentation process.These experimental findings were consistent with kinetic studies.Long stagnation time and low effective gas production time indicated that the inhibition of the fermentation process was irreversible;while low stagnation time and low effective gas production time indicated high gas production efficiency,or conversion of organic matter for methane.High stagnation time and high effective gas production time indicated a lower gas production rate and a longer fermentation period.?3?The fermentation process significantly affected the degradation of C,N,and P,and the appropriate C:N,C:P,and N:P thresholds.All the above mentioned fermentation processes promoted the biodegradation of C,N and P,and the sedimentation of P in the fermentation system,especially at the high temperature of 55°C for the synergic fermentation process.Therefore,as the fermentation proceeded,the N content gradually increased,whereas the C and P contents rapidly decreased.The C:N ratio gradually decreased,and C:P and N:P gradually increased.Due to enhanced inhibition from the intermediates,suitable C:N,C:P,and N:P thresholds decreased at a high temperature of 55°C for the synergic fermentation process.The threshold values varied with different fermentation processes and fermentation time.Therefore,the operating state of the fermentation system can be evaluated by using C:N,C:P,and N:P ratios,or using these ratios for the regulation of the fermentation process.?4?The enzyme activities showed very similar trend under the different fermentation processes,but with different response.The activity of urease,acetate kinase and coenzyme F₄₂₀ gradually decreased,and the activity of alkaline phosphatase gradually increased.The pretreatment of wheat straw with10%ammonia increased the activity of urease,acetate kinase and coenzyme F₄₂₀,and the addition of 3.0g magnetic powder improved the alkaline phosphate activity.Under the synergic fermentation process,the activity of the same enzyme tends to be consistent.The activity of urease,alkaline phosphatase and acetate kinase was increased during the fermentation process.The activity of coenzyme F₄₂₀ is increased in the early stage of fermentation,but inhibited in the later stage of fermentation.The microbial activity and diversity were higher when 3.0 g of magnetic powder was added,or 3.0 g of magnetic powder and 10%ammonia were used to pretreat the wheat straw.A high temperature of 55°C and its synergy with other conditions reduced the abundance of microbial communities.For single-factor fermentation process at the high temperature of 55°C,the community structure had significant time series changes and succession.For synergic fermentation process?55°C?,there occurred significant changes in the fermentation process and its succession,while increasing the relative abundance of microorganisms.The functional groups of methanogen community were Methanoculleus,Methanosarcina and Methanobrevibacter under various fermentation conditions.The fermentation process notes the change of hydrogenophilic microbial community to acetophilic microbial communities.The functional flora of the bacteria are Firmicutes,Bacteroidetes,Spirochaetes,and Proteobacteria.?6?Under the fermentation processes,C is the key factor;the factors driving the changes and succession of the microbial community are different during the fermentation process,and the key factor is C:N.C is the main influencing factor of the fermentation system.It directly influences the system's self-buffering capacity,stability,and the migration and transformation of P,C:P,and N:P by directly affecting VFA.pH is the key factor influencing the enzyme activity and the migration and transformation of P.Under different fermentation processes,the main factors driving the change of microbial community structure and its succession are different:C:N,N:P,and urease for a single-factor fermentation process,and C:N,urease,and coenzyme F₄₂₀ for the synergic process.The main environmental drivers of bacterial community structure change are C:N,urease,and acetate kinase under a single-factor fermentation process,and C:N,urease,and coenzyme F₄₂₀ under the synergic process.This shows that the key indicators of the fermentation processes are different.In practical applications,simple physical or chemical indicators can be used to reflect the operating status and microbial characteristics of complex anaerobic systems,so as to achieve more targeted regulation of the fermentation process.