| Energy shortage has become an important problem facing by the world today;development and utilization of renewable energy are the basic way to solve the problem,especially anaerobic digestion.Municipal solid waste,especially the kitchen waste due to its rich Energy is one of the important material bases for human and economy social development.Lots of negative effects on environment are brought by the continued consumption of traditional petrochemical energy.Facing the limited reserves of traditional energy sources and increasingly serious environmental problems,the development and utilization of renewable energy and improvement of anaerobic digestion efficiency have become a hot issue in the current study.The energy development potential of agricultural waste as raw material could not be ignored with the development of global intensive animal husbandry in full swing.The main research object is common agricultural municipal waste in this study.First of all,determine the optimum temperature,initial pH range of common stalks and livestock manure in anaerobic digestion.Anaerobic digestion of the mixed raw materials,which were combined according to the characteristics,was optimized in different temperature and initial pH values to get the optimum temperature,initial pH and mixing ratio of high efficient anaerobic digestion.Secondly,effects of each index on methane production were explored by principal component analysis of monitoring indexes in different periods of temperature drop and pH control co-digestion.Finally,in order to improve the efficiency of co-digestion and reduce the fermentation input,the optimal temperature drop fermentation temperature and pH value were obtained.The conclusions are as follows:1.There are significant differences in organic matter anaerobic digestion efficiency in different temperatures.High fermentation temperatures do not mean the fermentation time is short.Among the common agricultural wastes,the cow manure optimum fermentation temperature range was high,which was more suitable for thermophilic fermentation.But swine manure optimum fermentation temperature range was moderate,which was more suitable for mesophilic fermentation.Maize has the fastest fermentation speed.Rice has the argest methane production potential.At the same fermentation temperature,the type and proportion of the substrate affect the length of the stagnation period,which resulted in the difference of total biogas production.In the anaerobic co-digestion,the optimum fermentation condition of swine manure/maize stalk was mesophilic fermentation,and that of cattle manure/maize stalk was thermophilic fermentation.There was no significant difference in methane production rate between the two co-digestion substrates when the fermentation goes into the methane production stage.During the fixed fermentation time with the same digestion temperature,2.The initial pH value will significantly affect the start-up time,peak duration and peak value of the anaerobic digestion depending on the substrate characteristic.The results showed that the pH value resilience of cattle manure was the best,the VFA/alkalinity ratio remained stable and was not higher than 0.4,which showed that the fermentation substrate with cattle manure had better buffer performance and made stable fermentation system.3.In the early stages of fermentation,the highest positive/negative correlations of cumulative methane production are temperature and C/N ratios respectively.The manure content in the middle stage of fermentation was proportional to the resilience of pH.There was a positive correlation between manure content and ammonia nitrogen accumulation.Compared with the thermophilic anaerobic co-digestion,mesophilic condition was more suitable for the methanogenic phase,and ammonia nitrogen accumulation was closely related to the C/N of fermentation substrate.Based on the principal component synthesis model score of each treatment,the first three highest scores of cattle manure/maize stalk and swine manure/maize stalk treatments were: 55?cattle manure/maize stalk 70:30-8.0,35 ?cattle manure/maize stalk 70:30-8.0,55 ? cattle manure/maize stalk 70:30-7.5,35 ? swine manure/maize stalk 70:30-8.0,35?swine manure/maize stalk 70:30-7.5,and 55?swine manure/maize stalk 70:30-8.0,respectively.According to the three-factor regression equation model of manure/stalk,when the content of swine manure was 47.98% and the initial pH value was 8.0,the maximum methane production(193.74 m L/g VS)was obtained by swine manure/maize stalk mesophilic(35?)anaerobic co-digestion;when the content of cattle manure was 56.85% and the initial pH value was 7.5,the maximum methane production(205.11 mL/g VS)was obtained by cattle manure/maize stalk thermophilic(55?)anaerobic co-digestion4.The effect of temperature drop on anaerobic digestion was determined by the characteristics of substrate.The promotion/inhibition effect of temperature drop on anaerobic co-digestion was not increased with the increase of manure content.In a certain range of manure/straw,the promotion/inhibition of temperature drop could reach the maximum.During the thermophilic anaerobic co-digestion,appropriate range of temperature drop could effectively reduce the concentration of ammonia in the substrate.The temperature drop test of each raw material showed that the effect of temperature drop on swine manure/maize stalk anaerobic co-digestion has been promoted.In a certain range of temperature drop can effectively increase and extend the number and duration of biogas production peak,improve pH resilience,enhance the cumulative methane production;cattle manure/maize stalk fermentation was more sensitive to the temperature drop,which the pH value could not stay stability.5.Characteristics determine the sensitivity of the substrate on pH control.It is possible to shorten the fermentation stagnation period and fermentation cycle,increase the biogas yield,reduce the energy consumption and make reasonable use of resources by adjusting the pH value of the fermentation matrix within a reasonable range.When the C/N ratio was high,the pH control effectively suppressed the increase of ammonia nitrogen concentration;with the decrease of the C/N ratio,the effective effect of pH on the concentration of ammonia nitrogen was significantly reduced.Alkaline fermentation substrate was one of the ways to increase methane yield and achieve higher methane production.6.Both temperature drop and pH control will significantly affect the cumulative methane production.In the production of methane efficiency,to ensure the smooth progress of fermentation and reduce the consumption of energy consumption under the premise of partial alkaline cooling regulation was the best choice.Alkaline fermentation substrate and small temperature regulation of temperature drop are the best choice,because the treatment could improve methane production efficiency,ensure the smooth progress of fermentation and reduce the consumption of fermentation energy.The optimum experimental results show that the maximum unit methane yield of 279.40 m L/g VS was obtained by adjusting the pH value of 7.65 and the drop temperature of 9?.Anaerobic co-digestionprocess operation norms of cattle manure/maize stalk on temperature drop and pH control are developed for the actual production to provide a reference basis. |
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