Research On Technologies Of Dry Anaerobic Fermentation Based On Regulating Biogas Pressure

Biogas technology is considered to be one of renewable energy research emphases because of two functions: organic waste disposal and clean energy production.Dry anaerobic fermentation,as the core technology of biogas process,has become an important choice for many countries around the world to treat organic solid wastes and produce clean energy.However,it has been limited applied due to mass transfer limitation and high energy consumption.A novel technology based on regulating biogas pressure was proposed as mixing strategy,namely “periodic pressurization by biogas accumulation,intermittent spray to enhance mass transfer,instantaneous biogas release to depressurize”,which is designed to reduce energy consumption of dry fermentation,strengthen mass transfer,improve biogas production and biogas quality,so as to output directly biogas with high methane content in dry fermentation.In this paper,the theoretical analysis on effects of pressure on anaerobic dry fermentation system was carried out.The simulation experiment on self-stirring effects based on biogas pressure regulation was conducted,and the preliminary study on dry anaerobic co-digestion based on pressure regulation was developed.The simulation experiment was carried out with compressed air,systematacially study influence of mixing effect on pressure,relief pressure time and the distribution of gas space.Box fractal dimension was regarded as quantitative evaluation index for mixing effect of materials which reveal the local image structure feature.And two mesophilic fermentation experiment groups were carried out with Giant Reed straw and fruit-vegetable waste co-substrate.The total solids concentration was 15% and 20% respectively.The results were as follows.(1)The microorganisms in anaerobic fermentation has adaptability to pressure change,and metabolism is not affected by high pressure.As a result,dry anaerobic fermentationprocess is not affected within a certain pressure range.According to Henry’s law,the biogas pressure itself can be used for methane in-situ enrichment,producing directly biogas with high methane content.(2)The way “periodic pressurization by biogas accumulation,instantaneous biogas release to depressurize” achieved self-mixing.The fractal dimension linearly tended to increase in pace with gas pressure,namely the mixing effect appeared as pressure increased.It increased by 12.06% when pressure gradually reached at 0.7MPa.The fractal dimension grew with shortening the time and incremental gas pressure,which attained positive peak0.1584 in condition of 0.6~0.8s and 0.3~0.4MPa.The mixing effect was more conspicuous.(3)The technology “periodic pressurization by biogas accumulation,intermittent spray to enhance mass transfer,instantaneous biogas release to depressurize” improved biogas yield and raw materials digestibility,producted 80% methane content biogas directly.The max daily biogas yield of regulating biogas pressure group was 62.55ml/g VS,which was increased by 29.64% compared to control group.The pH fluctuated between 7.0 and 7.69 during 50 days.The cumulative biogas yield was 820.47ml/g VS which was 2.09 times than control group.Meanwhile,the cellulose degradation rate of regulating biogas pressure was 30.2% that was about 1.2 times than control group.Therefore,the regulating technology was a novel way to product methane enrichment biogas which could improve biogas production in dry anaerobic fermentation eventually.