Effect Of Mechanical Mixing On Dry Anaerobic Co-Digestion Of Pig Manure With Rice Straw

With the rapid development of intensive and large-scale agriculture,the discharge of livestock and poultry manure and the incineration of crop straw have caused serious environmental pollution.Biotechnology can turn these wastes into benefits.Anaerobic digestion technology can efficiently utilize this kind of biomass energy.Compared with single material anaerobic digestion,anaerobic co-digestion can not only significantly improve the anaerobic digestion performance,but also utilize animal manure and crop straw at the same time.In order to obtain better gas production performance,the first step is to study the ratio of fermentation materials.Secondly,due to the high energy consumption of wet anaerobic digestion technology and the excessive discharge of biogas slurry,dry anaerobic digestion technology has become a research hotspot for the treatment of agricultural waste,but it has a technical bottleneck of poor mass and heat transfer.Mechanical mixing can promote the effective contact between fermentation substrates and microorganisms,which is an important way to improve the mass and heat transfer effect in dry anaerobic digestion process.In this study,by investigating the daily gas production,cumulative VS methane production,synergistic effect and microbial diversity in the process of dry anaerobic digestion of pig manure and rice straw with different VS mass ratios,the better substrate ratio was determined.And under this conditon,the cumulative VS methane yield was used as the evaluation index of mixing effect,the mixing intensity and mixing period were taken as influencing factors.The effects of mechanical mixing on the gas production performance,technological mechanism and microbial metabolism mechanism of dry anaerobic co-digestion of pig manure and rice straw were studied by orthogonal experiment,in order to provide theoretical and technical guidance for the mechanical mixing system of dry anaerobic digestion biogas engineering.The main results are as follows:(1)The effect of manure-straw ratio on the dry anaerobic co-digestion performance of pig manure and rice straw showed that the cumulative methane yields on volatile solids reached 188.8,204.0,213.4,198.1,168.5,169.6 mL/g and 124.7 mL/g from various substrate ratios of pig manure and rice straw at 1?0,3?1,2?1,1?1,1?2,1?3 and 0?1,respectively.The highest cumulative methane yields on volatile solids was from pig manure ? rice straw=2?1,which increased by 13.0% compared to that from the sole pig manure as substrate.Synergistic effect analysis showed that synergistic effects existed between pig manure and rice straw at the different mass ratios.The highest synergistic effect was from pig manure ? rice straw=2?1,and increase rate was 27.5%.The analysis of archaeal communities showed that the decline of the Shannon index before and after fermentation was consistent with the change of methane production.When the substrate ratio of pig manure and rice straw was 2?1,the Shannon index decreased the most,reaching 29.1%.Methanosphaerula is the dominant genera in our anaerobic digestion,and the abundance of Methanosphaerula is positively corelated to methane production.(2)The test results of mechanical mixing on dry anaerobic co-digestion performance of pig manure and rice straw showed that different treatments T1(mixing intensity 15 rpm,mixing period 6 h),T2(mixing intensity 15 rpm,mixing period 12 h),T3(mixing strength 45 rpm,mixing period 6 h),T4(mixing strength 45 rpm,mixing period 12 h),CK(no mixing)cumulative VS methane yield were 193.3,226.7,182.5,230.6 and 245.4 mL/g,respectively.T2 and T4 treatment was not significantly different from CK treatment(P<0.05).Visual analysis of orthogonal design data indicated that T2 treatment was the optimal combination.Environmental factors analysis showed that mixing could aggravate the accumulation of volatile fatty acids(VFAs)in the early stage of fermentation,and the acids accumulation was more serious in the treatment with shorter mixing period.The analysis of archaeal communities showed that in the early stage of fermentation,mixing increased the relative abundance of Methanobrevibacter;And in the peak period of fermentation,mixing reduced the diversity of archaeal communities;VFAs and SCOD are the main environmental factors affecting archaeal communities.For practical project application,the substrate ratio of pig manure and rice straw at 2?1 is recommended,and the mechanical mixing parameters can be set up with the mixing intensity of 15 rpm and the mixing period of 12 hours.