The Mechanism And Critical Parameters Of Two-stage Anaerobic Co-digestion With Maize Straw And Pig Manure

At present,there is 0.84 billion tons straw resource in theory in China,in which 0.7 billion tons quantity can be recollected.About 247 million tons straws are discarded or directly combusted for lack of available treated ways,as a result that not only contaminate the environment but also cause great resource waste.China is also a big country for the swine breeding.According to the statistic data of 2012,swine manure yield is approximate to 3 billion tons.Therefore,it is very urgent to find reasonable and effective ways to dispose the straws and manure.In this paper,the mixture of crop straws and swine manure were selected as digestion substrate,the characteristics and BMP of solid organic materials were analyzed in detailed.Key technical parameters,influence factors and the reaction mechanism of and the dynamic vary rule of microbial population structure for the two-stage of solid-phase acid yielding stage and liquid-phase methane yielding stage were studied in detailed by the experiment,as well as the experimental effects during the two-stage anaerobic digestion of maize straws and swine manure were studied,and the dynamic variation rule of microbial community structure in the two-stages anaerobic digestion were was probed with the molecular biology tech T-RFLP.All the achievements that will provide theory and technical support for the innovative co-digestion technology with an optional new approach for the harmless treatment and resource utilization of crop straws and livestock manure as substrate.Based on the analysis result of 13 ligno-cellulose materials characteristics and BMP,the relationship of accumulated biogas production,accumulated methane production with the amount of semi-cellulose is active and there exist no predominant relationship with WSC?VS/TS?TOC?TC and C/N.The BMP of maize straw was 478.6Nml/gVS,252.2Nml/gVS respectively.Biogas and methane of swine manure were 617 N mL/g VS,337 N mL/g VS,the highest of 39.7 N mL/(g·d)VS.Optimized processing conditions of the solid yielding acid fermentation were that 2:1 swine manure to the straw,25% biogas slurry reflux,12-24 h interval time in the biogas slurry reflux.The static solid yielding acid process in 6-10 d was the peak and maintained to the lower level after 20 d.Solid yielding acid digestion was the acetic fermentation.Acetic acid occupied over 60% of the total organic acid in the digestion product VFA.Methylacetic mass concentration was lower than 1.0g/L that avail to the methane yielding in anaerobic digestion.The experiment of liquid yielding methane was showed that the biogas yielding rate in 35? was higher than that in 55? in the same pH level.In the same digested temperature,the biogas yielding rate was lowered down with pH increasing when the pH was higher than 7.0.The results were showed that 35? and pH 7.0 were the optimum parameters of methane yielding in the fermentation.In mesophilic digestion,the methanogen in acetic acid nutrient variety “Methanosaeta” was the dominant methane bacteria that yielded the methane with the acetic acid oxidation.Relative abundance in pH 6.5-7.5 was higher than 70%.In thermophilic digestion “Methanosarcina” was the dominant methanogen.Relative abundance in pH 7.0-7.5 was higher than 60%.It used H2 and CO2 to yield the CH4 but the speed was relatively lower so that made the methane products lower than in the mesophilic digestion.Free ammonia increasing was the main reason for the reduction of methane yielding rate.Regarding to the anaerobic digestion of organic wastes contained with high nitrogen,thermophilic anaerobic digestion was inappropriate to use.By means of continuous dynamic experiments,optimum parameters include the proportion of swine manure to the straw,the biogas slurry reflux,interval time in the reflux,available capacity in the solid yielding acid reactor to the liquid yielding methane reactor,retention time in the solid digestion,organic load in the liquid digestion stage and HRT in two-stages anaerobic digestion were got.Experimental results were showed that slurry reflux apparently impacted on the pH for modulating the acid yielding digestion system.Biogas slurry reflux amount and interval time were the key parameters for the modulation of solid acid digestion.The parameters were influenced by the liquid yielding methane digestion parameters,which was the focal point for coupling two-stage anaerobic digestion and reducing the slurry discharge.The results were showed that there was apparent succession of the dominant populations of the bacteria and archaea along with the digestion time prolonging in the solid yielding acid stage,carrying out the molecular microbiology experimental test on the population structure in different stages in two-stage anaerobic digestion.Therein the Firmicutes,Proteobacteria,Bacteroidetes and Planctomycetes were the dominant population.Methanobacterium in hydrogen nutritional type was the dominant population in the archaea.The bacteria and archaea community structure were stable in the methane yielding stage.Firmicutes was the dominant population in the bacteria.Methanobacterium and Methanoculleas in hydrogen nutritional type together with Methanosarcina in acetic acid were the dominant populations.The manometric measurement of the methane yielding potential of the solid materials was used in the paper that owned the characteristics covered easy to operate and stable results.Using the process combined with the carport solid acid reactor and improved CSTR two-stage anaerobic digestion was available to enhance the gas volume yielding rate in the reactor for reducing the biogas slurry discharge.Integrated the swine manure with the maize straws in the anaerobic digestion,the biogas producing could be increased and the reactor running could be stable.Experimental results were showed that two-stage biogas anaerobic digestion would be running steadily with the optimized parameters.