| The excessive dependence and consumption on fossil fuels caused great negative impactfor environment, which lead to serious threat to the raise of human health and global climate.Therefore, it is necessary to develop alternative energy sources and renewable energy. The useof anaerobic digestion method to product biogas is becoming a major way to biomassutilization for its advantage of simple technology, widespread source and low cost. During thepast two decades, anaerobic digestion has been used as an effective biological technique tosolve the energy shortage and mitigate environmental pollution caused by fossil fuels.In this study, goat manure was used as the major digestion substrate. Firstly, comparedthe efficiency of biogas production between goat manure and others animal manure (includingcow manure, swine manure and chicken manure) with anaerobic digestion of single rawmaterial. Secondly, the biogas production with different total solid content and differentmixing ratio of goat manure and crop residues in anaerobic digestion was studied, and theoptimum mixing ratio for anaerobic digestion was also determined. Finally, to further improvethe efficiency of mixing fermentation, the promote effect of three additives to sheep anaerobicfermentation were also been studied. Meanwhile, the biogas potential and main direction ofgoat manure were evaluated, which will provide a theoretical base for practice production.The results of this study as follows:1. As the main test material, the anaerobic digestion result of goat manure (GM) wascompared with cow manure, swine manure and chicken manure, separately, at psychrophylic(20°C), mesophylic (35°C), and thermophylic (50°C) conditions. During30d digestionperiod, The results of biogas production of all treatments showed that cow manure> GM>chicken manure> swine manure. The results of biogas production at different temperaturesshowed that35°C>50°C>20°C. The biogas production of GM was significantly higherthan that of swine manure and chicken manure, but slightly lower than cow manure. Theresults indicated that using GM as substrate was suitable for anaerobic digestion for biogasproduction.2. To study the relationship between total solid (TS) concentration and goat manuremono-digestion, five different TS contents (4%,6%,8%,10%and12%) were used for anaerobic digestion. The results showed that the cumulative biogas production was obtainedat8%TS content. When the TS content maintained4%, the peak period of biogas productionwas earlier during the fermentation. This is due to the lower TS concentration lead tomicroorganisms degraded substrate easily. However, the total biogas production was restrictedby the limited substrate, thus the fermentation process was also terminated earlier. The resultsof biogas production at different TS contents showed that8%>10%>6%>12%>4%.According to the regression equation, the optimum condition was obtained. When the initialTS content at8.27%, the maximum cumulative biogas production could reach5531.18mL.This result provide a theoretical basis for further optimization of goat manure anaerobicfermentation process.3. For co-digestion, GM was mixed with wheat straw (WS), corn stalks (CS), and ricestraw (RS) at different ratio (10:90,30:70,50:50,70:30and90:10), respectively. Theresults showed that co-digestion with GM and crop residues is not only an effective way toprolong the period of the highest gas production, but can effectively reduced the C/N ratios ofanaerobic digestion. The ANOVA indicated that the optimum mixing ratios of substrate wereGM/CS30:70, GM/CS70:30, GM/RS30:70, and GM/RS50:50, respectively. However, noapparent increasing trend was observed in the biogas production of GM/WS. Thisphenomenon possibly resulted from the significantly higher lignin content of WS. The studyalso indicated that the pH value was closely related to VFA, the accumulation of VFA in thedigestion system caused the drop of pH, thus inhibiting the hydrolysis rate of the fermentationsubstrate.4. Diammonium phosphate (DAP), Halogoton arachnoideus ash (HAA) and bentonitewere selected as additives, to study their roles in promoting the anaerobic digestion with goatmanure. The1g/L,4g/L and7g/L concentration of DAP, HAA and bentonite were added inanaerobic digestion systems, respectively. The results showed that all3additives couldpromote the biogas production and methane contents with different digestion substrates.According to methane content, promoting effect is most obvious when the concentration ofDAP reached4g/L. however, the biogas production was declined when the concentration ofDAP reached7g/L. The most likely reason is that DAP is alkaline, and ammonia inhibitionoccurred easily at higher concentration of DAP. Meanwhile, the methane production had alarger increase either the concentration of HAA and bentonite reached4g/L or7g/L,indicating that the better acceleration of addtion of HAA and bentonite was obtained at4g/Lconcentration.5. Through the statistics and estimation of goat manure resource in China, the hugebiogas potential of goat manure can be found. Theoretical annual biogas production of goat manure up to1.29×1010m3, equivalent to9.21million tons of standard coal; theoretical CO2emission reductions up to1.22×107t, SO2emissions amounted to1.23×105t, it isremarkable environmental benefits. The analysis result of the regional distribution of goatmanure resource indicated that northern and western of China, the main pastoral region, arethe major distribution areas, especially in Inner Mongolia and Sinkiang. The goat manurebiogas potential in these two provinces accounted for more than30%of China’s totalproduction potential, maintained2.33×109m3and1.59×109m3, respectively. However, dueto the limitations of traditional fermentation processes, complex climatope of sheepresource-rich areas and the lack of enthusiasm for the development of biogas, the currentstatus of goat manure biogas is still in a lower level. With the analysis of the relevantconstraints, the countermeasures about rational distribution, increase investment and improvecountermeasure was proposed, in order to provide guidance and theoretical basis for furtherimprove goat manure biogas production levels in China. |
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