梯度有机负荷下农业废弃物厌氧发酵特性及微生物群落

为了解梯度负荷对不同C/N农业废弃物厌氧发酵特性及微生物群落的影响,该试验以猪粪、金针菇菌包、稻秆和甘蔗叶等C/N差异较大的废弃物作为原料,通过逐渐提高全混合厌氧反应器(continuous stirred tank reactor,CSTR)的有机负荷率(organic loading rate,OLR),研究物料在4个OLR(1.11、1.67、2.22和2.78g/(L·d),以可挥发性固体计)下的产甲烷特性和微生物群落结构变化.结果表明:4种物料的日甲烷产量均随OLR递增而增加,但单位物料甲烷产率与微生物菌群结构则因物料C/N差异而表现出不同的变化趋势.其中:猪粪的日甲烷产量最高,细菌和古菌的菌群结构与对照组相比变化不大;多样性指数先增后减,甲烷产率也在OLR达到1.67g/(L·d)后逐渐下降.金针菇菌包甲烷产率相对稳定,细菌和古菌的多样性指数随OLR递增而增长.稻秆和甘蔗叶同属于碳质量分数高的秸秆类物料,二者的细菌和古菌的菌群结构变化明显;但在OLR达到2.78g/(L·d)时,稻秆受系统酸化(VFA/TIC>0.8)影响,甲烷产率下降明显,细菌和古菌的多样性指数也出现下降;而甘蔗叶则因VFA/TIC<0.8,其甲烷产率在发酵过程中未出现明显下降.此外,不同C/N物料对优势菌的形成存在影响.其中:Methanolobus zinderi为猪粪物料特有的优势古菌;Proteiniphilum acetatigenes,Acetivibrio cellulolyticus为金针菇菌包、甘蔗叶特有的优势细菌;Methanospirillum hungatei为稻秆物料独有的优势古菌.

Anaerobic digestion characteristics and microbial structure of agricultural wastes under gradient organic loadings

In recent years, along with the rapid development of modern large-scale and intensive agriculture in China, the output of agricultural wastes shows a rapid increasing trend. Some objective reasons (the lagged development of resource utilization technology and equipment, the attributes of property rights of agricultural wastes, the difficult government regulatory, and so on) lead to the extensive cyclic utilization and even direct combustion or arbitrary discard of agricultural wastes, which has caused serious harms to the rural ecological environment, agricultural production environment and farmers' living environment in China. The preparation of biogas through anaerobic fermentation is a high-engineering technology for the energy-oriented use of agricultural wastes, and the quantity, species and activity of anaerobic microorganisms for anaerobic fermentation, as well as the fermented substance are the key factors affecting the efficiency of biogas production. C/N, an important character of the fermented substance, can directly affect the metabolism of microorganisms, and also can affect the methane yield through influencing the transformation of carbon in organic matters. In order to understand the effects of gradient organic loadings on the anaerobic digestion characteristics and microbial community structure of greatly different C/N-containing agricultural wastes, the author investigated the performance of methane production and the changes in microbial community structure of anaerobically-digested swine manure, Flammulina velutipes fungal bag, rice straw, and sugarcane top in continuous stirred tank reactor (CSTR) under gradient organic loading rates (OLRs) [1.11, 1.67, 2.22 and 2.78 g/(L·d), being counted as volatile solid]. The results showed that the daily methane yield of the above four substrates all increased with the increase in OLR, but their methane productive rate and microbial community structure revealed different variation trends due to different C/N ratios of substrates. Among four substrates, swine manure with C/N of 13:1 had the highest daily methane yield, and its bacterial and archaea community structure was similar to that in the control group; whereas due to the increase in OLR and the enhancement of ammonia inhibition, the diversity index of bacteria and archaea increased firstly and then decreased, and the methane productive rate decreased gradually when the OLR reached 1.67 g/(L·d). Because Flammulina velutipes fungal bag contained a suitable C/N (about 23.7:1) for anaerobic digestion, it had a relatively stable methane productive rate, and its diversity index of bacteria and archaea increased with the increase in OLR, but its microbial community structure was obviously different from that in the control group. Rice straw and sugarcane top had a higher carbon content, with C/N as 66:1 and 121:1 respectively, and their community structure of bacteria and archaea changed obviously in the anaerobic digestion process. When OLR reached 2.78 g/(L·d), due to the acid accumulation and VFA/TIC above 0.8, the methane productive rate of rice straw decreased obviously, and its diversity index of bacteria and archaea also reduced. However, the methane productive rate of sugarcane top did not decrease obviously in the course of anaerobic digestion, because its VFA/TIC was less than 0.8. Furthermore, the substrate with different C/N had effects on the formation of specific dominant microbial species, and it was found that: Methanolobus zinderi was the specific dominant archaea species in the digested swine manure; Proteiniphilum acetatigenes and Acetivibrio cellulolyticus were the specific dominant bacterial species in the digested Flammulina velutipes fungal bag and sugarcane top, respectively;Methanospirillum hungatei was the specific dominant archaea species in the digested rice straw.