基于改进秸秆床发酵系统的厌氧发酵产沼气特性

摘要

为同时解决农业秸秆和分散式畜禽养殖废水的资源化问题，以打捆秸秆为固定相，以猪粪废水为流动相，构筑秸秆床厌氧反应器，并在反应器后部连接废水二级厌氧反应器，研究秸秆床发酵系统的产气特性及可行性。结果表明：秸秆床发酵系统可同时处理打捆秸秆和猪粪废水，且不影响各发酵原料的厌氧生物转化率，秸秆床发酵系统中秸秆干物质产气量为394.96 mL/g，略高于秸秆单独发酵（382.11 mL/g）；秸秆床发酵系统产气稳定性大幅提高，避免了单一发酵原料日产气量波动较大的问题，对产气中平均甲烷体积分数影响明显，秸秆床发酵系统、纯猪粪废水和纯秸秆发酵产气中平均甲烷体积分数分别为57.40%、60.37%和47.32%；与各物料单独发酵相比，秸秆床发酵系统平均容积产气率大幅提高，纯秸秆和猪粪废水单独发酵容积产气率仅为秸秆床发酵系统的69.42%和66.94%；试验35 d后，秸秆机械强度和孔隙度明显降低，秸秆互相粘结导气性下降，造成秸秆上浮严重及进水短流，反应器出水化学需氧量浓度快速增加并稳定在较高浓度，故在秸秆床反应器后部必须连接废水二级厌氧反应器以进一步处理秸秆床反应器出水。综合以上结果，采用秸秆床发酵系统同时处理打捆秸秆和猪粪废水是可行的，但需解决发酵后期秸秆上浮、导向性下降和进水短流等问题。%Agricultural straw and livestock wastewater were the main source of agricultural contaminant, how to reduce, reuse and recycle these wastes has become more and more important. Anaerobic digestion is an attractive technique for bio-waste treatment which can produce biogas and bio-fertilizer. Co-digested two and more wastes is beneficial for anaerobic digestion. By this way, we can not only get more biogas, but also reduce the investment of biogas plant. Two or more agricultural wastes were converted to biogas in one anaerobic bioreactor. Although much work has been done on anaerobic co-digestion of two or more bio-wastes, but most work was done with batch model and there was no report on anaerobic co-digestion of agricultural straw and livestock wastewater. In pig farming, swine wastewater is the main contaminant and is generated every day, so swine wastewater must be added to the anaerobic digester daily, which means that we must use semi-continuous feeding bioreactor in a pig farm biogas plant. In this study, the feasibility of straw-bed anaerobic bioreactor (SAB) was investigated. In the straw-bed bioreactor, baling straw was used as the stationary phase and swine wastewater was used as the mobile phase, and a wastewater advanced anaerobic bioreactor (USR) was connected to the posterior of the straw-bed bioreactor. The results showed that the straw-bed anaerobic digestion system (SADS) was feasible and there was no significant difference between co-digestion and mono-digestion of straw and swine wastewater. The total solid biogas yield of straw of SAB and mono-digestion were 394.96 and 382.11 mL/g, respectively. Compared to mono-digestion, the stability of daily biogas yield and average methane content of co-digestion was improved significantly. The average methane content of SADS, baling straw and swine wastewater digested alone were 57.40%, 47.32% and 60.37%, respectively. The volumetric biogas production was also improved significantly and the volumetric biogas production of treatment of baling straw and swine wastewater digested alone were 69.42% and 66.94% to that of SADS. After 35 days reaction, air permeability of baling straw was decreased which leading to more serious floating of baling straw and short flow of influent. After that, COD content of effluent increased sharply and then maintained at higher level. Meanwhile daily biogas yield of wastewater advanced anaerobic bioreactor increased sharply. Therefore, it is necessary to connect a wastewater advanced anaerobic bioreactor to the posterior of straw-bed bioreactor in order to deep purification of effluent of SAB. The above results indicated that co-digested baling straw and swine wastewater in straw-bed anaerobic digestion system is feasible and is beneficial for biogas production.