秸秆床厌氧发酵产沼气系统优化试验

针对前期研究中发现秸秆床反应器内秸秆在发酵后期上浮、进水短流等问题,采取在秸秆床反应器内增加导气管、在秸秆捆底部预留缓冲空间以及2种方式组合的方式,研究改进措施对秸秆床反应器及整个发酵系统产气、化学需氧量(chemical oxygen demand,COD)去除等的效果。结果表明:直接以打捆秸秆为固定相,以猪粪废水为流动相的处理在猪粪废水有机负荷为2.13 kg/(m3/d)条件下出现轻度酸化,产气受到明显抑制,日产气量明显低于其它处理,继续提高猪粪废水有机负荷后各处理间无明显差别;采用增加导气管、增加缓冲空间以及导气管+缓冲空间的方式改善了秸秆床反应器内发酵环境,未出现酸化现象,日产气量稳定性明显提高。试验结束时,各处理秸秆床反应器累积产气量较对照分别提高了18.90%、9.05%和22.48%,累积产甲烷量较对照分别提高了23.02%、9.34%和25.21%;采用该研究提出的改进措施对二级反应器产气组成无明显影响,各处理平均甲烷含量均在68%左右,对整个秸秆床发酵系统累积产气量、平均甲烷体积分数以及COD去除率无明显影响。以上结果表明,在秸秆床反应器内增加导气管对提高反应器产气量、甲烷含量及产气稳定性有较好的效果,在条件允许的情况下可以考虑在反应器底部增加缓冲空间。

Optimization experiment of straw-bed anaerobic fermentation system for biogas production

Livestock wastewater and agricultural straw are the two main sources of agricultural nonpoint source pollution, then how to deal with these wastes is becoming more and more important.Anaerobic digestion is an attractive technique for bio-wastes treatment, which can convert bio-wastes into bio-fuel and bio-fertilizer.Straw-bed anaerobic fermentation system is a new anaerobic bioreactor for biogas production, which digests livestock wastewater and agricultural straw in one bioreactor at the same time.The straw-bed anaerobic fermentation system is composed of straw-bed bioreactor and wastewater advanced anaerobic bioreactor(USR), and effluent of straw-bed bioreactor is added as inlet into wastewater advanced anaerobic bioreactor.In straw-bed bioreactor, baling straw is used as stationary phase, and livestock wastewater is used as mobile phase.Our previous study indicated that co-digested baling straw and swine wastewater in straw-bed anaerobic digestion system was feasible and beneficial for biogas production.However, in straw-bed bioreactor, baling straw floated upward and inlet short flow appeared in the late stage.In order to solve these problems, gas guide tube was added in baling straw and reserve buffer space at the bottom of straw-bed bioreactor and the combination of the two methods were set up.There were four treatments in the study, i.e.CK (No improvement measures), adding guide tube (GT), buffer space (BS) and guide tube + buffer space (GT+BS).Meanwhile, effect of improvement measures on biogas production, and COD (Chemical Oxygen Demand)removal rate of straw-bed fermentation system were conducted.The results showed that daily biogas yield of CK was significantly inhibited during the first 25 days (organic loading rate of swine wastewater was less than 2.13 kg/(m3/d)) which was much lower than that of the other treatments.However, after 25 days'' reaction, there was no significant difference of daily biogas yield between control and other treatments.By adding improvement measures, fermentation environment was ameliorated and the stability of daily biogas yield was enhanced obviously.After 50 days'' reaction, cumulative biogas yield and cumulative methane yield of GT, BS and GT+BS were 18.90%, 9.05%, 22.48%, 23.02%, 9.34% and 25.21% higher than that of CK, respectively.Wastewater advanced anaerobic bioreactor (WAAB) is an important part of straw-bed fermentation system.The gas production results showed that, there was no significant difference for that of CK and the other treatments with the gas composition of WAAB.All treatments had the average methane content of 68%.Meanwhile, there was almost no significant influence on cumulative biogas yield, average methane content and COD removal rate of the straw-bed anaerobic fermentation system by adding improvement measures.The above results indicated that adding gas guide tube to straw-bed bioreactor was beneficial to improve biogas production, methane content and gas stability, adding buffer space can also be considered as conditions permit.