沼液回流对棉花秸秆产甲烷效率及微生物群的影响

Effect of Slurry Recirculation on Methane Production of Cotton Stalk and Its microflora

试验在中温条件下采用连续搅拌反应器(CSTR)研究了沼液长期回流对棉花秸秆厌氧发酵的影响,对固定进水负荷下的发酵罐运行参数的动态变化进行了持续监测。结果发现:在水力停留时间为15 d,进水有机负荷为4 g TS·L^(-1)d^(-1)的条件下,与未回流组相比,回流组在第153天时产气受到抑制,产气下降了23.1%;pH值在7.1上下波动而未回流组为6.8;氨态氮浓度为108 mg·L^(-1),未回流组在71 mg·L^(-1)左右;粘度由54 mPa·s增至139m Pa·s;VFAs含量高于未回流组,其中乙酸和乳酸积累较为明显。结果表明:一方面,沼液回流提高了反应器有机负荷率及缓冲能力,大大节约淡水资源,同时对产沼气体系产生搅拌作用,节约资源和能源。另一方面,回流组沼液粘度的增加、乙酸和乳酸的积累是其产甲烷率降低的原因,其纤维素分解菌种类较少,但主要产甲烷菌-甲烷鬃毛菌随着乙酸的积累而增长,对稳定沼液回流条件下的厌氧发酵体系起到了重要作用。

The effect of recirculating the slurry （ liquid fraction of digestate） on the mesophilic anaerobic digestion of cotton stalk was investigated using laboratory-scale continuous stirred tank reactors. The hydraulic retention time （HRT） of 15 d was employed. Recirculation was implemented after the anaerobic digestion process was stable at the organic loading rate of 4 gTS · L^-1d-1. The result showed that, comparing with control group, the daily biogas yield of recirculating group was inhibited on the 153＇h days and the yield decreased by 23.1% ; the pH was 7.1 while the control group was 6.8; the viscosity increased from 54 mPa . s to 139 mPa . s while the control didn＇t change distinctly; the concentration of ammoniacal nitrogen was 108 mg . L-1 while the control was 71 mg .L-1. In addition, the recirculating group had higher accumulation of VFAs, especially acetic acid and lactic acid. These result showed that, on the one hand, the liquid digestate recirculation might increase organic loading rate, have role of stirring the system, reducing emission of slurry and saving fresh water; but on the other hand, the liquid digestate recirculation had higher slurry viscosity and more accumulation of acetic acid and lactic acid, and so make the methane yield lower. Its cellulose-decomposition bacterium was limited. The main methanogens, Methanosaeta, increased with accumulation of acetic acid.