Effect of different organic loads on the performance and microbial community mechanism of dry anaerobic digestion

Abstract

In this study, the vertical continuous push-flow dry anaerobic digestion (AD) reactor was developed independently. Typical agricultural organic waste straw and cow dung were used as raw materials in this paper to carry out long-term continuous mixed dry AD experiments on a controlled laboratory scale. The experimental results showed that the system was in low-stress operation at an organic load rate (OLR) of 3 g VS L-1 d-1, the VS methane production rate was located at 225 ∼ 272 mL CH4 g VS-1, and the volumetric methane production rate was located at 0.95 ± 0.08 L (L·d)-1, and the combination of the volumetric methane production rate, VS methane production rate, methane content of the gas, and the VS removal rate showed that the system's operational performance in this stage was in the best condition in the whole set of experiments. When the OLR reached 25 g VS L-1 d-1, the content of VFAs all began to climb rapidly above 8000 mg/L, with the content of acetic acid increasing most significantly due to the fact that the activity of acetic acid-type methanogenic bacteria was the first to be inhibited. Eventually, because of the kinetic differences between the hydrolytic acidifying bacteria and the methanogenic archaea, the final acidification destabilisation of the anaerobic digestion reactor occurred and the system was irreversibly destabilised. The system performance at this stage was in the best condition in the whole set of experiments. The study of microbial community succession and metabolic mechanisms showed that Methanoculleus and Methanobacterium play a key role in sustaining methane production, and the increased abundance and dominance of hydrogen methanogens implies that methane is produced via the hydrogen methanogenic pathway under high organic loading conditions.