Exploring instability mechanisms of overloaded anaerobic digestion based on the combination of degradation dynamics of acetate and propionate and metagenomics assay

To investigate the underlying causes of instability, reactor overload was induced by implementing step-type disturbances in the organic load rate (OLR), followed by a comprehensive characterization of microbial com-munities (genes), process parameters, and kinetics parameters. The results revealed significant reductions in kacetate and kpropionate, with decreases of 52.87 +/- 0.14 % and 73.23 +/- 0.94 %, respectively, compared to their maximum values (1.74 +/- 0.09 gVS/(gVSS center dot d) and 0.71 +/- 0.05 gVS/(gVSS center dot d)), when the OLR was set at 3 kgVS/ (m3 center dot d) and the methane yield (MY) was stabilized at 0.52 +/- 0.02 L/gVS. Similarly, at an OLR of 3.5 kgVS/ (m3 center dot d), the significant deviations of kacetate and kpropionate from their normal range (kacetate: 0.71 +/- 0.02-1.74 +/- 0.09 gVS/(gVSS center dot d); kpropionate: 0.39 +/- 0.02-0.71 +/- 0.05 gVS/(gVSS center dot d)) were observed and a substantial decline in MY subsequently was observed. Notably, the continuous and significant decline in the relative abundance of SPOB, AMA, and their related metabolic genes (prpE, ACADM, paaF, PCCA, MCEE, sucD, cdhC, and metF) in response to the high OLR stress was observed, providing valuable insights into the reduction in kacetate and kpropionate, ultimately leading to their accumulation. Moreover, intricate interactions between acetate and pro-pionate metabolism under overload conditions were revealed, with propionate metabolism displaying the highest sensitivity.