Consecutive batch anaerobic digestion under ammonia stress: Microbial community assembly and process performance

Abstract

To reveal the effects of the degree and mode of total ammonia nitrogen (TAN) stress on community assembly, composition, and process performance, sequential batch experiments of anaerobic digestion (AD) of food waste were conducted with three different ammonia levels (1800, 3000, and 6000 mg/L) and two exposure modes (stepwise and direct). The selected TAN levels varied in the degree to which they inhibited the AD process. However, deterministic processes may play a larger role in shaping the microbial community than stochastic processes regardless of the level and mode of TAN stress. Under controlled conditions, long-term exposure can lead to the convergence of the community to a specific equilibrium state. The key link affecting community function was acetogenesis. The relative abundance of hydrolytic and acidogenic bacteria under the 1800, 3000, and 6000 mg/L TAN groups was 67.36 ± 3.59%, 68.54 ± 5.73%, and 77. 09 ± 2.69%, respectively. The resistance and redundancy of functional bacteria can maintain the hydrolysis and acidification function of the AD process. Methanogens can also maintain their metabolic performance through the transfer of dominant methanogens from Methanosaeta and Methanospirillum to Methanosarcina and Methanoculleus. Acetogens, especially Pelotomaculum, were inhibited at 6000 mg/L TAN. This led to a decrease in their abundance and the accumulation of longer-chain volatile fatty acids, which was the main reason for the deterioration of the AD process. A new method that promotes acetogenesis under high ammonia stress needs to be developed to achieve efficient AD performance.