Different bioaugmentation regimes that mitigate ammonium/salt inhibition in repeated batch anaerobic digestion: Generic converging trend of microbial communities

Bioaugmentation regimes (i.e., dosage, repetition, and timing) in AD must be optimized to ensure their effectiveness. Although previous studies have investigated these aspects, most have focused exclusively on short-term effects, with some reporting conflicting conclusions. Here, AD experiments of three consecutive repeated batches were conducted to determine the effect of bioaugmentation regimes under ammonium/salt inhibition conditions. A positive correlation between reactor performance and inoculum dosage was confirmed in the first batch, which diminished in subsequent batches for both inhibitors. Moreover, a diminishing marginal effect was observed with repeated inoculum introduction. While the bacterial community largely influenced the reactor performance, the archaeal community exhibited only a minor impact. Prediction of the key enzyme abundances suggested an overall decline in different AD steps. Overall, repeated batch experiments revealed that a homogeneous bacterial community deteriorated the AD process during long-term operation. Thus, a balanced bacterial community is key for efficient methane production.