To further clarify the key stage and microorganisms responsible for ammonia inhibition instability, three sequential batch experiments were conducted with various ammonia concentrations and different exposure modes. Acetate metabolism was most sensitive to ammonia, however, after continuous ammonia exposure, acetate metabolism was well restored by a shift in dominant microorganisms. In contrast, the metabolism of longer-chain volatile fatty acids (LCVFAs, C₃–C₅) was only inhibited under a high ammonia concentration (≥6000 mg/L), however, once inhibited, continuous exposure neither restored the abundance of functional microbes nor induced new microorganisms to perform metabolic functions. Therefore, LCVFA metabolism was the key stage responsible for process instability under ammonia stress. Moreover, the deterioration of LCVFA metabolism was caused by the inhibition of syntrophic acetogenic bacteria (SAB) induced by total ammonia nitrogen, rather than the feedback inhibition from methanogenesis. That is, SAB were the key microorganisms involved in process instability.

为了进一步弄清造成氨抑制不稳定性的关键阶段和微生物，在不同的氨浓度和不同的暴露方式下进行了三个连续的分批实验。乙酸代谢对氨最敏感，但是，连续暴露于氨后，优势微生物的转移使乙酸代谢得到了很好的恢复。相反，长链挥发性脂肪酸（LCVFAs，C ₃ –C ₅）仅在高氨浓度（≥6000mg / L）时被抑制，然而，一旦被抑制，连续暴露既不能恢复功能性微生物的丰富，也不会诱导新的微生物发挥代谢功能。因此，LCVFA代谢是氨胁迫下导致工艺不稳定的关键阶段。此外，LCVFA代谢的恶化是由总氨氮引起的对营养性产乙酸细菌（SAB）的抑制而不是甲烷化产生的反馈抑制引起的。也就是说，SAB是涉及过程不稳定的关键微生物。