Accelerating process recovery through "0 + 1 > 1" phenomenon: Enhanced anammox bacteria growth in mixed...

Practical applications of anaerobic ammonium oxidation (anammox) are often hindered by slow recovery following operational failures. In this study, a novel "0 + 1 > 1" phenomenon was observed when using mixed inactive-active sludge as inoculum. In this context, "0" represented inactive sludge caused by excessive aeration, while "1" denoted active sludge. The mixed inactive-active sludge achieved faster recovery than either inactive or active sludge alone under identical conditions, demonstrating "0 + 1 > 1". Two distinct anammox genera were used: Candidatus Kuenenia as active sludge while Candidatus Brocadia as inactive sludge, revealing the primary mechanism was enhanced growth of anammox bacteria from active sludge rather than the reactivation of inactive sludge, which was related with increased relative gene abundances of enzymes involved in N metabolism, enhanced amino acid synthesis and quorum sensing (QS) communication. Reactivation of inactive sludge was excluded due to irreversible damage of hdh. This study presents a cost-effective strategy for accelerating anammox process recovery.