Sequential nitrification/mixotrophic denitrification process in single bioreactor: Performance and microbiology of two types of sequencing batch bioreactors

The integration of sequential nitrification/mixotrophic denitrification (SNMD) in a single bioreactor is rarely reported. This study adapted an industrial inoculum to SNMD in a single bioreactor configuration, comparing a conventional sequencing batch reactor (SBR) and a zeolite-carrier SBR (SBBR) over 276 days across three phases: sequential nitrification heterotrophic denitrification (SNHD) adaptation, increased TAN loading, and SNMD with sulfide (HS^--S) addition. Under SNHD conditions, both systems achieved > 99 % TAN removal with complete NO₃^–-N reduction. After HS^--S addition, NO₂^–-N accumulated, yet denitrification recovered after 90 days. Under SNMD, TAN removal averaged 93.4 ± 5.6 % in the SBR and 90.0 ± 10.6 % in the SBBR (p > 0.05). While performance remained similar, zeolite influenced microbial community composition, particularly under sulfur-driven conditions. Therefore, the SNMD process was successfully developed in a single reactor, with or without zeolite, which only affected microbial abundance.