Successful start-up of anammox process from activated sludge and anaerobic sludge in a sequencing batch reactor using an unconventional strategy

In this study, the start-up of anammox in a sequencing batch reactor (SBR) using conventional activated and anaerobic sludge in 1:1 ratio (v/v) as inoculum was achieved using an unconventional strategy. The ratio of NH4+-N to NO2−–N in the influent was not maintained as per the stoichiometry (1:1.32) of anammox and rather varied depending on the effluent characteristics. Nitrite was omitted during its accumulation period to avoid its toxicity during the start-up phase. The SBR having polyurethane foam impregnated with activated carbon (Levapor® carriers) was operated for 212 d (temperature, 37 °C; influent pH, 8). Anammox process was started up in ~95 d with 85% average total nitrogen (TN) removal. Thereafter, the reactor showed average TN removal efficiency of 85% and exhibited an average NH4+-N and NO2−–N removals of 99.9% each at maximum influent NH4+-N and NO2−–N concentrations of 200 mg L−1 and 264 mg L−1, respectively. The 16S rRNA gene amplicon sequencing analysis of suspended sludge samples (100 d, 150 d, and 186 d) from the reactor revealed the dominance of infrequently occurring anammox bacterial genus Candidatus Jettenia in the reactor. The phyla Chloroflexi, Proteobacteria, and Bacteriodetes were also detected in the reactor. [Display omitted] •Start-up (~95 d) of anammox process was reported using activated and anaerobic sludge as seed.•Regulation of nitrite is crucial to avoid nitrite toxicity and successful start-up of anammox process.•Stable nitrogen removal (85% TN; 99.9%, NH4+-N; 99.9%, NO2−) was observed between 150 and 187 d.•Infrequently occurring anammox bacterial genus Candidatus Jettenia dominated in the reactor.•Planctomycetes abundance doubled from 12.2% (100 d) to 24.86% (186 d) in the reactor.