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 (R) carriers) was operated for 212 d (temperature, 37 degrees C; influent pH, 8). Anammox process was started up in similar to 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.

Automated summary

The study successfully started anammox process in a sequencing batch reactor using a mixture of conventional activated and anaerobic sludge as inoculum, achieving efficient nitrogen removal. Analysis of sludge samples revealed the dominance of an uncommon anammox bacterial genus Candidatus Jettenia in the reactor, with other phyla such as Chloroflexi, Proteobacteria, and Bacteriodetes also detected. The results of this study have important implications for future applications.