Fast start-up of anammox process with hydrazine addition

The anammox process is an economically favourable nitrogen removal process; however, low growth rates of anammox biomass block its more widespread application. As different approaches on techniques for anammox bacteria growth acceleration were tested, this study focused on long-term evaluation of hydrazine addition in the start-up phase. Effect of hydrazine addition (dose 3.7 mgN2H4 dm−3) was investigated in a pilot-scale SBR treating ammonia-rich reject water from sludge dewatering after partial nitritation process, and effects were compared to a reference reactor. Hydrazine addition resulted in much higher anammox biomass enrichment observed as higher nitrogen removal rate [0.512 kgN (m3 d)−1 with hydrazine versus 0.256 kgN (m3 d)−1 without reagent]. Sludge from chemically stimulated reactor revealed also higher (by 22.6%) specific anammox activity rate than the reference. After the hydrazine addition was stopped, observed process rates remained stable and no regression in the nitrogen removal efficiency could be noticed. In the final phase, nitrogen removal rate was only 48.7% of process rate in the reactor previously stimulated by hydrazine. Results of the experiment confirmed positive effect of hydrazine presence on anammox bacteria enrichment process.