Rapid achievement of nitrification in CSTR and SBR treating reject water at high ammonia levels

Abstract

The ability of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) to carry out nitrification in an environment with high ammonia levels was evaluated with the aim to suggest a suitable strategy for a quick start-up of nitrifying reactors treating reject water. It was proved that nitrification could be initiated even without any inoculation of nitrifying biomass. The nitritation was achieved faster (23 d after beginning of reactor operation) than nitratation (after 180 d) due to the presence of AOB and the absence of NOB in raw reject water. Free ammonia (FA) concentration reaching up to 160 mg N L−1 strongly inhibited nitrifying bacteria during the initial phase of reactor operation. Consequently, free nitrous acid (FNA) with a concentration up to 1.25 mg N L−1 supported NOB inhibition after the initiation of AOB activity. High AOB, as well as NOB, activity was observed even during the first day of the operation in a completely stirred tank reactor (CSTR, nitrogen loading rate—NLR 0.5 kg N (m3 d)−1, nitrogen oxidation rate—NOR 0.25±0.05 kg N (m3 d)−1) as well as a sequencing batch reactor (SBR, NLR 0.3 kg N (m3 d)−1, NOR 0.14±0.01 kg N (m3 d)−1) inoculated with common activated sludge at a zero initial total ammonium nitrogen concentration. It was proved that temporary inhibition of NOB activity induced by FA concentration elevated to 88 mg N L−1 may lead to the permanent transformation of standard nitrification into shortcut nitrification in SBRs, thanks to periodical exposition of NOB to high FA and FNA concentration during SBR cycle. Thus, it was demonstrated that the possibility to initiate this process very quickly is essential as a first stage for subsequent anaerobic oxidations of ammonium or shortcut denitrification.