Ameliorating nitrite inhibition in a low-temperature nitritation-anammox MBBR using bacterial intermediate nitric oxide

The long-term sustainability of an anaerobic ammonium oxidation (anammox) process in a moving bed biofilm reactor (MBBR) treating highly concentrated (mean of 740 mg NH4 (+)-N L-1) wastewater was demonstrated by 1600 days of efficient operation. A high maximum total nitrogen removal rate (TNRR) of 1.5 g N m(-2) d(-1) was achieved at the low temperature of 20 A degrees C. For nitrogen removal recovery in cases of nitrite inhibition, anammox intermediate nitric oxide (NO) was tested in batch experiments as an N-removal accelerating agent. The effect of the addition of various NO dosages (8-72 mg NO-N L-1) was studied under inhibitory nitrite concentrations (> 100 mg NO2 (-)-N L-1) for anammox bacteria. Optimal maintained NO concentration was 58 mg NO-N L-1 and brought about the highest biofilm-specific anammox activity (SAA). Compared to a blank test, the minimum concentration of added NO of 40 mg NO-N L-1 showed a statistically significant (p < 0.05) accelerating effect on SAA. No inhibition of SAA by NO was observed, although at NO concentrations exceeding 72 mg NO-N L-1, the acceleratory effect upon SAA was decreased by 8%. Changes in the bacterial consortia involved in nitrogen conversion were determined concurrently for the different nitrogen removal rates and operational conditions. Quantities of Planctomycetales clone P4 strains, which are the closest (99% similarity) relative to Candidatus Brocadia fulgida, increased from 1 x 10(3) to 1 x 10(6) anammox gene copies per g total suspended solids during reactor operation days 568-1600, which was determined by quantitative polymerase chain reaction. During the operation of the MBBR, the abundance of ammonium-oxidizing bacteria (AOB) increased proportionally (up to 30%). The abundance of nitrite-oxidizing bacteria (NOB) did not increase (remaining below 10%) during days 232-860. AOB became predominant over NOBs owing to the inhibition of free ammonia spiking on NOBs.