Anaerobic ammonium oxidation of ammonium-rich waste streams in fixed-bed reactors

The feasibility of anaerobic ammonium oxidation (Anammox) in fixed-bed reactors was evaluated on laboratory and pilot scales. Using synthetic wastewater, the specific nitrogen removal rate was increased from 0.05-0.1 kgNm(-3) (reactor)d(-1) to 0.35-0.38 kgNm(reactor)(-3)d(-1) within a year (T= 22-27degreesC) in all applications. However, the anammox activity was seriously and repeatedly inhibited at prolonged high nitrite concentrations (e.g. six days at 30-50 gNO(2)-Nm(-3)) and recovery was always a lengthy process. But even at a moderate nitrite concentration (11 +/- 10 gNO(2)-Nm(-3)), the observed specific growth rate was only 0.018 d(-1) at 26.4 +/- 0.8degreesC, which corresponds to approximately 0.025 d(-1) at 30degreesC (doubling time: 28 days). In a second experimental period for another 250 days, one of the laboratory reactors was fed with partially nitrified sludge liquors from a domestic wastewater treatment plant (WWTP). In this case, the specific elimination rate was as high as 3.5 kgNm(reactor)(-3)d(-1) at 26-27degreesC. Independently of the feed, the average nitrogen elimination rate lay between 80-85% in all applications. An appropriate hydraulic design is essential to prevent clogging and local nitrite inhibition in fixed-bed reactors.