Impact of free ammonia on anammox rates (anoxic ammonium oxidation) in a moving bed biofilm reactor.

Using a bench scale moving bed bioreactor (MBBR), the effect of free ammonia (FA, NH(3), the un-ionized form of ammonium NH(4)(+)) concentration on anoxic ammonium oxidation (anammox) was evaluated based on the volumetric nitrogen removal rate (NRR). Although, a detailed microbial analysis was not conducted, the major NRR observed was assumed to be by anammox, based on the nitrogen conversion ratios of nitrite to ammonium and nitrate to ammonium. Since the concentration of free ammonia as a proportion of the total ammonia concentration is pH-dependent, the impact of changing the operating pH from 6.9 to 8.2, was investigated under constant nitrogen loading conditions during continuous reactor operation. Furthermore, the effect of sudden nitrogen load changes was investigated under constant pH conditions. Batch tests were conducted to determine the immediate response of the anammox consortium to shifts in pH and FA concentrations. It was found that FA was inhibiting NRR at concentrations exceeding 2 mg N L(-1). In the pH range 7-8, the decrease in anammox activity was independent of pH and related only to the concentration of FA. Nitrite concentrations of up to 120 mg N L(-1) did not negatively affect NRR for up to 3.5 h. It was concluded that a stable NRR in a moving bed biofilm reactor depended on maintaining FA concentrations below 2 mg N L(-1) when the pH was maintained between 7 and 8.

Autotrophic ammonium removal from reject water: partial nitrification and anammox in one-reactor versus two-reactor systems.

Removal of total nitrogen from anaerobically digested sludge reject water by a fully autotrophic process in either one- or two-reactor systems was compared. Autotrophic nitrogen removal is currently most often applied in the one-reactor system primarily in the DEMON configuration. The two-reactor systems had a similar nitrogen removal rate to the one-reactor systems. It was evident that the limiting step was partial nitrification. Increase in partial nitrification can be difficult in a one-reactor system, where the overall conditions, such as the oxygen concentration or substrate concentrations, would progress to full nitrification. The partial nitrification of the two-reactor system may be improved by adjusting key parameters: the un-ionized form of the substrates, the oxygen concentration or the solids residence time. The impact of two process configurations on the operational stability and process performance was presented based on two cases--DEMON and the SHARON-ANAMMOX process.

Importance of the operating pH in maintaining the stability of anoxic ammonium oxidation (anammox) activity in moving bed biofilm reactors.

Two bench-scale parallel moving bed biofilm reactors (MBBR) were operated to assess pH-associated anammox activity changes during long term treatment of anaerobically digested sludge centrate pre-treated in a suspended growth partial nitrification reactor. The pH was maintained at 6.5 in reactor R1, while it was allowed to vary naturally between 7.5 and 8.1 in reactor R2. At high nitrogen loads reactor R2 had a 61% lower volumetric specific nitrogen removal rate than reactor R1. The low pH and the associated low free ammonia (FA) concentrations were found to be critical to stable anammox activity in the MBBR. Nitrite enhanced the nitrogen removal rate in the conditions of low pH, all the way up to the investigated level of 50mg NO(2)-N/L. At low FA levels nitrite concentrations up to 250 mg NO(2)-N/L did not cause inactivation of anammox consortia over a 2-days exposure time.