NITRIFICATION IN A MOVING-BED BIOFILM REACTOR

A new biofilm reactor, the moving bed reactor, was studied for nitrification purposes. The study was partly on laboratory-scale with a prepared water, and partly on pilot-scale with primary or secondary effluent as feed water. The experimental results showed that when alkalinity was in excess and there was no organic load, either the ammonium or the oxygen concentration would be limiting for the nitrification rate. The shift from the ammonium to the oxygen concentration being rate limiting occurred for an oxygen to ammonium concentration ratio of about 3 g O-2 (g NH4-N)(-1). The oxygen concentration had a great influence on the nitrification rate when oxygen was rate limiting. The nitrification rate was then close to a first-order function of the oxygen concentration, indicating liquid film diffusion to be the important rate limiting mechanism. Nitrification rates were reduced by increased organic loads. When the organic load exceeded 5 g total BOD(7)m(2)d(-1), the nitrification became insignificant. With a secondary effluent feed, nitrification rates of 0.7-1.0 g NOx-N (NO3-N + NO2-N) m(-2) d(-1) were achieved at oxygen concentrations between 4.5 and 5 g O-2 m(-3). Curves were constructed for nitrification at different organic loads when the oxygen concentration was rate limiting.