Accelerated start-up of a partial nitritation-anammox moving bed biofilm reactor

The formation of anammox biofilm is a lengthy process, leading to reactor start-up times of several months even with addition of anammox inoculum. To demonstrate the effectiveness of combining bio-primer technique with seed carriers in further accelerating the start-up time of anammox reactors a pilot moving bed biofilm reactor was set-up at a dewatering facility of a municipal wastewater treatment plant. The reactor was filled to 40% with plastic media with a specific surface area of 402 m(2) m(-3) and was operated at 34 +/- 1 degrees C. Using bio-primer coated media it was shown that a surface nitrogen removal rate of 2.5 g-N m(-2) d(-1) could be achieved in as little as 56 days. Free ammonia (FA) was thought to be the predominant inhibitor of nitrite oxidizing bacteria activity rather than the selective wash-out of nitrifying biomass. A minimum FA concentration of 2 mg NH3-N L-1 was suggested for optimal performance of partial nitritation and to prevent the build-up of nitrates. Biomass from the pilot reactor had developed a specific anammox activity of 19 +/- 2 mg-N g-VSS-1 h(-1) which was 75% higher than the seed biomass from an anammox-only reactor fed with synthetic wastewater.