Improvement of start-up and nitrogen removal of the anammox process in reactors inoculated with conventional activated sludge using biofilm carrier materials.

The start-up of the anaerobic ammonium oxidation (anammox) process in three up-flow column reactors seeded with common mixed activated sludge and added with three materials, sponge (R1), sponge + volcanic rock (R2) and sponge + charcoal (R3), as carriers for biofilm formation were comparatively investigated in this study. The supplement of volcanic rock and charcoal could significantly shorten the start-up time of the anammox process, which primarily occurred in the activity-enhanced phase, with ammonium and nitrite removal efficiencies stabilized above 92.5% and 93.4% after an operation period of 145, 105 and 121 d for R1, R2 and R3, respectively. After the successful anammox start-up, R2 performed significantly better in TN removal (p < .05), achieving an average rate of 91.0% and 191.5 g N m-3  d-1 compared to R1 of 88.4% and 172.1 g N m-3  d-1 , and R3 of 89.9% and 180.1 g N m-3  d-1 in the steady running phase. The ratios of consumed [Formula: see text] and generated [Formula: see text]/consumed [Formula: see text] after anammox start-up were lower than the theoretical values, probably suggesting the simultaneous existences of anammox, denitrification as well as nitrification processes in the reactors. A reddish brown biofilm was wrapped on the carriers and morphological detection of biofilm displayed the presentations of thick and compact floc aggregates and some filamentous bacteria on the sponge, and spherical-, ovoid- and shortrod-shaped microorganisms on the volcanic rock and charcoal. Using porous material as carrier for biofilm development is an effective strategy for practical application of the anammox reactor.