Enrichment of Anammox biomass from municipal activated sludge: Experimental and modelling results

Anaerobic Ammonia Oxidising (Anammox) biomass was enriched from sludge collected at a municipal wastewater treatment plant, employing a Sequential Batch Reactor (SBR). After 60 days Anammox activity started to be detected, by consumption of stoichiometric amounts of NO₂ ^- and NH₄⁺ in the system. Fluorescence In Situ Hybridisation analysis confirmed the increase of Anammox bacteria concentration with time. A final concentration of enriched biomass of 3-3.5 gVSS dm^-3 was obtained, showing a Specific Anammox Activity of 0.18 gNH₄⁺-N gVSS^-1 d^-1 The reactor was able to treat nitrogen loading rates of up to 1.4 kgN m^-3 d^-1, achieving a removal efficiency of 82 %. On the other hand, the start-up and operation of the Anammox SBR reactor were consequentially modelled with the Activated Sludge Model nr 1, extended for Anammox. The simulations predicted quite well the experimental data in relation to the concentrations of nitrogenous compounds and can be used to estimate the evolution of Anammox and heterotrophic biomass in the reactor. These simulations reveal that heterotrophs still remain in the system after the start-up of the reactor and can protect the Anammox microorganisms from a negative effect of the oxygen.