Anammox Start-up Using Low Activity Inoculum to Treat Low- Strength Uasb Effluent

In this work autotrophic nitrogen removal was implemented through the combined biological processes of short-cut nitrification and anoxic ammonium oxidation (anammox) in a single sequencing batch reactor (SBR). The SBR received the effluent of an upflow anaerobic sludge blanket (UASB) that treated low strength synthetic wastewater. The main challenge was to develop anammox bacteria that will be able to adapt to the particular characteristics of low strength UASB effluent using low activity inoculum as a starting point. The work focused on the examination of the biomass characteristics and on the autotrophic nitrogen removal rate accomplished by the anammox bacteria. Microscopic investigation involved Gram and Neisser stains as well as fluorescence in situ hybridization (FISH) analysis. The operating temperature was set at 30C and the average volumetric nitrogen loading rate (vNLR) was 0.13±0.11 kgN/m-d. FISH analysis confirmed the stable presence of anammox bacteria in the biomass from the initial stages of SBR operation. Microscopic examination revealed the presence of numerous filamentous microorganisms (Filament Index= 2.5-3.5) several of which appeared to be in a state of endogenous respiration. The dominant filamentous microorganisms were Thiothrix, Type 1701, Νοstocoida limicola, Τype 0041, Type 021N and Microthrix parvicella. Filamentous microorganisms were favoured by the long solids retention time (SRT) that was adopted. However, sludge settling problems were not encountered (average SVI=120 mL/gSS). Nitrogen removal rate due to anammox bacteria was equal to 2.27±1.31 mgN/gVSS-h at the temperature of 30C, which represents an increase of 161% compared to the inoculum anammox activity. The denitrifying heterotrophic biomass activity decreased to very low levels after the first 30 days (<0.1 mgN/gVSS-h) probably owing to the decrease of the organic loading rate. The results of this work have shown that it is possible to maintain anammox bacteria for the treatment of low strength wastewater. Although low activity anammox inoculum was used, it was possible to achieve satisfactory autotrophic nitrogen removal rates.