Autotrophic nitrogen removal by a two-step SBR process applied to mixed agro-digestate

The aim of this research was to evaluate the applicability of partial-nitritation/anammox processes for biological N removal from a centrifuge supernatant coming from a full scale anaerobic digester fed on a mixture of piggery manure, poultry manure, and agro-wastes. Stable partial nitritation was achieved at pilot-scale (650 L SBR), obtaining a suitable influent for the anammox lab-scale SBR reactor (3 L). The anammox lab scale reactor was fed with increasing fractions of the partial nitritation effluent, blended with synthetic wastewater. In the last 100 days no dilution was used. The nitrogen loading rate applied to the anammox reactor was 0.5–0.6 g N L−1 d−1 and the average nitrogen removal was 91 ± 10%. During the first days of operation with undiluted supernatant, the maximum anammox activity in the SBR decreased, but recovered afterwards, suggesting the ability of the anammox biomass to acclimate to the wastewater. N2O emissions in both reactors were also measured.