Two-Stage Start-Up to Achieve the Stable via-Nitrite Pathway in a Demonstration SBR for Anaerobic Codigestate Treatment

The supernatant effluent from full scale anaerobic codigestion of waste-activated sludge and the organic fraction of municipal solid waste was treated by a demonstration sequencing batch reactor for short-cut nitrogen removal. After inoculation with conventional municipal activated sludge, the strategy of two-stage start-up allowed us the fast speciation of ammonia oxidizing bacteria (achieved within 20 days), then the achievement of the maximal treatment potential (0.8 kgN m–3 d–1) for nitritation–denitritation. By automatic indirect control of the free ammonia and the free nitrous acid concentrations, the via-nitrite pathway was fully and stably achieved under aerobic conditions (DO of 1.5 mg L–1) and T of 15 °C. Under ordinary operation, the specific nitritation rates were 15–20 mgN gMLVSS–1h–1, while the denitritation rate was 45–50 mgN gMLVSS–1h–1. In-situ and ex-situ respirometry and gene-based molecular techniques demonstrated the stable presence of a dominant, restricted ammonia oxidizing bacterial population after the first-stage aerobic start-up. We therefore demonstrated that codigestion and advanced nitrogen removal from anaerobic supernatant may optimize the performances of an integrated municipal treatment plant.