Fast start-up and controlled operation during a long-term period of a high-rate partial nitrification activated sludge system

Abstract

Partial nitrification of a high-strength ammonium wastewater (1150 ± 150 mg N-NH L⁻¹), mimicking reject water, was achieved in an activated sludge pilot plant with a configuration of three continuous reactors in series plus a settler. Stable and robust partial nitrification was maintained during 800 days of operation at 30°C with a sludge retention time (SRT) of 8 ± 3 days. A high volumetric ammonium oxidation rate (2.0 g N L⁻¹ d⁻¹) was obtained with a [N-NO]/[N-NO] ratio of 1, i.e. full nitritation. The start-up of the partial nitrification system was quickly and successfully performed with an on-line control system using municipal wastewater treatment plant (WWTP) sludge as inoculum. An ammonia-oxidizing bacteria (AOB) fraction of 72 ± 10% was obtained after only 30 days of start-up. The applied SRT of 7–10 days with the combination of free ammonia inhibition and dissolved oxygen limitation provided the selective washout of nitrite-oxidizing bacteria (NOB) and an active nitrifying population with high ammonium oxidizing rates.

Keywords:

• control
• nitritation
• NOB washout
• SRT
• start-up

Acknowledgements

This work was supported by the European Commission (REMOVALS project, Contract FP6-018525). The authors are members of the GENOCOV group (Grup de Recerca Consolidat de la Generalitat de Catalunya, 2009 SGR 815). Josep Anton Torà is grateful for the grant received from the Spanish M.E.C. (Ministerio de Educación y Ciencia).