Influence of carbon/nitrogen ratio and non-aerated zone size on performance and energy efficiency of a partially-aerated submerged fixed-film bioreactor

•Partially ASFF system has potential for the treatment of ammonia-rich wastewater.•Increasing loading rates up to 2.8 kgCOD/m3d at constant HRT and COD/N increases nitrogen removal up to 60%.•Increase of non-aerated zone volume increases the nitrogen removal.•Energy performance coefficient evaluates energy efficiency of the system fairly.

Performance and energy efficiency of an upflow partially aerated submerged fixed-film (UP/ASFF) bioreactor was evaluated during a 10-month operation period. Increasing loading rates at constant HRT and COD/N increased nitrogen removals. Increase of non-aerated zone could also improve the nitrogen removals up to 83%. Energy performance coefficient based on required electrical energy showed that the energy efficiency of the system increases at lower COD/N value and bigger non-aerated zone for simultaneous COD and nitrogen removal from the synthetic wastewater. The present study showed also similar performance for municipal wastewater, demonstrating the potential of UP/ASFF system to treat high-ammonium municipal wastewaters.