A continuous biofilm process for enhanced biological nitrogen and phosphorus removal with alternating flow direction and carbon management

Journal article, 2026

More compact wastewater treatment is attractive for handling increased loads and stricter effluent requirements.
The moving bed biofilm reactor (MBBR) can achieve high carbon and nitrogen removal capacity at a small
footprint but is challenged to also reach efficient enhanced biological phosphorus removal (EBPR). This pilot
study evaluated a new approach to promote EBPR and high nitrogen removal in continuous flow MBBRs by
operating with alternating flow direction and intermittent aeration, thus enabling the cyclic anaerobic and
aerobic/anoxic conditions required for polyphosphate accumulating organisms (PAOs). The MBBRs utilised a
novel bio-based support material with external biofilm growth for improved mass transfer and were fed prefiltered
municipal wastewater. To increase the availability of readily biodegradable carbon for nutrient
removal, the influent was supplied with volatile fatty acids (VFA), mimicking fermentation of sludge from primary
filtration. The 460-day long study demonstrated stable nitrogen removal and EBPR. The presence of PAOs
in the biofilm was demonstrated in batch tests as well as by microbial analysis, with Ca. Phosphoribacter, Tetrasphaera
and Ca. Accumulibacter being detected in high relative abundances. Both aerobic and anoxic phosphate
uptake were observed, indicating denitrifying PAO activity. The VFA addition had a strong impact on the
EBPR, which increased when directing the VFA to the anaerobic phases, compared to dosing VFA continuously.
With VFA dosing in the anaerobic phases, nitrogen and phosphorus removal were 84 ± 5% and 68 ± 18%,
respectively, demonstrating the possibilities with this novel process for future full-scale installations.