Performance of a hybrid activated sludge/biofilm process for wastewater treatment in a cold climate region: Influence of operating conditions

The main aim of the study was to investigate a hybrid MBBR process, mostly in terms of organic matter removal and nitrification, when operating with different values of the mixed liquor sludge retention time (SRT), and highlighting the influence of temperature on the process. Based on experience in practice it was hypothesized that nitrification could be maintained at far lower SRT's than in conventional activated sludge systems and with high organic loading rates applied. A field gathering campaign has been carried out on a hybrid activated sludge/biofilm. The obtained results highlighted that the pilot plant was capable to remove the organic matter at loading rates up to 3.00 kg TCOD m−3 day−1, also showing very high nitrification activity. Ammonia uptake rate (AUR) batch test showed that biofilm nitrification activity increased when the mixed liquor SRT decreased. The final suggestion is that it is possible to run a hybrid reactor with low mixed liquor SRT values, as well as low temperatures, still having a high ammonium removal efficiency, since a large fraction of nitrification activity will take place in the biofilm.