Airlift bioreactors: Application to wastewater treatment
After an introductory review, this paper presents a three-phase reactor fluid dynamic model that is used in the development of a generic process for upgrading existing wastewater treatment plants (WWT). The aim is to incorporate nitrification and de-nitrification without additional reactor volume. The core of the process consists of an attached growth airlift reactor (AGAR) in which a biomass carrier is used. Mixing is provided in the aerobic stages by partitions that create an airlift effect. The design procedure for large airlift elements in an aeration basin containing floating solid carriers is based on classic airlift calculation procedures adapted to this specific case. The combination of the organized flow pattern and the low density of the media enable hydraulic prevention of carrier migration between different process stages, eliminating the need of screens. Process performance in a demonstration plant, expressed as airlift liquid velocity, confirms the predicted values within a reasonable range.