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This paper presents an advanced stage in the development of a generic process for upgrading existing wastewater treatment plants, with the intent to incorporate nitrification and de-nitrification without additional tankage. The process tested is an attached growth airlift reactor (AGAR), wherein a biomass carrier is used, and mixing is provided in the aerobic stages by partitions that create an airlift effect.

The airlift hydraulics provide an organized flow pattern in the reactor, which can be used to lower the shear forces on the bio-film attached to the carriers, thus reducing sloughing off of biomass. The design procedure for large airlift elements in an aeration basin containing floating media is based on classic airlift calculation procedures adapted to this specific case. The adaptation of hydraulic models includes modifications of holdup correlations for the shaped floating carriers and terms for pressure drop in liquid circulation.

The Combination of the organized flow pattern and the low density of the media enables hydraulic prevention of carrier migration between different process stages, eliminating the need for screens.

Process performance in a demonstration plant confirm the design values within a reasonable range, with respect to airlift hydraulics, attached biomass equivalent MLSS and BOD and nitrogen removal rates.
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Document Type: Research Article

Publication date: 01 January 2002

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