Performance range

HybridTM Process

HybridTM Process – The two-stage activated sludge process for nitrogen removal

The incorporation of existing facilities during plant enlargement and modification, often makes excellent economic sense with regard to cost minimisation, but can be technically difficult. The Hybrid process, jointly developed by WABAG and the Vienna University of Technology, is ideal for this purpose. It meets the new requirements and due to its two-stage structure possesses specific advantages:

Process stability:
The first process stage provides optimum load compensation, which even in the case of low wastewater temperatures secures the denitrification capacity of the second stage. This is an especially important advantage when dealing with industrial effluents or seasonal peak loads.

Economies over conventional single-stage plants:
The Hybrid process facilitates a considerable reduction in the tank volume required. Design comparisons for various plants have shown that in terms of total volume, approximately 30% can be saved.

The Hybrid process has already been used on a large-scale for the enlargement of the main wastewater treatment plant in Vienna from 2,100,000 p.e. to 4,000,000 p.e. The client, Entsorgungsbetriebe Simmering, decided to employ the Hybrid process as an alternative to the by-pass process due to its ability to provide operational advantages and improved wastewater quality.

The technology
The Hybrid process is based on the conventional two-stage activated sludge process. However the biozenoses of both stages are not separated, but advantageously mixed through two innovative hybrid sludge cycles. The volume of theses cycles is relatively low (approx. 3% of raw water inlet). Cycle 1 transfers sludge from the first to the second stage, providing active denitrifying biomass and carbon sources. The denitrification capacity of the second stage can therefore be controlled via the amount of sludge transferred and is not limited by the degree of carbon removal in the first stage.

On the other hand, activated sludge from the second stage is transferred by cycle 2 into the first stage. Continuous seeding of the nitrifying biomass results, which provides nitrification despite the low sludge age (high sludge load) in this stage. The nitrate produced is denitrified at a rapid rate due to high biomass activity. Improved phosphorous removal can be achieved biologically by means of an aerobic tank upstream of the first aeration tank, or by simultaneous precipitation.

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