Membrane separation

Comparison of population dynamic and kinetics of nitrifiers in activated sludge treatment with secondary clarifier and membrane separation The use of submerged membranes in the activated sludge process (short MBR for Membrane BioReactor) is a promising alternative to the conventional process with secondary settling tanks. This technology implies high effluent quality, small footprint and reduced sludge production. The main drawback are the still overall higher costs compared to the conventional treatment process.
With respect to the biomass two properties are important:

• The membrane (typical pore size of 0.01-0.4 µ) rejects all bacteria (diameter ca. 1 µm, which means that there is no selection of floc-forming organisms, as it happens in the conventional process. Therefore smaller structures or even single cells would theoretically be able to accumulate in the system.

• MBR can be processed at higher sludge ages. The higher sludge retention time theoretically allow for the accumulation of slow-growing organisms, which would be washed out at typical sludge ages of 10-15 days. This could be advantageous regarding the degradation of micropollutants.

The goal of this project is to study the impact of these process parameters on the nitrifying population in comparison to the conventional process. This includes determination of the performance and modelling of the nitrification process, especially at high sludge ages.

Investigations take place on two membrane pilot plants operated in parallel with a pilot plant with a secondary settler, fed by the same wastewater. The identification and quantification of the organisms will be performed by fluorescent in-situ hybridisation (FISH). Classical batch experiments provide kinetic information.