Disc filtration for separation of flocs from a moving bed bio-film reactor

A Discfilter with 10 and 18 mu m filter openings, respectively, was placed in parallel to a flotation plant for separation of biological flocs from a post-denitrifying Kaldnes Moving Bed (TM) Process, the last treatment step at the municipal wastewater treatment plant at Sjolunda, Malmo, Sweden. The effluent concentrations from the 10 and 18 mu m filter were 2-5 and 2-8 mg SS L-1, respectively, which is comparable to, or better than, the flotation plant. Comparison with experiences from activated sludge plants shows that the Discfilter works especially well after the Kaldnes process. Particle size distribution (PSD) studies show that particles larger than the filter openings of 10 and 18 mu m are separated with approximately 90% efficiency, whereas most of the smaller particles pass the filter. This fact indicates that the major particle separation mechanism is physical blocking. These findings point to the possibility of improving the prediction of the separation efficiency by combining measurements of turbidity and suspended solids with particle size analysis.