As shown in Fig. 1, DFCm relies on a single UF membrane (X-flow F5385, inside-out, ID=8 mm, nominal pore size 0.03 μm) under cross flow condition of 1 m/s to estimate the membrane fouling propensity of mixed liquor. Flux is maintained constant at 80 LMH by vacuum using a peristaltic pump. Temperature, pH, flux, dissolved oxygen (DO) concentration are recorded. The TMP at the feed, concentrate and permeate are also recorded over the course of the experiment (Evenblij, 2006; Van den Broeck, 2011)
Subsequently, Rtotal (=Rm+Rc+Rf) is calculated using the resistance in series model, which is based on Darcy’s law, as shown in Fig. 2. The Rtotal at the permeate production of 20 L/m2 is denoted as ΔR20 and is used to compare membrane fouling propensities of different mixed liquors. Filterability is qualified as poor when ΔR20 is higher than 1×1012 m-1, moderate when 0.1 x1012 m-1 <ΔR20< 1×1012 m-1 and good when ΔR20 values are lower than 0.1×1012 m-1.a
This method provides closer imitation of real membrane filtration than the above methods. The flux used, i.e. 80 LMH, however, is much higher than the flux commonly found in the MBR with immersed membranes. The high flux might be inevitable to expedite the membrane fouling so that the test can be completed within a reasonable time. As discussed here, the squeezing pressure on cake layer is directly affected by the flux rather than TMP. Therefore, cake layer compaction becomes much more severe in DFCm than in actual MBR. Under this circumstance, the effect of fine particles, EPS, and SMP can be over expressed by filling up the void spaces of cake layer.
Fig. 1. Picture and flow diagram of the apparatus of DFCm (Geilvoet, 2010)
Fig. 2. Schematic representation of filtration characterization unit, DFCm (Krzeminski, 2010).
© Seong Hoon Yoon