Impact of aeration rates on particle colloidal fraction in the biofilm membrane bioreactor (BF-MBR)

In BF-MBR, as in all sMBR systems, sufficient aeration is necessary to maintain local cross-flow conditions for sustainable membrane operation. Aeration rate is normally based on previous experiences and manufactures’ recommendations. BF-MBR with an external submerged membrane unit, designed only for particle separation, could be relatively easily optimized in terms of membrane aeration. Combining observed fouling rates with measured particle size distribution and minimizing both parameters indicates a desirable sustainable aeration rate for given wastewater characteristic, operating parameters (i.e. production/backwash flux, recovery) and membrane module geometry.

The aim of this study was to define a procedure that can determine sustainable aeration rates for a BF-MBR process with a given membrane reactor design, sustainable flux and wastewater characteristics. The results show the importance of finding the relationship between sufficient aeration to minimize membrane fouling, while preventing formation of colloidal particles due to excessive share forces caused by the aeration. An approach to define optimal operating conditions with respect to aeration rates is proposed. By evaluating overall fouling rates and PSD analysis based on an assessment of the differential number percent of submicron particle, recommenda- 0,20 0,18 0,14 0,12 0,10 0,08 0,06 PSD [number %] Fouling rate - dTMP/dt [bar/h] 0,16 0,04 0,02 0,00 SADm [Nm /m h] Fig. 5. Fouling rate and PSD values of the most present submicron fraction for different aeration rates (SADm).