The effect of organic loading on process performance and membrane fouling in a submerged membrane bioreactor treating municipal wastewater

The results of experiments on municipal wastewater primary effluent are presented for a pilot-scale submerged membrane bioreactor (SMBR). The SMBR pilot plant employed an ultrafiltration membrane with a nominal pore size of 0.035 μm and was operated at a constant membrane flux of 30 L/m2 h. The mixed liquor suspended solids (MLSS) concentration was maintained at 8±2 g/L and steady-state fouling rates were determined for 10, 5, 4, 3, and 2-d MCRTs, corresponding to food-to-microorganism (F/M) ratios of 0.34, 0.55, 0.73, 0.84, and 1.41 gCOD/gVSS d, respectively. Membrane fouling rates increased as the F/M was increased. Steady-state membrane fouling rates were correlated with total soluble microbial products (SMP) concentrations. The membrane fouling rates did not correlate well with soluble COD measured on a 0.45 μm membrane filtrate of mixed liquor or with soluble COD rejection (effluent COD/soluble COD).