Fouling control of submerged hollow fibre membrane bioreactor with transverse vibration

The present study further examines the effectiveness of transverse vibration for the fouling control of hollow fibre membranes in a submerged membrane bioreactor (SMBR) with real mixed liquor. The scope of the investigation included both short and long duration tests. The short duration tests incorporated both continuous and intermittent vibration in different concentrations of mixed liquor, and compared among longitudinal vibration, transverse vibration and combined transverse vibration and low aeration. The results indicated that continuous transverse vibration with low frequencies was very effective towards the fouling control, and was more so than longitudinal vibration. Intermittent vibration was somewhat less favourable, but it provided significant energy savings. With intermittent vibration, a short non-vibration time interval of less than 120 s was also found to be necessary to prevent irreversible fouling during this time interval when the permeated extraction continued. For the first time we found that transverse vibration can be more effective for fouling control when combined with low aeration due to the turbulence enhancement by the moving bubbles. The long duration tests confirmed that transverse vibration could be effectively used in the SMBR to control the membrane fouling and prolong the membrane filtration period without chemical cleaning, with high removal efficiencies of both organics and nutrients in the reactor. Higher frequencies of transverse vibration produced larger shear stresses on the membrane surface and enhanced the membrane filtration performance, at the same time the risk of fibre breakage also heightened with the increase in periodic stress cycles on the hollow fibres. The characteristics of the biosolids in the reactor were monitored during the long duration tests. The results showed that both soluble microbial products (SMP) and extracellular polymeric substances (EPS) affected the membrane filtration performance under transverse vibration, but SMP was found to be key membrane fouling contributor. Overall, the study demonstrated that transverse membrane vibration is practical and beneficial for fouling control in the SMBR.