Abstract
The impact of the application of mechanically-imposed shear on the propensity for fouling and clogging (or “sludging”—the agglomeration of sludge solids in the membrane channel) of an immersed flat sheet (iFS) membrane bioreactor (MBR) was studied. The bench-scale test cell used contained a single flat sheet fitted with a crank and motor to allow the membrane to be oscillated (or reciprocated) vertically at a low rate (20 RPM). The membrane was challenged with sludge samples from a local MBR installation treating petroleum industry effluent, the sludge having previously been demonstrated as having a high sludging propensity. Sludging was measured by direct visual observation of membrane surface occlusion by the agglomerated solids, with fouling being notionally represented by the rate of transmembrane pressure increase. Results demonstrated membrane reciprocation to have a more beneficial impact on sludging amelioration than on suppressing fouling. Compared with the stationary membrane, sludging was reduced by an average of 45% compared with only 13% for fouling suppression at the reference flux of 15 L·m−2·h−1 applied. The specific energy demand of the mechanical shear application was calculated as being around 0.0081 kWh·m−3, significantly lower than values reported from a recent pilot scale study on a reciprocated immersed hollow fibre MBR. Whilst results appear promising in terms of energy efficiency, it is likely that the mechanical complexity of applying membrane movement would limit the practical application to low flows, and a correspondingly small number of membrane modules.
Highlights
The principle of employing mechanical, rather than aeration-imposed, shear to sustain the flux of an immersed hollow fibre membrane was reported more than 12 years ago [1,2]
%C, the measured occlusionor the membrane by surface agglomerated solids perinrecorded in the absence of revealed shear was revealed to increase with sludge(Figure viscosity unit time) the absence of shear was to increase with sludge viscosity
Sludging was quantified through visually determining the occlusion of the membrane surface by the attached solids
Summary
The principle of employing mechanical, rather than aeration-imposed, shear to sustain the flux of an immersed hollow fibre (iHF) membrane was reported more than 12 years ago [1,2]. These studies demonstrated the improvement in flux from applying a mechanical shear to immersed systems by vibrating (or oscillating or “reciprocating”) the iHF membrane, in much the same way as the more extensively reported and reviewed rotating and vibrating membrane disc systems [3,4]. The applied shear itself generates a flux J in m3 ·m−2 ·h−1 , the P0 /J ratio equating to the key normalized energy parameter of specific energy demand (SED) in kWh·m−3 .
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