Fouling control strategies for direct membrane ultrafiltration: Physical cleanings assisted by membrane rotational movement
Date
2022Abstract
Recently, interest in the application of direct membrane filtration (DMF) in wastewater treatment has increased
as an alternative to conventional activated sludge technologies. However, membrane fouling remains the main
limitation for its application on an industrial scale. Dynamic shear-enhanced membrane systems, such rotating
hollow fibre membranes (R-HFM), have shown to be effective in fouling control and mitigation with complex
suspensions (e.g. anaerobic membrane bioreactors). In fact, previous works with DMF demonstrated the capa-
bility of membrane rotation to prevent matter deposition during the filtration cycles. Nevertheless, physical
cleanings aided by membrane rotation in systems where there is no biological organic matter degradation has not
been previously explored.
Therefore, the current study addresses a physical cleaning strategy based on membrane module rotation for
DMF. The effect of rotational speed (0 – 340 rpm) and relaxation time (0 – 270 s) on filtration performance was
studied at dead-end lab scale trials. Pre-treatment effectiveness by in-situ and ex-situ sewage coagulation on
fouling mitigation has been also assessed. DMF improved with pre-coagulation, reducing significantly membrane
fouling. Ex-situ coagulation was identified as the best pre-treatment mode since flocs breakage and foulants
releasing are avoided. In addition, the rotational speed increase during the backwashing stage enhanced erosion
and dispersion of detached foulants. Besides, the addition of a relaxation stage (tR ≥ 180 s) enhanced the
effectiveness in fouling re-dispersion. The physical cleanings demonstrated their effectiveness during long term
trials, allowing operation at high permeate fluxes (24 L⋅h 1⋅m 2) with moderate organics up-concentration.