Abstract
The submerged membrane filtration concept is well-established for low-pressure microfiltration (MF) and ultrafiltration (UF) applications in the water industry, and has become a mainstream technology for surface-water treatment, pretreatment prior to reverse osmosis (RO), and membrane bioreactors (MBRs). Compared to submerged flat sheet (FS) membranes, submerged hollow fiber (HF) membranes are more common due to their advantages of higher packing density, the ability to induce movement by mechanisms such as bubbling, and the feasibility of backwashing. In view of the importance of submerged HF processes, this review aims to provide a comprehensive landscape of the current state-of-the-art systems, to serve as a guide for further improvements in submerged HF membranes and their applications. The topics covered include recent developments in submerged hollow fiber membrane systems, the challenges and developments in fouling-control methods, and treatment protocols for membrane permeability recovery. The highlighted research opportunities include optimizing the various means to manipulate the hydrodynamics for fouling mitigation, developing online monitoring devices, and extending the submerged HF concept beyond filtration.
Highlights
Low-pressure membrane processes, such as microfiltration (MF) and ultrafiltration (UF), are popular technologies in the water industry due to their proven efficiency in removing particles, colloids, and high molecular weight organics [1,2]
It has been observed that at high gas flowrates, a maximum flux was observed, after which the flux started to decline [212]. This phenomenon was explained by the relationship between the bubble size and air flowrate; since bubble size tends to increase with the air flowrate, the bubbles become so large after an optimum air flowrate that they start to prevent the liquid from reaching the membrane surface, a phenomenon that is linked to slugging flow
In a little over two decades, submerged hollow fiber (HF) have gone from a curiosity to the mainstream of membrane technology
Summary
Low-pressure membrane processes, such as microfiltration (MF) and ultrafiltration (UF), are popular technologies in the water industry due to their proven efficiency in removing particles, colloids, and high molecular weight organics [1,2]. Submerged membrane systems have to deal with fouling, which represents a major drawback that restricts the application of membrane processes in the water industry [8]. An important development that coincided with the introduction of submerged HFs was the realization that dead-end filtration was attractive for dilute feeds (surface waters, RO pretreatment). In this case the filtration is operated in cycles, with the dead-end forward flux interrupted by backwashing and periodic surface flushing [25] or relaxation [26]. As HF membrane performance continues to improve, submerged HF systems are increasingly becoming more attractive for water treatment, in membrane bioreactor (MBR). This review focuses on recent developments in submerged hollow fiber (HF) membrane systems, the challenges and developments in fouling control methods, and treatment protocols for membrane permeability recovery
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