Mechanical reliability of microporous membranes in water recycling applications
The increase in population growth has driven the demand to produce water from non-potable sources via membrane technology. Microfiltration (MF) and ultrafiltration (UF) membranes, encased in a pressure vessel or submerged in a bioreactor, are used to filter suspended solids, microbial products and organic molecules from water and wastewater, which cause membrane fouling. Microporous membranes provide exceptional pre-treatment only if fouling of the membrane is kept to a minimum and the integrity of the hollow fibres are maintained.
The incidence of fibre failure can be broadly divided into three categories: 1) damage due to the presence of foreign forces (air scouring); 2) damage by chemical attack; and 3) damage due to the faulty membrane module structure. The design of membrane modules and aeration patterns are critical to ensuring the reliability of membrane elements. Additional stresses may occur when the hydrodynamics of the system are adjusted for fouling control. It has been reported that 40-50% of the fouling control can be attributed to fibre movement. The effect of the bubbling is enhanced if the fibres are loosely held so that continuous movement occurs. However, excess fibre movement could cause fibre damage. These conflicting observations pose a dilemma for the design and operation of hollow fibre elements and also highlights the need for membrane modules to be optimised in terms of membrane configuration (fibre length, packing density, fibre diameter, looseness), module geometry (orientation and shape of the module), and aeration systems (bubble size, air intensity, nozzle direction and layout).
Fouling control is also achieved by either frequent in situ backwash or offline cleaning using strong oxidants, such as sodium hypochlorite. The cumulative exposure of polymeric membranes to this oxidant can result in the degradation of the membranes. However, the concurrent impact of membrane fouling and chemical cleaning on the mechanical and structural properties of hollow fibre membranes and the prediction of the subsequent time to failure has not been addressed.
This project aims to use advanced fatigue analysis techniques and Finite Element Analysis (FEA) to understand and predict failure of different membranes and module configurations caused by both repetitive stress-based phenomena and shock loading.
Funding body: UNSW Faculty of Engineering Early Career Research (ECR) grants
Tng KH; Antony A; Wang Y; leslie, 2015, 'Membrane ageing during water treatment: Mechanisms, monitoring, and control', in Basile A; Cassano A; Rastogi NK (ed.), Advances in Membrane Technologies for Water Treatment, pp. 349 - 378, http://dx.doi.org/10.1016/B978-1-78242-121-4.00011-3
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