Abstract
A major cause of ultrafiltration (UF) membrane fouling is the accumulation of microorganisms and their associated soluble products. To mitigate fouling the application of pulsed short-wavelength ultraviolet (UVC) light (around 254 nm) within the membrane tank together with pre-coagulation was investigated. In mini-pilot-scale tests carried out in parallel with conventional pre-treatment (CUF), the impact of pulsed UV (CUF-UV) at different UV irradiances and fluxes on the increase of trans-membrane pressure (TMP) was evaluated and explained in terms of the quantity and nature of membrane deposits in the membrane cake layer and pores.The results indicated that at a flux of 20 L m−2 h−1, the pulsed UV (1 min within 31 min cycle) at 3.17 × 10−2 W/cm2 prevented any measureable increase in TMP over a period of 32 days, while there was a fourfold increase in TMP for the conventional pre-treatment. For the CUF-UV system the concentration of bacteria and soluble microbial products was much less than the conventional CUF system, and the cake layer was thinner and contained less biopolymers (proteins and polysaccharides). In addition, the pores of the CUF-UV membrane appeared to have less organic deposits, and particularly fractions with a high molecular weight (>10 kDa).At a lower UV irradiance (1.08 × 10−2 W/cm2), or higher flux (40 L m−2 h−1) with the same UV irradiance, there was a measurable increase in TMP, indicating some fouling of the CUF-UV membrane, but the rate of TMP development was significantly lower (∼50%) than the conventional CUF membrane system. Overall, the results show the potential advantages of applying intermittent (pulsed) UVC irradiation with coagulation to control UF membrane fouling.
Highlights
Membrane separation is a rapidly developing treatment technology for the supply of drinking water, but the blockage/reduction of membrane pores, ‘fouling’, caused by particles, organic matter and microorganisms, remains a limitation to its wider application (Lin et al, 2000; Her et al, 2003; Laabs et al, 2006; Huang et al, 2007)
In view of the potential advantages of this novel form of UV technology, we have evaluated the use of pulsed-UVC light, applied within an ultrafiltration membrane module, together with coagulation, as a method to control membrane fouling
extracellular polymeric substances (EPS) extracted from the cake layers and sludges, and organic matter in the waters from the two membrane systems, were analyzed by SEC based on a unit mass of material after drying, using UV254 absorbance (Myat et al, 2014) to determine their apparent molecular weight (MW) distribution of UV-active substances
Summary
Membrane separation is a rapidly developing treatment technology for the supply of drinking water, but the blockage/reduction of membrane pores, ‘fouling’, caused by particles, organic matter and microorganisms, remains a limitation to its wider application (Lin et al, 2000; Her et al, 2003; Laabs et al, 2006; Huang et al, 2007). Some pre-treatment methods, such as chemical coagulation before membrane filtration, are effective and relatively low cost approaches for improving general water quality and controlling membrane fouling (Peiris et al, 2013; Kimura et al, 2014; Wray et al, 2014). This is partly because coagulation substantially reduces the compressibility of the cake/gel layer (Tabatabai et al, 2014). Effective microbial inactivation and low energy), we have evaluated the use of pulsed-UVC light, applied within an ultrafiltration membrane module, together with coagulation, as a method to control membrane fouling. The underlying reasons/mechanisms for the improved performance are discussed in detail
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