Browsing by Author "Porcelli, Nicandro"

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    Chemical cleaning of potable microfiltration and ultrafiltration membranes
    (Cranfield University, 2009-06) Porcelli, Nicandro; Judd, Simon J.
    Concerns over possible waterborne disease forced drinking water supply companies in England and Wales to adopt microfiltration and ultrafiltration technologies rapidly. MF and UF membrane plants are designed to produce water of a consistent quality regardless of throughput and fluctuations in the feedwater quality. To operate well they need to maintain flux and balance the rate of fouling, and chemical cleaning performance is critical to this. Giant steps have been taken into characterizing the foulants scientifically in the last few years while cleaning is reactive and ad hoc. This thesis explores the basis for a corresponding cleaning science for the technology to develop quantitively. Cleaning performance was defined in terms of a response to combinations of explanatory variables in a materials limited cleaning envelope. The study focused on applying variations of cleanant concentration, applied temperature and soak times to a variety of membranes fouled with different waters and regimes. An experimental design was developed and applied consistently to a number of different sampled sites; allowing an optimised recovery from the polynomial expressions for each treatment, through factorial analysis of the data. The size and variety of the data set analysed allowed comparison and quantification of the different deviations from optimal cleaning response. This effect was seen to vary temporally and with operating regime and the methods usefulness as a practical tool in the membrane plant lifecycle was considered. Cost evaluation of the variation in cleaning response showed that sub-optimal cleaning costs and energy use may be significant and the thesis also illustrated how module geometry affects initial cake deposition and thus cleanability. By demonstrating the potential for cleaning factor analysis, the potential for a combined heuristic and predictive cleaning control science is possible, but will need new strategies to manage technology change.
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    Chemical cleaning of potable water membranes: A review
    (Elsevier Science B.V., Amsterdam., 2010-02-01T00:00:00Z) Porcelli, Nicandro; Judd, Simon J.
    The literature on chemical cleaning of polymeric hollow fibre ultrafiltration and microfiltration membranes used in the filtration of water for municipal water supply is reviewed. The review considers the chemical cleaning mechanism, and the perceived link between this and membrane fouling by natural organic matter (NOM)—the principal foulant in municipal potable water applications. Existing chemical cleaning agents used for this duty are considered individually and their cleaning action described, along with the most commonly applied cleaning protocols (i.e. the cleaning conditions, cleaning sequence and method of cleaning agent application). It is concluded that chemical cleaning is poorly understood and not extensively investigated, in marked contrast to the much more widely studied area of membrane fouling generally, for which there are thousands of published studies. Studies of chemical cleaning specifically have instead been generally limited either to qualitative measurements, such as the use of surface or other analytical tools to characterise membrane foulants and record their removal, or incidental permeability recovery recorded from cleaning events during pilot or full-scale trials. It is proposed that a chemical cleaning index is needed, analogous to the recently proposed general membrane fouling index, based on empirical data to inform cleaning protocols for specific duties and feedwater qualit
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    Chemical cleaning of potable water membranes: The cost benefit of optimisation
    (Elsevier, 2010-03) Porcelli, Nicandro; Judd, Simon J.
    A study of the variability in chemical cleaning factors on permeability recovery for potable water microfiltration (MF) and ultrafiltration (UF) systems has been carried out employing a cost model simulating plant fouling and cleaning regimes. The impact of a range of operating and cleaning factors on operating cost variation was computed using algorithms describing operational and cleaning factor relationships with permeability recovery data measured from bench scale tests on fibres sampled from full-scale operational plants. The model proceeded through sequencing of the cleaning and backwashing operations to generate transmembrane pressure (TMP), and so head loss, transients. A number of cleaning scenarios were considered for each plant, based on employing either a threshold TMP or fixed chemical cleaning intervals. The resulting TMP profiles were then converted to operational costs. The effect of the variability in permeability recovery on annual operating costs was calculated for each of the simulations. It was evident that significant operating cost reductions were possible from optimisation of the cleaning protocol. Cost benefit varied according to facets of plant design and operation; the innate variability in permeability recovery precluded the correlation of cleaning efficacy with fouling characteristics.