Browsing by Author "Henderson, Rita Kay"

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    Carbonaceous and nitrogenous disinfection by-product formation from algal organic matter
    (Elsevier, 2016-12-10) Goslan, Emma Harriet; Seigle, Céline; Purcell, Diane; Henderson, Rita Kay; Parsons, Simon A.; Jefferson, Bruce; Judd, Simon J.
    Seasonal algal blooms in drinking water sources release intracellular and extracellular algal organic matter (AOM) in significant concentrations into the water. This organic matter provides precursors for disinfection by-products (DBPs) formed when the water is subsequently chlorinated at the final disinfection stage of the potable water treatment process. This paper presents results of AOM characterisation from five algal species (three cyanobacteria, one diatom and one green) alongside the measurement of the DBP formation potential from the AOM of six algal species (an additional diatom). The character was explored in terms of hydrophilicity, charge and protein and carbohydrate content. 18 DBPs were measured following chlorination of the AOM samples: the four trihalomethanes (THMs), nine haloacetic acids (HAAs), four haloacetonitriles (HANs) and one halonitromethane (HNM). The AOM was found to be mainly hydrophilic (52 and 81%) in nature. Yields of up to 92.4 μg mg−1 C carbonaceous DBPs were measured, with few consistent trends between DBP formation propensity and either the specific ultraviolet absorbance (SUVA) or the chemical characteristics. The AOM from diatomaceous algae formed significant amounts of nitrogenous DBPs (up to 1.7 μg mg−1 C). The weak trends in DBPFP may be attributable to the hydrophilic nature of AOM, which also makes it more challenging to remove by conventional water treatment processes.
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    The impact of differing cell and algogenic organic matter (AOM) characteristics on the coagulation and flotation of algae
    (Elsevier, 2010-06) Henderson, Rita Kay; Parsons, Simon A.; Jefferson, Bruce
    The aim of this study was to compare the coagulation and flotation of different algae species with varying morphology and algogenic organic matter (AOM) composition in order to link physical and chemical algae characteristics to treatment. Microcystis aeruginosa (cyanobacteria), Chlorella vulgaris (green algae), Asterionella formosa and Melosira sp. (diatoms) were treated by coagulation with aluminium sulphate and flotation. The AOM was extracted and treated separately. Analyses included cell counts, dissolved organic carbon, aluminium residual and zeta potential. Removal efficiencies in the range 94–99% were obtained for each species. Cells, AOM and aluminium were concurrently removed at a coagulant dose that was related on a log–log basis to both cell surface area and total charge density, although the relationship was much stronger for the latter. This was attributed to a significant proportion of the coagulant demand being generated by the AOM. The implications of such findings are that relatively simple charge measurements can be used to understand and control coagulation and flotation of algae.
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    PosiDAF for algae removal
    (Cranfield University, 2007-10) Henderson, Rita Kay; Jefferson, Bruce
    During algac blooms, coagulation is frequently unsuccessful resulting in poor flotation duc to complex algal character. 11iis thesis cxplorcs tlic link between algal character and conventional treatment and the potential for developing morc appropriatc algac trcatmcnt tcclinologics. Specifically, dissolvcd air flotation (DAF) that has bccn adaptcd by dosing cationic clicmicals to the saturator to modiry bubbic surfaccs, such that it docs not rcly on coagulation, is invcstigatcd. 1'his proccss is tcrmcd PosiDAF. Analysis of dissolved algogcnic organic mattcr (AOM) extracted from problcmatic species enabled investigation of the impact of morphology and AOM on coagulation- flocculation-flotation. Both increasing surface area and charge density of algae systcrns, werc rclatcd to increasing coagulant dcmand. Application of the appropriate coagulant dcmand ensured removal of all thrcc components - cclls, AOM and coagulant. Maintaining the zcta potential bct-%vccn -10 mV and +2 mV ensured optimum rcmoval was obtained. PosiDAF trials were conducted by dosing chemicals that had previously been shown to alter bubble charge, including co3gulant, surfactant and polymer, to the saturator. Coagulants were unsuitable for use in PosiDAF as they did not remain at the bubble surface. Highly hydrophobic, cationic surfactants were observed to remove cells according to a theoretical model, such that removal improved with increasing bubbic: particic ratio and with cell size. The polymer, polyDADNIAC, achieved greater removal cfficiencies than those predicted theoretically, attributed to an increase in the swept volume of the bubble. However, polyDADMAC was sensitive to changes in AOM composition. A chemical that combines attributes of both surfactant and polyDADMAC may overcome the barriers to PosiDAF implementation.
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    The practical application of fractal dimension in water treatment practice-the impact of polymer dosing
    (Taylor & Francis Inc., 2008-07-01T00:00:00Z) Jarvis, Peter; Parsons, Simon A.; Henderson, Rita Kay; Nixson, Nicholas; Jefferson, Bruce
    The application of floc fractal dimension has been investigated in this work to determine if this parameter can have operational significance in water treatment. Natural organic matter suspensions were coagulated with aluminium sulphate and varying concentrations of a non‐ionic polymer. The fractal dimensions of the flocs formed were measured using light scattering and settling combined with image analysis. By using the correct methodology, optimum floc properties could be determined using the floc fractal dimension combined with the floc size and strength data.