Browsing by Author "Carra, Irene"

Now showing 1 - 14 of 14
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    Are microbubbles magic or just small? a direct comparison of hydroxyl radical generation between microbubble and conventional bubble ozonation under typical operational conditions
    (Elsevier, 2022-01-24) John, Alexander; Carra, Irene; Jefferson, Bruce; Jodkowska, Monika; Brookes, Adam; Jarvis, Peter
    The application of microbubbles for water treatment is an emerging technology which has been shown to significantly enhance gas–liquid contacting processes. When applied to ozonation, microbubble technology has been shown to enhance mass transfer and the speed and extent of compound removal compared with conventional bubbling techniques. One explanation as to why microbubble systems outperform conventional systems is that microbubbles shrink, collapse and spontaneously generate hydroxyl radicals which is thought to enhance the speed of compound removal. This study compared microbubble (mean diameter 37 μm) and conventional bubble (mean diameter 5.4 mm) ozonation systems under identical conditions. The experiments were normalised for effective ozone dose to determine whether microbubble ozonation generated significantly more hydroxyl radicals than conventional bubble ozonation. 4-chlorobenzoic was used as the hydroxyl radical probe and the proportion of hydroxyl radicals generated for a given effective ozone dose was quantified. The •OH-exposure to O3-exposure (the ) was used to compare the systems. The ratio of the mean to mean was 0.73, 0.84 and 1.12 at pH 6, 7 and 8 respectively. Statistical assessment of the showed that there was no significant difference between the bubble systems. No evidence was found to support the hypothesis that microbubble systems generate more •OH. Instead, the level of •OH-exposure is linked to the effective dose and pH of the system and future designs should focus on those factors to deliver •OH based benefits.
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    Ceramic vs polymeric membrane implementation for potable water treatment
    (Elsevier, 2022-03-08) Jarvis, Peter; Carra, Irene; Jafari, M.; Judd, Simon J.
    The continued technological developments and decreased purchase costs of ceramic membranes have seen increased recent interest in the technology as an alternative to the more widely used polymeric membranes. This paper assesses the relative technical, practical and economic merits of the two membrane materials in the context of potable water production from surface water sources. The work focuses on phenomena of direct technoeconomic significance, namely cleaning efficacy (manifested as permeability recovery), membrane integrity and incurred labour effort. Topics reviewed thus comprise: (a) practical comparison of the two technologies challenged with the same feedwater, (b) comparative technoeconomic analyses, (c) membrane integrity studies of polymeric membranes - incorporating aged samples extracted from operating installations, (d) sludging incidents, and (e) pilot and full-scale data. Available relevant data reveal: (a) bench-scale comparative tests do not indicate a consistent significant difference in the net permeability between the two membranes; (b) polymeric membranes are subject to a decline in both mechanical strength and permeability from the loss of the hydrophilic agent over a period of years from the action of hypochlorite used for cleaning; (c) the decreased mechanical strength with age of polymeric membranes increases the manual repair requirement and shortens membrane life, respectively impacting on labour and membrane replacement costs where the latter is also determined by the permeability; (d) the chemical and mechanical robustness of ceramic membranes permits more aggressive chemical cleaning, which then affects the chemicals consumption cost; and (e) anecdotal evidence suggests that polymeric membranes challenged with pre-coagulated surface waters may be subject to sludging, the agglomeration of solids in the membrane channels, which may also be age-related. Notwithstanding the above, data from published comparative technoeconomic studies indicate a linear relationship between the overall cost benefit and the membrane module cost ratio mitigated by the relative membrane life and operating flux.
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    Disinfection by-product formation during UV/Chlorine treatment of pesticides in a novel UV-LED reactor at 285 nm and the mitigation impact of GAC treatment
    (Elsevier, 2020-01-07) Carra, Irene; Lozano, Javier Fernandez; Autin, Olivier; Bolton, James R.; Jarvis, Peter
    The UV/Chlorine process has gained attention in recent years due to the high quantum yield and absorbance of the chlorine species. However, there are still many unknowns around its application as a treatment for drinking water. The potential for the formation of disinfection by-products (DBPs) is one of them. There are no studies reporting on the formation of trihalomethanes (THMs) or haloacetic acids (HAAs) in complex matrices, such as real source waters, at UV wavelengths tailored to the UV/Chlorine process, which has been possible thanks to the development of light emitting diodes (LEDs). In addition, consideration of mitigation measures that might be needed after UV/Chlorine treatment for full scale application have not been previously reported. Specifically, the novelty of this work resides in the use of an innovative reactor using UV-LEDs emitting at 285 nm for the removal of three pesticides (metaldehyde, carbetamide and mecoprop), the evaluation of THM, HAA and bromate formation in real water sources by UV/Chlorine treatment and the mitigation effect of subsequent GAC treatment. A new parameter, the applied optical dose (AOD), has been defined for UV reactors, such as the one in the present study, where the irradiated volume is non-uniform. The results showed the feasibility of using the UV/Chlorine process with LEDs, although a compromise is needed between pH and chlorine concentration to remove pesticides while minimising DBP formation. Overall, the UV/Chlorine process did not significantly increase THM or HAA formation at pH 7.9–8.2 at the studied wavelength. At acidic pH, however, THM formation potential increased up to 30% after UV/Chlorine treatment with concentrations up to 60 μg/L. HAA formation potential increased between 100 and 180%, although concentrations never exceeded 35 μg/L. In all cases, GAC treatment mitigated DBP formation, reducing THM formation potential to concentrations between 3 and 16 μg/L, and HAA formation potential between 4 and 30 μg/L.
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    Effect of elevated UV dose and alkalinity on metaldehyde removal and THM formation with UV/TiO2 and UV/H2O2
    (Elsevier, 2015-11-26) Jefferson, Bruce; Jarvis, Peter; Bhagianathan, Govind Kannoly; Smith, Heather M.; Autin, Olivier; Goslan, Emma Harriet; MacAdam, Jitka; Carra, Irene
    Drinking water production needs to increasingly consider removal of background organic matter and trace micropollutants without increasing disinfection-by-product (DBP) formation potential. The presented data demonstrates the efficacy of both UV/H2O2 and UV/TiO2 in removing the pesticide metaldehyde to below drinking water compliance levels in both real and synthetic waters. This pesticide has proven to be unaffected by conventional water treatment processes such as granular activated carbon and is responsible for many of the water company compliance failures in the UK. The potential of UV/H2O2 is further demonstrated to offer an alternative approach for the removal of recalcitrant organic matter to ensure DBP compliance as long as extended UV doses of over 10,000 mJ cm−2 are applied at the optimum peroxide dose of 8 mM. Alkalinity and UV dose have an impact on DBP formation: at low UV fluences, increased alkalinity reduced the DBP formation. The UV/TiO2 process was observed to be inhibited in the presence of alkalinity. Aggregation studies and comparison of the catalyst fractal dimension showed that the process inhibition is mainly due to aggregation. This restricts the surface area available for reactions, rather than changes in the catalyst properties or carbonate radical scavenging, which is often the reasoning attributed to photocatalysis inhibition. Hence, the presented results indicate that decreasing the catalyst aggregation is the key to apply photocatalysis as drinking water treatment.
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    Enhancement of ozonation using microbubbles – Micropollutant removal, mass transfer and bromate formation
    (Elsevier, 2023-10-13) John, Alexander; Carra, Irene; Jefferson, Bruce; Bertolaso, Lucie; Brookes, Adam; Jarvis, Peter
    Microbubble technology is a promising development in the optimisation of gas–liquid contacting processes. When applied to ozonation, microbubbles have demonstrated significant enhancements to mass transfer, dissolved ozone residual and the speed and extent of compound removal. However, the mechanism by which microbubbles enhance performance over conventional bubbles is not well understood and numerous explanations exist within the literature. To elucidate the critical components that drive such enhancements the performance of microbubbles (Sauter mean diameter 37 µm) and conventional bubbles (5.4 mm) were compared under identical conditions in terms volumetric mass transfer coefficient, steady state dissolved ozone concentration, rate constant for ozone self-decomposition and the rate constant for degradation of two pesticides: mecoprop and metaldehyde. Overall, the improvement observed in performance can be attributed to the increase in the volumetric mass transfer coefficient through the combination of an increase in specific interfacial area and a decrease in the mass transfer coefficient. The increase in area outweighed the decrease in mass transfer coefficient such that an overall improvement factor of 1.6 was observed for microbubbles over conventional bubbles. All other differences were an artefact of the enhanced mass transfer leading to higher dissolved ozone concentrations when operating at a fixed input dose. For the first time it has been shown that when normalised to the amount of ozone transferred to the water, no enhancement in hydroxyl radical production, bromate formation or impact from the background constituents could be observed.
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    Feasibility study of suspended ion exchange for organic matter removal and disinfection by-product minimisation in UK lowland waters
    (Institute of Water, 2021-12) Fernandez-Lozano, Javier; Jarvis, Peter; Dunn, Clair; Carra, Irene; Brookes, Adam
    This investigation compared the performance of suspended ion exchange (SIX) and granular activated carbon (GAC) filtration for organic matter removal and reduction of trihalomethane (THM) and haloacetic acid (HAA) formation potential. SIX treatment resulted in increased organic matter removal (60%) when compared with GAC (45%). SIX treatment produced a stable treated water Dissolved Organic Carbon (DOC), while changes in brine concentration had no effect on the removal of organic disinfection by-product (DBP) precursors. Liquid chromatography organic carbon detection analysis (LC-OCD) showed that the differences in the organic matter removal by SIX in comparison to GAC were caused by the increased affinity of the SIX process towards the 1 kDa and 0.5-0.35 kDa organic matter size bands. These were the molecular weight fractions comprising most of the overall DOC. Organic matter removal was consistent with the minimisation of THM and HAA formation. THM formation was reduced by 50% and 65%, whereas HAA formation was lowered by 60% and 70% in comparison to the untreated water, after GAC and SIX treatment, respectively. A linear correlation between the Br:DOC ratio and the bromine substitution factor was found for THMs and HAAs, suggesting that the formation of Br-DBPs was not selective to the treatment but attributed to bulk organic matter removal and bromide content at source. The use of resin in chloride form increased the chloride to sulphate mass ratio and Larson Index suggesting a risk for increased corrosivity of SIX treated water in the distribution network.
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    Impact of resin loading on ion exchange equilibrium for removal of organic matter and inorganic ions
    (Elsevier, 2022-02-19) Pidoux, Lucie; Shorney-Darby, Holly; Vaudevire, Elisabeth; Martijn, Bram; Jarvis, Peter; Carra, Irene
    Ion Exchange (IEX) applications for drinking water can be limited due to high volumes of brine, brine waste and treated water corrosivity. Reusing the resin by operating at reduced regeneration frequency can overcome this. However, assessing changes on the resin loading over reuse cycles is complex because multiple presaturant ions participate in the exchange and existing models only account for the exchange with one presaturant ion. This study developed a theoretical multicomponent model for the determination of IEX equilibria when the resin loading increases due to reuse. The model suggested that both electrostatic interactions and admicelle formation were the separation mechanisms. The model revealed that under reduced regeneration frequencies, brine use and waste generation can be reduced by more than 90%, where the bicarbonate-form resin offered the potential for lower corrosivity. However, changes in resin loading after 5 reuse cycles showed that the risk of corrosion increased. For the tested source water, reusing the bicarbonate-form resin every 5 cycles would achieve the most sustainable option with 41% NOM removal and 79% brine and waste reduction. Under these conditions, almost 100% of exchange capacity is recovered after regeneration.
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    Low-pressure membrane technology for potable water filtration: true costs
    (Elsevier, 2021-01-08) Judd, Simon J.; Carra, Irene
    The overall cost, expressed as the present value (PV), of the construction and operation of low-pressure membrane filtration of inland water for potable water supply has been determined for membrane installations across the UK. The analysis was based on 15 full-scale installations installed with hollow fibre and capillary tube polymeric membranes, for which cost and related data were available. The analysis encompassed labour, in addition to energy, chemicals and critical component replacement. PV data were presented as functions of flow capacity (i.e. as cost curves), delineated as capital (CAPEX), operating (OPEX) and total PV normalised against flow rate (PV’) the CAPEX excluding the site-specific civil engineering costs. Captured CAPEX data revealed these to be lower than those previously reported, and with a reduced economy of scale. The OPEX PV exceeded the CAPEX by a factor of 3-6 based on a 20-year life cycle, the difference increasing with decreasing flow capacities. Costs associated with unplanned (or “reactive”) maintenance, partly associated with the repair of breached membranes and/or permeability recovery following membrane clogging, were found to make up around half the labour costs. Labour costs as a proportion of the flow increased with decreasing flow, exceeding the CAPEX at flows below 30,000 m3/d. Outcomes indicate labour costs associated with process upsets to contribute significantly to the overall cost of the installation over its life cycle, particularly at flows below ~30,000 m3/d. A clear trade-off exists between supplementary capital investment to allay process upsets and the operational costs associated with such events.
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    Microbubbles and their application to ozonation in water treatment: A critical review exploring their benefit and future application
    (Taylor & Francis, 2020-12-22) Alexander, John; Brookes, Adam; Carra, Irene; Jefferson, Bruce; Jarvis, Peter
    Ozonation is a widely applied water treatment process, used for oxidation of contaminants, as well as for the disinfection of water. However, the conventional ozonation process demands a high energy requirement and deep tanks to ensure effective mass transfer and oxidation. Microbubble technologies have emerged which have the potential to improve gas-liquid contacting. Microbubbles have diameters of 1–100 µm, while conventional bubbles used in ozonation are between 2 and 6 mm. Microbubbles have many favorable characteristics that make them suitable for ozonation. In this review, the attributes of microbubbles for ozonation have been compared with those of conventional bubbles. The higher interfacial area and lower rise velocity of microbubbles compared with conventional bubbles means that ozone in the gas phase can be more efficiently transferred into the liquid phase. This is due to a higher contact time and increased contact area of the bubble with the bulk liquid. The analysis reveals that the volumetric mass transfer coefficient can be significantly enhanced through the use of microbubbles. In addition, the steady state dissolved ozone concentration was positively impacted by the use of microbubbles. Microbubbles were shown to be able to oxidize a broader range of organic compounds more quickly than for conventional bubbles. However, the review highlighted that comparison of microbubbles with conventional bubbles is not always carried out in a fair and consistent way with respect to reactor configuration. Requirements for future research, more consistent experimental comparisons and the steps needed to enable implementation of microbubbles have been discussed.
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    Organic matter removal with bicarbonate-form ion exchange: water quality, kinetics and mass transfer mechanisms
    (Elsevier, 2021-10-09) Fernandez, Javier; Jarvis, Peter; Brookes, Adam; Knott, Stuart; Carra, Irene
    Ion Exchange (IEX) has been widely explored for the removal of organic matter. Chloride is traditionally used as counter-ion, but its release into water can increase the risk of corrosion. Research has shown that bicarbonate IEX can be an efficient alternative, and whilst some studies have compared its efficiency to chloride IEX, none have compared their performance in relation to the potential for disinfection by-product (DBPs) formation. The differences in organic matter removal between the two regenerants were assessed by looking at the molecular weight fractions derived from liquid chromatography organic carbon detection (LC-OCD) and dissolved organic carbon (DOC). Uptake kinetics, resin age and mass transfer diffusion were also investigated. DOC removal was similar for both chloride and bicarbonate resins, achieving ca 50% DOC removal. LC-OCD analysis revealed that organic matter between 0.35 and 1 kDa was the most efficiently removed, with slightly better uptake with bicarbonate IEX. However, these differences did not impact DBP formation potential. Trihalomethane (THM) and haloacetic acid (HAA) formation potentials followed the trends of DOC removal with up to 70% reduction after IEX treatment with both resin forms. However, the bromine substitution factor (BSF) increased with resin age -from 5 to 10% for THMs and from 4 to 7% for HAAs. Resin age resulted in up to 20% decrease in the organic matter uptake rates (from 0.19 to 0.15 min−1) and up to 34% decrease in pore diffusivities (from 9.4 × 10−12 to 7.1 × 10−12 m2/s for chloride IEX and from 1.0 × 10−11 to 6.6 × 10−11 m2/s).
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    Removal of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) by coagulation: influence of coagulant and dosing conditions
    (Elsevier, 2025-03-01) Wang, Pin; An, Guangyu; Carra, Irene; Hassard, Francis; Campo Moreno, Pablo; Sakar, Hacer; Jodkowska, Monika; Wang, Dongsheng; Jefferson, Bruce; Chu, Wenhai; Jarvis, Peter
    Per- and polyfluoroalkyl substances (PFAS) pose significant risks to the environment and human health. Perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) are two of the most frequently detected PFAS in the environment. In most surface water drinking water treatment works (WTW), coagulation is the first processes exposed to a range of contaminants, including PFAS. While not designed to be a process for removal of micropollutants, it is important to understand the fate of PFAS in coagulation processes, intended or otherwise, to determine whether water treatment sludge can be a significant sink for this group of micropollutants. This work advances understanding of PFAS removal in coagulation processes by comparing the removal of PFOA and PFOS by four metal coagulants (Zr, Zn, Fe, and Al) from real water matrices. The coagulant performance followed the order Al > Fe > Zr > Zn. Al was taken forward for further evaluation, with significant removal of PFAS (>15 % for PFOA and > 30 % for PFOS) being observed when the pH<5.5 and the dose was > 5 mg Al·L-1. The adsorption of PFOA and PFOS onto flocs through hydrophobic interaction was the primary removal route. The impacts of background matrix on the mechanisms of coagulation for PFAS were explored using five organic compounds. Macromolecular organic compounds contributed to an increase in removal due to the sorption of PFAS and subsequent removal of the organic-PFAS aggregate during coagulation. Low molecular weight organic matter inhibited the removal of PFAS due to the ineffective removal of these compounds during coagulation.
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    Sorptive removal of disinfection by-product precursors from UK lowland surface waters: impact of molecular weight and bromide
    (Elsevier, 2020-09-05) Carra, Irene; Lozano, Javier Fernandez; Johannesen, Scott; Godart-Brown, Max; Goslan, Emma H.; Jarvis, Peter; Judd, Simon J.
    The current study compared the impact of three different unit processes, coagulation, granular activated carbon (GAC), and a novel suspended ion exchange (SIX) technology, on disinfection by-product formation potential (DBPFP) from two UK lowland water sources with medium to high bromide content. Specific attention was given to the influence of the organic molecular weight (MW) fraction on DBPFP as well as the impact of bromide concentration. Whilst few studies have investigated the impact of MW fractions from Liquid Chromatography with Organic Carbon Detection (LC-OCD) analysis on dissolved organic carbon (DOC) removal by different processes, none have studied the influence of DOC MW fractions from this analysis on DBP formation. The impact of higher bromide concentration was to decrease the total trihalomethane (THM) and haloacetic acid (HAA) mass concentration, in contrast to previously reported studies. Results indicated that for a moderate bromide concentration source (135 μg/L), the THM formation potential was reduced by 22% or 64% after coagulation or SIX treatment, respectively. For a high bromide content source (210 μg/L), the THM formation potential removal was 47% or 69% following GAC and SIX treatment, respectively. The trend was the same for HAAs, albeit with greater differences between the two processes/feedwaters with reference to overall removal. A statistical analysis indicated that organic matter of MW > 350 g/mol had a significant impact on DBPFP. A multiple linear regression of the MW fractions against DBPFP showed a strong correlation (R2 between 0.90 and 0.93), indicating that LC-OCD analysis alone could be used to predict DBP formation with reasonable accuracy, and offering the potential for rapid risk assessment of water sources
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    Treatment options for reclaiming wastewater produced by the pesticide industry
    (Sciforschen - Open HUB for Science Research, 2017-11-10) Goodwin, Lindsey; Carra, Irene; Campo, Pablo; Soares, Ana
    The pesticide production industry generates a high strength wastewater containing a range of toxic pollutants (2,4-dichlorphenoxy acetic acid: 2,4-D; 4-(2,4-dichlorphenox) propionic acid: 2,4-DP; 4-(2,4-dichlorophenox) butyric acid: 2,4-DB; 2,4-dichlorophenol: 2,4-DCP; 2,4,6-trichlorophenol: 2,4,6-TCP; 4-chlororthocresol: PCOC; 4-chloro-2-methyl phenoxyacetic acid: MCPA, 4-(4-chloro-2-methylphenoxy) butyric acid: MCPB and 2-(4-chloro-2-methylphenoxy) propionic acid: MCPP). These pesticides can enter the natural environment and water sources if not removed in a wastewater treatment plant. Treated effluents are regulated by legislation such as the Water Framework Directive (WFD). Most studies found in literature focused on synthetic solutions, synthetic wastewater, at lab-scale or pilot-scale. Although these studies can provide information on the removal mechanisms and provide a comparison between process efficiency, they have limited practical applicability. The process that has been more widely used to treat high strength wastewaters rich in recalcitrant compounds at full-scale, is the combination of biological/granular activated carbon and granular activated carbon/biological processes. The pesticide production wastewater contains a variety of compounds, that can be removed by 80-90% using biological processes (such as membrane bioreactors) and granular activated carbon has been shown to selectively remove the pesticides, potentially creating a high quality effluent. Nevertheless, in order to assert processes design, efficiencies or costs, it is crucial to evaluate these processes experimentally.
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    Understanding the difference between the nano and micro bubble size distributions generated by a regenerative turbine microbubble generator using ozone
    (Elsevier, 2025-02-01) John, Alexander; Brookes, Adam; Carra, Irene; Jefferson, Bruce; Jarvis, Peter
    There is a genuine paucity of data concerning the relative significance of the nano and the microbubble size distributions that are collectively generated when operating microbubble generation devices. Accordingly, the current work aimed to address this knowledge gap by measuring the two size distributions generated by a regenerative turbine microbubble generator using ozone and assess the relative significance of the nanobubble fraction. The microbubble fraction was measured with a focus-beam reflectance measurement device and the nanobubble fraction with a nano particle tracking instrument. The latter was calibrated using latex spheres to understand method uncertainty and to optimise the measurement approach. Sauter mean diameters of 217 nm and 37 μm were reported for the nano and microbubble fractions, respectively, with half of the microbubbles being <5000 nm in size. A comparison of the size and number concentrations of the different bubble types revealed that the majority of the gas was contained within the microbubble fraction, and hence, this controlled the overall mass transfer performance of the system. Further, the nanobubbles were observed to be stable for 18 h with little change in their size or number, indicating there was no net transfer of their gaseous contents. Overall, the work revealed that when considering enhancing gas-liquid mass transfer processes with micro-nano bubble generators, the microbubble fraction is key.