Browsing by Author "Brookes, Adam"

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    Achieving drinking water compliance levels for metaldehyde with an acclimated sand bioreactor
    (Elsevier, 2020-07-06) Rolph, Catherine A.; Jefferson, Bruce; Brookes, Adam; Hassard, Francis; Villa, Raffaella;
    Metaldehyde removal was delivered to below the 0.1 µg L-1 regulatory concentration in a laboratory scale continuous upflow fluidised sand bioreactor that had undergone acclimation through selective enrichment for metaldehyde degradation. This is the first reported case of successful continuous flow biological treatment of metaldehyde from real drinking water sources treating environmentally realistic metaldehyde concentrations. The impact of the acclimation process was impermanent, with the duration of effective treatment directly related to the elevated concentration of metaldehyde used during the enrichment process. The efficacy of the approach was demonstrated in continuous flow columns at both laboratory and pilot scale enabling degradation rates of between 0.1 and 0.2 mg L-1 h-1. Future work needs to focus on optimisation of the sand bioreactor and the acclimation process to ensure viability and feasibility of the approach at full scale
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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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    Chemically reactive membrane crystallisation reactor for CO2–NH3 absorption and ammonium bicarbonate crystallisation: Kinetics of heterogeneous crystal growth
    (Elsevier, 2019-11-22) Bavarella, Salvatore; Brookes, Adam; Moore, Andrew; Vale, Peter C. J.; Di Profio, Gianluca; Curcio, Efrem; Hart, Phil; Pidou, Marc; McAdam, Ewan J.
    The feasibility of gas-liquid hollow fibre membrane contactors for the chemical absorption of carbon dioxide (CO2) into ammonia (NH3), coupled with the crystallisation of ammonium bicarbonate has been demonstrated. In this study, the mechanism of chemically facilitated heterogeneous membrane crystallisation is described, and the solution chemistry required to initiate nucleation elucidated. Induction time for nucleation was dependent on the rate of CO2 absorption, as this governed solution bicarbonate concentration. However, for low NH3 solution concentrations, a reduction in pH was observed with progressive CO2 absorption which shifted equilibria toward ammonium and carbonic acid, inhibiting both absorption and nucleation. An excess of free NH3 buffered pH suitably to balance equilibria to the onset of supersaturation, which ensured sufficient bicarbonate availability to initiate nucleation. Following induction at a supersaturation level of 1.7 (3.3 M NH3), an increase in crystal population density and crystal size was observed at progressive levels of supersaturation which contradicts the trend ordinarily observed for homogeneous nucleation in classical crystallisation technology, and demonstrates the role of the membrane as a physical substrate for heterogeneous nucleation during chemically reactive crystallisation. Both nucleation rate and crystal growth rate increased with increasing levels of supersaturation. This can be ascribed to the relatively low chemical driving force imposed by the shift in equilibrium toward ammonium which suppressed solution reactivity, together with the role of the membrane in promoting counter-current diffusion of CO2 and NH3 into the concentration boundary layer developed at the membrane wall, which permitted replenishment of reactants at the site of nucleation, and is a unique facet specific to this method of membrane facilitated crystallisation. Free ammonia concentration was shown to govern nucleation rate where a limiting NH3 concentration was identified above which crystallisation induced membrane scaling was observed. Provided the chemically reactive membrane crystallisation reactor was operated below this threshold, a consistent (size and number) and reproducible crystallised reaction product was collected downstream of the membrane, which evidenced that sustained membrane operation should be achievable with minimum reactive maintenance intervention.
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    CO2 absorption into aqueous ammonia using membrane contactors: Role of solvent chemistry and pore size on solids formation for low energy solvent regeneration
    (Elsevier, 2022-03-16) Bavarella, Salvatore; Luqmani, Benjamin A. ; Thomas, Navya; Brookes, Adam; Moore, Andrew; Vale, Peter C. J.; Pidou, Marc; McAdam, Ewan J.
    Solids formation can substanitally reduce the energy penalty for ammonia solvent regeneration in carbon capture and storage (CCS), but has been demonstrated in the literature to be difficult to control. This study examines the use of hollow fibre membrane contactors, as this indirect contact mediated between liquid and gas phases in this geometry could improve the regulation of solids formation. Under conditions comparable to existing literature, NH4HCO3 was evidenced to primarily crystallise in the gas-phase (lumen-side of the membrane) due to the high vapour pressure of ammonia, which promotes gaseous transmission from the solvent. Investigation of solvent reactivity demonstrated how equilibria dependent reactions controlled the onset of NH4HCO3 nucleation in the solvent, and limited ‘slip’ through transfomation of ammonia into its protonated form which occurs prior to the phase change. Crystallisation in the solvent was also dependent upon ammonia concentration, where sufficient supersaturation must develop to overcome the activation energy for nucleation. However, this has to be complemented with a reduction in solvent temperature to offset vapour pressure and limit the risk of gas-phase crystallisation. While changes to the solvent chemistry were sufficient to shift from gas-phase to liquid phase crystallisation, wetting was observed immediately after nucleation in the solvent. This was explained by a local region of supersaturation within the coarse membrane pores that promoted a high nucleation rate, altering the material contact angle of the membrane sufficient for solvent to breakthrough into the gas phase. Adoption of a narrower pore size membrane was shown to dissipate wetting after crystallisation in the solvent, illustrating membrane contactors as a stable platform for the sustained separation of CO2 coupled with its simultaneous transformation into a solid. Through resolving previous challenges experienced with solids formation in multiple reactor configurations, the cost benefit of using ammonia as a solvent can be realised, which is critical to enabling economically viable CCS for the transition to net zero, and can be exploited within hollow fibre membrane contactors, eliciting considerable process intensification over existing reactor designs for CCS.
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    Data for the paper "From full-scale biofilters to bioreactors: engineering biological metaldehyde removal"
    (Cranfield University, 2019-07-17 11:45) Hassard, Francis; Jefferson, Bruce; Villa, Raffaella; Brookes, Adam; Choya, Andoni; Iceton, Gregg; Rolph, Catherine
    Datasets for Rolph, C.A., Villa, R., Jefferson, B., Brookes, A., Choya, A., Iceton, G. and Hassard, F., 2019. From full-scale biofilters to bioreactors: engineering biological metaldehyde removal. Science of the Total Environment, 685, pp.410-41.
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    Data supporting: 'CO2 absorption into aqueous ammonia using membrane contactors: Role of solvent chemistry and pore size on solids formation for low energy solvent regeneration'
    (Cranfield University, 2022-10-13 16:42) Bavarella, Salvatore; Luqmani, Benjamin A.; Thomas, Navya; Brookes, Adam; Moore, Andrew; Vale, Peter C. J.; Pidou, Marc; McAdam, Ewan
    Solids formation can substantially reduce the energy penalty for ammonia solvent regeneration in carbon capture and storage (CCS), but has been demonstrated in the literature to be difficult to control. This study examines the use of hollow fibre membrane contactors, as this indirect contact mediated between liquid and gas phases in this geometry could improve the regulation of solids formation. Adoption of a narrower pore size membrane was shown to dissipate wetting after crystallisation in the solvent, illustrating membrane contactors as a stable platform for the sustained separation of CO2 coupled with its simultaneous transformation into a solid. Through resolving previous challenges experienced with solids formation in multiple reactor configurations, the cost benefit of using ammonia as a solvent can be realised, which is critical to enabling economically viable CCS for the transition to net zero, and can be exploited within hollow fibre membrane contactors, eliciting considerable process intensification over existing reactor designs for CCS.
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    Demonstrating commercial hollow fibre membrane contactor performance at industrial scale for biogas upgrading at a sewage treatment works
    (MDPI, 2021-01-13) Houlker, Sam; Rutherford, Tony; Herron, Daniel; Brookes, Adam; Moore, Andrew; Vale, Peter C. J.; Pidou, Marc; McAdam, Ewan J.
    Hollow fibre membrane contactor (HFMC) technology has been developed for CO2 absorption primarily using synthetic gas, which neglects the critical impact that trace contaminants might have on separation efficiency and robustness in industrial gases. This study, therefore, commissioned a demonstration-scale HFMC for CO2 separation at a full-scale anaerobic digester facility to evaluate membrane integrity over six months of operation on real biogas. The CO2 capture efficiency identified using real biogas was benchmarked at comparable conditions on synthetic gas of an equivalent partial pressure, and an equivalent performance identified. Two HFMC were subsequently compared, one with and one without a pre-treatment stage that targeted particulates, volatile organic compounds (VOCs) and humidity. Similar CO2 separation efficiency was again demonstrated, indicating limited impact within the timescale evaluated. However, gas phase pre-treatment is advised in order to ensure robustness in the long term. Over longer-term operation, a decline in CO2 separation efficiency was observed. Membrane autopsy identified shell-side deposition, where the structural morphology and confirmation of amide I and II groups, indicated biofouling. Separation efficiency was reinstated via chemical cleaning, which demonstrated that proactive maintenance could minimise process risk.
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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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    From full-scale biofilters to bioreactors: Engineering biological metaldehyde removal
    (Elsevier, 2019-05-21) Rolph, Catherine A.; Villa, Raffaella; Jefferson, Bruce; Brookes, Adam; Choya, Andoni; Iceton, Gregg; Hassard, Francis
    Polar, low molecular weight pesticides such as metaldehyde are challenging and costly to remove from drinking water using conventional treatment methods. Although biological treatments can be effective at treating micropollutants, through biodegradation and sorption processes, only some operational biofilters have shown the ability to remove metaldehyde. As sorption plays a minor role for such polar organic micropollutants, biodegradation is therefore likely to be the main removal pathway. In this work, the biodegradation of metaldehyde was monitored, and assessed, in an operational slow sand filter. Long-term data showed that metaldehyde degradation improved when inlet concentrations increased. A comparison of inactive and active sand batch reactors showed that metaldehyde removal happened mainly through biodegradation and that the removal rates were greater after the biofilm was acclimated through exposure to high metaldehyde concentrations. This suggested that metaldehyde removal was reliant on enrichment and that the process could be engineered to decrease treatment times (from days to hours). Through-flow experiments using fluidised bed reactors, showed the same behaviour following metaldehyde acclimation. A 40% increase in metaldehyde removal was observed in acclimated compared with non-acclimated columns. This increase was sustained for >40 days, achieving an average of 80% removal and compliance (<0.1 μ L−1) for >20 days. An initial microbial analysis of the acclimated and non-acclimated biofilm from the same filter materials, showed that the microbial community in acclimated sand was significantly different. This work presents a novel conceptual template for a faster, chemical free, low cost, biological treatment of metaldehyde and other polar pollutants in drinking water. In addition, this is the first study to report kinetics of metaldehyde degradation in an active microbial biofilm at a WTW.
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    Immersed Membrane Bioreactors for Produced Water Treatment
    (Cranfield University, 2005-10) Brookes, Adam; Judd, Simon J.
    The performance of a submerged membrane bioreactor for the duty of gas field produced water treatment was appraised. The system was operated under steady state conditions at a range of mixed liquor suspended solids (MLSS) concentrations and treatment and membrane performance examined. Organics removal (COD and TOC) display removal rates between 90 and 97%. Removal of specific target compounds Benzene, Toulene, Ethylbenzene and Xylene were removed to above 99% in liquid phase with loss to atmosphere between 0.3 and 1%. Comparison of fouling rates at a number of imposed fluxes has been made between long term filtration trials and short term tests using the flux step method. Produced water fed biomass displays a greater fouling propensity than municipal wastewater fed biomass from previous studies. Results indicate an exponential relationship between fouling rate and flux for both long and short term trials, although the value was an order of magnitude lower during long term tests. Moreover, operation during long term trials is characterised by a period of pseudo stable operation followed by a catastrophic rise in TMP at a given critical filtration time (tfi, ) during trials at 6 g. L"1. This time of stable operation, tfit, is characterised by a linear relationship between fouling rate and flux. Results have been compared with the literature. Data for membrane fouling prior to the end of t fit yielded a poor fit with a recently proposed model. Trends recorded at t> trlt revealed the fouling rate to follow no definable trend with flux. The system showed resilience to free oil shocking up to an oil concentration of 200ppmv. Following an increase in oil concentration to 500 ppmv, rapid and exponential fouling ensued.
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    Integrating decision tools for the sustainable management of land contamination
    (Elsevier Science B.V., Amsterdam., 2004-06-05T00:00:00Z) Pollard, Simon J. T.; Brookes, Adam; Earl, N.; Lowe, J.; Kearney, T.; Nathanail, C. Paul
    The approach to taking decisions on the management of land contamination has changed markedly over 30 years. Change has been rapid with policy makers and regulators, practitioners and researchers having to keep pace with new technologies, assessment criteria and diagnostic methods for their measurement, techniques for risk analysis and the frameworks that support decision-makers in their efforts to regenerate historically contaminated land. Having progressed from simple hazard assessment through to ‘sustainability appraisal’ we might now consider piecing together the experience of decision-making for managing land contamination. Here, we critically review recent developments with a view to considering how better decisions can be made by integrating the decision tools available. We are concerned with the practicality of approach and the issues that arise for practitioners as decision criteria are broade
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    Is chemically reactive membrane crystallisation faciliated by heterogeneous primary nucleation? Comparison with conventional gas-liquid crystallisation for ammonium bicarbonate precipitation in a CO2-NH3-H2O system
    (American Chemical Society, 2020-01-27) Bavarella, Salvatore; Hermassi, Mehrez; Brookes, Adam; Moore, Andrew; Vale, Peter C. J.; Di Profio, Gianluca; Curcio, Efrem; Hart, Phil; Pidou, Marc; McAdam, Ewan
    In this study, membrane crystallisation is compared to conventional gas-liquid crystallisation for the precipitation of ammonium bicarbonate, to demonstrate the distinction in kinetic trajectory and illustrate the inherent advantage of phase separation introduced by the membrane to crystallising in gas-liquid systems. Through complete mixing of gas and liquid phases in conventional crystallisation, high particle numbers were confirmed at low levels of supersaturation. This was best described by secondary nucleation effects in analogy to mixed suspension mixed product removal (MSMPR) crystallisation, for which a decline in population density was observed with an increase in crystal size. In contrast, for membrane crystallisation, fewer nuclei were produced at an equivalent level of supersaturation. This supported growth of fewer, larger crystals which is preferred to simplify product recovery and limit occlusions. Whilst continued crystal growth was identified with the membrane, this was accompanied by an increase in nucleation rate which would indicate the segregation of heterogeneous primary nucleation from crystal growth, and was confirmed by experimental derivation of the interfacial energy for ammonium bicarbonate (σ, 6.6 mJ m-2), which is in agreement to that estimated for inorganic salts. The distinction in kinetic trajectory can be ascribed to the unique phase separation provided by the membrane which promotes a counter diffusional chemical reaction to develop, introducing a region of concentration adjacent to the membrane. The membrane also lowers the activation energy required to initiate nucleation in an unseeded solution. In conventional crystallisation, the high nucleation rate was due to the higher probability for collision, and the gas stripping of ammonia (around 40% loss) through direct contact between phases which lowered pH and increased bicarbonate availability for the earlier onset of nucleation. It is this high nucleation rate which has restricted the implementation of gas-liquid crystallisation in direct contact packed columns for carbon capture and storage. Importantly, this study evidences the significance of the membrane to governing crystallisation for gas-liquid chemical reactions through providing controlled phase separation.
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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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    Mitigating phase changes in the gas-phase that disrupt CO2 capture in membrane contactors: CO2-NH3-H2O as a model ternary system
    (Elsevier, 2024-06-01) Liqmani, Ben A.; Nayak, Vignesh; Brookes, Adam; Moore, Andrew; Vale, Peter C. J.; Pidou, Marc; McAdam, Ewan J.
    Solid and liquid products can form in the gas phase of membrane contactors applied to reactive ternary systems for CO2 absorption, which poses a critical barrier for carbon capture applications. The mechanism initiating these unwanted phase changes in the gas phase is unclear. This study therefore systematically characterises CO2 absorption in distinct regions of the vapour-liquid equilibrium (VLE) within an illustrative ternary system (CO2-NH3-H2O), to provide an explanation for the formation and mitigation of these solid and liquid products in the gas-phase. Unstable CO2 absorption and increased pressure drop indicated product formation within the gas-phase, which occurred at high CO2 capture ratios. Temporal analysis of gas-phase composition enabled gas-phase products to be related to the relative ternary composition. This was subsequently correlated to distinct regions of the VLE. Consequently, mitigation strategies can be developed with recognition for where products are least likely to form. Pressurisation was proposed to modify the relative gas-phase ammonia composition to reposition conditions within the VLE. The commensurate increase of CO2 into the solvent shifts the ammonia-ammonium equilibrium towards ammonium to indirectly reduce vapour pressure. This synergistic strategy allows sustained operation of membrane contactors for CO2 separation within reactive ternary systems which are critical to delivering carbon capture economically at scale.
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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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    Recovery and concentration of ammonia from return liquor to promote enhanced CO2 absorption and simultaneous ammonium bicarbonate crystallisation during biogas upgrading in a hollow fibre membrane contactor
    (Elsevier, 2020-01-27) Bavarella, Salvatore; Hermassi, Mehrez; Brookes, Adam; Moore, Andrew; Vale, Peter C. J.; Moon, I. S.; Pidou, Marc; McAdam, Ewan
    In this study, thermal desorption was developed to separate and concentrate ammonia from return liquor, for use as a chemical absorbent in biogas upgrading, providing process intensification and the production of crystalline ammonium bicarbonate as the final reaction product. Applying modest temperature (50°C) in thermal desorption suppressed water vapour pressure and increased selective transport for ammonia from return liquor (0.11MNH3) yielding a concentrated condensate (up to 1.7MNH3). Rectification was modelled through second-stage thermal processing, where higher initial ammonia concentration from the first stage increased mass transfer and delivered a saturated ammonia solution (6.4MNH3), which was sufficient to provide chemically enhanced CO2 separation and the simultaneous initiation of ammonium bicarbonate crystallisation, in a hollow fibre membrane contactor. Condensate recovered from return liquor exhibited a reduction in surface tension. We propose this is due to the stratification of surface active agents at the air-liquid interface during primary-stage thermal desorption which carried over into the condensate, ‘salting’ out CO2 and lowering the kinetic trajectory of absorption. However, crystal induction (the onset of nucleation) was comparable in both synthetic and thermally recovered condensates, indicating the thermodynamics of crystallisation to be unaffected by the recovered condensate. The membrane was evidenced to promote heterogeneous primary nucleation, and the reduction in the recovered condensate surface tension was shown to exacerbate nucleation rate, due to the reduction in activation energy. X-ray diffraction of the crystals formed, showed the product to be ammonium bicarbonate, demonstrating that thermal desorption eliminates cation competition (e.g. Ca2+) to guarantee the formation of the preferred crystalline reaction product. This study identifies an important synergy between thermal desorption and membrane contactor technology that delivers biogas upgrading, ammonia removal from wastewater and resource recovery in a complimentary process.
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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.