Browsing by Author "McAdam, Ewan"
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Item Open Access Ammonia inhibition and toxicity in anaerobic digestion: a critical review(Elsevier, 2019-07-20) Jiang, Ying; McAdam, Ewan; Zhang, Yue; Heaven, Sonia; Banks, Charles J.; Longhurst, PhilipAs a waste management technology which offers environmental benefit and renewable energy production, anaerobic digestion (AD) has become the preferred technology for the treatment of organic waste. However, in such waste streams nitrogen contents are likely to be high. There is prevailing literature evidence suggests that high ammonia concentration especially its free molecular form (NH3), derived from nitrogen content in substrates is the cause of inhibition and sudden failure of the AD process. This paper comprehensively reviews previous knowledge from digestion studies using high nitrogen waste streams as feedstocks and critically analysed the considerable variations in the inhibition/toxicity levels reported for ammonia. Literature evidences suggest methanogens, particularly acetoclastic methanogens are most susceptible to ammonia toxicity, and therefore this review has a particular focus on the mechanism of the ‘selective’ inhibition to methanogens and the impact of ammonia toxicity to the overall methanogen population in an AD digester. This population change explains in many reported cases that sufficient acclimatisation can significantly alleviate the phenomenon of inhibition and specific requirement of certain trace nutrients. Currently available mitigation strategies for high nitrogen content feedstock digestion are reviewed and discussed in relation to the population change and trace nutrient requirements.Item Open Access Ammonia recovery and utilisation for biogas upgrading in membrane contactors.(Cranfield University, 2023-07) Luqmani, Benjamin A.; McAdam, Ewan; Pidou, MarcThis thesis has developed an innovative system for biogas upgrading using hollow fibre membrane contactors (HFMC) whilst recovering ammonia from wastewater as a reactive solvent to intensify CO₂ absorption. An expanded two- phase region for ammonia-water separation was identified and exploited to foster selective, low energy recovery of concentrated gas-phase ammonia from wastewater by vacuum thermal stripping. Selective stripping was translated to a gas-liquid contacting column which demonstrated mass transfer rates analogous to commercially established stripping processes. Investment in selective ammonia recovery from anaerobic digester centrate represents a cost saving over a 20-year economic lifetime relative to biological nitrogen removal. During physical CO₂ absorption in HFMC, solvent chilling and gas pressurisation were observed to increase flux and selectivity, thereby reducing membrane area and path length for biogas upgrading. Chilled conditions will promote wetting resilience to favour the application of microporous membranes, which are low- cost and technologically mature. Translation to recovered ammonia solvents will further intensify CO₂ absorption, but can result in gas-side reactions within the ternary CO₂-NH₃-H₂O system which reduce process stability. In a positive synergy, chilled, pressurised conditions could limit ammonia ‘slip’ and maintain the system below a critical threshold to prevent gas-side reactions and improve process resilience. Pressurised, reactive crystallisation in HFMC during CO₂ absorption by ammonia solvents was demonstrated for the first time, and observed to occur at a consistent supersaturation level. Consequently, ammonium bicarbonate crystals exhibited consistent characteristics independent of pressure which supports simplified online control and solids recovery for scale- up. The integrated system proposed in this thesis presents a cost effective, circular economy solution for ammonia recovery and biogas upgrading which is closely aligned to net zero ambitions within the water sector and wider society.Item Open Access Anaerobic membrane bioreactors in upflow anaerobic sludge blanket configuration for energy neutral sewage treatment.(2018-03) Wang, Kanming; McAdam, Ewan; Soares, AnaAnaerobic membrane bioreactors (AnMBRs) are emerging as a promising technology to offer the prospect to achieve energy neutral sewage treatment. The key challenges limiting full-scale application of AnMBR for municipal wastewater treatment are high operational cost of energy demand for fouling control and high capital cost of membrane investments. This thesis explores a novel pseudo dead-end gas sparging regime for membrane fouling control, enabling a high sustainable flux (15 L m ¯² h¯¹) with low energy demand (0.14 kWh m⁻³ ) in upflow anaerobic sludge blanket (UASB) configured AnMBR, sufficient to achieve energy neutral sewage treatment. However, this strategy is only possible within low solids environment, emphasising the importance of solids management in the UASB reactor. Solids accumulated in the sludge blanket enhances UASB treatment efficiency during the steady-state operation, indicating to control the sludge blanket at a threshold between the sludge blanket development and steady-state period. The granular inoculum has good stability which exerts a positive influence on reactor stability and sustained permeability, whilst the flocculent inoculum enables to deliver similar sustained membrane operation provided the sludge blanket is controlled. Low temperatures (average temperature of 10 °C) cause the instability of UASB reactor especially for the one with flocculent inoculum biomass. It is therefore proposed to keep relatively high upflow velocity (Vup) of 0.8-0.9 m h⁻¹ in the UASB reactor for granular AnMBR to promote the stratification of particular and granular material, whilst reducing Vup to 0.4 m h⁻¹ for flocculent AnMBR to minimise solids washout and sustain membrane operation at low temperatures. The potential for permeability recovery following peak flow (diurnal peaks and storm water flows) has been investigated and evidenced, suggesting that membrane surface area for AnMBR can be specified based on average flow, providing a considerable (67 %) capital cost reduction compared with the design based on peak flows (three times of average flow). Importantly, this thesis promotes UASB configured AnMBR as a highly reliable and more economically viable technology, facilitating to achieve the energy neutral sewage treatment at ambient temperature.Item Open Access Anaerobic ponds for domestic wastewater treatment in temperate climates(Cranfield University, 2014-05) Cruddas, Peter; McAdam, Ewan; Cartmell, EliseEnergy demand, greenhouse gas emissions, and operational costs are continuing to rise year on year in the wastewater treatment sector, with traditional treatment options unable to provide sustainable solutions to increasing volumes and tightening quality standards. Current processes produce inherent fugitive greenhouse gas (GHG) emissions, whilst also generating large quantities of sludge for disposal. Anaerobic ponds (APs) are natural wastewater treatment processes that have traditionally been confined to a pre-treatment stage of larger stabilisation pond systems. Consequently, current standard guidelines are not suited for low temperature, weak strength wastewaters, or for the emerging usage of APs for energy recovery and enhanced organic breakdown. To establish effective guidelines for adapting AP design for this purpose, this thesis explores the fundamental mechanisms with APs, in order to provide design alterations to enhance AP performance for full flow domestic wastewater treatment with a focus on the UK water sector. Initially, a literature review of current AP design guidelines was conducted to determine the current state of the art and understand the fundamental design processes currently adopted. The review found that most APs are currently underloaded, largely to avoid malodour emissions, but this leads to unnecessarily large footprints and inhibits the digestion process through restricting biomass/substrate contact. It was concluded that the current design guidelines are not suitable for recent AP developments and application, such as covering to prevent odour escape, and the use of baffling to improve mixing and enhance organic degradation. A pilot scale study was conducted on UK domestic wastewater to gain insight into the limitations of current AP design for this application and identify areas for optimisation. The pilot trial demonstrated the efficacy of AP usage for low temperature, weak strength wastewaters, even with unoptimised design. Decoupling hydraulic and solids retention time lead to biomass retention and subsequent acclimatisation, and was able to compensate for the low temperatures and weak wastewater. It was concluded that APs can provide an attractive alternative to current primary treatment options, through reducing GHG emissions and providing less frequent desludging requirements. To optimise AP design, the effect of baffle configuration on AP hydrodynamics and the subsequent impact on treatment efficiency was investigated, in order to develop structural designs specifically targeting enhanced anaerobic degradation. Advantages found in baffling APs included improving mixing patterns between baffles, enhancing biomass/substrate contact, and creating an overall plug flow effect through the entire pond enabling the retention of biomass. Furthermore, the removal mechanism with the pond can be manipulated with use of baffles, with different orientations generating different flow patterns and therefore creating conditions preferential for greater solids settlement and capture, or mixing and contact. Following trials on single stage alternate baffling configurations, the development of a novel two stage AP design was trialled, applying knowledge gained from trials of differing baffle orientations to target separate stages of organic breakdown. Further trials were conducted on the staged AP to establish optimal loading rates to be applied to APs in order to maximise performance and reduce physical footprint. These trials led to recommended design improvements including shorter hydraulic retention times (HRTs) to enhance mixing and decrease physical footprint, and improvements to the staged AP design to greater separate the stages of anaerobic digestion and provide optimal conditions for the stages at different points in the AP. Finally, the knowledge gained from experimental work was used to present evidence for the inclusion of APs into decentralised WWT through flowsheet modelling of a proposed AP treatment works compared to a current base case. Advantages were found in decreasing sludge management requirements whilst providing suitable primary treatment, with additional potential benefits in renewable energy generation, which could increase both with improved biogas yields and the option of combining with other renewable technologies. In some circumstances, it may be possible for an AP flowsheet to operate entirely off-grid, eliminating the need for costly infrastructure such as permanent access roads and national electrical grid connection.Item Open Access Biogas enhancement with membranes(Cranfield University, 2014-04) McLeod, Andrew J.; McAdam, Ewan; Jefferson, BruceBiogas is generated during anaerobic digestion (AD) of sewage sludge at wastewater treatment works (WWTW) and consists of approximately 50-70 % methane (CH4) balanced primarily by carbon dioxide (CO2). It is commonly used directly as a fuel gas for the renewable generation of electricity on-site by combined heat and power (CHP) engines. However, as a result of governmental incentivisation, biogas possesses a greater value when applied to the national gas grid as a natural gas substitute. However, this requires enhancement of the CH4 content to that comparable to natural gas by selective removal of CO2; a process known as biogas upgrading. This thesis explores the potential of hydrophobic micro-porous hollow fibre membrane contactors (HFMCs) to biogas upgrading. HFMCs allow non-dispersive contact between the biogas and a liquid solvent for the preferential absorption of CO2, which is conventionally facilitated by packed-column gas scrubbing technology. However, recent gas absorption literature has demonstrated many practical and operational advantages of HFMCs, which suggests they may be effective for biogas upgrading at WWTW. In this thesis, HFMCs were used to explore the mechanism and controllability of the undesirable co-absorption of CH4, known as methane slip. This was found to be attributable to the phase limiting mass transfer, with liquid-limited physical absorption in water exhibited 5.2 % slip whereas gas-limited chemical absorption displayed just 0.1 %. Ammonia-rich wastewaters were investigated as sustainable chemical absorbents using HFMCs and exhibited comparable chemically enhanced absorption to analogue synthetic ammonia solutions. The recovery of the subsequent reaction product (ammonium bicarbonate) by crystallisation facilitated by the membrane was also examined. The potential of this approach was summarised within two hypothetical wastewater flowsheets, where upgrading using a return liquor absorbent acts as a return liquor treatment and where ion exchange allows 100 % application of wastewater derived ammonia to biogas upgrading. These both offered potential economic advantages versus conventional flowsheets with 100 % biogas application to CHP.Item Open Access Chemically reactive membrane crystallisation reactor for CO₂ separation and ammonia recovery.(2018-10) Bavarella, Salvatore; McAdam, Ewan; Pidou, MarcThis thesis introduces an integrated system comprised of a thermal stripper and a hollow fibre membrane contactor (HFMC) for concentration of ammonia (NH₃ ) from wastewater and control of chemically mediated membrane crystallisation of ammonium bicarbonate (NH₄HCO₃ ) to enable simultaneous ammonia removal, biogas upgrading (through carbon dioxide, CO₂, separation), fertilizer production and harvesting within a single and economical process. In particular, recirculation of a refrigerated aqueous ammonia absorbent within the chemically reactive membrane crystallisation reactor (CR-MCr), demonstrated to reduce free ammonia introduction into the gas phase and convert NH₃ into non-volatile ammonium (NH₄+), thus preventing gas side crystallisation, which leads to process blockage, and promoting liquid side crystallisation of NH₄HCO₃ . The thermodynamic and kinetics of the CO₂-NH₃ -H₂O system have also been investigated to facilitate shell-side (liquid side) crystallisation of the ammonium salt within the CR-MCr. A transition from large (PTFE) to tight (PP) membrane pore size material obviated wetting and enabled consistent and reproducible NH₄HCO₃ crystallisation on the membrane-liquid interface. The X-ray diffraction analysis of the crystals produced with the absorbent recovered from return liquor, indicated the products to be reasonably pure ammonium bicarbonate, which evidenced the reduction in cationic competition through application of pre-treatment. A comparison between batch and membrane crystallisation kinetics demonstrated the hydrophobic fibre to underpin primary heterogeneous nucleation in an unseeded supersaturated solution and laminar regime, decoupled from secondary nucleation and growth, which mainly occur in the bulk downstream, contrarily to batch crystallisation where primary and secondary homogeneous nucleation are followed by growth and agglomeration, promoted by enhanced mixing and CO₂ bubbling, within the same environment. As a result, an increasing population density at raising levels of supersaturation has been observed in the first case, against a declining population density vs. supersaturation in the latter. A slower pH transient in membrane crystallisation, compared with conventional batch operation, could be balanced by raising the membrane-liquid interfacial surface area, which would increase the nucleation rate, whilst the yield of ammonia removal could be maximised up to 99% (ammonium bicarbonate solubility limit) through an increase in absorbent pH, which would eliminate the partial conversion of solute (bicarbonate) into carbonic acid, caused by a dynamic reaction zone, therefore closing the gap to control nucleation and growth in membrane crystallisation of ammonium bicarbonate.Item Open Access Comparable membrane permeability can be achieved in granular and flocculent anaerobic membrane bioreactor for sewage treatment through better sludge blanket control(Elsevier, 2019-02-05) Wang, Kanming; Soares, Ana; Jefferson, Bruce; McAdam, EwanMBR, to establish the impact of biomass selection on sustaining membrane permeability for sewage treatment. When operated as an UASB (10 °C), similarly poor organics removal was observed for both inocula, which was overcome by membrane integration, producing solids-free permeate and consistently low CODt (34–39 mg L−1) and BOD5 (10–13 mg L−1), sufficient to meet discharge standards. At an average sewage temperature of 22 °C, membrane permeabilities in granular (G-AnMBR) and flocculent (F-AnMBR) systems were comparable. However, at lower temperature (10 °C), significant fouling was observed in F-AnMBR at a flux of 7.5 L m−2 h−1. The permeability decline was ascribed to a decreased particle settling velocity which induced washout of smaller particles into the membrane tank, subsequently increasing the colloidal concentration due to the floc erosion induced by gas sparging. This was confirmed by halving UASB upflow velocity in the F-AnMBR, which reduced pCOD and colloidal load by 31–36% onto the membrane, permitting comparable permeability to G-AnMBR. The UASB configured AnMBR promoted low solids loading onto the membrane, enabling pseudo dead-end gas sparging to be used which reduced specific energy demand. Analysis of the dead-end filtration cycle attributed the primary resistance (85–88%) to the development of a concentrated but less compact cake. Importantly, this study evidences comparable permeabilities in G-AnMBR and F-AnMBR through controlling solids retention, and specifying filtration cycle length to minimise solids deposition, such that low energy membrane operation can be achieved (<0.122 kW h m−3).Item Open Access Comparison of fouling between aerobic and anaerobic MBR treating municipal wastewater(IWA Publishing, 2018-11-26) Wang, K. M.; Martin Garcia, N.; Soares, Ana; Jefferson, Bruce; McAdam, EwanThe key driver for anaerobic membrane bioreactors (AnMBR) for municipal wastewater treatment is enabling the transition to energy neutral wastewater treatment. However, municipal wastewater delivers a comparatively constrained methane yield, which means energy conservation must be prioritised to achieve the proposed energy neutral ambition. A critical focus on membrane fouling is therefore warranted, as membrane operation represents the primary energy demand in MBRs. This review seeks to quantify the characteristics of the prevailing AnMBR biological suspension and to ascertain whether knowledge transfer exists between fouling characteristics in aerobic and anaerobic MBRs for municipal applications. Analysis of literature data revealed that the level of extractable extracellular polymeric substrate is slightly higher in aerobic MBRs than in anaerobic MBRs. However, AnMBR comprises considerably higher soluble microbial product concentrations, which have been widely reported to increase fouling propensity in aerobic systems. More distinct is the difference in the colloidal and fine solids fraction (between 1 and 10–15 μm), which is likely to dominate fouling in anaerobic systems and limit knowledge transfer from aerobic MBRs. Literature data on energy production was compared to that employed for membrane operation, and evidences that despite the challenging character of the particle matrix, energy neutral operation is achievable for AnMBR applied to municipal wastewater treatment.Item Open Access Conceptual environmental impact assessment of a novel self-sustained sanitation system incorporating a Quantitative Microbial Risk Assessment approach(Elsevier, 2018-05-26) Anastasopoulou, Aikaterini; Kolios, Athanasios; Somorin, Tosin; Sowale, Ayodeji; Jiang, Ying; Fidalgo, Beatriz; Parker, Alison; Williams, Leon; Collins, Matt; McAdam, Ewan; Tyrrel, SeanIn many developing countries, including South Africa, water scarcity has resulted in poor sanitation practices. The majority of the sanitation infrastructures in those regions fail to meet basic hygienic standards. This along with the lack of proper sewage/wastewater infrastructure creates significant environmental and public health concerns. A self-sustained, waterless “Nano Membrane Toilet” (NMT) design was proposed as a result of the “Reinvent the Toilet Challenge” funded by the Bill and Melinda Gates Foundation. A “cradle-to-grave” life cycle assessment (LCA) approach was adopted to study the use of NMT in comparison with conventional pour flush toilet (PFT) and urine-diverting dry toilet (UDDT). All three scenarios were applied in the context of South Africa. In addition, a Quantitative Microbial Risk Assessment (QMRA) was used to reflect the impact of the pathogen risk on human health. LCA study showed that UDDT had the best environmental performance, followed by NMT and PFT systems for all impact categories investigated including human health, resource and ecosystem. This was mainly due to the environmental credits associated with the use of urine and compost as fertilizers. However, with the incorporation of the pathogen impact into the human health impact category, the NMT had a significant better performance than the PFT and UDDT systems, which exhibited an impact category value 4E + 04 and 4E + 03 times higher, respectively. Sensitivity analysis identified that the use of ash as fertilizer, electricity generation and the reduction of NOx emissions were the key areas that influenced significantly the environmental performance of the NMT system.Item Open Access The cost of a small membrane bioreactor(IWA Publishing, 2015-07-23) Lo, C. H.; McAdam, Ewan; Judd, Simon J.The individual cost contributions to the mechanical components of a small membrane bioreactor (MBR) (100–2,500 m3/d flow capacity) are itemised and collated to generate overall capital and operating costs (CAPEX and OPEX) as a function of size. The outcomes are compared to those from previously published detailed cost studies provided for both very small containerised plants (<40 m3/day capacity) and larger municipal plants (2,200–19,000 m3/d). Cost curves, as a function of flow capacity, determined for OPEX, CAPEX and net present value (NPV) based on the heuristic data used indicate a logarithmic function for OPEX and a power-based one for the CAPEX. OPEX correlations were in good quantitative agreement with those reported in the literature. Disparities in the calculated CAPEX trend compared with reported data were attributed to differences in assumptions concerning cost contributions. More reasonable agreement was obtained with the reported membrane separation component CAPEX data from published studies. The heuristic approach taken appears appropriate for small-scale MBRs with minimal costs associated with installation. An overall relationship of net present value = (a tb)Q(−c lnt+d) was determined for the net present value where a = 1.265, b = 0.44, c = 0.00385 and d = 0.868 according to the dataset employed for the analysis.Item Open Access Data in support of "The role of mixing on the kinetics of nucleation and crystal growth in membrane distillation crystallisation"(Cranfield University, 2024-06-27) McAdam, EwanItem Open Access Data related to "Examining disruptive gas-phase reactions during CO2 capture in membrane contactors: CO2-NH3-H2O as a model ternary system"(Cranfield University, 2024-05-23 17:10) Luqmani, Benjamin A. ; Pidou, Marc; McAdam, EwanData related to figures for "Examining disruptive gas-phase reactions during CO2 capture in membrane contactors: CO2-NH3-H2O as a model ternary system"Item Open Access Data related to "Membrane-assisted reactive crystallisation for the recovery of dissolved phosphorus in vivianite form from liquid effluents"(Cranfield University, 2023-08-31 14:38) McAdam, Ewan; Chen, Lo-I; Le Corre Pidou, KristellData supporting article titled "Membrane-assisted reactive crystallisation for the recovery of dissolved phosphorus in vivianite form from liquid effluents"Item Open Access Data related to "Rheological characterisation of synthetic and fresh faeces to inform on solids management strategies for non-sewered sanitation systems"(Cranfield University, 2021-10-11 17:11) Bajón fernández, Yadira; Mercer, Edwina V.; USHER, SHANE; McAdam, Ewan; Stoner, Brian R.Data related to "Rheological characterisation of synthetic and fresh faeces to inform on solids management strategies for non-sewered sanitation systems"Item Open Access Data related to "The role of solvent temperature and gas pressure on CO2 mass transfer during biogas upgrading within porous and dense-skin hollow fibre membrane contactors"(Cranfield University, 2023-04-14 14:37) Luqmani, Benjamin A. ; McAdam, Ewan; Pidou, MarcSource data for published works: 'The role of solvent temperature and gas pressure on CO2 mass transfer during biogas upgrading within porous and dense-skin hollow fibre membrane contactors'.Item Open Access Data related to figures from "Transitioning through the vapour-liquid equilibrium for low energy thermal stripping of ammonia from wastewater..."(Cranfield University, 2023-04-21 14:29) Luqmani, Benjamin A. ; Pidou, Marc; McAdam, EwanSupporting dataset related to figures in the following work : "Transitioning through the vapour-liquid equilibrium for low energy thermal stripping of ammonia from wastewater...".Item Open Access Data supporting "Modifying supersaturation rate with membrane area can minimise scaling and improve control over crystal growth in membrane distillation crystallisation"(Cranfield University, 2023-06-30 11:09) Ouda, Alaa; McAdam, Ewan; Bajón fernández, YadiraThis Excel file consists of the data used to generate the figures in this paper. Each figure is placed in a separate Excel sheet while the formatting of the figures was consistent with a Word file.Item Open Access Data supporting the publication "Transforming wastewater ammonia to carbon free energy: Integrating fuel cell technology with ammonia stripping for direct power production"(Cranfield University, 2022-03-08 09:18) Davey, Christopher J.; Luqmani, Benjamin A. ; Thomas, Navya; McAdam, EwanData File supporting article titled "Transforming ammonia to carbon free energy: Integrating fuel cell technology with ammonia stripping for direct power production"Item Open Access 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, EwanSolids 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.Item Open Access Data supporting: 'Downscaling reverse osmosis for single-household wastewater reuse: towards low-cost decentralised sanitation through a batch open-loop configuration'(Cranfield University, 2022-10-31 09:16) Thomas, Navya; McAdam, Ewan; Davey, Christopher J.There is a significant demand for water recycling in low-income countries. However, wastewater infrastructure is primarily decentralised, necessitating the development of affordable household-scale reclamation technology. In this study, a batch open-loop reverse osmosis (RO) system is therefore investigated as a low-cost clean water reclamation route from highly saline concentrated blackwater
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