CERES :: Browsing by Author "Mercer, Edwina V."

Browsing by Author "Mercer, Edwina V."

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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"
Open Access
Figures and tables from "Hybrid membrane distillation reverse electrodialysis configuration for water and energy recovery from human urine: An opportunity for off-grid decentralised sanitation."
(Cranfield University, 2019-05-15 14:12) Mercer, Edwina V.; McAdam, Ewan; Davey, Christopher J.; Pidou, Marc; Tyrrel, Sean; Williams, Leon; Jiang, Ying; Parker, Alison; Tierney, Ross; Azzini, Daniele; Eusebi, Anna
This data compiles the dataset required to generate the tables and figures for the paper - "Hybrid membrane distillation reverse electrodialysis configuration for water and energy recovery from human urine: An opportunity for off-grid decentralised sanitation."
Open Access
Hybrid membrane distillation reverse electrodialysis configuration for water and energy recovery from human urine: an opportunity for off-grid decentralised sanitation
(Elsevier, 2019-05-06) Mercer, Edwina V.; Davey, Christopher J.; Azzini, D.; Eusebi, Anna L.; Tierney, Ross; Williams, Leon; Jiang, Ying; Parker, Alison; Tyrrel, Sean; Pidou, Marc; McAdam, Ewan
The integration of membrane distillation with reverse electrodialysis has been investigated as a sustainable sanitation solution to provide clean water and electrical power from urine and waste heat. Reverse electrodialysis was integrated to provide the partial remixing of the concentrate (urine) and diluate (permeate) produced from the membrane distillation of urine. Broadly comparable power densities to those of a model salt solution (sodium chloride) were determined during evaluation of the individual and combined contribution of the various monovalent and multivalent inorganic and organic salt constituents in urine. Power densities were improved through raising feed-side temperature and increasing concentration in the concentrate, without observation of limiting behaviour imposed by non-ideal salt and water transport. A further unique contribution of this application is the limited volume of salt concentrate available, which demanded brine recycling to maximise energy recovery analogous to a battery, operating in a ‘state of charge’. During recycle, around 47% of the Gibbs free energy was recoverable with up to 80% of the energy extractable before the concentration difference between the two solutions was halfway towards equilibrium which implies that energy recovery can be optimised with limited effect on permeate quality. This study has provided the first successful demonstration of an integrated MD-RED system for energy recovery from a limited resource, and evidences that the recovered power is sufficient to operate a range of low current fluid pumping technologies that could help deliver off-grid sanitation and clean water recovery at single household scale.
Open Access
Impact of fouling, cleaning and faecal contamination on the separation of water from urine using thermally driven membrane separation
(Taylor & Francis, 2018-02-12) Kamranvand, Farhad; Davey, Christopher J.; Sakah, H.; Autin, Olivier; Mercer, Edwina V.; Collins, Matt; Williams, Leon; Kolios, Athanasios; Parker, Alison; Tyrrel, Sean; Cartmell, Elise; McAdam, Ewan
In this study, membrane distillation is evaluated as a technology for non-sewered sanitation, using waste heat to enable separation of clean water from urine. Whilst membrane fouling was observed for urine, wetting was not evident and product water quality met the proposed discharge standard, despite concentration of the feed. Fouling was reversible using physical cleaning, which is similar to previous membrane studies operating without pressure as the driving force. High chemical oxygen demand reduction was achieved following faecal contamination, but mass transfer was impeded and wetting occurred which compromised permeate quality, suggesting upstream intervention is demanded to limit the extent of faecal contamination.
Open Access
Membrane technology for water reuse in decentralised non-sewered sanitation systems: comparison of pressure driven (reverse osmosis) and thermally driven processes (membrane distillation and pervaporation)
(Royal Society of Chemistry (RSC), 2024-11-01) Mercer, Edwina V.; Davey, Christopher J.; Bajón Fernández, Yadira; Septien, Santiago; Tyrrel, Sean; Cartmell, Elise; Pidou, Marc; McAdam, Ewan J.
Membrane processes are an established barrier technology for water reclamation from wastewater. Applied at a household scale to improve sanitation practice, membrane technology can disrupt the source–receptor pathway, alleviate water scarcity through eliminating flush water and recover clean water for reuse. However, blackwater comprises a distinct composition compared to municipal wastewater, and there is only limited understanding on whether membrane selectivity is sufficient to produce water of sufficient quality for reuse. In this study, pressure driven and thermally driven membranes are evaluated for their potential to treat blackwater, by relating selectivity to relevant water quality standards (ISO 30500) and the transmission of volatile organic compounds (VOCs) that are primarily associated with faecal odour, and thus constitute a critical challenge to water reuse. Both pressure driven (reverse osmosis) and thermally driven (membrane distillation and pervaporation) membranes were able to produce water that conformed to category B of the ISO 30500 standard for the majority of determinants. A critical limiting factor was in the selectivity for ammonia and odorous VOCs which were generally poorly removed by reverse osmosis and membrane distillation. The high ammonia transmission was accounted for by the elevated pH of blackwater which shifted the ammonium equilibria toward volatile ammonia which is poorly separated by RO polymers, and is free to diffuse through the gas-filled micropores of the membrane distillation membrane. In contrast, greater ammonia and VOC separation was evidenced for the pervaporation membrane due to advanced polymer–solute interactions. In a preliminary assessment, the hydrophilicity exhibited by the membrane was also advantageous to withstanding fouling. If complemented with a polishing step to target the residual COD and VOCs (that may be of similar origin), pervaporation could deliver to category A standard for non-potable reuse. This is particularly advantageous for water scarce regions where solar or liquified fuels may be applied in favour of electricity for off-grid sanitation.
Open Access
The nano membrane toilet: separation processes.
(Cranfield University, 2019-03) Mercer, Edwina V.; McAdam, Ewan; Pidou, Marc
It is estimated that 61 % and 29 % of the global population lack safely managed sanitation and clean water services respectively. The water Sustainable Development Goals (SDG 6) actioned by the UN, aim to provide global access to sanitation and clean water by 2030. However, in low income countries (LICs) conventional centralised wastewater treatment plants are economically unfeasible and for affordable decentralised alternatives, only 22 % of the waste is safely managed, leading to contamination of water resources. The Reinvent the Toilet Challenge (RTTC) initiated by the Bill & Melinda Gates Foundation (BGMF) proposes to innovate off-grid, self- sustaining systems, which are able to safely manage human waste and provide opportunity for resource recovery, at ≤US$0.05 user⁻¹ d⁻¹. In response, the Nano Membrane Toilet (NMT) developed at Cranfield University propositions a household scale sanitation system which combusts human faeces and provides an off-grid opportunity for advanced treatment technologies to treat the liquid fraction, comprising faecally contaminated urine (FCU). This thesis investigated a series of potential separation processes which integrate with the combustor, for FCU treatment. It was demonstrated that solids liquid separation can be facilitated post flush with a screw auger, which allowed for effective faecal solids recovery for the combustor. Thermally driven membrane processes, which operate from heat energy, evidenced that high water quality where reuse standards could be achieved (with operational optimisation) in a single stage. In addition, they proved robust to faecal contamination and manipulated odour profiles to change negative perception. The most adaptable process, membrane distillation (MD), provided a salinity gradient consisting of a concentrated retentate and deionised permeate where salinity gradient energy was converted to electrical energy through reverse electrodialysis (RED), sufficient to power an auxiliary low voltage fluidic device (0.25 W) for 4.9 hours. Importantly, the integrated separation processes within this thesis, evidenced high quality water and energy recovery, which are the foundations of an SDG 6 solution.
Open Access
On the compressional rheology of fresh faeces: evidence for improving community scale sanitation through localised dewatering
(Elsevier, 2021-08-06) Mercer, Edwina V.; Usher, Shane P.; McAdam, Ewan J.; Stoner, Brian; Bajón Fernández, Yadira
Non-sewered sanitation is currently dependent upon pit latrine emptying, the safety of which is compromised by the high costs of faecal sludge transport to centralised treatment facilities. Transport in turn is hindered by the complex rheology of pit latrine sludge. This study therefore characterised the compressional rheology of fresh faeces and modelled the implications for passive (gravity) or mechanical (forced) solid/liquid separation. This informs on the viability of decentralising dewatering for more efficient volume reduction and improve the economics of transportation. The gel point (ϕg) is the solids concentration where the material has a networked structure and signifies the point when mechanical intervention is required for further solid-liquid separation. For fresh faeces, ϕg ranged between 6.3 and 15.6% total solids (TS) concentration. This is significantly higher than the ϕg observed for wastewater sludge at centralised facilities, and it implies that passive gravity driven processes can suffice to improve localised dewatering. The kinetics of passive sedimentation of faecal material were modelled and illustrate thickening from 3 to 10% TS concentration in <0.5h. This highlights that early intervention to thicken faeces while fresh can improve solid/liquid separation efficiency. Filtration of fresh faeces was characterised by lengthy cake filtration times and comparably short compression times, more similar to mineral slurries than to wastewater sludge. Consequently, fresh faeces presented improved dewatering characteristics, supporting higher final cake solids concentrations and improved dewatering kinetics. By complementing thickening with 300kPa filtration, a 1.4 cm thick 25% TS product could be achieved in <24h. Investigation of matrix properties highlighted that increased conductivity (e.g. exposure to urine) negatively influenced dewaterability, an effect which could be mitigated by introducing solid-liquid separation earlier. The thermodynamically favourable compressional rheology of fresh faeces has identified that focussing on localised dewatering could radically improve the economics of faecal sludge management, primarily through reducing transport costs.
Open Access
Quantification of liquid phase faecal odourants to evaluate membrane technology for wastewater reuse from decentralised sanitation facilities
(Royal Society of Chemistry, 2018-11-29) Mercer, Edwina V.; Davey, Christopher J.; Campo Moreno, Pablo; Fowler, Dawn; Williams, Leon; Kolios, Athanasios; Parker, Alison; Tyrrel, Sean; Walton, Christopher; Cartmell, Elise; Pidou, Marc; McAdam, Ewan J.
Public willingness to use decentralised sanitation facilities or arising water products is discouraged due to malodour, preventing improved sanitation practices or water reuse opportunities in low income countries Whilst odour is characterised in the gas phase, it originates in the liquid phase. Consequently, controlling odour at source could prevent gas-phase partitioning and limit produced water contamination. This study therefore developed an analytical method for the quantitation of a range of liquid phase volatile organic compounds (VOCs) classified into eight chemical groups, known to be primary indicators of faecal odour, to provide characterisation of real fluids and to permit evaluation of several potential membrane separation technologies for liquid phase odourant separation. The gas chromatography mass spectrometry method provided quantitation in the range of 0.005 mg L-1 to 100 mg L-1 with instrument detection limits ranging from 0.005 mg L-1 to 0.124 mg L-1. Linear calibration curves were achieved (r2 >0.99) with acceptable accuracy (77-115%) and precision (<15%) for quantitation in the calibration range below 1 mg L 1, and good accuracy (98-104%) and precision (<2%) determined for calibration in the range 1-100 mg L-1. Pre-concentration of real samples was facilitated via solid phase extraction. Subsequent application of the method to the evaluation of two thermally driven membranes based on hydrophilic (polyvinyl alcohol) and hydrophobic (polydimethylsiloxane) polymers evidenced contrasting separation profiles. Importantly, this study demonstrates the methods utility for liquid phase VOC determination which is of use to a range of disciplines, including healthcare professionals, taste and odour specialists and public health engineers.
Open Access
Rheological characterisation of synthetic and fresh faeces to inform on solids management strategies for non-sewered sanitation systems
(Elsevier, 2021-09-16) Mercer, Edwina V.; Usher, Shane P.; McAdam, Ewan J.; Stoner, Brian; Bajón Fernández, Yadira
In order to obviate the economic issues associated with pit latrine emptying and transport such as high water additions and rheologically difficult sludge properties, the implications of prompt solid/liquid separation were investigated. This was achieved through rheological characterisation of fresh human faeces and synthetic faeces, and comparison with aged faecal sludges. Shear yield stress, thixotropy and post-shear structural recovery were characterised for a total solids (TS) concentration range of 5–35% total solids (TS) and stickiness yield stress was determined for concentrations up to 100% TS. Fresh faeces rheology proved to be favourable when compared to aged matrices, evidenced by a lower shear yield stress and higher gel point solids concentration, suggesting that aging could alter the physico-chemical properties of faecal sludge. Fresh and synthetic faeces exhibited similar shear thinning, thixotropic behaviour with the majority of structural breakdown occurring at a low shear rate of 10 s−1, and the extent increasing with higher solids concentrations. At 32% TS, fresh faeces shear yield stress was permanently reduced by 80%, suggesting that low shear pumping could reduce the energy demand required for faeces transport. The sticky phase, which represents the region to avoid faecal transport and mechanical drying processes, was identified to range from 30 to 50% TS, with 25% TS as ideal to commence dewatering processes. This also coincides with the average solids concentration of faeces, which is achievable by source separation. This study has identified that handling of fresh faeces as opposed to aged faecal sludges would result in economic and environmental benefits, with energy, water and labour savings.
Open Access
Selection of screw characteristics and operational boundary conditions to facilitate post-flush urine and faeces separation within single household sanitation systems
(Royal Society of Chemistry, 2016-09-15) Mercer, Edwina V.; Cruddas, Peter; Williams, Leon; Kolios, Athanasios; Parker, Alison; Tyrrel, Sean; Cartmell, Elise; Pidou, Marc; McAdam, Ewan J.
To ensure adequate access to sanitation in developing economies, off-grid single household sanitation has been proposed which obviates the need for significant infrastructure capital investment. Whilst treatment at this scale is most efficient when coupled to source separation (i.e. urine from faeces), existing source separation solutions have proved difficult to implement in this context. In this study, screw extrusion is therefore investigated to provide ‘post-flush’ source separation. Both screw characteristics and operational boundary conditions were evaluated. Preferential screw characteristics included tapering of the shaft and progressive pitch reduction, linked to a small extrusion aperture, the combination of which enhanced solids extrusion efficiency and promoted higher solids concentration in the extruded fraction. Whilst maximum extrusion efficiency was observed at high rotational speeds (over 400 rpm), this also promoted free water transport. Operating below 300 rpm instead introduced selectivity for transport of faecal sludge over urine, enabling phase separation. Constraining the volumetric ratio of urine to faeces also enhanced the extrusion rate of faecal sludge by increasing feed viscosity sufficient to overcome backpressure imposed by unmasticated food particles that would otherwise restrict separation. Importantly, this study demonstrates the feasibility of screw extrusion for ‘post flush’ separation of urine and faeces which constitutes a significant advancement towards realising sanitation at a single household scale.
Open Access
Tube-side mass transfer for hollow fibre membrane contactors operated in the low Graetz range
(Elsevier, 2016-09-28) Wang, C. Y.; Mercer, Edwina V.; Kamranvand, Farhad; Williams, Leon; Kolios, Athanasios; Parker, Alison; Tyrrel, Sean; Cartmell, Elise; McAdam, Ewan J.
Transformation of the tube-side mass transfer coeﬃcient derived in hollow ﬁbre membrane contactors (HFMC) of diﬀerent characteristic length scales (equivalent diameter and ﬁbre length) has been studied when operated in the low Graetz range (Gz < 10). Within the low Gz range, mass transfer is generally described by the Graetz problem (Sh=3.67) which assumes that the concentration proﬁle comprises a constant shape over the ﬁbre radius. In this study, it is experimentally evidenced that this assumption over predicts mass transfer within the low Graetz range. Furthermore, within the low Gz range (below 2), a proportional relationship between the experimentally determined mass transfer coeﬃcient (Kov) and the Graetz number has been identiﬁed. For Gz numbers below 2, the experimental Sh number approached unity, which suggests that mass transfer is strongly dependent upon diﬀusion. However, within this diﬀusion controlled region of mass transfer, tube-side ﬂuid velocity remained important. For Gz numbers above 2, Sh could be satisfactorily described by extension to the Lévêque solution, which can be ascribed to the constrained growth of the concentration boundary layer adjacent to the ﬁbre wall. Importantly this study demonstrates that whilst mass transfer in the low Graetz range does not explicitly conform to either the Graetz problem or classical Lévêque solution, it is possible to transform the experimentally derived overall mass transfer coeﬃcient (Kov) between characteristic length scales (dh and L). This was corroborated by comparison of the empirical relationship determined in this study (Sh=0.36Gz) with previously published studies operated in the low Gz range. This analysis provides important insight for process design when slow tube-side ﬂows, or low Schmidt numbers (coincident with gases) constrain operation of hollow ﬁbre membrane contactors to the low Gz range.

Browsing by Author "Mercer, Edwina V."

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