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" Performance of Breathable Laminated Membranes for Drying of Fecal Sludge in Container-Based Sanitation Systems "
Bakhshayesh, Babak Ebrazi
Imhoff, Paul T.
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Latin Dissertation
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English
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| Record Number
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1057971
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TL57088
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| Main Entry
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Bakhshayesh, Babak Ebrazi
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| Title & Author
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Performance of Breathable Laminated Membranes for Drying of Fecal Sludge in Container-Based Sanitation Systems\ Bakhshayesh, Babak EbraziImhoff, Paul T.
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| College
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University of Delaware
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| Date
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2020
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| Degree
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Ph.D.
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2020
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| Note
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201 p.
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| Abstract
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A new sanitation technology has been proposed in which a laminated hydrophobic membrane contains and enhances drying of fecal sludge in a toilet, with particular focus on application to urban regions of low-income countries. The proposed technology uses a laminated hydrophobic membrane liner as an integral component of container-based sanitation systems. The focus of this study is to quantitatively evaluate the laminate's clogging after repeated use, which will affect replacement interval and might limit the laminate's application in container-based toilets. The membrane of the laminated hydrophobic membrane used in this process is hydrophobic and only allows vapor transport. Drying of fecal sludge using the laminated hydrophobic membrane occurs due to moderate temperature or humidity gradients, while other constituents such as aqueous dissolved solutes of fecal sludge are retained. Controlled laboratory experiments evaluated repeated use of a laminated hydrophobic membrane for fecal sludge drying, with mild brushing/rinsing of the laminate between each application. Drying occurred at a constant rate as long as the fecal sludge moisture content exceeded 11.6 (g/g), below which water activity <1. Over five drying cycles, at a significance level of α = 0.05 the dimensionless drying rate in the constant-rate period was not reduced. While scanning electron microscopy and energy dispersive X-ray analyses of used laminated hydrophobic membrane showed deposition of fecal sludge on the inner fabric of the laminate, particulate accumulation was never sufficient to alter the fecal sludge drying rate. These data demonstrate that clogging of the laminated hydrophobic membrane is minor over five cycles of fecal sludge drying with mild rinsing between cycles, indicating that use of the laminate may be feasible in many field applications. Previous experimental data were described with a stagnant film model but resulted in an effective diffusive length for the laminate (λ) that increased with system scale and was not a fixed property of the laminate. Computational fluid dynamics (CFD) was used to determine λ for a commercial laminate (eVent® fabric) that is invariant with system scale, to verify the applicability of CFD modeling for describing drying from laminate-lined CBS systems, and to predict the performance of a laminate-lined 40 L toilet in a CBS system for five developing countries. CFD modeling described drying well for experimental systems ranging from centimeter to meter scale using a single, laminate-specific λ, since CFD modeling allowed accurate characterization of the temperature and relative humidity in the vicinity of the laminate. Using λ determined for the eVent laminate, drying of FS from a laminate-lined 40 L toilet was estimated for developing countries selected to cover a range of climatic conditions with an assumed loading rate of 7.8 L FS per day. CFD model predictions showed that the filling time of the laminate-lined 40 L drum increased from 5.1 days with no laminate to 5.3–9.4 days, depending on the location and wind conditions. These modest increases in filling time might be enhanced significantly for alternative container designs that allow more uniform airflow near the laminate enclosure. Finally, CFD simulations were utilized to evaluate the performance of two alternative toilet designs for different climatic conditions and air speeds. The modifications to the current toilet design included removing plastic encircling the laminate to increase the surface area for drying, and removing plastic coupled with increased air speed/mixing conditions near the toilet. Removing the plastic coupled with forced convection improved drying performance. According to the results, this promising alternate design work well for warm and dry climatic conditions at higher air speeds. Results show that the utility of the promising design for Addis Abba Ethiopia, which has a cold and humid climate (T=16 °C and RH=67%), increase days to fill (tdf) from 5.5 days, associated with the current design of the toilet and air speed = 0.1 m/s, to 6.54 days, associated with the promising toilet design and air speed =3.4 m/s. While, for Kuraymah, Sudan, which has a warm and dry climate (T=29 °C and RH=23%), tdf increase from 6.97 days for the current design and air speed = 0.1 m/s, to 15.6 days for the promising design and air speed = 3.4 m/s. Finally, it was shown that design curves developed by applying SFM to CFD-determined drying rates for the laminated-lined 40L toilet could be used to estimate the toilet performance reasonably well. The findings showed that tdf obtained using the SFM with the design curves led to a good agreement between CFD-determined and SFM-determined tdf .
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Civil engineering
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Environmental engineering
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Imhoff, Paul T.
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University of Delaware
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