Assessing clogging of laminated hydrophobic membrane during fecal sludge drying

Abstract

HighlightsA laminated hydrophobic membrane permitted significant fecal sludge (FS) drying over 5 cycles.Particulate accumulation from FS between cycles occurred but did not reduce drying.FS drying rate decreased below a critical moisture content, when water activity <1.FS drying was 10–30% slower than water evaporation through laminated hydrophobic membrane.

Drying of fecal sludge in 3D laminate enclosures for urban waste management

“…The membrane is supported by a hydrophobic 300D polyester fabric (0.15 mm) on one side and a hydrophilic 20D mesh-like tricot layer backing fabric on the other side. If the hydrophilic fabric of the eVent laminate is placed next to drying sludge, the diffusive pathway for water vapor is smaller than if the hydrophobic fabric contacts the sludge, and drying is enhanced (Bakhshayesh et al, 2018).…”

“…Gore & Associates, Inc., DE, USA). Bakhshayesh et al (2018) examined repeated 1D drying of fecal sludge from centimeter-scale jars covered with eVent laminate (Laminate P4PS4039-3L, eVent fabrics, Lee's Summit, MO, USA) and found no significant reduction in drying performance over five drying cycles, if a moderate brushing/rinsing cleaning procedure was followed between use. Saxena et al (2019) proposed a container-based toilet system with the eVent laminate lining containers that allowed drying of fecal sludge during collection, thus reducing the frequency of container replacement and sludge disposal.…”

“…Instead, mass transfer was adequately described with only molecular diffusion through a single composite layer that accounted for resistance through the membrane and fabrics (Marzooghi et al, 2017). Similarly, Bakhshayesh et al (2018) determined that the fecal sludge's aqueous phase was blocked by a hydrophobic eVent laminate, while water vapor diffused through the laminated hydrophobic membrane with the flux controlled by gradients of relative humidity and temperature, and the laminate's resistance to diffusion. Bakhshayesh et al (2018) determined that less than a 2% error in predicted moisture transfer occurred through the three-layer eVent laminate if Knudsen diffusion was neglected, and thus mass transfer was described by molecular diffusion alone (see Supplementary data).…”

“…Similarly, Bakhshayesh et al (2018) determined that the fecal sludge's aqueous phase was blocked by a hydrophobic eVent laminate, while water vapor diffused through the laminated hydrophobic membrane with the flux controlled by gradients of relative humidity and temperature, and the laminate's resistance to diffusion. Bakhshayesh et al (2018) determined that less than a 2% error in predicted moisture transfer occurred through the three-layer eVent laminate if Knudsen diffusion was neglected, and thus mass transfer was described by molecular diffusion alone (see Supplementary data). Since in this work the eVent laminate is also used, in the analysis below molecular diffusion was assumed to describe moisture transport through laminated hydrophobic membranes.…”

“…The effective diffusion length, λ (m), is defined asλ=italicδτ/εwhere δ is the laminate thickness (m), τ is the dimensionless tortuosity, and ε is the porosity. The effective diffusion length is a measure of mass transfer resistance through the breathable laminate and was previously fitted to experimental data for 1D drying in centimeter-scale laminate jars (Bakhshayesh et al, 2018) and decimeter-scale envelopes (Saxena et al, 2019). In this study, the effective diffusion length was fitted to data from 3D laminate enclosures at decimeter and meter scales.…”