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On the compressional rheology of fresh faeces: Evidence for improving community scale sanitation through localised dewatering.

Publication ,  Journal Article
Mercer, E; Usher, SP; McAdam, EJ; Stoner, B; Bajón-Fernández, Y
Published in: Water research
October 2021

Non-sewered sanitation is currently dependant 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 improving 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 <0.5 h. 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 300 kPa filtration, a 1.4 cm thick 25% TS product could be achieved in <24 h. 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.

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Published In

Water research

DOI

EISSN

1879-2448

ISSN

0043-1354

Publication Date

October 2021

Volume

204

Start / End Page

117526

Related Subject Headings

  • Water
  • Wastewater
  • Waste Disposal, Fluid
  • Sewage
  • Sanitation
  • Rheology
  • Feces
  • Environmental Engineering
 

Citation

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Mercer, E., Usher, S. P., McAdam, E. J., Stoner, B., & Bajón-Fernández, Y. (2021). On the compressional rheology of fresh faeces: Evidence for improving community scale sanitation through localised dewatering. Water Research, 204, 117526. https://doi.org/10.1016/j.watres.2021.117526
Mercer, Edwina, Shane P. Usher, Ewan J. McAdam, Brian Stoner, and Yadira Bajón-Fernández. “On the compressional rheology of fresh faeces: Evidence for improving community scale sanitation through localised dewatering.Water Research 204 (October 2021): 117526. https://doi.org/10.1016/j.watres.2021.117526.
Mercer E, Usher SP, McAdam EJ, Stoner B, Bajón-Fernández Y. On the compressional rheology of fresh faeces: Evidence for improving community scale sanitation through localised dewatering. Water research. 2021 Oct;204:117526.
Mercer, Edwina, et al. “On the compressional rheology of fresh faeces: Evidence for improving community scale sanitation through localised dewatering.Water Research, vol. 204, Oct. 2021, p. 117526. Epmc, doi:10.1016/j.watres.2021.117526.
Mercer E, Usher SP, McAdam EJ, Stoner B, Bajón-Fernández Y. On the compressional rheology of fresh faeces: Evidence for improving community scale sanitation through localised dewatering. Water research. 2021 Oct;204:117526.
Journal cover image

Published In

Water research

DOI

EISSN

1879-2448

ISSN

0043-1354

Publication Date

October 2021

Volume

204

Start / End Page

117526

Related Subject Headings

  • Water
  • Wastewater
  • Waste Disposal, Fluid
  • Sewage
  • Sanitation
  • Rheology
  • Feces
  • Environmental Engineering