Dear Barbara,

Thanks a lot for bringing your paper to our attention here! Much appreciated. I have copied some segments from your paper below to draw more attention to it but also to ensure this thread is found when someone does a keyword search within the discussion forum.

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Abstract
Unpredictable dewatering performance is a barrier to the effective management and treatment of faecal sludge. While mechanisms of dewatering in sludges from wastewater treatment are well understood, it is not clear how dewatering of faecal sludge fits into the framework of existing knowledge. We evaluate physical-chemical parameters, including EPS and cations, and demographic (source), environmental (microbial community), and technical factors (residence time) as possible predictors of dewatering performance in faecal sludge, and make comparisons to the existing conceptual model for wastewater sludge. Faecal sludge from public toilets took longer to dewater than sludge from other sources, and had turbid supernatant after settling. Slow dewatering and turbid supernatant corresponded to high EPS and monovalent cation concentrations, conductivity, and pH, but cake solids after dewatering was not correlated with EPS or other factors. Faecal sludges with higher EPS appeared less stabilised than those with lower EPS, potentially a result of inhibition of biological degradation due to high urine concentrations. However, distinct microbial community compositions were also observed in samples with higher and lower EPS concentrations. Higher EPS faecal sludge was comparable in dewatering behaviour and EPS content to anaerobically digested and primary wastewater sludges. However lower EPS faecal sludges had different dewatering behaviour than wastewater sludges and may be governed by different mechanisms.

Authors: Barbara J.Ward, Jacqueline Traber, Amadou Gueye, Bécaye Diop, Eberhard Morgenrot, Linda Strande

EPS = extracellular polymeric substances

5. Conclusions
Based on the observations in this study, the key conclusions are:
• EPS is important for faecal sludge dewatering performance observed in this study. Higher concentrations of soluble and colloidal EPS are likely to contribute to clogging of sand drying beds, filters, and other dewatering technologies. However, EPS fractions (mg/gTSS) do not measurably contribute to flocculation or cake moisture content, as is observed in activated and anaerobically digested wastewater sludge.

• The observed relationships between EC, pH, supernatant turbidity, and dewatering time could be further developed and applied in online monitoring of faecal sludge. This would be relatively quick and inexpensive to implement, and could predict dewaterability at treatment plants, or be used for dosing of conditioners for enhanced dewatering.

• For planning of community-to city-wide faecal sludge management, including the design of transfer stations and treatment plants, relationships between demographic factors (e.g. source) and physical-chemical characteristics of faecal sludge could provide a relatively low-cost way to help pre-determine or predict dewatering performance.

(this last point is my take-home message from your paper):
• Faecal sludges behave differently than wastewater sludges. There will not be one reference sludge that is appropriate to serve as a proxy for faecal sludge, based on the vast differences in redox conditions, biomass, nutrients, salts/ions, stabilization, particle size, EPS, undigested plant fibers, etc. Hence this emerging research topic needs to be approached in different ways and cannot be solved with just a direct transfer of wastewater knowledge. Looking to other fields of dewatering, for example pulp and paper, sediment dredging, and food science, could provide fresh insights for meeting this challenge.

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As with any important paper I have quickly added some content to the relevant Wikipedia article. Check here how I have cited you in the Wikipedia article on FSM and if you agree: en.wikipedia.org/wiki/Fecal_sludge_manag...#Treatment_processes . It's in the section on drying beds. In my understanding, dewatering and drying go hand in hand in drying beds, right?

Regards,
Elisabeth

Dear all,

Unpredictable dewatering performance is a barrier to effective management and treatment of faecal sludge. In our new article, our team from Sandec/Eawag and Delvic SI investigated predictors of dewatering performance, including physical-chemical, demographic, environmental, and technical parameters. We also make comparisons with the well-documented dewatering behavior of wastewater sludges.

Read, use and share:
doi.org/10.1016/j.watres.2019.115101