Faster dewatering of faecal sludge

  • Moritz
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Faster dewatering of faecal sludge

Dear all,

We would look to share a recently published open source research article on urban faecal sludge management with you.

Follow this link: www.tandfonline.com/doi/abs/10.1080/09593330.2016.1165293

Worldwide, wastewater sludge is mixed with lime, salt and polymers (called conditioners) to be able to remove water faster. Removing water from sludge means less treatment space or higher treatment capacities. Faster dewatering could also make decentralized dewatering possible. Currently, 95% of what vacuum trucks are transporting around cities is water! This suggests that conditioners would be a great way to improve faecal sludge management.

However, import of conditioners is sometimes difficult, environmentally use not sustainable and expensive. In this study, we assessed the use of Moringa oleifera seeds and Chitosan for faecal sludge conditioning in Dakar, Senegal. These conditioners could be produced locally, for example, chitosan from shrimp waste. Locally should be seen in relative terms, for example, Chitosan produced in Senegal might also be able to provide benefits for faecal sludge management in other West African countries.

The results show that based on available shrimp waste quantities and faecal sludge dewaterability results Chitosan was the most promising locally conditioner tested. The efficiency of improving faecal sludge dewatering were in reason with commercially available conditioners from Europe.

We are currently building on these findings with research in Dar es Salaam and Kampala to learn more about Chitosan conditioning with other faecal sludge types and how it can be best implemented for full-scale faecal sludge treatment.

We hope this helps some of you. It would be great to assist you implementing it in one of your projects.

Cheers,
Moritz

Moritz Gold
PhD student ETH Zurich & Eawag/Sandec
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  • JKMakowka
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Re: Faster dewatering of faecal sludge

Definitely interesting. How does Chitosan react to changes in pH? Could it be combined with ammonia/urea treatment (raises pH) to have a similar effect as lime in regards to deactivation of pathogens?

In case anyone wonders, here is a recent paper on how chitosan could be produced relatively easily from shrimp shell waste using lactic acid fermentation:
www.fisheriesjournal.com/archives/2014/vol1issue6/PartB/150.pdf

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  • Moritz
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Re: Faster dewatering of faecal sludge

Excellent point. We did not vary the pH as part of the study but we can certainly do it as part of future research in the laboratory. I will also ask our current Chitosan supplier (Heppe Biolog in Germany).

Moritz Gold
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  • JKMakowka
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Re: Faster dewatering of faecal sludge

As a follow-up: I found this quote on the IWA Water Wiki which seems to indicate that chitosan works best in acidic conditions:

In acidic solutions, chitosan becomes an extended chain and charged, while in neutral solutions, chitosan is a more coiled structure and only slightly charged (Pan et al. 1999). Swimming pool water pH must be maintained around 7.5 for human comfort and equipment safety concerns. Thus, chitosan did not suit for swimming pools. A non-charge coagulation mechanism has been proposed for chitosan (Parsons et al. 2007), but the non-charge mechanism did not appear to result in significantly increased microsphere removals by chitosan coagulation under the conditions examined in the present study.


The referenced papers are:

Pan, J.R., Huang, C., Chen, S. & Chung, Y. 1999 Evaluation of a modified chitosan biopolymer for coagulation of colloidal particles. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 147(3), 359-364.

Parsons, S.A., Jefferson, B., Jarvis, P., Sharp, E., Dixon, D., Bolto, B. & Scales, P. 2007 Treatment of waters with elevated organic content. London: AWWA Research Foundation, IWA Publishing.

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  • Moritz
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Re: Faster dewatering of faecal sludge

Very interesting. Thanks for your research. I suspect that concentrations of solids are very important. Coagulation in swimming pools is to remove solids and very low concentrations whereas faecal sludge has very high concentrations. So, maybe the relative effect is lower, but it still makes a big difference considering the high solids concentrations. I will keep my eyes open.

What we currently see with some research in Kampala is that electric conductivity (EC) concentrations really matter. Pit latrine FS in Kampala has an around three times higher EC (because of the urine which gets concentrated in lined pits) compared to septic tank FS. This appears to inhibit conditioning with Chitosan. We are currently dilution the sludge to lower EC concentration to see whether electric conductivity is really the driving force here (pH is still around 7).

Moritz Gold
PhD student ETH Zurich & Eawag/Sandec
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