Transfer Tanks in dense slum area - for pit latrine waste in dense settlements of Nairobi - dewater in a mobile manner?

  • nicolag
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Transfer Tanks in dense slum area

Hi All

I am working on a project to trial transfer stations for primarily pit latrine waste in dense settlements of Nairobi. We are hoping to acquire a new site at the drain where the manual emptiers already bring their waste at a rate of approx 10m3/day. We are finding ~5% solids.

In order to build some trust with local officials, we'll be first running a basic transfer station model where we collect the waste in a tank, and exhaust. Though over time, we would like to dewater on site; and ideally send liquids to the sewer network (in an ideal world we might just dump all of the waste in there after some screening).

The sewer network is unpredictable in its function so in the near term (and maybe beyond) it would be preferable to deal with the liquids on site. Though this quite a swampy area with a dense population. That said, we may manage to acquire ~30m2+ for our set-up and the existing site is at a bit of a distance to the surrounding communities (~500m).

It may also be of interest to dewater in a mobile manner and transport the liquids to a functioning sewer (subject to lots of negotiation of course!)

I know that space constraints will mean expensive solutions to dewatering and effluent disposal; but I am interested to hear them...if you have any that are tried and tested. I am looking at some package treatment plants but struggling to decipher one from another and ascertain how they will deal with our relatively potent faecal sludge.

Apologies for the rather vague problem statement but I don't want to rule out any options just yet!

Many thanks,

Nicola
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  • awhitesell
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  • Beaumont managed the Fecal Sludge Omni-Ingestor project on behalf of the Bill and Melinda Gates Foundation between October 2011 and November 2015, and has been developing FSM technology since 2011.
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Re: Transfer Tanks in dense slum area

Hi Nicola,

This is an interesting project you are working on and conceptually similar to something I explored on paper but didn't turn into a project (due to a lack of funding, not because of some fundamental issue with the concept). It seems to me that disposing of 10 cubes of 5% solid waste into the sewer network won't be a major burden on the WTP although you should check with plant and also see if the infrastructure between the access point and the WTP can handle it. As you suggest, skipping the dewatering would be ideal as that step will prove to be the most challenging technology-wise. As I'm sure you are aware, the physio-chemical properties of the pit contents can vary quite a bit -
and dewatering equipment works best when the incoming material has consistent properties. Dewatering of the sludge, and more specifically, dosing of the polymers used to cause flocculation, will be your biggest technical challenge.

If you visit our old website, www.fsmtech.org , you'll see some of the concepts we were considering/developing within the Omni-Ingestor program. The Fixed Pre-Processor is similar in principle to your platform, and the original Omni-Ingestor concept, the Mobile Pre-Processor is similar to your mobile platform idea except that it also includes pit/tank evacuation.

I'm happy to talk with you more about the project if you like.

Cheers,

Andrew

Andrew Whitesell
Founder/Owner of Beaumont
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  • nicolag
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Re: Transfer Tanks in dense slum area

Hi Andrew

I missed this response - my apologies!

You have perfectly predicted the issues - the site has been an great success now receiving 10m3/day of waste from manual pit latrine emptiers (arriving in 200 L drums)- very variable in content - I'm not sure that any amount of measurement would give a definitive answer on what we are actually collecting.

Now we are looking toward the most basic methods of solids recovery - preferably just gravity based given what you mention about the variable floc needs...of course finding anything tailored to sludge of ~5% TS is an issue with most literature examining ~1% septage.

Nicola
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  • JKMakowka
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Re: Transfer Tanks in dense slum area

Please find attached a recent study on dewatering fecal sludge in Uganda using geotextiles (and Chitosan). Might be a good start and should be quite robust to varying inputs.

Microbiologist & emergency WASH specialist
WASH news aggregator at: news.watsan.eu

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  • tgurksi
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Re: Transfer Tanks in dense slum area

Hi Nicola,

Andrew brings up a good point that I forgot to mention when we talked...chemistry variations and their effect on flocculation. To the best of my knowledge, this has never been explored (doing so was one of the main recommendations that came out of my OI project), so at best we can say that it is a potential problem. My experience is with a constantly changing supply of US septage, and all 3 flocculants we used (including organically derived chitosan) worked every time. My suspicion is that as long as you're talking about relatively uncontaminated fecal sludge, it won't be an issue for a fixed location (region to region or country to country may require changes). The bigger concern, in my opinion, would be the effect of a contaminant, such as diesel or industrial chemicals. It's not KNOWN if they pose a significant risk to floc chemisty, but they might. I would suggest that having a relatively small "batch" size and a contingency plan in case of periodic contamination would be sufficient mitigations.

Cheers,
Tom
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