Solid substrate fermentation (SSF) for faecal sludge, to produce higher value products?

  • indiebio
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Solid substrate fermentation (SSF) for faecal sludge, to produce higher value products?

Has anyone come across using faecal sludge as substrate in solid substrate fermentation (SSF)? Composting can be seen as a SSF process, but I am more interested in SSF for higher value products, for example: organic acids or other commodity chemicals, polymers or industrial enzymes.

Solid-state (substrate) fermentation is generally defined as the growth of micro-organisms on (moist) solid material in the absence or near absence of free water.

I have not seen any work on SSF and fecal sludge. The closest thing I found was composted sludge for growing orchids on.

I have not done targeted research on this yet, but faecal sludge beneficiation to commodity products (more valuable than fertiliser or biogas) emerged as a research need from my PhD, and I hope to investigate it further soon.

SSF – solid substrate fermentation or solid state fermentation – originates from fermented foods in the East, an example is the “Koji” fermentation process. SSF has been used in producing biopolymers from swine manure, for example [1].

It is not a commonly used method for industrial biotechnology, because it has poor heat transfer, and is difficult to scale. But it is a cheaper process than liquid fermentation, more suitable to complex materials like faecal sludge, and in my opinion better suited to fungal bioproduction. The main products include industrial enzymes, organic acids, polymers and perhaps packaging material [2, 3].

Two books which introduces the concept:
* Chen H, 2013. Modern Solid State Fermentation: Theory and Practice, Springer. [4]
* Mitchell DA, Krieger N, Berovic M (Eds.), 2006. Solid-State Fermentation Bioreactors: Fundamentals of Design and Operation, Springer. [5]

[1] – www.prairieswine.com/pdf/3197.pdf
[2] – www.ecovativedesign.com/mushroom-packaging
[3] – www.dell.com/learn/us/en/uscorp1/corp-comm/mushroom-packaging
[4] – www.springer.com/us/book/9789400760424
[5] – www.springer.com/gp/book/9783540312857
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  • muench
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Re: Solid substrate fermentation (SSF) for faecal sludge?

Hi Bernelle,

Your questions are very interesting, have you progressed this further in the meantime?

You mentioned that your PhD thesis got you onto this topic (you said "faecal sludge beneficiation to commodity products (more valuable than fertiliser or biogas) emerged as a research need from my PhD") - could you post your PhD thesis as well?

And if you want to take conventional faecal sludge as input to solid substrate fermentation, wouldn't that have far too much water in it? Might it work better with dried faeces from urine-diversion dry toilets (UDDTs)?

This research project from a few years ago (title: Biofuels From Digested Sewage Sludge (Washington University, USA)) might have some similarities to your work?:
forum.susana.org/forum/categories/169-pr...-university-usa#3464

Or are biofuels not part of the higher value products that you're looking at?
There are a few more mentioned in this sub-category:
forum.susana.org/forum/categories/169-pr...-fuel-or-electricity

I think though that in most cases the production process gets too expensive and you can't recover the costs from selling your "higher value product". Remember that faecal sludge is also full of rubbish and other impurities that you'd first have to remove (this is less of a problem for dried faeces from UDDTs). And then there are the transport costs for the faecal sludge to your processing site, too. Would be hard to make this economically viable?

Regards,
Elisabeth

P.S. there is also this paper if you haven't seen it yet:
forum.susana.org/forum/categories/53-fae...-improved-sanitation

A value proposition: Resource recovery from faecal sludge — Can it be the driver for improved sanitation?

Stefan Diener, Swaib Semiyaga, Charles B. Niwagaba, Ashley Murray Muspratt, Jean Birane Gning, Mbaye Mbéguéré, Joseph Effah Ennin, Christian Zurbrugg, Linda Strande

Dr. Elisabeth von Muench
Independent consultant in Frankfurt, Germany
Community manager of this forum via SEI project ( www.susana.org/en/resources/projects/details/127 )
This email address is being protected from spambots. You need JavaScript enabled to view it. Twitter: @EvMuench
Sanitation Wikipedia project: en.wikipedia.org/wiki/Wikipedia:WikiProject_Sanitation
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
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  • indiebio
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Re: Solid substrate fermentation (SSF) for faecal sludge?

Hi Elisabeth

Thanks so much for your thoughtful and thorough reply.

I am currently writing up my PhD, the thesis is not yet available. I have not done actual work on this, but am currently establishing the required infrastructure and permissions for a small scale study. I hope to pursue this after the PhD. Part of the PhD and wider research project is doing an overview of resource recovery from wastewater, we have one Water Research Commission (WRC) project published, and just finishing up the second one.

You can find the first report here:
wrc.org.za/Pages/DisplayItem.aspx?ItemID...+concept%26start%3d1

I agree that the conventional FS may be too wet, but it may still have potential, and pre-treatment to reduce the moisture, or to make a blend with dry substrates may work (especially in high sunlight, semi-arid places like South Africa, where I am based). But I agree that dry toilets are more promising, generally.

I think biofuels, or any energy vehicle, is still not of high enough value (but of course good for a final 'mopping up' conversion, to be used on site). I am thinking along the lines of industrial enzymes, organic acids, surfactants... because I agree the cost is a problem, and one will require a high-value, (low volume) product to offset that, while stabilising the solids.

The entire system would have to be designed or retrofitted to reduce the impurities and improve the process, yes, and this represents more cost, but modular (smaller) scales of operation may address this better, and yes, again the dry sanitation may be easier here.

It would be best to be able to process this on site, or in close proximity. I have the idea of bringing back the night-soil concept and have processing plants per neighbourhood / around 10 000 ppe, but not sure how viable that is! I do think it's important to explore how this might work in both affluent and poorer areas. The concept of a 'biorefinery' rests on symbiosis between partners situated close to each other.

Lastly, many thanks for the article links, it looks promising!

best regards
Bernelle
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  • ddiba
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Re: Solid substrate fermentation (SSF) for faecal sludge?

Hi Bernelle,
I find the biorefinery concept in your work to be interesting though as Elisabeth pointed out, there is need for more work to develop economically viable models for obtaining biofuels and other "high value products" from wastewater.
You mentioned that your PhD involves "doing an overview of resource recovery from wastewater". Is this still ongoing or have you published something out of it yet? I also wonder if this "overview" is focusing only on wastewater or it includes other waste streams like faecal sludge and perhaps excreta from UDDTs and other dry toilet systems. Or is it only focusing on possible byproducts through "biorefinery" processes? I would be interesting in learning more about your work in this area.

Regards,
Daniel

DDIBA Daniel Isaac Waya
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  • indiebio
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Re: Solid substrate fermentation (SSF) for faecal sludge?

Thanks Daniel, apologies for the delay.

The PhD is in it's final stages, this report from IWA might be useful in the interim: www.iwa-network.org/cluster/resource-rec...y-from-water-cluster

Our overview only focuses on wastewater, but my future work would be more aimed at the faecal sludge and excreta from various dry toilets.

We are currently only looking at biologically produced products - the biorefinery, but I will be keen to investigate physico-chemical beneficiation as well, specifically employing concentrated solar thermal applications.

This is a huge area so I doubt I'll get round to doing all of it though :)
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