Vermi composting of biogas sludge?

  • Marijn Zandee
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Vermi composting of biogas sludge?

Dear all,

A friend on mine in Kathmandu has a big biogas digester to digest the organic waste from a hospital, I think it is a 25 cubic meter dome.
To increase the fertilizer potential (and value) of the sludge he is thinking of vermi-composting it. We are now looking at a good "recepie" to thicken the sludge so it would be acceptable to worms. I am now thinking of a mix of straw and saw-dust. Does any one have any experience with thickening sludges for vermi-composting and have some experiance to share?

Kind regards

Marijn Zandee

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  • Otterpohl
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Re: Vermi composting of biogas sludge?

Dear Marijn,

we have worked extensively on vermicomposting of very wet exctreta sieved from flush toilets. Worms can start working in relatively high moisture content even at 85% but they need their 'Home' earth pack from where they can start working. Addition of woody materials is indeed a good idea, aso some stone dust of dry earth will be helpful. See www.tuhh.de/aww the doctorate of Chris buzie on this issue (free download)

Ralf
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  • emmanuel
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Re: Vermi composting of biogas sludge?

Dear Ralph,

In Marijn case, the vermicomposting is going to be done without contact with the earth.
how many time the worms can survive in such conditions and what element do they need to continue to live ?
Do you think that it is important to import new worms after a certain time ?
You says also that it is good to add woody materials but wood transformation is realy much longer than sludge. What will be a good composting time with or without woody material ?
Is dust stone or dry earth is better or just different ?
I did not see that in the Thesis of Chris Buzie
Do you have any answers ?
Thank you

Emmanuel
Ecodomeo

Emanuel Morin
Ecodomeo - France
www.ecodomeo.com
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  • Otterpohl
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Re: Vermi composting of biogas sludge?

Dear Emmanuel,

if the conditions are right (Temperature between 20 and 30 °C or tropical specie 35°c, not too wet) worms will multipy in the batch. A worm-kompost starting place of a few litres will facilitate startup. Addition of woopdy material is more to make it more valuabel later, it should be really fine and will balance nutrients, help forming humic acdids and make more compost mass. It is not needed. Vermicomposting is relatively fast, so after 2 to 3 month the material should be rich humus. It can easily become too dry... Chris is still at my institute, you can find his contat in our web site. Even the compostworms like Eisenia Foetida do not really love human excreta, but with no choice they will manage. If in any compost there is a thermophilic phase to be expected, add there after. Compost with worms can get a really good price in areas with demand for starter cultures and be sold in kilogram-packs.

Ralf
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  • Marijn Zandee
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Re: Vermi composting of biogas sludge?

Dear Ralph, Emanuel,

Thank you for your inputs, I do have some experience working with E-foetida in Nepal from one of my current projects where we work on composting farmyard manures.

I am a bit worried about using the sludge without additives, as we seem to have lost a lot of worms recently due to conditions being too wet (in our farmyard manure program). The wood material I would like to apply in the bio-gas sludge wood be saw-dust, with the intention of creating more lignine based humic substance. I think we will also try to see if we can mix some rice straw in, I have good experience using that to create some air pockets in the composting pile for the worms.

I think my friend has access to a moisture meter, so I guess I will advice him to make a sludge, straw and sawdust mixture and to adjust that mix until we are at around 85% moisture. We will throw in some soil to give the worms something for their gizzards.

For bedding, I think I will take my own experience, 1 inch of soil and then 2 inches of bedding material, in this case I think we can work with cardboard as that is collected in the same project.

Then I think we will add the sludge mixture in layers of about 15 cm and wait between layers until some composting activity becomes evident in the most recent layer. Overall maximum thickness should probably not exceed about 60 cm.

If anyone has some more ideas on this let me know.

Kind regards

Marijn

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