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Old 04-04-2013
elspru elspru is offline
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Biogas Producing Holding Tank

Hey,
I've been thinking how it could be a good use of a holding tank,
to collect the biogas that it produces, and use it for heating or cooking.

Making and using biogas is even more environmentally friendly than doing aerobic composting, while also providing a useful resource.

Depending on the size of boat and holding tank it could work.
Granted that most likely the biogas will only be an extra fuel.
it takes about 26lt of gas to boil 1lt of water [1],
perhaps less if using super-efficient stove and pot.

1 lt of waste produces about 1lt of biogas per day [2],
at 20C is takes at least 20 days to decompose [1].

if a person generates at least 2lt of waste a day,
of about 1.5 lt liquids and 0.5lt of solids,
and about 0.5lt for the flush of solids[3].
would need at least 50lt per person holding tank for 20 days.

I've read that average holding-tank is around 100lt,
perhaps if there were two, then one could ferment,
while the other fills up. And once it's done,
it would be compost grade slurry.
could get methane from both at same time.
200lt of gas per day would allow to cook 3 meals [1].
Though considering that those 200lt wont be full all the time would need some extra buffer.

Two 208lt (55gal) barrels would be enough for a family of 4, leaving plenty of extra gas.
Ideally however it would be some very efficient cookware and stove, as 4 people also eat more..

Could probably store them in the stern near the engine or something, similar to how intestines are near the rear.

Anyways, wondering what you guys think about it.

sources:
1. Project
2. The Complete Biogas Handbook: How to build a 55-gallon drum biogas digester
3. Gravity Discharge Toilets - Dometic
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