[Digestion] biogas from coffee grounds and used mushroom substrate

[Wayne Zschech]

G'day all,

Our 10m3 pilot reactor should be assembled, Lord willing, over the next
couple weeks.  I have been working up to this point for years!

In the meantime we have been talking with a local cafe chain. They would
like their coffee grounds to be used for renewable energy or at least
diverted from the city garbage.  I'm looking for the best option as far as
economic effect as well as energy production. I've read that coffee grounds
make a great substrate for oyster mushroom but I'm thinking that maybe
putting them through a digester first would yield a reasonable amount of
biogas as well as sanitise the grounds (we'll only be collecting them
weekly).  I wonder if I should expect a decrease in mushroom yield since
the digester removes energy or perhaps affects the availability of certain
necessary ingredients for mushroom growing.  Apart from lignin content,
what else do they need to grow?  I'm told that there is about 14% oil in
the grounds. That should make a fair amount of gas.

I'm also thinking that it might be possible put the used substrate into
another digester to increase gas yield.  Can I expect significant biogas
yields since the mushrooms have broken down a lot of the lignin/cellulose?
Any thoughts or advice on how I can make this process sustainable?

Could I make the coffee grounds the sole or main feedstock?  What retention
time would you suggest? Any inputs would be appreciated.

Blessings,
Wayne
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