What common household trash can be used to make bio gas?

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Basil Jackson
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What common household trash can be used to make bio gas?

I am designing a bio-gas system for use in urban environments. One of the
key questions concerning sizing the system is how much raw material is
typically available to feed the device.  In order to determine that, I need
to know what materials are acceptable and which aren't.  A typical household
may have material which is ok to throw in the bio-trash or on the
compost pile, but may NOT be good in a bio-gas digestor, for example because
it takes too long to break down.  An easy example may be peanut shells,
chicken bone, egg shell, avocado seed, coffee grinds, tea bags, (dog) hair...
So, the question is: Does anyone know of anyone who has ever done research as to
what items from a typical (European) household are good to use and which may
not be? Does anyone know of a listing anywhere?

Nick Chase
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Realy difficult are citric

Realy difficult are citric fruits. They cause problems.

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Basil Jackson
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Thanks... but...

Thanks for the comment. Over 65000 viewers before you never left one...
However, it would be interesting to know WHAT problems Citrus fruits may cause... Can you describe the situation where citrus fruits caused you problems? How were you able to solve the problem?

Nick Chase
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This is a theoretical answer:

This is a theoretical answer: For example if you are using orange peel waste the orange peel contains Limonene. Limonene is known to be an antimicrobial agent which therefore impedes the biogas production. Read http://www.hindawi.com/journals/bmri/aa/494182/

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Martin Funk
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How to feed your baby?

Orange peels are not really poison, you can always add some.
But your stomach will get to acid if you eat to much of it.

And when the digester is to acid it is not so much fun to emty it and start it new.

Thomas H. Culha...
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Balanced diet works almost every time

It's like yo' mamma said.  I think the problem with feeding a digestor comes when people want to make a profit and start feeding single feedstocks to maximize gas production.  We've never had to worry about feeding the digester when using our table scraps because we mix everything and this balances nutrients and pH.  If you are collecting fruit rinds in a separate bucket and doing a separate feeding, yeah, be careful.  But we use a food grinder and mix everything up, then pour (in fact we don't think about it, we just grind as we produce waste and let it be pumped or poured in the digester.). 
Also, preliminary experiments this summer in Germany feeding my digester with pure sugar and white flour showed that if I added half the quantity of washing powder (sodium carbonate) I didn't experience acid events. So buffer with baking soda or drain cleaner or washing powder when you have acid stuff and see what happens. Should work fine. 

Of course we need more data and experience, and we all want a good cheap pH meter to get the data and record it, but for most people the rule of thumb is going to be "eat a balanced diet and put in a balanced diet of food scraps as a result  and 'fuggedabaddit' "

Basil Jackson
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Good comments

Thanks for the comments. Innoventor, I'm with you. Nick pointed out a theoretical potential problem, Martin added a level of reality. You closed the issue byimplying that mono-culture is not a good idea but mixing different things usually will result in good results. An apple a day keeps the doctor away. An orange peel a day won't kill the biogas digester. I would be REALLY interested in what types of things Innoventor has put in his digester. I really don't think food scraps (from the table) are a problem at all. My real question is, what else can be used. Like I asked in the initial question, anyone have any experience with things like peanut shells, chicken bone, egg shell, avocado seed, coffee grinds, tea bags, (dog) hair...

Shue76
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re Chicken Bones

Ive been putting cooked chickens through my Insinkerator. They come out like pureed chicken pate. Very very smooth and silky. Ive been feeding this to my Redworm stock and have not found any pH or other issues for the worms. Sooo they may be just fine for Biodigesting...

Bob Dodds
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Some seeds are the best thing

Some seeds are the best thing for biogas--the oily ones. It might be good to run seeds through a blender or spice grinder. A friend of mine made almond nut butter in a blender with oil, so a seeds may grind well in one.

Egg shells are not going to change much though they may dissolve and alkalize. You could mix egg shells with citrus waste, see if the egg shelves dissolve, if so you just neutralized your acid.

Some bacteria produce acid, others alcohol. Sugar feeds the alcohol kind but a diverse input should be fine, as everyone agrees.