How to use 250 lbs or more per week of fruit and veggie waste

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Robert Segraves
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How to use 250 lbs or more per week of fruit and veggie waste

I am working at a fruit and vegetable distributor where we package locally grown produce for home delivery.  Because it is a for profit business we ship out only top quality produce.  We sort and grade every head of lettuce, tomato, apple, or bunch of carrots.  Those that don't measure up to grade 1 standards are not sent to customers.  a limited amount of Grade 2 produce is taken by local charities but for the most part the remainder is currently consigned to the land fill.  Having just discovered the benefits of biogas conversion, I was wondering if a we could put a system in our parking lot to generate gas that could create electricity to run our lights, refrideration, and maybe even power our truck fleet. 

We are located in Raleigh NC.  I have no idea whether or not there would be codes/laws that we would have to deal with, etc. 

Any advise would be welcome.

 

Basil Jackson
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That all depends

250 pounds is a good amount of waste and that can definitely be used to generate bio gas.  How much bio gas is generated depends on several factors that the term "250 pounds" just doesn't cover.  Generally speaking, the more calories the "waste" has, the more gas it produces.  While bacteria are better at converting calories in for example salad than we humans are, fact remains that the more calories, the more gas.  Therefore 250 pounds of apples just isn't the same thing as 250 pounds of carrots.  Also, how much of the 250 pounds is basically water?

I found a table which suggested that one "dry pound" of food waste would produce about 3 1/2 cubic feet of bio gas. I suppose you can use that as an estimate as good as any other figure.  Therefore, your 250 pounds, assuming half of that in "dry weight", would produce 125 * 3.5 = 437.5 cubic feet of bio gas.

I don't suspect there is enough gas there to power vehicles... but it's a good start!

Robert Segraves
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How to start?

437.5 cubic feet - Not schooled in biogas and it's capabilities, what does that mean in terms of energy use?  Is it boiling one kettle of water for tea, cooking on a char grill for an hour or what? 

To make the gas, I need a biogas generator - where do I start? 

Basil Jackson
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Start by building a bio-gas digester

Hello, bio-gas is created in what's called a bio gas digester.  Using that term in Google should get you a million ideas to start with.  Personally, I started with the one from Shaun at http://shaunsbackyard.com/746/biogas-digester/#more-746

His plan is simple, fairly easy to build, fairly inexpensive as a "get started" project. At that website, he has plans, and a couple of videos (feeding the digester as well as cooking coffee using the gas).

Shaun does this as a hobby and therefore he feeds the digester very little and because of that he only gets about 15 minutes of cooking gas a day. I am more than confident that with that same digester, you could feed a good quantity of your fruits and vegetables and get a reasonable amount of gas.

Bio gas is not as energy potent as natural gas because bio gas is only about 50% methane whereas natural gas is near 100% methane.  To get you started, don't worry about that part.  Just build a digester and get started.

Once you know how to generate the gas, move to the next step and decide how to use it.  Burning it for heating or cooking is of course the easiest.  Running a combustion engine to generate electricity works too but you usually need to "scrub" the bio gas before running it into the engine to remove the sulfur which would otherwise corrode the engine.  Cross that bridge when you get to it...