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Digest Colonizers, Make Gas, Cook Beans...

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Submitted by strypey on 14 December 2012 - 4:42pm | Blog entry

I’ve been wondering for a while how much work and resources would be required to build a prototype for a neighbourhood scale organic-waste-to-energy plant, with a pedal-powered mulcher. I’ve heard a lot of theory about biogas digesters, but this article entitled ‘DIY Methane Generator‘ seems to be based on the experience of some people who have actually experimented with it on their permaculture farm, with some success.

“Just about any organic waste can be decomposed as a methane generator - plant (soft material is better than woody material) and animal wastes, and even human waste.”

This got me thinking. Soft material. Like convulvulus and periwinkle? Twitch? Grass clippings? Animal waste, who has a dog and feels guilty putting its do-do into landfill, and weird about putting it in the compost? Human waste. Hmm. I wonder how many kilograms of humanure a household produces each day?

“Each kilogram of biodegradable material yields around 0.4 m³ (400l) of gas… 2 gas rings for a couple of hours a day will use between 1-2 m³”

So that means you’d have to be able to process about 2.5kg to 5kg of colonizing weeds, dog poo, and humanure per day, per household, to supply enough gas for daily cooking needs. I presume this material would need to be mulched fairly finely for efficient digestion. Maybe this could be done with wind power, where it’s available, but what about cycle power?

Cycle power has the benefits of being available when it’s not windy, and providing an exercise opportunity for humans (assuming you have humans around who want some exercise). Think about all those people at the gym, riding exercycles which aren’t hooked up to anything! Turning human pedalling power directly into mechanical work is much more efficient than turning it into electricity and back into work, and there is almost certainly more embedded energy in the various hardware needed for electrical generation and storage than there would be in a pedal-powered machine. Also, according to this article in Low Tech Magazine, a stationary bike custom-built to provide energy from pedal-power is much more efficient than hooking up a standard bike, whether you’re trying to generate electricity, or power a machine directly.

So what I’m thinking is this. Each neighbourhood could have a gym, with exercycles designed for ease of harvesting the energy output of the person exercising, using a direct mechanical drive with some sort of gearing system, to allow riders to work their way up to the force necessary for a given job. A standard socket could allow a variety of mobile machines to be hooked up to it, anything from a smoothie maker to the mulcher discussed above. When nobody is using the energy directly, the exercycles could be set up to store it by charging banks of communal electric batteries, or even by winding up clockwork, compressing air, or charging electromagents.

This is something the energy group of a Transition initiative could start working on right now.

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Methane

Submitted by Richard on 16 December 2012 - 8:51am.

Hi Stypey

There is plenty of information out there on methane digestion. The Chinese Biogas manual is a pretty good place to start. Also Jean Pain the legendary French composter wrote a couple of books. These manuals were written in the 70's and maybe hard to source these days but I do have scanned electronic copies somewhere.

David Blume also has some info on methane digesters in "Alcohol can Be a Gas".

However you can almost buy large scale Methane digestion off the shelf these days as they are becoming more common place on the larger dairy and pig farms in NZ. So the technology and information is there, it just requires the advocacy, organisation and drive to get it happening on the community/municipal level. A job for a forward thinking national organisation like Peramaculture in New Zealand perhaps?

Not to sure about a pedal powered mulcher. The force required would be immense. However as Blume often points out, when you are producing energy from local sources and using your energy locally you are more than likely to come out with a net EROEI gain if you are smart about production methods. Hence if you are producing local ethanol or methane you already have the energy to run your production.

cheers
Richard

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Biogas

Submitted by lainephillips@g... on 17 December 2012 - 5:41pm.

Hi Strypey,
Biogas is definitely an areas where we could be utilising many resources that we currently waste. I looked into this for dairy farms about 10 years back and there was nothing happening in NZ. At that time there were several trials happening in the US on feed lot based farms. There is huge potential to be running all dairy farms off biogas. I come from a dairy farm background as a kid, and the amount of cow manure that is washed away from milking sheds each day is pretty huge. Richard, great to hear it is making its way into NZ. With some proven case studies I am sure there will be farmers out there wanting in - the electricity costs of running milking sheds is pretty high, and money talks. Cows spend up to 3 hours or so a day standing on yards. Assuming they relieve themselves more in the day than night, that's quite a proportion of methane from the breakdown manure that could be captured. Burning the gas would still produce CO2, but it is much less harmful that the methane itself in terms of global warming. If you are really cleaver, scrubbers can take the CO2 out of the waste vent and be turned into a fuel too. An NZ company is doing this in China on big manufacturing factory smoke stacks.

Some councils in NZ have been doing this stuff a long time. I studied Microbiology at Massey, and we toured the Palmerston Norths waste water treatment plant in 1997. They had a then not new biogas digester, generating all the electricity needed for the plant. How amazing would it be if all houses had a unit in the garage doing the same thing on a small scale, whether using the gas directly or generating electricity from it. And the digested residue could then be used in the garden, reducing the infrastructure costs for councils, and power costs for houses.

Ideas like this seam so simple don't they? Maybe the technology still needs work at household scale. I don't know.

Smiles

Laine

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