I assume home based means that this will be a DIY-project and will use organic wastes of one household, tehre's no lifestock present.

I know no detailed desciptions. These people seemingly have a small scale digester in their garden, maybe that's helpful: http://solarcities.blogspot.de/2012/12/fuel-without-end-amen.html

Though I won't vouch for th quality of the information.

Thank you! Yes for now the focus will be on food waste as there is not livestock waste present. Thanks for the tip

Generally speaking, there are four types of small digesters that might be used in a home (or any small-scale) situation. Each is discussed at www.completebiogas.com.

David

Thanks David!

With regard to your second question about electricity and pressure: I would be astonished if you were able, with a small digester, to produce enough biogas to power a genset. A) There is nearly no point in having a genset smaller than can be powered by a ~10 HP engine. B) It takes 15+ cu ft per HP per hr to power such a device, and C) given that a digester, at body temp and using manure-based substrates, will (rule of thumb) generate 1 cu ft of biogas per cu ft of digester per day, then you would need... a hell of a lot of organic matter fed t o a LARGE digester to make much electricity during any significant fraction of the day. (Food waste might, maybe generate 2 cu ft per cu ft of digester, but that is not enough to change the basic situation.) Ergo D), biogas from small digesters should be used first and almost exclusively for uses powered by direct burning (cooking, light), second (and only perhaps) for indirect uses (mechanical energy from an engine: threshing, water pumping), and third (and generally speaking _never_) for tertiary or quaternary uses (engine==> generator==> electricity==> radio).

With proper design of the storage equipment, pressure will be sufficient for any rational use. Appliances need 2-5 inches pressure, the biogas process will produce >400 inches pressure.

David

Thanks everyone, I appreciate your suggestions.

The Canadian video (on youtube) interviewing Harold Bate, the British inventor that produced methane in his farm and used it to power his car (1960's - 1970's).

Michael,

Unfortunately Harold Bates was something of a P.T. Barnum figure. He had a chicken farm, and thus might have been able to produce enough biogas to run his car. But widely distributed pictures showing his "digester"-- a tank of perhaps 30 gallons-- are very misleading.

The common rule of thumb for manure-fed digesters is that they produce 1 volume of biogas per volume of digester per day. 30 gallons is about 4 cu ft. An internal combustion engine requires >15 cu ft of biogas per HP per hour. Bate's Hillman car had a 100 or more HP engine, requiring >1,500 cu ft per hour to run.It does not take a very sharp pencil to see the discrepancies.

It certainly seems that he was implying by his repeatedly being photographed with the tiny digester that it was the source of biogas he used to run his car. Four cu ft of biogas is likely not be enough to merely start (not run) a lawnmower, much less run a car around town. And the tank that he showed in the Hillman (see a photo thereof in the Mother Earth News article about him) could not possibly have held enough biogas (under any reasonable pressure) to run the car for more than a few minutes, if that. (Methane is extremely difficult to liquefy-- it requires very high pressure and very low temperatures-- and the tank appears to be a low-pressure, ambient temperature variety.)

Further, in at least one interview about the process, Bate offered estimates for the amount of biogas that could be produced from a certain amount of manure that were flat wrong. It was the equivalent of saying that you could generate enough electricity to run your house by harnessing the water dripping out of your faucet.

Recall finally that he was selling a hardware unit that was supposed to convert cars to run on biogas. Jerry Friedberg, who produced a widely praised kit that would help convert VWs to propane, said that Bate's device did not work, and was dangerous. (http://www.motherearthnews.com/green-transportation/bate-autogas-convertor-device-zmaz72mjztak.aspx) 

In sum, I would suggest that proponents of biogas should let Harold Bate slip quietly into historical obscurity.

Hello David,

Thanks for providing technical data into this story. 

Harold Bate was an inventor nevertheless. He was not a trained engineer, so his methods may have lacked the rigorous testing requirements to get a reliable product. I doubt very much that he was a crook and faked his use of biogas in his car.

The world will be a better place if ideas and devices like Bate’s were studied and improved instead of throwing them into obscurity.

Michael,

Bate said, "The method is really very simple. You just put about three buckets of manure into a sealed oil drum. Put a small oil heater under the drum to keep the manure at a steady 80 degrees.... I keep replenishing my manure supply. I run my car for about six months before I clean out the tank and start with fresh dung."

The claim violates the laws of physics in several ways. If he actually ran his car on biogas, he knew that it was not so "very simple". By contrast, if his car ran (say) on propane, then he knew that he was not running his car on biogas. Is there a third alternative?

The ideas, the technology, that's one thing. Bate and P.T. Barnum are another. Keep the ideas, sure, but what should we do with Bate? Celebrate egregious and almost certainly deliberate errors? Better to forget.

I think providing factual and verifiable information is a better method of making progress. By contrast, tall tales-- such as the idea that anyone can run a car around town on three buckets of manure-- will tend to "inoculate" people _against_ the whole idea of biogas, or so it seems to me.

d.