Household Methane Digester

In podcast 1028, Jack Spirko talks about small methane digesters and the business opportunity there is in that field.

Basically, a company could offer to install small household methane digesters to provide people with gas for cooking. The only thing one would have to do is call the company when the gas pressure is getting low, the company would come to recharge the digester and haul away the composted material, which could then be sold. Such a business could use food that would otherwise end up in landfills and make use out of it.

I've always been intrigued by the roof top digesters in India The barrel in a barrel style fueled by household waste and pressure increased by just by putting a few bricks on top of the sliding barrel. I know a thing so simple is probably going to be illegal at some level and would probably need to be bootlegged in currently. I'd like to see gas lights around a restaurant or grocery store maybe, something with a compostable waste stream already.

Robert, do you have any pictures of that?

Given the amount of gas present, it can probably be much safer or at least as safe as the big propane tanks people have beside their houses. Maybe some sort of rubber bladder would be more acceptable for the regulatory bodies than the two barrels and bricks.

The ones that I have personally seen are made from the blue barrels you see everywhere. When more pressure was needed rocks or bricks are placed on the floating barrel. Access to the spent waste from a gate valve at the bottom and used on directly on the garden.

Here's a video of a more polished version of the barrel in barrel style:
http://www.ruralcostarica.com/biogas-india.html

another
http://bio-gas-plant.blogspot.kr/2012/04/step-by-step-guide-to-constructing.html

An explanation of the telescoping design:
http://www.bing.com/videos/search?q=bio+gas+in+india&view=detail&mid=4909E9F326F097F34DD54909E9F326F097F34DD5&first=121

Anyone seen one working through a cold winter? I wondered about having one in it's own cellar below frost line, but it could be a real death trap accessing something like that in a confined environment if you didn't have it sealed well. Maybe buried but with an insulated hatch cover at ground level for access to add material? How would sludge be removed?

I don't think I'd bury. Sludge removal and an explosive gas in a confined area would be a concern.

Fascinating stuff. I have been working on re-purposing refrigerators and freezers, as giant insulated boxes. This seems like it could be a good use. I am concerned about the storage of the gas, though the barrel in barrel method seems ideal.To make it more "official", could one store the gas in standard propane containers? I suppose getting it in an out could be a problem. What about using water to displace the gas?
Setting aside the standard propane containers for a moment, how about a bladder inside of a tank, to be filled with water, thus creating pressure in the gas?
Or simply adding water to a tank filled with biogas.

I have a preference for the bladder idea. I think it is safe and requires very little maintenance, but I am far from being an expert.

I really like the long, flexible digester systems in India and South America. AG bags and greenhouse plastic is inexpensive, and I could see one of these systems getting started for under $50.

The other thing about that design is that it is a flow-through system, so a little feedstock is added each day and a little effluent is removed each day. It seems to fit the daily routine of most folks.

Here's what they look like: http://www.afrigadget.com/2010/06/09/solving-the-flexible-biogas-digester-problems/

Here's another low tech option, using tire tubes. They use kitchen waste, instead of manure, and 3 kg of waste produces 1 m3 of biogas: https://energypedia.info/index.php/TyreTube_Biogas_Plant

ive ehard of biogas before, especially when talking about guinea pigs poo in one video i watched, they had quite the system and used tires to store the gas so it didnt really appeal to me at the time

but the double barrel, piston-like design seems really simple and just great to me, like its just what i'd like to persue eventually.
anyone have figures on approximately how much this type of system costs to construct?
also, it seems like the top barrell is loosly placed, which means a lot of methane would escape via the sides rather than going into the barrel, im sure soem ruber could solve this, but is it nessacary to make a good seal or is it good enough to just leave the barrel there and allow it to capture what gas is created directly beneath it
also, what about putting a 50lb weight on top to pressurize it more? such as one used on a weightlifting bar so that it could go around your gas exit...

I remember an old Science News article that stated that it should go thru a section of clear and then lightproof, to really enhance the output of gas , and to encourage the different bacteria.

Devon if you look at some of the digesters used in India you will see rocks on top of the inner barrel that increase the pressure.

thats what gave me the idea, it seems like most weights however dont do much to help stabilize the barrel, and im thinking one may have a bit of extra leakage when the barrel leans to one side or the other, so im thinking a weight designed for weightlifting bars because theorhetically you can place it around the gas outlet and you would have a more balanced and even pressure distribution to increase that pressure

also, is 50lbs too much from anyones experience?

We're looking at methane, so it's a heavier than air gas that is not going to go up and out of the barrel just on its own, i.e., "leaking" is only an issue when pressure either builds up due to volume production or is applied - say by any weight on the top barrel.

On a guess, since these systems are actively in use and obviously working the benefit that might be gained by a gasket on the floating barrel is not worth the effort involved. I suspect that the "feed tube" needs to be set at a sufficient height to prevent methane from escaping by that outlet too easily.

I don't know how much air the bacteria involved need in order to do their digesting - that might be another reason not to have the system sealed too well...

Interesting. I had not understood how profoundly simple one of these systems could be.

It's so simple, I'm surprised it wasn't done hundreds of years ago. Or maybe it was and I just haven't heard about it yet

London sewer gas lights is something I've always heard about. I'm told that coal gas was also used and this link seems to confirm that, but the sewer gas light sounds interesting.

http://www.waymarking.com/waymarks/WM9A43_Last_London_Sewer_Gas_Lamp

Peter Ellis wrote:We're looking at methane, so it's a heavier than air gas that is not going to go up and out of the barrel just on its own

Methane is lighter than air, I believe.

Peter Ellis wrote:I don't know how much air the bacteria involved need in order to do their digesting - that might be another reason not to have the system sealed too well...

it needs to be sealed from outside air, they are anaerobic bacteria.

Those water piston units in India are supposed to supply enough methane to cook with each day, but would not make anywhere near enough methane to power a generator every other day or so to charge a battery bank.
Still, they look inexpensive to build, especially if repurposing scrap barrels. Seems a shame to not make methane just because it can't power an entire house by itself. I'd really like to know what the production rate is vs the amount required to meet all a home's energy needs. I'm curious as to how many would be needed for that.
Also, what feedstock would you all use to feed it, keeping in mind you need to add some each day.

production rate depends on the feedstock and how much you have. If you have a few pigs or a cow or 2 or a chicken farm, you can supply all the gas you need for cooking.

I've got 2 old horses, but I heard that using the manure to get the bacteria started, then adding food waste, out performs manure only digesters. The theory was that the manure is already processed while the food scraps weren't; more energy in the undigested food scraps than the digested manure.
Don't know if that's correct or not.

They say the ones in India produce enough gas for cooking, no problem. But, it's supposed to be difficult to produce enough methane to run a generator often enough to consistently charge a battery bank.
Then again, perhaps if it made enough to charge a battery bank 5 times per month, that would be 5 fewer days per month of grid electricity used.

As you can see, I'm clear as mud on methane production & use.

Can enough methane feasibly be made at the home user level to feed a gas refrigerator or freezer? Lehmans had a freezer that required 2 1/2 gallons of NG per day.

I know digesters aren't consistent producers, varying in output depending on several factors. I figure the methane might be able to reduce the amount of NG one has to supply.

Anyone know what size digester would be needed to meet that demand each day?

Refrigeration is one of the difficult ones to meet off the grid without patrolium fuel. It might be possible with solar panels, though, and perhaps a generator run off homemade methane as a backup for cloudy/rainy stretches.