Inside The Anaerobic Methane Digester

[freetazz]

hi sir, i'm just wondering what bacteria is mixed with the waste and water?

[LordVaader]

@freetazz

Good question. I use the freeze dried septic pak bacteria for Septic systems available at the hardware store.

[freetazz]

@LordVaader But can we culture our own bacteria? so that we won't keep on buying?

[LordVaader]

@freetazz

Yes, the bacteria will grow itself after you get everything started. If you want a cheaper alternative to septic paks use animal waste including cow dung or dog waste, ect.

[freetazz]

@LordVaader Thanks for the information Sir! how will the bacteria propagate?

[LordVaader]

@freetazz

At temperatures between 70-80F they will grow by eating the waste material that you add to the digester, the result will be methane and liquid fertilzer.

[muzicalman]

does that barrel have an inner plastic lining and would it be necessary?

[LordVaader]

@muzicalman

The barrel does not have a plastic lining. Plastic lining would keep metal from rusting due to hydrogen sulfide accumulation. A plastic barrel is actually a better choice then metal.

[muzicalman]

@LordVaader so would the white stuff lining the bottom help prevent rust? i noticed your tank doesn't have a flashback arrestor why is that?

[LordVaader]

@muzicalman

The white stuff is expand a foam to provide surface area for the bacteria to grow throughout the liquid levels. I use a biogas filter as my backflash arrestor. Please see my video, Biogas Filter.

[Davi6993]

how much gas does it produce in a day?

[LordVaader]

@Davi6993

On a warm day, 85F, about a truck inner tube worth.

[ozawablog]

Your video is a favorite on Kiribati

[LordVaader]

@ozawablog

What a beautiful country. Please share videos of your digesters at work!

[madjimms]

Wouldn't it help the bacteria feed better with some sort of thin plastic/metal plates going vertical in the middle? or vertical aiming metal screens?

[LordVaader]

@madjimms

That would be an excellent design recommendation. Anything to increase surface area inside the tank would be beneficial to the number of bacteria growing and their contact with the nutrients.

[madjimms]

@LordVaader Would it be something you would try? I would be eager to see if it helps or not. :-)

[LordVaader]

@madjimms

I have plans to build a new one next year. I will incorporate your idea into the design. Thank you!

[LordVaader]

You are correct. Gas is stored in air bladders then run through an anti backflash valve to any device that uses propane.

[enticed2zeitgeist]

So... food breaks down and you catch the gas the is emitted? How do you store it and use it in devices?

[AlternativePowerMan]

Any comments about the positioning of the side drain pipe. Some designs like yours have it on the side, but others have the piping rigged so that it would remove it from the top. Also any comments about the slurry level in the tank? 50%, 75% to the top? Should the down pipe be long enough to position new 'feed stock' towards the bottom, middle, or higher up in the tank? Just curious. Trying to find a nice big plastic barrel now. :-)

[LordVaader]

@AlternativePowerMan

1. Drain pipe on the side is gravity fed. Others may use top drain and require gas pressure to create flow.

2. Slurry level is usually between 50-75% with the remaining space reserved for gas storage.

3. The feed stock pipe should be below the drain pipe to prevent air from entering the system. My design almost goes completely to the bottom to eliminate any chance of air entering.

Post your results when complete. Should be interesting.

[AlternativePowerMan]

@LordVaader Right on thanks, I was at the hardware store today looking at the various fittings and stuff. I was even thinking a small thrash pump could be used to (a) pump the barrel empty, and (b) act as a mixer to move the slurry around inside.

[Omnimeister]

This guy is like Master Blaster running the methane production in Bartertown....

[LordVaader]

@Omnimeister

As you wish, my master....

[verymuchmoremilk]

Would this size of digester able to run a small motor and generator set?

[LordVaader]

@verymuchmoremilk,

You would have to try it. I know that I couldn' t generate enough gas to power a car but I could power a lawn mower. You can collect the gas in a tractor tire for storage and bleed it out into a motor intake.

[heycatmon]

I'm interesting in doing the similar. How much solid waste do you have to remove if at all? The effluent comes out but what gets left at the bottom? How do you often (and how) have to clean if you do? Sounds like a messy job if not designed cleverly so curious vs. reinventing the wheel myself. Also, do you have to use additives to get the digestion started?

[LordVaader]

@heycatmon,

I remove about 3-6 inches of carbon and phosphorus rich semi solid waste from the bottom each year. I use septic system bacteria (rid x) to get things started. If you designed a new digester from scatch I would look into building one similar to the one below that self regulates the water level.

Biogas from vegetarian food waste-UF BioEnergy

You might even look at putting a pump on the bottom to suck out the semi solid waste for use in a garden instead of manually.

[imatelly]

how hot does the unit get,wandering if there is a reason u cant use a plastic berral,also wandering if concreat is fine to use if put underground

[LordVaader]

@imatelly ,

Unit does not get hotter than 100F. You can use a plastic barrel it will corrode less. Also you could build an underground concrete unit.

[yammivicdrum]

@LordVaader ....like a septic tank??? :)

[LordVaader]

@yammivicdrum,

Exactly.

[alienbaroque]

So the pipe that goes from the opening (the entrance) all the way down into the water stops methane from escaping when you open it up to put in the waste food, right?

[ncbookz]

good job! all the other guys had a moving top part as the gas increased the top moved up your idea seems better

[vox1philippines]

ohhhh yeee... thats nice...pls watch my small scale biogas digester, pig dung....

thankz vox

[levicool2]

it is probably not safe as of now to compress methane in your own back yard I would us extreme cation when considering this

methane is much harder to compress to liquid than propane

[LilyISay]

Every household and food vendor should have one of these- I live for that day. Do you find it smelly at all? I'm trying to convince my boss we should use one for poultry feces and he's convinced it would stink. Having read up on it, I disagree, but have little personal experience with small operations like this.

[LordVaader]

I did have some odor associated with the effluent. To solve this I will be running the effluent into a drain field in my garden underground. Odor solved.

[kenteckman]

Lord Vaader,

When the drum is full, at 5psi or so, would there be enough volume to grill a few steaks?

[gtuplayer]

ok i'm a debater and i need to finfd negitve evidence on anaerobic digestion from a credible source... any ideas?

[ShiningMountainMedia]

Nice video on the components. I'd be interested to see your Anaerobic Digester in action, and how much it produces over a period of time. Otherwise, thanks for your demo. Much appreciated.

[LordVaader]

Thanks,

I will have it up and running this summer. I just moved.

[piercedsquid]

Is there a practical method of compressing and bottling the gas to use in your car engine or a camp stove? The only thing I can think of would be to run the output hose to a large airtight chamber, and have and air compressor in the chamber, but would the compressor provide enough pressure? And would a propane cylinder withstand the pressure?

[jayceepark]

are there any laws in place for pressure vessils in domestic use? and can i transfer the methane into a gas bottle to power my bbq?

[LordVaader]

The gas pressure generated is only 5-7 PSI. The digester does not pose a danger of exploding due to low pressures involved. Also the gas production will be severely limited if pressure is allowed to build too high, therefore the reaction is self limiting.Yes you can use the gas generated from the digester to power a burner, generator, or grill. It does take a lot of energy to compress methane into gas bottles so it is easier to store it in low pressure air bladders and vent off as needed.

[Thebigbambeano]

it takes 1000 psi to compress methane

[sumgai777]

That's not true -- ANY pressure will compress gas -- it's Boyle's law.

(You may mean "to compress methane enough so that it's a liquid phase at room temp". ;-)

[astrialkil]

@jayceepark In the us the department of transportation has laws on the construction of gas cylinders because gas cylinders all get moved at some point. Why else would you want to put it in a nice easy to move cylinder unless you wanted to transport it some where? You could just put your grill near the digester and run a hose to the grill with a flame arrester and a adjustable low pressure regulator.

[broomhandle1]

I have a question. Couldn't one cut the bottom of that barrel and place on top of an opened septic tank, and gain more fuel?

[LordVaader]

Broomhandle1,

I have heard of people installing a gas line on top of their septic tank to capture the methane for use. This may be dangerous however. I built the digester because I live in town and do not have a septic system. It is important to note that the gas street lights of early America were powered by methane gas from the sewers.

[tslc04]

how far doest the pipe go down and do i add water? how much water and how much food?

[LordVaader]

Pipe goes down about 5 inches from the bottom of the barrel. Fill the drum about 1/4 the way with water and fill to the 1/2 way mark with food waste. Allow to decompose for 2-3 weeks at 70F or greater before gas production kicks in.

[HomeDistiller]

have you mesured the gas output of this unit? i will be building one almost identical as that unit but i may add a small heating coil and insulate it or use solar heating to help it out

[LordVaader]

The unit will produce gas as long as the temperature remains above 70F and you provide enough new material to digest over time. I "dispose" of the waste material in a drain field under my garden. I have not measured the gas output of this unit. A heating coil and insulation will go a long toward consistant gas production, however on a warm day solar radiation will work just fine.

[piercedsquid]

Rather than having to heat the digester, just put it in your greenhouse if you have one.

[rigionspm]

I'd like to know for how long you produce gas and how do you dispose of the end product. Do you take the cover off ?

[netlethe]

Insulated in the ground, could we gather free heat from this ???

[LordVaader]

The reaction does not generate much heat, however it requires about 90F for efficient gas production, hence I only operate it in the summer.

[VedicHawaii]

Very very cool.