Backyard Aquaponics
A place to discuss aquaponics

We have a large dairy operation in my project area. 3700 head of dairy cows. They use a methane digester. And really don’t like it. The gas is actually more of a biogas with high methane content and it will corrode any metal that is frequently in contact with the gas. They have had to replace their generators once already and it is only 4 or 5 years old. They are building an even larger opperation now, and outright refuse to use the methane digester.

I think this is a good concept but if it is highly corrosive over time that could be a huge problem.

A large portion of the gas is CO2 which is corrosive. I plan to bubble all my gas thru water, located in a base tank before letting the gas rise into in a floating tank. By draning the water down and changing it often it should absorb most of the CO2. The CO2 rich water will lowerthe PH of my well water then go to a garden or orchard . In fact the PH will stop falling when the water is saturated with CO2 and that will indicate time to change it.

Hmmm i thought there were saying somehting about sulferdioxide. or sulfersomething. But this is kindof hearsay.

A small unit would work well with a bubler system. Would it really be cost efective on a larger system. 3700 dairy cows is a lot of poop to digest.

Yep, thats also what stinks in it. To get rid of it place a large wad of steel wool at the digester tank outlet. There are farms that power their tractors and homes using the gas they produce. Sounds like the farm above has a sorry setup.

wow that is all it would take to remove the corrosive component? wonder if they can retrofit that into the system.

Newage, anything corrosive is usually either acid or alkaline. The disadvantage of this is that they desperately want to become pH neutral. So they eat anything that they can to become neutral, usually pipes, tank walls, anything metal, and sometimes other substances.
There is a protection technique called 'Sacrificial erosion'.
This is used on steel bridges, and steel boats, to stop them rusting. All you have to do is create a circuit with the corrosive substance, and have a more reactive substance (usually zinc I think) bolted onto the ships hull, below the waterline, so there's a circuit. (This is also why nails are zinc coated, but it wont rust even if scratched and the steel is bared.
It's sort of the same here. The gas will run through the steel wool, that has a VERY high surface area, and will rust more happily than the tank walls or pipes that have a nice fine structure.
Of course the steel wool will be a CONSUMERABLE, it will need to be replaced, as to neutralise the gas, it Must rust and break down.
Hope that made sense... It's not my field of expertise, so I could be a bit wrong in places, but the gist is right.

Making up words again KP

You wait OB, your time will come...
It's Christmas soon, so I'll be nice for a while in the spirit But after... Free for all

KP, you do have the jest of it, zinc and magnesium are sacrificial anodes and the steel wool by having the expanded surface area works well as a cheap anode but reacting hydrogen sulfide and or sulfur dioxide with steel wool creates iron sulfide which is pyrophoric (it auto ignites when exposed to air/oxygen) Which is not a real problem if when you replace your steel wool you wet all the surfaces and then just burn the spent steel wool. Don’t store it, it will heat up and auto ignite.

You're essentially duplicating the principles of an RSG filter.... adding iron to an anaerobic process, to convert the hydrogen sulfide....

ion exchange

thanks for the additional info. I understood the process just did not think something so simple could work so well.

I'll have to pester the Dairy operation and see if they employ some type of technique to remove the corrosive properties of the methane bio-gas. It would be wonderful to see bio-digesters to be used at the industry level

Just wondering but how would you properly dispose the used steel wool? Wonder if there is a know ratio of x volume of gas per day will need x volume of iron to rust.