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DIY anaerobic digester



  • Registered Users Posts: 1,427 ✭✭✭Big Lar

    Have one but we call it a septic tank, actually its a pity that it wasn't sealed better around the pipework and cover as it would be easy to take off the gas.

  • Registered Users Posts: 6,198 ✭✭✭Ubbquittious

    Imagine all the money that could have been saved buying drums of gas if every septic tank down through the years had a means of taking the gas off

  • Moderators, Education Moderators, Home & Garden Moderators Posts: 8,145 Mod ✭✭✭✭Jonathan

    MuGug are based down in Cork. I don't have one but an interesting product.

  • Registered Users Posts: 6,198 ✭✭✭Ubbquittious

  • Moderators, Home & Garden Moderators Posts: 5,975 Mod ✭✭✭✭graememk

    That's interesting. I do notice no prices on the website though.

    It seems like everything is broken down into a liquid. I wonder at what point it would be feasible to have something like that even on a farm, the liquid can just empty in the slurry tank.

    We put "slurry bugs" in one tank last year. Skipped this year to see if we notice any difference.. although this year.. with the price of fertilizer..

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  • Registered Users Posts: 2,389 ✭✭✭1874

    while it is probably the same principle, this is only for macerated food wastes, not even garden waste. I thought they'd have the macerater inside as an option, like a US style food disposal and gas outside, great idea, saw it before but forgot what they were called, recal the egg shaped digester, be interesting to know how much they cost, Id be astonished if the cost compares to paying for your food waste to be disposed in a brown bin or simply composting. Great green credentials and a use for biogas, shame they cant do a garden waste version, or make suggestions how to prepare other green garden waste or even just organic materials, as I dont think I'd have enough waste food to run the thing, but a garden could provide ample material to dispose of and get some benefit from.

    Having looked up other biodigesters, it seems they need additional input to alter the Carbon/Nitrogen balance for certain animal wastes, not impossible, as someone has come up with one for food, surprised they aren't available for septic tanks given their prevalence.

  • Registered Users Posts: 4,930 ✭✭✭paulbok

    sounds a bit too good to be true.

    It claims to handle up to 1 tonne of domestic waste a year, giving back the equivalent of 9 gas bottles.

    Then it also claims to provide avg of 1-1.5 hrs of cooking a day.

    I'd probably average 1hr a day on my gas hob, but I only use 2 such bottles a year.

  • Registered Users Posts: 6,198 ✭✭✭Ubbquittious

    In ideal conditions probably. They are also using electricity to keep the egg warm I think so you will lose the equivalent of a few yellow drums with that. I asked fo rthe price no reply yet

  • Registered Users Posts: 1,446 ✭✭✭denismc

    There is a farm based Cafe in West Cork that has one of these installed, basically all the waste from the cafe goes into it.

    I must ask about it next time I am in.

  • Registered Users Posts: 4,930 ✭✭✭paulbok

    Think on their website it uses nearly 1Kwh a day, which works out about 90% of what my 2 gas cylinders costs me a year.

    I already have a large composting bin setup that takes cardboard and most garden waste (not suitable for meat and dairy waste though) so not really gonna pay for itself or majorly reduce my carbon footprint.

    Depending on it's cost it may suit some people, but not for me.

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  • Registered Users Posts: 11,116 ✭✭✭✭the_amazing_raisin

    Saw a design from India for a digester made out of 2 water tanks and some plastic pipes. Claims it could turn food waste into biogas good enough for cooking or heating

    Apparently the concentration isn't high enough to cause an explosion if it's outdoors. I'm not particularly convinced though, I'd prefer something with at least a CE mark

    "The internet never fails to misremember" - Sebastian Ruiz, aka Frost

  • Registered Users Posts: 4,734 ✭✭✭Shoog

    Ireland is far from ideal for small scale biodigesters. The reason is there are two classes of mythogenic bacteria. One is adapted to live in the guts of ruminants and these are the ones you want to use - however they only really work at around 35C which is about 20C above normal ambient temps in Ireland. Production falls off a cliff below this sweet spot of temps. The other type of mythogens - the ones would have to use are sourced from natural sludges such as the bottom of lakes. These are adapted to work in the 5-15C temp range. However rate of production is extremely slow so you need a large volume to get any reasonable amounts of output.

    Second thing, unless you intend to go large (and I means farm scale) the last thing you want to feed a biodigester is **** ie what you would send to a septic tank. The reason is that all of the high grade energy source's in feaces has already be extracted by the digestive system so the **** is low energy and hard to extract. This means large volumes and long residence times. The only really practical feedsource for a small domestic digester is waste food - which in most cases is in limited supply.

    In order for small domestic digesters to work in Northern latitudes you really need to heat the digester into the sweet spot range of 35C. On a large enough scale this is easy to do by feeding back about a quarter of the produced gas into a gas heater. This is not really safe or practical on a single house digester so you have to resort to using electricity. i cannot be certain but my guess is that the electricity needed will cost more than the value of the gas produced since electricity is roughly 4x the price of gas for the same thermal output (the reason why heat pumps can only ever match gas in terms of cost to run).

    In short - its a nice idea but not really suited to Irealnd.


  • Registered Users Posts: 11,116 ✭✭✭✭the_amazing_raisin

    On a vaguely related topic, has anyone seen a gas generator being powered by a biogas digester? I'm guessing the gas from the digester would probably need to be filtered somehow to remove contamination first

    If you had solar PV and batteries, then a digester might be of some use where you could use it once the tank is full and charge up your batteries for later use

    It would also get around any issues of air quality indoors when using the gas for cooking

    "The internet never fails to misremember" - Sebastian Ruiz, aka Frost

  • Registered Users Posts: 6,198 ✭✭✭Ubbquittious

    This is why I'm interested in digesters. I am trying to convert a Honda generator to run on a yellow drum of gas for now but eventually hope to swap it out for digester gas. It is kind of working but not quite there yet, printing a new carburetor for it at the minute

    Here is the old one running:

  • Registered Users Posts: 4,734 ✭✭✭Shoog

    If you adventurous producer gas is a great source of combustible gas with high yields for small feedstock. However its highly dangerous as the main component is Carbon Monoxide which is highly flammable.

    Post edited by Shoog on

  • Registered Users Posts: 11,116 ✭✭✭✭the_amazing_raisin

    Yeah I was researching it a while back and there seems to be a lot of cleaning of the generated biogas needed before you can put it in a generator

    Seemed like a lot of hassle and I couldn't find much info on how exactly to filter it

    "The internet never fails to misremember" - Sebastian Ruiz, aka Frost

  • Registered Users Posts: 6,198 ✭✭✭Ubbquittious

    "The average composition of ordinary producer gas according to Latta was: CO2: 5.8%; O2: 1.3%; CO: 19.8%; H2: 15.1%; CH4: 1.3%; N2: 56.7%;"

    I think you lose a lot of power burning that in an engine. Digester gas should be better

  • Registered Users Posts: 2,505 ✭✭✭bullit_dodger

    I wish I knew more about this. Very interesting topic people! Respect!

    Still for some reason as I'm reading this I can't get the word "unabomber" out of my mind. LOL!