DIY anaerobic digester

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.

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.

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.

Shoog

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

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!