Does anyone have a DIY biogas system in full use?

[julian]

I have been reading some, and ive seen a fair bit of discussion, but i havent found any comments from somone who has actually built a diy system, and has it in full use (ie real world use, rather than just testing / experimentation)

I would really like there to be someone, as it kind of puts me off that there seems to be quite a lot of talk, but no action (as it were!)

...yep, yep, i know someone will say "go on then" but, like i say, im concerned that others seem to have done plenty of experiments, with no end result, so i doubt that id do any better than them!

I know itlld be possible to build a very manual system, store the gas, and cook with it, as per the indian (etc.) examples, but im more interested in slightly more automated applications.  It always going to be hands-on, i know, but there is a lot of difference between having a selection of IBC batch digestors plumbed in with pipework / valves etc. into a chp engine etc than the idea of filling up an inner tube at the bottom of the garden and hooking it up to a stove.  Im sick enough of carrying cans of waste veg oil arround as it is! (but not sick enough to go to the petrol station mind!)

Anyhow, im just interested to know if anyone has an example in full use at all, and what they use it for, how they find it, etc.etc.

Thanks, Julian

[smegal]

What feedstock are you looking at using?

[julian]

...whatever i can lay my hands on

(as per usual)

...but, no, i dont have an exact plan yet.  We're in the process of moving location, so future supplies are a little uncertain.

I got into the idea from looking into what to do with the glycerol i have from biodiesel production, and my interest went from there  - i know that glycerol restricts activity above, some say, 3%, whilst others say 6%.

I have a lister engine, which i will be running off veg at the new place (again, supplies permitting) and ive been trying to find out if a percentage of methane in the air inlet to that would be beneficial (ie not running on gas at all, running on liquids, but with a small percentage of gas)

...thatlld meen storage wasnt needed.

[smegal]

From what I've seen glycerol really does digest well. A colleague of mine is adding 18g along with 500ml of cattle slurry and is getting over 20 litres of biogas a day (in a 9 litre reactor). I currently get about 10 litres a day off 100ml of waste yeast.

The only issue with feeding your lister is that biogas has a tendency to break things because of the water and H2S content. 

[Ivan]

smegal - any pics?

[smegal]

Here is a pic of my digesters in a 37^o room.

[Ivan]

Pretty cool. From it's setting, it doesn't look like you're doing it for fun - are you collecting data?

[smegal]

It's my MSc project. I am trying to speed up the digestion of yeast waste from a yeast extract factory.

I am collecting data on COD removal, gas output and composition mainly.

[Ivan]

Sounds exciting. Hope you're planning to publish the project somewhere on the internet (post a link, if you do). Have you found anything that works well.

Your reactors reminded me of one of my first ideas for running a digestor - using a demijohn (usually for wine making) with a standard demijohn airtrack to funnel the gas for collection - also useful as a cheap and cheerful production rate indicator. I never got it off the ground though, as in the early days of Navitron, I used all my old demijohns to supply solar antifreeze when I ran out of containers!

[smegal]

Unfortunately the only methods that I have found to work either have an excessive energy requirement (sonicaiton) or too costly (enzymes). I tried using bacteria (Bacillus Subtilus) but it didn't touch the yeast. These were measured by monitoring the gas yields of a control and test reactor) If the gas yield of the test increases, the cells have been seen to have become more readily digestible.

Yeast waste has such a high level of organic carbon (~200 g/l) that if an energy.cost effective method of breaking the cells is found then there is the potential for massive amounts of gas to be generated from it. The company that I am working with generates 60 odd tonnes of this waste a day, the major breweries will be producing much more.

I'll be more than happy to send you a copy over, although due to me starting my job a week before the deadline this report is not going to be as well polished as I'd hoped.

I wish I had the money to build my own LARGE scale AD plant, there is the possibility of making a lot of money from a well operated plant, not to mention saving landfill space and generating renewable electricity,gas and heat.

[Ivan]

Everything I've ever read (reports of practical experimental work), suggests that mechanical agitation is essential, without which gas production drops to a low level - I guess the bugs might get swamped with excess CH4 concentration (like yeast gets overcome by excess alcohol)

[smegal]

I'd agree with that. When my stirrer broke on one of my digesters this weekend, the gas yield dropped down to a much lower level than the other reactor.

I'll find out a bit more on that front on Friday.

[smegal]

Everything I've ever read (reports of practical experimental work), suggests that mechanical agitation is essential, without which gas production drops to a low level - I guess the bugs might get swamped with excess CH4 concentration (like yeast gets overcome by excess alcohol)

The methanogens settle to the bottom without stirring, as well as the stirring liberates the gas. Basically stirring is not essential but certainly helps.

[Ivan]

From what I've read (I stress 'read' ), the digester will form a scum on the top (septic tanks do, too - I've noticed). This thick scum stops the digester working  I presume may be due to a local build-up of methane perhaps poisoning the methanogens?

[smegal]

It depends on the waste, some e.g. cattle slurry, which has a lot of lignocellulose present that will float can be quite prone to forming a layer, especially without stirring.

If anything was poisoning the methanogens it'd be the CO₂ as it is much more sluble than CH₄.

If you were trying to produce an usable amount of gas, you would without doubt agitate, for an experimental digester it is less important, and a ballache/expensive, for example those digester pictured including stirrers will be in excess of £1000 each (I admit that is mostly down to laboratory equipment being extortionate, when a 5lt demijohn can cost less than £10 yet the 10lt "quickfit fermenters" cost over £200).