[permaculture-oceania] biodigesters (was An Inconenient Truth - More Ways Than One)

[adam f]

I agree with Tom that biodigesters will be an import part of an energy 
mix.  

Tom, I don't know if they're as well known here as you think, and 
probably need a champion such as yourself to help build demonstration 
sites people can see, and work on promoting them in and out of 
permaculture circles.  (Perhaps working with Ceres Cafe, who were really 
interested -- we should talk again!)  In person I've appreciated your 
positive enthusiasm, and I think that approach will win more converts. 

The way I think about it, biodigesters might offer the evolution of 
composting, on the farm or community scale.  This is an enormous thing 
in itself. 

For those that don't know, biodigesters are a way of anaerobically 
fermenting animal / human / food wastes in a tank which produces compost 
and a mixture of gases including methane, useful as a cooking fuel. (And 
Tom thinks an automobile fuel - but I'm yet to be totally convinced on 
it's scale/convenience).  There are over a million biodigesters in India 
and China.  But as far as I'm aware, still no small scale community ones 
in Australia.  (There are a few big ones attached to industrial 
piggeries.)  They don't really suit the backyard / home toilet scale 
because you need a fair bit biomass to get a worthwhile amount of gas.

There's some background and an audio presentation about them here by 
Melbourne-based biodigester builder Dr Lu Aye: 
<http://greeningtheapocalypse.com/index.php?option=com_content&task=blogcategory&id=0&Itemid=28>

Biodigesters appeal to one of the core principles I learnt from 
permaculture (capture and store energy ... and try to slow down and 
utilise that energy in as many ways possible).

So why might they be an evolution over composting?

When we compost, we are taking a relatively high energy quality material 
such as manure or food scraps -- too high energy to apply directly to 
plants, too 'hot' -- and waiting for microorganisms and chemical 
reactions to break it down into a lower energy source which plants can 
handle.  So actually a whole lot of potential energy is wasted in 
composting.  This is actually evident in the heat being produced by our 
hot piles.  Biodigesters capture some of that otherwise lost energy in 
the form of methane, and you still get good compost at the end.   By 
analogy that's akin to moving water from a hilltop spring across a water 
wheel on it's way down, rather than letting it flow directly to the 
bottom of the hill under-utilised.

Adam Fenderson in Melbourne



Tom Duncan wrote:
<snip>
> Please someone prove me wrong - I would love to know of any projects 
> in Australia that have a biodigester working efficiently.  How much 
> money has been spent on permaculture education in Australia? My 
> estimates that if you take all the PDCs done in Australia, and total 
> that, and then look at if just a small percentage of that money had 
> been put into developing biodigester technology by the permaculture 
> community and feeding back trials info then we would have a rich body 
> of info - but I believe one of the stumbling blocks to this has been 
> the whole focus of doing compost toilets. worm farming, mulching etc, 
> eclipsing biodigesters from the design vision. Perhaps permaculturists 
> have been moddle coddling themselves from the hard reality that the 
> only sustainble energy source is from our own wastes, and that 
> composting toilets,worm farming and mulching doesn't have to eclipse 
> biodigesters as part of the system? And believeing that solar and wind 
> will be their saviour? ...
...
> Why has permaculture consistently ignored biodigesters? When your shit 
> goes into the compost toilet, it releases methane - surely there would 
> be a better transformation pathway for it than going straight to the 
> compost stage?
>

</snip>