[permaculture-oceania] Re: Atn Tom Duncan

[Tom Duncan]

Hi Liane,

I'll try an keep my writing in smaller paragraphs as you requested. I can't give a strict definition of a biodigester, as there are so many different types, so I have tried to give the basic process in more detail below.

A biodigester is a container that can be shaped into many configurations and patterns. There are some general designs that are common:
1)The old petrol tank, cutted and fitted to become a biodigester (you find them sitting under extinct petrol stations where the owners didn't want the cost of taking it out of the ground) such as the UASB biodigester (Upflow anaerobic sludge blanket) design as used by George Chan.
2) A long polyethylene plastic tunnel
3) A concrete or mud brick tank, similar in shape to a rainwater tank or septic system.
4) A dome shaped container - even 44 gallon drums, or smaller plastic drums
5) Big tall stainless steel biodigesters
6) Long horizontal stainless steel biodigesters
7) Fibreglass biodigesters
8) Plenty more...

Personally, I like the old stainless steel petrol tanks from extinct petrol stations, at it smacks or bittersweet irony.

A Biodigester has an input of organic matter and water usually, and holds this mixture for a certain period (known as Hydraulic Retention Time most often), in the absence of inflowing oxygen, that will hold a mixture of organic matter and water and the organic matter can be very varied whether its animal or human manures, azolla, algae, shredded biomass/ paper, animal wastes ie. slaughterhouse materials or in a farm type system bits like intestines and stomachs etc that people generally don't use and are therefore a 'waste product' suitable for biodigester, unless that is you do biodynamic agriculture and make chamomile sausages to produce a compost tea from the cow intestine microbes (which I might say is a very good usage of a 'waste product' and a flower that grows prolifically in temperate climates) etc or cow mesentry for other compost teas.....or make real suasages from intestines etc....and this biodigester container does not allow oxygen into the container during methanogenic operational periods. 

It is therefore termed anaerobic digestion, or an anaerobic biodigester, which will produce biogas. Methanogenesis (the production of methane) is performed by anaerobic(prefer to operate in the absence of oxygen) bacteria that as part of the biomass breakdown, produce methane. This methane flows  upwards out of the biodigester due to it's gaseous nature, then held in a container (or sometimes the biodigester is the gas container  as well) (some people use big polyethylene bladders, or big plastic bags, or recycle other containers) and then through various different approaches piped the biogas which is about 60-70% methane and 30-40% carbon dioxide to kitchen stoves for cooking gas or can be more methane efficient if certain technologies are used, or if enough excess, compress it into cylinders and use similarly to LPG, but it is termed Compressed Natural Gas(CNG) to run vehicles or generators, or if there is even more biogas excess use it as part of an electricity generator process to produce electricity. There are now even fuel cells that run off methane to produce electricity. 

Normally human and animal manures methane and carbon dioxide is released on site or at another site like a sewage works or even landfill or other miscellaneous sites. Under a tree, next to a bush.... so a design system needs to reflect the fact that when shit happens, your biodigester is nearby to transform it into biogas. Biodigesters are optimised when other biomass is used, as manures are not such a complex thing to breakdown and the energy values are quite low if taken by themselves. For instance, if an ecovillage did an accounting for all the oil used in cooking, and how much waste oil was put into worm composting or composting systems, you would get a figure that would demonstrate that this grease, would be a great addition to a biodigester and create a good energy accounting as far as methane production goes, as grease produces high methane output in certain biodigesters such as the UASB digesters which I prefer.

Biodigester effluent for example is nutrient rich, and therefore azolla ponds or algae ponds are good at sucking up all that nutrient and then greywater reedbeds for growing plenty of biomass to shred and put back into the biodigester or used as mulch/ etc in the system or irrigating orchards or other tree crops responsibly. Not suitable for growing root crops or other crops that are eaten raw as the possibility of worm eggs etc. and other nasties can be present when using manures of any sort. Yes the biodigester gets up to and above 60 degrees celcius potentially but better to be safe than sorry in my opinion.

Here is a nice low tech step by step guide for biodigesters in the tropics as done in places like Equador http://www.ias.unu.edu/proceedings/icibs/ibs/info/ecuador/install-polydig.htm. There are many approaches. I prefer George Chan's approach. You can google George Chan and find plenty of articles on him and the systems he designs.

Biodigesters are now being used extensively in Sweden, in fact a town called Linkoping a town of approx. 100,000 people is powering all it's taxis, buses and some trains by Compressed Natural Gas (CNG) from biodigesters. In Australia some truck fleets are running on CNG, but that is from Natural Gas that is a non-renewable deposit over a coal bed or other such site.

To answer your question Liane about Energy Descent and Peak Oil and what is the difference, I will try an put forward my limited view: Energy Descent is a term, (and I'm not sure, but I believe termed by David Holmgren - any experts here on Energy Descent - perhaps David himself could chime in here?) to paraphrase the scenario societies are facing when the consequences of Peak Oil are in effect and other factors inlcuding the passage of time and the growth of population and the scarcity of non-renewable resources, and how we respond to this scenario. Peak Oil issues such as diminishing oil reserves and ever more scarce oil and higher oil prices, are driving Energy Descent in a sense, as are other things like principles, ethics and other factors like expectations and emotions and attitudes and the global market.  Some action planning processes such as Energy Descent Action Plans, as discussed by the good folks at http://www.eatthesuburbs.org/edap-primer/ .  Others are investing in biodiesel and ethanol and biodigester energy as part of their Energy Descent plan.... everyone has a different view on what life after cheap Oil will be like.......Some of the effects of Peak Oil are already here, and that is rising oil prices. The effects are wars in the middles east and Africa to secure oil resources. Oil scarcity will make local food more attractive financially and Peak Oil is one of the drivers. Energy Descent is already here. This saturday I'm going to join an organic food coop for example which will hopefully be sourcing locally grown seasonal organic veg more direct and cheaper than if I bought it at an organic food shop or supermarket like Macro Wholefoods. People have been doing this for years. CSA (Community Supported Agriculture) is a nice model for this, I think in the Permaculture Designers Manual it is called "Farm Link" or something like analagous.

Energy Descent and the action plans associated with Energy Descent focus on permaculture solutions for localising food and energy production and consumption and the repatterning of urban and rural communities around these patterns that permacutlure design principles can effect. Descent culture as positioned by David Holmgren is a sustainable low energy user society that has learnt and adapted to using low energy for an ecologically and socially and economically sustainable future. I think this approach is a very valuable addition to the sustainability debate and takes a whole of community and bioregion approach to the sustainability questions such as: How do we live in an Energy Descent Future where oil is scarce and non-renewable resources are scarce in general - David's book "Pathways Beyond Sustainability" takes at least a 500 year time line in his analysis. I am trying to emphasise biodigesters as one of the technical components in permaculture systems design, to equip communities, farmers and others with sustainable cooking gas and limited electricity production methods as a sensible, attainable and rational approach to the energy futures mix.

For instance, George Chan, an 82 year old biodigester expert who has talked at International Permaculture Conferences and I've tried to get him an invite to the next one coming up in Brazil in 2007, is working in Mauritius where he lives, with a group of 25 small holder farmers, where they bring their animals daily for milking, and all the manures go to a single biodigester, instead of having 25 farmers having separate herd manure areas and small biodigesters, he has designed a system that allows them to bring all the herds together and collect all the manures at the one site for the biodigester he designed. Takes a lot of patience to do the work he is doing.  There are algae ponds, then fish fingerling ponds, then 6 level fish polyculture ponds, with aquaponics, then any leftover nutrient laden water can be fertigated.

Luckily in Australia we have larger farm holdings and ecovillages often have livestock/ food prodcution systems as part of the mix. What this needs is a concerted effort to integrate biodigesters into the mainstream into new developments, ecovillages, farms etc. Transforming waste into energy, and then letting it become compost, or mulch or whatever you want to do, or orchard fertigation etc. A biodigester sits in before these processes and adds value. That is what we as permaculturists need to be offering, the adding of value energetically, not just as compost and mulch which is part of an ecological system's energy matrix and holding in soil and water and productivity, but there is the hard technologies that need to be energetically powered and things such as cooking gas is a good place to start.

Liane, seeing as you have not done a permaculture design certificate yet (PDC), I will let you know that I am looking forward to Bill Mollison's and Geoff Lawton's PDC in Melbourne Jan 2007, as I know Bill and Geoff talk a fair bit about biogas and various approaches to it. I hoping to be able to give a slideshow or two during the evenings about George Chan's projects that involve biodigesters, livestock, aquaculture and aquaponics.  I'm also looking forward to the Bendigo PDC to be held at Gravel Hill Community Garden coming up this October, starting on 21st October, where David Holmgren and Darren Doherty and others will be teaching. I'll be holding a small session on aquaculture and biogas on one of the days. Beck Lowe is organising the PDC. Her email is becklowe at bigpond.com

Cheers, Tom

Message: 1
Date: Fri, 22 Sep 2006 09:45:52 +1000
From: Liane Colwell <lianecolwell at iprimus.com.au>
Subject: [permaculture-oceania] Atn Tom Duncan
To: permaculture-oceania <permaculture-oceania at lists.cat.org.au>
Message-ID: <C1396150.674E%lianecolwell at iprimus.com.au>
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Hi Tom

Sorry to be so ignorant. Could you please give some definitions pls [I am
new to permaculture, sorry and havent done a course yet]

What is energy descent and how is it different from peak oil?

What is biodigester? I gather its using faeces but would like a strict
definition.

Also pls, when you are doing a long post, would you mind, breaking it up
into smaller paragraphs so it is easier to read.

Kind regards

Liane 
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