[Digestion] R.R.R. ->was-> Re Digestate as fertilizer

[David Fulford]

Bennett, Hello,

There have been systems that do all that you have suggested - animal 
dung in biogas plant, effluent to ponds and compost, growth of duckweed 
and other crops, methane running engine, with engine coolant heating 
plant, electricity used to run system. The only thing that you have left 
out is fish ponds. People have been advocating such ideas since the 
1980s, especially in places such as China.

However, while most of these systems have been very successful at an 
experimental level, but have proved difficult to popularise. Such an 
integrated farming system relies on all the components running properly 
and problems with one component (e.g. the engine) upsets the whole system.

Greenfinch Ltd in the UK had a biogas plant running on food wastes in 
the 1990s, with the liquid effluent used to grow duckweed, which fed 
fast growing talapia fish. They had also started to used the solid 
compost for vermiculture. They now have a commercial food waste plant 
running in Ludlow in the West of the UK, but this does not include the 
duckweed and fish aspects. The liquid is recycled through the plant, 
while the solids are composted elsewhere. The plant does generate about 
500 kW of electricity, which is delivered to the power grid. The heat 
from the engines is used for the biogas plant and to pasteurise the compost.

So, your idea is not far out.

Regards,

David F

On 19/11/2010 02:44, bennett at frognet.net wrote:
>> As a result some people see AD as "biogas", some as "Carbon", some as
>> "waste disposal", some as "pathogen reduction" and some as "fertiliser".
>> What we really need to do is see anaerobic digestion as all of the above
>> and as part of a larger system. This involves a move away from the typical
>> Western "linear" approach (of extract, use, discard) to a more cyclic
>> approach (we have a Reuse, Recycle, Reduce slogan going around, sometimes
>> with a 4th R that I can't remember). I know some areas have been doing
>> this for centuries, and even Westerners used to be better at it (before
>> coal and oil!).
>>
> Okay... since we're on a roll here, tell me if you think a scenario
> similar to the following sounds TOO FAR OUT:
>
> animal manure goes into an in-ground plug/flow digester;
> spent digestate goes to both sediment pond and aerobic compost pile;
> sediment pond produces duckweed and nutrient for hydroponic grow beds;
> duckweed is harvested and dried for animal feed;
> methane produced runs an engine;
> engine coolant keeps digester warm (radiator coils wrap around digester);
> engine runs generator to produce electricity;
> electricity lights and runs pumps for hydro
> .... what have I forgotten?
>
>
>
>
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>

-- 

********************************************************************
Dr David Fulford CEnv MEI, 15, Brandon Ave, Woodley, Reading RG5 4PU
d.j.fulford at btinternet.com <mailto:d.j.fulford at btinternet.com>, Tel: 
+44(0)118 326 9779 Mob: +44(0)7746 806401
Kingdom Bioenergy Ltd, www.kingdombio.com <http://www.kingdombio.com>, 
davidf at kindombio.com <mailto:davidf at kindombio.com>

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