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

[Björn Dahlroth]

Sounds nice but with all systems where matter is going around in cycles one
should try to check the losses and environmental effects. In systems
involving digestion and recycling to agriculture it is especially the losses
of methane, ammonia and nitrous oxide to air and the losses of nitrate to
water. This has nothing to do with the recycling theory but instead with how
you build and manage the system.
Energy efficiency is also interesting as the raw material e g manure and
agricultural residues although renewable still might become a limited
resource. So how to tune and optimize the system and not only the digestion
plant. Something to think about.
Bjorn Dahlroth

-----Ursprungligt meddelande-----
Från: digestion-bounces at lists.bioenergylists.org
[mailto:digestion-bounces at lists.bioenergylists.org] För bennett at frognet.net
Skickat: den 19 november 2010 03:44
Till: paul.harris at adelaide.edu.au; For Discussion of Anaerobic Digestion
Ämne: [Digestion] R.R.R. ->was-> Re Digestate as fertilizer

> 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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