[Digestion] Re Digestate as fertilizer

Paul Harris paul.harris at adelaide.edu.au
Thu Nov 18 17:58:40 CST 2010


G'day All,

 

As a generalisation Westerners tend to have "tunnel vision", so only
concentrate on one thing (I know this does not apply to all members of this
group!). This is from my observations and I don't have too much experience
in other cultures for comparison. I think it really results from our
"reductionist" approach, or maybe the approach is a result of this
limitation.

 

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!).

 

Happy digesting,

HOOROO

 

Mr. Paul Harris, Room S116b, Waite Main Building Faculty of Sciences, The
University of Adelaide, Waite Campus, PMB 1, Glen Osmond SA 5064 Ph    : +61
8 8303 7880      Fax   : +61 8 8303 4386 mailto:paul.harris at adelaide.edu.au
http://www.adelaide.edu.au/directory/paul.harris

 

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From: digestion-bounces at lists.bioenergylists.org
[mailto:digestion-bounces at lists.bioenergylists.org] On Behalf Of P M Allison
Sent: Thursday, 18 November 2010 6:06 PM
To: digestion
Subject: [Digestion] Re Digestate as fertilizer

 

The use of digestate for crop fertilizers, is to me the very best option. 

The material contains all the nutrients required by plant-life as it is made
up of the very same ingredients. 

Laboratory analysis of the spent material confirms this.

A very similar substance is derived from vermiculture.

The main problem with spent digestate is the fiber content. This will create
nozzle lock-up on any spray delivery system. Fiber is not digested by
anaerobes or worms.

If the digestate is splayed too thick it will smother soil and emerging
plants.

The simple solution is to vibro filter the fiber and undigested material
from the slurry. The solid matter is ideal for pelletizing and broadcast
delivery.

The resultant liquid component is a colloidal nutrient complex containing
the same ingredients as the original material but in plant ready form.

This liquid does contain particulate matter which can clog nozzles. My
solution to this is to centrifuge the liquid and trap out the sedimentary
material leaving a purely colloidal substance. This can be used as a foliar
fertilizer when diluted with water as the substance is too rich to be used
neat.

The trapped debris is a rich nutrient mud, primordial ooze so to speak. This
is also rich in nutrient and the finest of carbon flocs. An ideal binder for
pelletizing the solid matter  initially extracted.

By the way, the carbon flocs are the same as those used carbon-fiber
production.

Biogas is a wonderful bonus to the system, but should not be the be-all and
end-all of the process. The spent material is the sort of substance which
will make sustainable agriculture a much better option than what chemical
farming will ever do. The crop improves, the soil improves, the soil biology
improves, soil moisture holding capacity improves, soil carbon increases.
Remember, it's the dark matter  which differentiates soil from being just
lifeless dirt.

Regards,

Peter.

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