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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