[Digestion] Digestate

[Paul Harris]

G’day All,

 

When I visited the Digester at Mead, Oregon, the operator was quite proud of his “prize” vegetables planted straight in the digested solids (they could drain, though, so it was not strictly in digestate liquid). I guess if you plant many seeds in water (without the benefit of cotton wool for support) they will also die. Many studies show improved plant performance for digestate compared to both synthetic fertiliser and no addition.

 

Happy digesting,

HOOROO

 

Mr. Paul Harris, Room 202 Charles Hawker 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

Roseworthy Campus, Ph  : +61 8 8303 7929

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From: digestion-bounces at lists.bioenergylists.org [mailto:digestion-bounces at lists.bioenergylists.org] On Behalf Of Jim McNelly
Sent: Monday, 5 December 2011 3:09 PM
To: For Discussion of Anaerobic Digestion
Subject: Re: [Digestion] Digestate

 

 

On Fri, Dec 2, 2011 at 9:38 PM, Murali Krishna <bmkrishna6 at gmail.com> wrote:

Good day Alex,

Undoubtedly the spent slurry is the best nutrient source to plants/crops, provided that necessary care is taken, and it is free from pathogens and in the available form.  

SNIP

Krishna

 

Krishna

 

This sounds nice, but the fact is that digestate is toxic to plants. If you were to take digestate and try and plant seeds in it, none would come up. You have to apply digestate at least five months into the soil prior to planting seeds, at modest application rates to enable soil microbes to further decompose the organic matter so that plants can grow.  This means apply in the fall to plant in the spring.

 

You mention earthworms....  If you were to try to feed digestate to earthworms, they would die within hours. As such the ASTM Earthworm Contact Test would fail the anaerobically digested organic material as unstable or unsuitable for unrestricted distribution.

 

It is aerobically digested solids that plants like and earthworms like; not anerobically digested solids. In my experience, organic matter is best utilized by plants following aerobic digestion.  

 

Anaerobic digestion makes biogas. Aerobic digestion makes plant food.

 

Your comments are correct as to the importance of organic matter in the soil, but should be qualified as to whether or not these organics are applied following anaerobic or aerobic digestion, and if anaerobic, then with sufficient time in the soil for aerobes to convert the organics into usable forms for plants.

 

 

-- 

Jim McNelly

 

Renewable Carbon Management, LLC

44 28th Ave N Suite J

Saint Cloud MN 56303

320-253-5076

 

www.composter.com

 

 

 

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