permaculture

["Lawrence F. London, Jr." <lfl@intrex.net>]

(Mike may be interested in this)

-------- Original Message --------
Subject: Biogas sludge as fertilizer
Date: Wed, 4 Dec 2002 16:57:34 +0900
From: Keith Addison <keith@JOURNEYTOFOREVER.ORG>
To: SANET-MG@LISTS.IFAS.UFL.EDU

A lot of biogas resources say something like this:

"The digested waste--sludge--is a high quality fertilizer. The
digestion process converts the nitrogen in the organic materials to
ammonium, a form that becomes more stable when plowed into the soil.
Ammonium is readily "fixed" (bonded) in soil so that it can be
absorbed by plants. In contrast, raw manure has its nitrogen oxidized
into nitrates and nitrites, which do not "fix" well in soil and are
readily washed away.

"Moreover, biogas systems offer a means to sanitize wastes. Simply
put, these systems are capable of destroying most bacteria and
parasitic eggs in human and animal wastes, enabling the digested
sludge to be applied safely to crops. Tests have shown that biogas
systems can kill as much as 90 to 100 percent of hookworm eggs, 35 to
90 percent of ascarid (i.e., roundworms and pinworms), and 90 to 100
percent of blood flukes (i.e., schistosome flukes, which are found in
water snails that commonly live in paddy fields and ponds)."

http://idh.vita.org/pubs/docs/ubg.html
Understanding Biogas Generation
Technical Paper #4
Volunteers In Technical Assistance (VITA)

It might contain useful quantities of N, P and K, but I think it also
contains VOAs and so on which might make it a less-than-ideal
"fertilizer", at least as far as the soil life is concerned. AFAIK it
kills worms and more, probably including mycorrhiza. And while it
might cut off parasitic eggs, I doubt it cuts off pathogenic bacteria
- after all, a biogas digester is rather like an intestine. I've
heard reports of problems with pathogens in the sludge. Also I think
biogas digesters can be rather troublesome.

I'm quite at home with composting and vermicomposting and so on, but
I have no hands-on experience with biogas systems. But that could
change soon.

Could anyone please comment on the "fertilizer" claims and pathogen
cut-off claims, and/or point me towards some authoritative work on
the subject (preferably by soil biologists rather than chemists)?

Many thanks

Keith Addison
Journey to Forever
Handmade Projects
Osaka, Japan
http://journeytoforever.org/