Thanks Bruce
but what you are referring to would be a commercial digester with a
well insulated tank, an integral mixer and perhaps a heater.
Unfortunately Home Biogas systems are far simpler - but are dependent on
local conditions to work. Even here in the wet tropics (16•S) winter
temperatures can go as low as 13C. Putting in a heater, would consume
a significant amount of our power (we are solar). Had we really been
aware - we could have installed an insulated jacket, but in this
environment
it would have failed quickly - moisture and various organisms setting
up home there (in fact they could have punctured the tank - chomp!). So
these are
great in warm and dry environments - and as they are inherently smelly
most would not want them too close to the dwelling.
However homogenisation really does speed things up.
There is obviously a market for a better design - but we have the issue
of gas storage - which HomeBiogas solves quite elegantly with the top
bladder (which takes no extra space). A gasometer style storage would be
fine
except for the space issue. Compression brings on a whole collection of
other
issues.
There is no free lunch! (or cooking heat)
Cheers
Hugh
On 07.05.2022 9:14 pm, Bruce Wilson Contracting wrote:
Just a quick primer on methane digesters, it is a two part process,
first is the acidification stage where bacteria turn the waste to
acids. The bacteria do not have teeth or mobility, so putting what you
put into the digester through a grinder helps break it down so the
bacteria can access the nutrients. These acid producing bacteria
produce CO2. After the acids are produced the methanogenic bacteria
digest the acids and produce methane. Gentle mixing is called for
because so that the bacteria can access the nutrients to be digested,
the bacteria that produce the methane stop producing methane when
agitated which is why gentle mixing is called for. There are two ideal
temperatures for digesters, 120 degrees F, or thermophylic and 100
degrees F mesophylic. A ten degree drop in temperature leads to a
twenty percent drop in gas output. Thermophylic produces more gas but
is more finicky, mesophylic is much more forgiving. Bacterial seeding
can help a digester get started.
On 5/4/2022 1:19 AM, [email protected] wrote:
Hi
we have one of the original Israeli HomeBiogas systems. Living where
we do - we had problems
getting fresh cow shit. It was a disaster - mostly CO2. So we
emptied, flushed and sterilized
it and a (not so local) dairy provided 60 litres of fresh cow shit.
Then Covid hit and our supply
of local ex-restaurant waste stopped. (we didn't produce enough
ourselves). 2 years later (the system
having been been totally ignored), it started to inflate. Evidently
the battle between the CO2
producers and the methanogens had finished, and to our delight the gas
appears to be pure methane. So
we have been using this now for months for a significant amount of our
cooking.
However - we homogenise everything.that goes in - this speeds up the
digestion process greatly,
and means that we are not getting a residue of indigestible material
in the digester tank
(which was a major problem with the initial clean out).
And yes - we should be using the copious liquid fertiliser that the
system produces - too much
else going on and not enough hands available.
Homogenising - we use a modified Kambrook Power-drive stick mixer -
with a modified end (cut the
loops off). So long as there is little fibrous material, or any really
hard stuff (bottle tops etc)
it is a quite amazing machine.
(also HomeBiogas have developed a toilet system that feeds the
digester directly. Wish we had had one!)
Worth the effort.
Hugh
www.austrop.org.au
On 04.05.2022 2:22 pm, Anand Karve wrote:
Dear all,
I developed in 2003 the urban domestic biogas plant which works
without dung, but uses only domestic food waste as feedstock. The
effluent slurry of this biogas plant is watery. I applied it
regularly
to an experimental plot of garlic. It was just a feeler trial to see
how the plants responded to the effluent. To my surprise, the plot
receiving the slurry gave higher yield of garlic bulbs than the plot
receiving the recommended dose of chemical fertilizers. The area of
both the plots was equal.
Yours Anand Karve
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