[Gasification] HomeBiogas

[hugh at austrop.org.au]

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, hugh at austrop.org.au 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
>>> 
>>