Ideal Biogas Harvesting Septic System?

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Cory J. Geesaman

Feb 2, 2022, 2:31:07 PMFeb 2
to DIYbio
I've read that a family of 4 produce enough methane waste in their septic system to yield about 40% of their home energy needs and would like to build a home system for this purpose.  Does anyone have any good research/sources on designs for methane/biogas-harvesting septic systems?  I'm assuming it's not as simple as using an air-tight tank and pumping off the gas from a storage bladder attached to it after drying - that the geometry of the tank and  the layout of various digesters/tanks would play a big role in actually reaching that 40%-of-total-energy-use quota worth of methane production and harvest.  Are there specific nutrients that should be monitored and potentially supplemented to maintain the optimal biogas generation rate for a given volume of mass?  Dwell times in gas-harvesting chamber(s) prior to moving on to subsequent stages in the septic system (such as waste storage for removal?)  Does it need a giant poop blender inside to keep it liquefied and churning around, or is a continuous-flow design possible to achieve the same efficiencies?  Any help answering these questions would be appreciated, and I'll post photos+data when I actually build the thing.

Cory J. Geesaman

Feb 2, 2022, 2:37:57 PMFeb 2
to DIYbio
Also, different designs for different scales would be welcome - my actual scale is a 4-family home, a few apartments, and a couple of businesses - probably the equivalent of about 20 people in annual poop production, but I'd like it to scale with additional input chutes as well because one of the businesses is a farm and there's plenty of animal waste I could toss into the system as well.  I might go at the scaling issue via separate house/apt systems and farm systems though, because I assume the nutrient balances will be somewhat different between the two, but would like the output to just be methane gas to feed a generator and fertilizer.

S James Parsons Jr

Feb 2, 2022, 3:48:28 PMFeb 2
Hi Cory,  here is a video I found

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Cory J. Geesaman

Feb 2, 2022, 5:59:51 PMFeb 2
to DIYbio
I actually toured a waste treatment facility as part of the biotech courses I took - the smell was stuck in my nose for months but it was somewhat elucidating; though I'm specifically looking for systems optimized for methane production/harvesting rather than a crash course in digestor designs.

boj Ko

Mar 10, 2022, 8:03:58 AMMar 10

чт, 3 февр. 2022 г. в 00:59, Cory J. Geesaman <>:

Cathal Garvey

Mar 10, 2022, 11:16:40 AMMar 10
to Diybio
Imhoff tanks look like pretty old technology that would be probably trivial to adapt for biogas collection:

Advantage here is that Imhoff tanks, being old tech, are probably purchaseable or salvageable.  And the design and maintenance parameters, even if you go and build your own, are by now well enough understood, I imagine.

Advantage again, is that the imhoff tank design does not assume any powered components, being powered only by the compressive force of new wastewater entering the upper chamber.

I don't know whether additional cellulose increases or diminishes biogas production in a system like this. The answer to this might inform whether the designer/user of a system like this would be better served with non-tissue/wipe based sanitation methods.

As with Septic Tank systems, care must be taken to not build such a system carelessly - if you live in a Karst region, then you should probably put your faith in a central sewage system (maybe vacuum-powered for maximum environmental safety) to avoid contaminating the complex local groundwater. If you live somewhere with a high water table, or rapidly flowing groundwater, then that needs to be factored carefully also. And if your neighbours have a well...

Also, the system spillway will be pretty rich in free N/P so make sure the local environment won't be harmed by that. Perhaps plant some fruit trees on the spillway, but definitely don't grow salads or low-growing edibles! :)

Dan Kolis

Mar 10, 2022, 12:23:33 PMMar 10
to DIYbio
You know all these "there is X Joules in thing Y we throw away", is usually completely deceiving. The quest for efficiency is a now a subset of finance more then engineering in the usual mindset.

For instance, if you decide 1/2 of digested food by human as feces has 1/2 the potential energy of the mtl food as dry weight, this observation will get you nowhere to get it out.

The Coef are sequential and are usually nasty: 0.5 0.3 0.7 product of 'my gain' * step, is ouchy.

This is not a reason to give up on the projects, its to note a few things like: the less you need at the far end of the formula, the better.

CH4 into a fuel cell is not bad. You have to get it out first. That leaves all sort of other covalently bonded stuff in there. Covelent bonds are tough, most don't even notice the boiling point of H20 !

Consider fat is 32K J per kG. so 2 lb of this high energy metaboite is 10W

In the elevator today a street guy had a big bag of aluminum cans he street scavenged. He is a hero to the planet: all the energy to get AL out of Balcite is huge and the Alum is super reusable, no new energy, almost none.

Street guy in elevator, big bad of cans. Ok. if you want to get back the investment in e from those, now what ? in principle you can revert them to Balcite, right ? Going in one direction took a huge building full of people, loaders, parking lot, pensions, Xmas parties, etc. Going the other way is so remote its nearly impossible to visualize as possible.

Matter to energy and back, is tough love.
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