Biogas methane digester project

(Alexander Tomasik) #81

Our society buries its’ garbage in holes, a little poo juice in the ocean shouldn’t be a big deal.


Since the most common size touted is that of a small city, maybe people that think it’s just…

Should spend some time at the local municipal waste-treatment facility.

At an average of 80.7 kg/177.9 lbs each

100 X 1 X 177.9 / 12 / 16 + ~ 92.66 lbs of poo-juice per day
92.66 X 365 ~ 33,819.5 lbs of poo-juice per year, per capita…

How many folks are on your seastead design?..

Maybe it’s time to rethink what ‘a little poo-juice’ really adds up to…


“The amount of biogas that can be yielded from human waste is limited in comparison with livestock manure and other feedstocks. Our stomachs are just too efficient! David House states in his excellent book that 1000 lbs of human waste produces about 0.6 cubic meters of biogas (enough cooking fuel for about 1 to 2 persons).”

So,… 33,819.5 lbs X 0.6 = 20,291.7 cubic meters of methane could be produced… That’s about how many individual meals it would cook, too, since 0.6 cu meters is the most commonly touted volume of methane to cook a meal…

100 x 3 x 365 = 109,500 meals for that 100 people, per year, and enough methane to cook about 20% of those meals, for the effort of using a biogas digester, in a place with no easy access to energy (everyone mentions renewables, anyway… Biogas is the ultimate renewable… As long as there are people, there will be poo…)

City Sewage and Food Supplies, as a combined topic

Slightly off-topic, but related…

Janice Kelsey and Joy Spangler, of Solar CITIES just gave a TedX talk on “Home-Scale Biodigester: Raising a baby dragon to save the world”

When I’m more active on FB and in the Solar CITIES group, where I set out my design for public critique for improvements, Janice is one of the people there that was helpful. IIRC, she’s the one doing the Digester Effluent to hydroponics gardening…

Looking forward to the video…

(system) #85

This topic was automatically closed 100 days after the last reply. New replies are no longer allowed.

(Francis Brunelle) #86


Toward my own digester design, and proof-of-concept, my wife and I are about to begin refitting and remodeling a 35ft Barth Commercial Custom panel ‘van’ into an RV.

The 1st stage of the digester is to be the toilet and kitchen sink. The toilet will be a recirculating-flush type, that recaptures and reuses the flush water. Instead of using chemicals and deodorizers, the recaptured water will be treated, using aeration, like an aerobics treatment tank does for many homes.

Initial treatment will be a preheating section that basically cooks the influent, essential for vegetative mass, like food-prep wastes. This increases the biogas output and raises the Methane content ratio, as well.

Post digester treatment will also be a heating stage, to sanitize the effluent, prior to storage and discharge. This is because it IS an RV, but sanitary bio-wastes can be safely discharged, whether tossing food out onto a compost heap, treated wastes from an RV, or at sea…

Yes, pumping treated sewage overboard is perfectly legal… NOT very efficient, or good for stationary positions, but legal. It will cause a localized algae bloom, so the negative side of dumping fertilizer will be evident, around any seastead that does so.

(Matias Volco) #88

Algae blooms or worse occur in rather stagnant coastal waters.

Usually in dense coastal cities the solution is to pump it furthest away fron the coast and allow the open sea to disperse it.


…and yet, quite often the topics eventually turn to the doldrums, or Sargasso sea… relatively stationary waters, where exactly that sort of thing occurs.

(Gavin Brown) #90

So jealous, very cool. Where do you get those? I’m looking for some so I can rig up grey water/ rain harvesting at my house.

(Gavin Brown) #91

I agree, a floating city platform could quite easily accommodate a biodigester or two. Liquid can be used to mix in with the hydroponics feed and the solid when finished with will be great mulch for the biodomes. The gas can be used for all kinds of stuff. Are man… I want my floating city.


Actually, digester effluent can be used as-is, or diluted, AS hydroponic plant food. Might need some balancing nutrients added, depending on the mix from the typical feedstock, but that’s going to take a hydroponics guru, to figure out…

Recirculating-flush toilets are available for RVs and marine use. Thetford is a rather high-end, but reputable brand.

(Larry G) #93

Some reproduced private messages:

What was the outcome of your biogas methane digester project?

That thread was closed, so I couldn’t reply there. I has specific questions about how well the pine cones and blackberry canes digested … thinking that perhaps the “burning wood smoke” electricity generators might be another alternative.

Also on fruit waste … have you tried distilling alcohol?

On a related note, the totes and their lids are HDPE … which melts at about 265°F and can be molded, welded, etc. Totes, in theory, should be an experimenter’s dream container for liquefied materials.

(Larry G) #94

Totes are pretty easy to come by. Single-use food grade totes run a couple-three hundred dollars around here with the port essentially right next door, but often you can find them for $50-75, which is what happened with this one. $75 and missing a cap- the caps cost about $10 new. In the end I didn’t even use the caps.
There is already a drain at the bottom, on one side. The top opening is about 6" and the bottom is (I think 3") with a valve. The valve is kind of the issue, when the gate inside the valve is open, it’s still not an unobstructed opening. The chunkiness of the effluent just doesn’t drain super efficiently. In a purpose-built setup, this wouldn’t be as much of a problem, but I’m dealing with an experimental, improvised rig that is meant to be as cheap and DIY as possible. I don’t have any equipment for welding HDPE, so I used bulkhead fittings where necessary.
The 4" PVC top-feed mechanism was a definite compromise, but the 4" to 6" rubber boot adapter made it feasible and cost-effective to seal it.

Top feeding is ergonomically inconvenient: too high off the ground, requires me to stand on a bucket or something of similar size. It makes a ram or plunger necessary to get the feed stock fully submerged and to clear the feed pipe. I had to be somewhat careful with the plunger because the top plastic is largely unsupported and flexes- had to be careful not to pull the rubber adapter loose. You’re pushing directly downward against the buoyancy of the feed stock, and you’re getting a few percent of gas from the effluent directly below the feed tube escaping directly upward.

Ideally, I would not top-feed, but rather make a low, side-entry 45 degree angled chute to feed it. This would also facilitate stirring, I think. I was looking for a 45 degree bulkhead fitting of reasonable size, but it is amazing how expensive large size plumbing fittings are. A 45 degree angle side-feed chute could have the feed pipe cut longer on the bottom, so almost zero gas bubbles up the tube.

Then the caps with the threaded fittings would be very convenient. I have a holding tank/RV sump pump that could be used for stirring, with some pipe threaded through the top cap to dump back into the main reservoir and another bulkhead fitting down low to draw from the main tank.

One of the benefits of the totes is the cage and pallet built around the reservoir. This also, however, limits access to bottom and side to a certain size by the grid openings of the cage. Without the cage/pallet, moving the thing would be very difficult and prone to breakage. Stacking would be impossible. My plan was to eventually have a second tote stacked on top of the first and plumbed together for gas collection and potentially a primary acidification stage.

The sludge that came out when I drained the liquid was clearly good quality organic compost fertilizer- it smelled earthy but not unpleasant, was a good dark earth color with lots of fibrous organic material in it to provide good soil structure/tilth. Mind you, there was a high percentage of very rank/sour smelling dog shit in there, but it was completely undetectable when it came out after several months in the digester. There was no detectable distinctive olfactory influence of any of the individual feed stock- fruit, feces, what-have-you.

I don’t have any place at my new house to continue these experiments, so I’m going to store the rig at a friend’s country place for the time being.

I have requested that the thread be re-opened, so I can copy this conversation out into the public forum.


So, @thebastidge

… your biodigester worked, but could benefit from more experimentation?

(Larry G) #96

That would pretty much sum it up. My experimentally-backed conclusion: it is a minimal effort, low-tech, very low cost means of producing a regular, small stream of multi-purpose fuel in a reasonably small space. I my opinion, every aspect of it recommends its wide-spread adoption by islanders and potential seasteaders.


Any activity on this in recent months, @thebastidge?

(Larry G) #98

No, the experiment is ended for now. I moved and don’t have space at my new house.


Hopefully we’ll see more experimentation on digesters in the future. It’s good info to know.

(Larry G) #100

Anaerobic Digestion

The two-stage anaerobic digester improves upon the conventional method of handling sanitary waste in The Bahamas, which is either spreading in a field, or engineered solutions that involved chemicals and deep well injection. Anaerobic digestion offers the opportunity to produce energy from a waste stream, cleaning the waste stream and providing nutrients for use in agricultural activities. CSD looks to the anaerobic digester as another input to the Waste-to-Energy plant that will share energy across multiple processes and pieces of equipment. Prospective research is in the areas of increased efficiency in biogas production, and effective means of utilizing this energy source either for cooking, heat, or electricity production.

Wastewater effluent from The Island School’s sanitary waste systems has traditionally been treated using passive bacterial treatment in wastewater gardens. During the winter of-2017, a modified trickling filter was installed, as the first effort at an engineered system to confidently treat sanitary waste.