Biogas methane digester project


Note construction projects around your local area, scrounge around, see a pipe you can use, ask if you can have it. If not for free, then for $10 so the guy can buy a 6-pack on the way home. Plumbing pipe or electrical conduit, it’s the same sizes. I got 30ft of straight 6" pvc and several long 90’s that way. Some steel gas pipe out here was being replaced, i asked and got 3ft of 10". The city replacing water mains because of damage or additions or improvements too, some of that scraps is good stuff. Look in the yellow pages for the bigger plumbing and electrical businesses, take a look at them in google maps, see if they have a scrap yard, drop by one day with some 5’s and 10’s, make some bartering sounds (“i need only 3ft, it’s ok if it’s scraped and nicked some” as you load in 15ft).


Yeas, look for horse fanatics, horses are delicate and picky eaters, those people will throw away bales of hay perfect for insulating and feeding to your digester. Any hay you use for insulation in winter can be fed to the digester after winter. If you have mold allergies, wear a mask. Cow and goat places too. Bedding hay can probably keep you in more methane than you can handle. Also, round bales kept on the ground have high rot rates at ground level, see some in a field, ask about them. Even cows will tolerate only so much. There’s pretty creative ways to use hay in cement construction too, and i’ve heard of people using automated feeders for chopped hay burners (versus burning wood, hay has very fast light-off and damp-down times).

Tip for scrounging: be prepared to haul your goodies right then, or within the hour if you must go get your trailer. Hay can weigh a lot.

(Larry G) #43

I love the concept of scrounging, largely fail at it in practice, because I simply don’t have the free time to be available when the good stuff is.

Between running my own business and having a full time job M-F where I have to put in face time, I simply don’t have time to get free stuff very often. Everything has a cost. Mine is time.

(Larry G) #44

Hopefully tonight I will have time to install the gas outlet. The feed sump works well enough, even though the aperture is frustratingly small, the advantages of using a pre-existing opening and the nice tight fit of the parts I have found for it make up so far. I played around with funnel solutions a bit last night, cardboard box material for a funnel held inside a wire tomato cage, but it didn’t work very well.

Speaking of the gas outlet: I have to go pick up another ~$13 bulkhead fitting because one of the mutts thought it looked like a chew toy while I ran to the home improvement store for something in the middle of my project. Arg. Doing some research on cheaper solutions for bulkhead fitting, I ran across this:

Given that I was looking for bigger fittings and found that 6" and 8" bulkhead fittings run between $400 ad $800 dollars each, I thought it was worth book-marking.


Did you look at sink, tub, toilet, or pool drain fittings?


Cooler drain fitting… $3.34+ s&h…?

(Larry G) #47

I’m looking for something that won’t corrode- this is before the H2S filter, trying to stay all plastic/inert. The bigger fittings are bloody expensive no matter the material.


Wasn’t thinking.


Online, i found 3 pvc toilet flanges, 4", for under $6. There’s a pvc “snap in” 4" drain for under $4, just saw out the grillwork on it, use it as a flange.

How about warming up some 1/16 or 1/8 plexiglass sheet until it’s soft, coil it over into a tube shape, hold till cool, then drill and goo and rivet it? You could coil it to a size you can get fittings for. Likewise, you can use pieces of 1/4 or 3/8 or make up sizes and glue them to pipe as flanges.


I’m getting confused, are you looking for large or tiny fittings? Because JL is finding stuff under 1/2 inch, and i am looking for anything over 3 inches.

Those “john guest” fittings are all plastic, come in many flavors. The tubing comes in clear and many colors. You can get it in 100ft coils.


Gas-line fitting, from tank to line for the HS2 scrubber

(Larry G) #52

Right now I am looking at gas line, so small. I’m keeping the future in mind for a large tank, farm-scal commercial operation or seastead size, and looking at prices for that- especially for feed sumps, because a 4" feed sump is a PITA to try and feed with a shovel or a bucket.

(Jonas Smith) #53

Have you thought about incorporating a shredder/grinder for feeding? Something like this:

I know it’s expensive, and I don’t know if I’d want dog poop flying out the other end, but feeding stuff into something like this might make things easier than stuffing it into a 4" pipe, right?

And it’s it more efficient in the digester to have the stuff all masticated up?

(Larry G) #54

If I were integrating as a system and not a stand-alone for initial experiment, I would be looking at a marine macerators, garbage disposal or something like that. Right now I am using an electric yard chipper for the yard debris that gets the woody and herbaceous material pretty finely chopped.

The windfall fruit mashes up pretty fast as it is, and the dog poo dissolves in the mix pretty fast as well.


SolarCities concept is the intent to use kitchen disposal units. Some of the commercial units (1 hp+) have a limited pumping capacity.

My goal is to use a sink, a dispoal unit, or macerator-pump a loop with a ‘T’ valve, so the pump can recirculate, while grinding, then pump it to the digester. All in all, I had to think the whole process through, in order to hammer out any weaknesses and keep the entire process as simplified as possible.

Close the gas-line off, open the outlet, to blow off internal pressure, open the inlet and pump in the new digestate, close off the inlet, close the outlet and open the gas line.

Then again, I’m also dealing with a 139 gallon, spun-fiberglass FRP sand-filter tank that is nearly 8 ft tall, on its’ stand…

(Larry G) #56

Got the gas outlet installed last night. Hopefully the last time I have to take the main feed sump off, but I took some pics of the inside while I had it open to see what the feedstock is doing so far, in a semi-aerobic composting environment.

It actually doesn’t smell very bad- a bit earthy. You can see a lot of it floats and has formed a pretty substantial scum cap on the water surface. This is about 1/3 full so there’s lots of room for more feedstock and water can be added to keep the water seal intact. Float-y material is being pushed down the feed sump to below this cap and then floating up underneath it, by means of the sump extending below the surface and using a plunger to get the feedstock inserted. As long as it stays moist I imagine the methanogenic bacteria will continue to work on it. But I do see a benefit to a stirring mechanism (which I don’t currently have.

I drilled a 1.25" diameter hole with the hole saw. That’s just about the inside diameter of the threads on the bulkhead fitting. So it required a little clean-up and expansion to get the fitting through the hole, and the outside diamater of the threads didn’t quite fit through.

The inside piece of the bulkhead adapter is reverse-threaded. Make sure you have a big enough wrench BEFORE you’re stuck on top of your project reaching into the moist, smelly environment, and don’t drop it into the goo.

Then it was a simple matter of putting in hose barb. I added an elbow so the soft clear tubing that will eventually be installed doesn’t have to stand upright under its own support , since it will probably sag in warm weather and might cut off gas flow.

Next up is constructing my hydrogen sulfide filter and gas storage/delivery solution while the main tank ‘cooks’. I still have lots of feedstock left to go in over time.


A dremel can be your friend for slightly enlarging holes, slightly removing rust or paint, slightly deburring threads and other sharp edges, as well as slightly sharpening your chain saw (use the right bit and go very lightly). You can keep an aweful lot of dremel bits in a peanut butter jar. Otherwise, a body grinder with accessories. I have built up a collection of files too.

Thanks for the pics.

I still recommend a windshield wiper as a stirrer, assuming you don’t need it running more than a few minutes every hour, or some similar rare timeframe. They are the right speed (on low), torquey, 12vdc (run off battery, electronic controls are easy and cheap), and cheap on ebay or you-pull-it car salvage sites. They have much hunkier gears than drills, and are built for far more load at low rpms.

(Larry G) #58

I was too lazy to go find it and get it set up when I had my Gerber on my belt. :smile:

Seems like a reasonable solution. Maybe in my next iteration. I have actually found some pretty good prices on 1000 and even 5000 gallon tanks. I just don’t have enough room to hide it from the wife at this current house.


If your inlet is up off the bottom, you could use a paint-mixer attachment and extension rod, on an electric drill.


There’s a man with dedication, he’s going to change houses to get a larger methane digester!

Come to think of it, in some places you can get recycled gas station tanks for cheap, all cleaned out and praps even painted.

Just some quickie rough math: pour a 12ft dia slab, put 4ft walls on it, you can put 3000 gallons into it and have ~6 inches clearance at the top. How that works out for an actual 3000 gallons of liquid plus the floating scum on top, i don’t have a clue. Hide it behind a pretty garden shed and a couple of bushes. When you sell the house, paint it and call it a swimming pool, charge extra, it’s an investment.