Biogas methane digester project


Probably find one, for free, if you look around, or look them up… The Google is your friend… >.<

Under $8 (plus s&h), online, for new, unused from the manufacturers…

(Larry G) #22

I just ordered three of the caps from the Lexington Container link above. Two plain caps and one with (2) 2" NPT threaded plugs. This will give me a couple options to experiment with.

I will try cutting a 4" hole in one of the plain caps, and using (2) 4" collars/couplers I will sandwich the cap between the collars with just enough pipe between the collars to connect them and hold the cap in place. With a round rubber gasket I should be able to seal this arrangement with some silicone caulking very tightly. The bottom coupler will hold my sump pipe for feeding below the water seal. The 4" pipe is only available in standard 10’ lengths from Home Depot, but I saw a piece that was already cut when I was there the other day, so I should be able to get a good deal on that piece. I only need about 40" of sump to get within 5" of the bottom, 2" of this is coupler already. I’ll cut the bottom of the sump at an angle, as well, which will help to make material exit the end of the feed pipe when ramming the feed stock down below water level.

I may even be able to fit a plastic 1/4" or 3/8" hose barb on the same cap for my gas outlet. That would let me return some PVC parts including the bulkhead fitting.

If all this works out, it’s an easily-replicable arrangement for more tanks later.

(Larry G) #23

With the vertical arrangement and 4" diameter I’ll be using for the feed sump, this will probably work pretty well. I can try this perhaps once a week. I’ll just factor this idea into the vertical distance I leave between the bottom of the feed sump and the floor of the tank.


Simple mod… cut/grind the bottom off of the pipe angle cut, so there’s a flat, pointed to the bottom, to help prevent poking through the tank, during all the fit/re-fit and all.


Well, they were. They have integrated your searches with advertising and any g* accounts you may have, as well as machine ID (such as lan card ID, mobile phone number, etc). They also set cookies and attempt to locate you physically (via GPS on mobile devices, etc). All searches are now logged forever. I use duckduckgo.


I find that the Great Stuff canned foam adheres to many things that silicone won’t, and it expands to fill voids. Give it a few hours to harden before applying stress. It comes in different flavors. Duct tape will seal the end of the can’s tube to keep the remaining can fresh.


I thought the feed stock was very macerated and liquid, and was pourable. It must be rammed? Isn’t ramming going to require a dirty ram to be set beside the tank, to be used with each feeding? And isn’t ramming going to be physically stressful to the pipe, tank top, and fittings? Plus, if you have some sort of liquid recirculation, wouldn’t pumping from the bottom of the tank to the top of this input pipe keep it clear of solids?

(Larry G) #28

Right now I don’t have any re-circ mechanism. I am going basic for my first attempt.


A lot of it floats. Since I’m using a water seal, if it isn’t pushed into the tank, it will just fill up the feed sump. Most of what I feed it won’t be liquid until it’s in the tank, because I am feeding it yard debris and dog-doo. Much of it is chipped branches, some windfall fruit, chipped up blackberry canes, leaves, and grass clippings.

Yes, I will have a dirty ram near the tank. “Ram” may have too forceful of a connotation, consider it a plunger. It shouldn’t be enough to stress the seals, by any means. I am brainstorming on it right now but I expect it to be a drain cover grate on the end of a piece of PVC pipe. If I were using a flush toilet-type system to feed the digester, I would not need it. If I were building a more sophisticated feed system, it might be some kind of rotating barrel lock above the water line, but this is being built on the KISS principle and a small budget. I may be able to use a T at the top to keep the ram semi-hygienically contained in a piece of pipe while still having a vertical feed pipe.

I have dirty yard tools out there anyway, pooper-scooper etc, so it’s a net neutral to me in my circumstances.

Good tip, thanks.

(Larry G) #29

The pond and stone version might be good. Since this is ABS and Polypropylene, plumber’s silicone I expect should have no problem. If it doesn’t look like it’s working out, I’ll try the foam.

The new caps should be here on the 31st, so I’ll be on hold til then.

(Larry G) #30

UPS says my parts should be here by end of day.


I’m not sure how detailed the data you may eventually intend to collect is, but I know people working on arduino logging sensors with regard to eventual automation of digesters. Some of it is, direct, such as temperature, while some is indirect, such as measuring electro-conductivity as a function of pH, which, in certain circumstances could be misleading, but is generally acceptable data.

(Larry G) #32

Going very basic to begin with. Just want to start making methane and using it for recreational purposes. I may get more detailed later, or not. I hope to purchase acreage in the next couple years (fingers crossed) at which time it might make more financial sense to get more precise. For right now, it doesn’t make sense for me to spend more time and money than just to demonstrate it’s feasible.

(Jonas Smith) #33

I must say…that is the most awesome thing I have heard recently. Kudos, sir!


(Larry G) #34

New caps came today. Pretty sturdy, should work fine to hold the feed tube in place. The one with 2" openings is threaded all the way through so it could have threaded pipe from the bottom or top, which is convenient, except for the small size.

(Larry G) #35

Picked up the rest of the pieces I should need to get started. Have to move it around the side out of sight in the garden- the wife doesn’t like the way it looks by my shed. Also picked up some concrete pier blocks to put it on and will need some hardy-board siding (~$35 for 4’ X 8’ sheet) to cover it for the same reasons of aesthetics. Since part of my reason for this is clearing up yard debris and dog poo, it’s relevant to mention I am having to clear a spot out of rampant blackberry canes and grapevine to put this in. I’m using an electric hedge trimmer and machete for this but it’s actually a considerable effort in itself.

Picked up a 10’ section of 4" PVC pipe (~$13), the couplers ($3.85 each x 2), and 4.5" hole saw (expensive: about $25) to cut a hole in the lid equal to the outside dimensions of the PVC (slightly bigger than the inner raised ring you can see in the above photo). I have 4" to 6" rubber boot ($5?) and a potential solution for a feed funnel using a sump drain cover ($6), but may not end up using that. 4" or even 6" is just a small aperture to try to dump nasty stuff into that I don’t want to touch, even given that I can generally just hose it off after feeding if I spill, once I have it all assembled.

(Larry G) #36

Changed up design yet again prior to installing. The 6" to 4" rubber coupler fits over the threaded opening well enough to simply cinch down with the included hose clamp. I couldn’t find one of these when I was planning the thing, then found one later.

So I eliminated the need to use 4" couplers above and below the screw-on lid, eliminated need for the lid, eliminated need for the 4.5" hole saw to cut through the lid, and took most of the extraneous stuff back for a refund.

I picked up the stuff I need for gas outlet to reduce from the bulkhead coupler down to a gas line. The bulkhead coupler needs a 1.25" hole cut in the top of the container, and then necks down to 1/2" threaded (NPT) PVC. From there I use a 1/2" pipe to 3/8" hose barb and I picked up 9’ of clear tubing that will feed my H2S filter. All plastic up to the filter. It takes some perusing through the plumbing section at a couple home improvement stores, because it’s apparently not a very standard setup. None of the parts are exotic, and if one were doing this in bulk or on a different scale, could probably just order parts more easily than finding them one at a time as a one-off solution.


Cool, finding that black adapter was a stroke of luck!

(Larry G) #38

I have about 60 or 70 lbs of material in it now, plus enough water to form a seal at the bottom of the feed sump. Mostly half-rotten pears, apples, dog poo, some leaves, and some detritus from a mushroom growing experiment (a box of wooden dowels for shitake plugs from a project that didn’t work out due to someone flaking out on me.) Next up will be a bunch of chipped-up branches and blackberry canes. You can see I’m clearing a corner of the property to place this in what used to be my garden corner. All of those canes and vines need to go, so they’ll gradually get fed in over the next few weeks as I have time.

My plan is any kitchen compostables will mostly go in here too, cardboard, plain paper, etc. I have tons of fir and pine cones to rake up in the yard- in they go. Daytime temperatures are fluctuating now down below efficient digestion temps, and we’ll eventually get a week or two of freezing temps. I may figure out some kind of heating coil before long, but if all I do is feed it until next spring, I don’t really care, as long as my tank doesn’t freeze and rupture. The biological action inside should keep it a bit warmer and theoretically safer from freezing, since we don’t get too much hard freeze here anyway.

I need a better feed funnel solution, I think I’m going to have to fabricate one from gutter flashing or something similar. I’m making this one with as little mods to the basic container as possible, but I’m already seeing some things that would benefit from a ground-up approach to design. The height is slightly too much for easy feeding, sitting on pier blocks, and I’m 6’ tall. Adding a funnel so I don’t have to be as precise about dumping will make it even taller. Counter-sunk into the ground would probably be beneficial with a bigger tank.I would prefer to feed from the side, but without a more elegant solution for plastic welding an angled flange onto it, this seemed less likely to leak. A bigger diameter feed sump would be an obvious improvement. It’s amazing how expensive large diameter PVC pipe is at retail prices. A 2’ piece of 6" PVC is about $15 at Lowe’s Home Improvement Store. That’s more than I paid for the 10’ section of 4". Connectors for the larger sizes are not as easy to find either, and cost a lot.

I’m going to need to block light to prevent algal growth so I can keep it anaerobic. Probably by painting the exterior black or tarping over it completely.


… and add insulation… I saw one with square-bales around it and a light deck over it, to support more. An 8 ft by 8 ft section of SIP would be a good find, too… Or maybe 2 4 ft by 8 ft sections that make a collar around the pipe…

(Larry G) #40

So what I ended up doing: cut the PVC pipe perpendicularly to the desired length. then, Using my miter box as a guide to start the cut, I just went far enough down that I left some flat instead of a sharp angle.

Seems to work well for getting stuff down the tube to not try to float straight back up it.