DIY insulated drum composter with a hand crank.
With all of my crazy – “ three in the morning, back of the cocktail napkin” – ideas, I’m always searching for designs that come with at least three pros attached to them. This “win, win, win,” scenario – or as I like to call it “win cubed” – is kind of my holy grail of design.
The reason I aim for this is that with three positives there is at least a chance of balancing out some of the inevitable flaws that always seem to occur in my late night designs.
A case in point is composting. With all my composting ideas the three wins I have shot for are:
a. More compost
b. Better compost
c. Less time
I have gotten pretty good at making compost over the last few years. As I’ve said in other posts, this was partly because of a desire to improve my garden soil but mostly out of self defense. With two horses, eleven chickens and five ducks, we generate an inordinate amount of “animal by-products” that pile up pretty quickly if nothing is done.
Hot Compost – compost where the pile is constructed to promote the growth of heat loving bacteria – has been the best answer I have come up with. In about a month I can produce quite a large amount of excellent compost. (a. More compost, b. Better compost, c. Less time)
The only fly in the ointment, as it were, is one stubborn downside. No matter what I do there seems to be no way around the fact that making good hot compost is a s**t-load of hard work. (Yes, that was a pun.)
Two of the essential ingredients of hot compost are providing oxygen and maintaining consistently hot temperatures. The only way I have found to achieve this is to build a HUGE pile with enough mass to hold the heat in, and then to turn the pile frequently to add oxygen. If you’ve ever done it, you know that wet steaming compost is HEAVY. Thus, making compost tends to be an arduous task. No fun.
One method I have seen to make turning compost easier is by building a drum composter. By simply rotating a drum filled with compost, oxygen can be introduced.
But drum composters have several drawbacks that make them problematic for hot compost.
a. They are usually uninsulated and too small to contain enough mass to hold in the heat required to kill off pathogens and weed seeds.
b. They are usually designed to add small amounts of material each day, thus resulting in compost that is not consistently decomposed.
Thus the compost from drum composters is often not as good as it should be.
I tried to solve problem a. by simply building a large drum composter. This design, while good in theory, had several flaws that made it impractical.
One possible answer to the problem, it seemed to me, was a smaller drum composter that could be insulated to hold the heat in, obviating the need for so much mass. If the composter could then be designed in such a fashion that the compost traveled through it as it decomposed, you could, build a small composter and add raw material to one end and harvest finished compost from the other end every day. In other words, a. More compost, b. Better compost, c. Less time, d. Less work. Win, win, win, win?
In my web searches I came across just such a composter. Manufactured by a company in Britain named Ridan, it seemed to incorporate all the design features I was looking for.
Instead of the drum turning, the Ridan has a shaft with tines that turns by means of a hand crank, aerating the compost and moving it along the tube.
The only problem was that Ridan wanted 3,000$ for their gizmo. Not only that, but there wasn’t a US dealer that I could find. Thus I would have to pay shipping and (alas) now, probably duties. ( Thank you President Trump for your lovely trade war.)
Needless to say, it is anathema to the tinkerer’s code to spend thousands of dollars on any manufactured gizmo, let alone one that you are not even sure whether it will work or not. Fortunately, after a really good Double Bluff CC Porter, 🍺 the answer slapped me in the face like a soggy bar towel.
The Answer: Build one myself.
Conceptually, the Ridan design is simplicity itself. A long tube with holes at either end. A shaft with tines to stir the compost. And insulation to keep in the heat.
The trick then? To come up with a design that satisfies my other Holy Trinity:
b. Easy to build
To make the tube I connected two 20 gallon drums.
The shaft I made out of 3/4 in. Pipe.
With threaded rods for the tines.
A base was built out of some scrap plywood and painted with salvage paint.
Add some rock wool insulation to keep in heat. (I’ve been wondering what to do with that left over insulation.)
Throw on a salvage tarp to keep out the rain and we’re done.
Will it work? No idea. Check back for updates.
Friday 13, 2018. 2:00 PM
Exterior temp, 75 degrees. Interior temp. 101 degrees. Add first bucket of table scraps and sawdust.
Friday 13, 2018. 9:25
Exterior air temp, 62 deg. Interior 74. Ridan instructions call for equal amounts of table scraps and sawdust. But sawdust is a hot compost killer. Think i’ll add a bit more nitrogen (coffee grounds) tomorrow to see if I can jump start the thermophylic bacteria.
Saturday July 14, 1:00 PM
Exterior air temp, 75 deg. Interior 95 and rising. Added grass clippings and coffee grounds to boost nitrogen. Several turns with hand crank to mix. Also added black vent stack to passively force warm air through the composter.
Temp still not hot enough. Suspect there is still a critical amount of compost (mass) necessary to create ideal environment for thermophylic bacteria.
Sunday July 15 3:00
Very disappointing! Outside air 87 degrees! Inside only 83! An outside pile made up of the stuff I threw in would be roasting by now. Could insulation actually be inhibiting heat from the sun from raising interior temp enough to get thermophylic decomp started? (Ironic) Or perhaps there is just not enough oxygen getting sucked in with low temps? Added lots of green grass clippings to pump up nitrogen and turned with crank to add oxygen.
Okay, I used a different thermometer. Exterior air temp. 79 F Interior compost temp 103! F Much better but still not hot enough. Check again tomorrow! 🌡
Mon July 16 8:00 AM
Exterior air temp. 59 deg. Compost temp 91 deg. Insulation definitely seems to be working to keep in heat. Today i’ll Add some more low carbon material to see if we can’t get the temp up higher. Have to remember it’s only been four days!
air temp 85 degrees. Interior 120 F! Temp definitely on the rise. Added chopped straw, duck and chicken manure and coffee grounds. Taking longer to ramp up than an outdoor pile. But perhaps because the amount of material is smaller.
One design change: added screening material to the intake hopper to keep out flies!
July 18, 8:00 AM
Day five. Ext. air temp 64 F, compost temp, 132! Not quite to the magic 140 degree mark, but respectable. The proof will be if I can sustain this temp on a consistent basis. Been adding a steady 5 gallons a day of material. Composter is now fairly full. As with my outdoor piles in order to get the compost hot I have been adding WAY more nitrogen than the books say to. (Cooler ambient temps in Pacific Northwest require this.)
I will continue to log temps for two weeks. If I can’t achieve 140-160 temp range I may have to re-evaluate the design.
July 19, 7:00 PM
air temp 70 deg. Compost temp 132. Consistent temps. Tines not advancing compost through the tube. Could be a problem.