Composting tower concept
I had an idea about a composting system last night. I have never heard of anything like it before but someone very well could have this thing sitting in their back yard already for all I know.
The concept is similar to a composting system I've seen that uses four compost piles laid out on the ground which are eventually consolidated into two, then into one pile of finished compost. Typically, a great deal of strenuous labor is involved in first creating the four piles, turning the piles, and then consolidating them in order to have sufficient mass for efficient composting.
The significant change would be to arrange the compost piles in bins or boxes vertically on a frame in order to use gravity for transferring, aerating and mixing the composting materials.
The structure would consist of a frame of wood or steel, seven large boxes or bins, and hinges and latches for trap doors on the bottom of six of the bins.
The system would begin with four horizontal primary bins at the top of a tower frame where they could be fairly easily loaded with lightweight brown and green material, either using a ladder and baskets (and a couple of helpers!) or a simple conveyor system. You get extra energy points if you are lucky enough to have a steep slope to build the structure on, so that you to have the top bins at or near ground level at the top.
When the material has composted down to half the original volume, side-hinged trap doors on the bottom of the bins could be opened to allow the composting material to simply fall into to the next level of two secondary bins. Trap doors hinged in pair of opposite sides would act as a funnel, directing flow of two upper bins into one lower bin. The doors would be fastened with pins that could be knocked out with a hammer while the door is bearing the weight of the compost. Side fins on the trap doors would reduce spillage. The composting material would be mixed and aerated during the gravity transfer.
When the contents of the secondary bins have reduced in volume by half again, the almost finished compost would be dropped to the single bottom bin where it would eventually be available for easy access.
An option to raise the whole thing up even higher to allow gravity feeding of the finished compost into a wheelbarrow or trailer through a chute below the bottom bin would make this thing darn near perfect.
Benefits of this system include having the most labor intensive portion of the process involved in lifting the lightest components. Gravity is used to transfer, mix and aerate the material as it moves through the composting process. The process could be continuous with material in different stages of composting present in all three levels at one time.
Problems to overcome would include the cost and construction of the frame, the work involved in lifting materials to the top bins, keeping the top bins moist enough in hot weather, and possible spillage.
I'm not the only one who dreams of composting systems!! Woo Hoo!!
I've had many ideas and seen many others, this is new to me. (sort of)
Your gravity flow idea is in place in a sense, at Vermont Compost (Karl Hammer) and there's a few videos (Justin Rhodes, Geoff Lawton) of his operation.
He is on a hillside, and his operation begins up top and finishes down below. The delivery trucks are doing the heavy lifting, so to speak. Karl's workers and machines slowly move it downhill.
I've stalled with compost vessel/bin ideas of my own when I've reached the volume/scale/fit question. That is, how much, and at what rate, will I be containing. The issue I struggle with is seasonal variation in volume, feedstock, rate of composting action.
I worry about Goldilocks-ing the thing... (not too big, not too small, just right!)
Your idea sounds like it will be TALL, like over 20 feet tall. Assuming 4 feet deep bins, and 3 feet height between for the funneling and a wheelbarrow. (3 tiers at 7 feet each = 21 feet)
If you had 4 foot high piles on the ground, (and this is super-sketchy math) 5 turnings of those 4 foot high piles equals 21 feet of lifting for your tower.
Your 4-2-1 scenario is 6 turnings plus 1 lift into a wheelbarrow, so 6 or 7 "lifts".
Except, that you don't really need to lift the whole pile 4 feet to turn it on the ground, you only need to "flop" it over to bury the outer/dry material inside.
I think you may be doing more lifting in the tower scheme, than on the ground...and...
The volume is decreasing, but I'm not sure the mass is changing much. Most of the material you end up with at the bottom, YOU hauled to the top in 4 trips!
I have seen this idea of stacked bins used to great effect in vermiculture.
I think that incorporating maceration of the additions, with a chipper for woody bits and a garberator-type in-drain food disposal for food waste, would greatly increase the rate and temperature of the initial compost.
I also think that if you simply had ever-decreasing grades of grating separating levels of a largely fixed tower of bins, you could employ an offset motor or something to vibrate the whole structure, encouraging stuff that really wants to break down mechanically and fall to the next stage to do so.
You could, I think, even do a worm stage at the end of your bin, or tweak the concept to use more than just the thermophiles to compost.
I think you could even do a dump-bucket on a chain lift on a pulley, if the tower proves too tall. You could simply pull a chain loop around a pulley at the top of the system to pull an attached bucket up and over, dumping the contents and returning to the ground.
Whatever you do, keep us posted, and good luck.
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Another thing about working on the ground, is the ability to use a tractor or loader to aid in the lifting/turning. The lifting is truly the hard part, hard on the body, especially once you get beyond 5-10 cubic yards. I was draining myself trying to manage 50 yards by hand.
But something like vermicomposting, in stackable upward migration type bins keeps the lifting manageable and low. You could use a hand truck or a beehive lifter to aid in that, and the WORMS do all the "turning" for you.
There's so many methods and some better suited to different materials than others, so without knowing what you are composting and why, it's hard to know where to point you John.
Chris, the idea of screening the compost as it is happening, has a flaw, in that the bulky/slow to breakdown materials are an aid to aerating the smaller materials by holding open some channels for circulation.
Chopping is useful to a point, then again you can run into aeration problems if you are trying to compost goop. I've been composting brewer's grain for years now, and it is tough without some bulky stuff mixed in.
I like the concept but worry about the feasibility of such a tall system for several reasons.
Wind resistance, how high speed do the winds get in your area? Wind can cause catastrophic failure of a tall structure that is inherently top heavy (which this would be since the highest section would also be the largest and heaviest).
Will you have this structure set up to dump the finished compost into a motorized carrier (truck, etc.) and if so, how high does the bottom of that last bin need to be to accomplish this?
Remember this is also going to add to the height of the first (start bin) and how are you going to get materials up there? belt or bucket lifts?
This concept might be great if inside a large building which would prevent wind buffeting of the apparatus.
Like I said, I like the concept but it will need some refining and be sure to try and cover all possible problems during the on paper stages.
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