Has anyone tried a passive aeration compost bin?

anney(Georgia 8)August 7, 2008

I may experiment with a closed compost bin that uses passive aeration instead of the contents requiring turning. Has anyone tried it?

Here is some information about the method:

PASSIVELY-AERATED COMPOST BINS

It is possible to use passively aerated bins for composting highly putrescible feedstocks, like food, on a small scale. Backyard composters do this routinely. Passive or natural aeration occurs by at least three routes:

  1. Oxygen diffuses into material because there is more oxygen outside than within;

2) Heat causes thermal convection as warm gases rise out of the composting mass and cool fresh air enters; and

3) Wind blows air through the materials....

The strength of the passively aerated bin approach is its simplicity. The bins are inexpensive. There are no moving parts, and there is no need for electricity. Success depends on the composting process working well. Therefore, operators must learn to be good at managing and reading the process.

An example of one commercial container intended for on-site composting of food residuals is the Hot Box, developed and patented by Open Road of New York, a nonprofit organization. Open Road licenses the Hot Box design, which is a solid one cubic yard bin, 3 feet by 3 feet by 3 feet in dimension. Its base and walls are made from wood or recycled plastic lumber. The bin is covered with planks or a hinged lid. One wall of the Hot Box is constructed with planks to facilitate unloading. Two rows of perforated PVC aeration pipes run across the lower and mid sections of the bin to enhance passive air movement. The pipes are inserted through holes in one wall and rest against a ridge on the inside of the opposite wall. One end of each pipe is open to the outside air.

After placing a base layer of wood chips, the bin can be filled gradually or in a single batch. Loading and unloading is accomplished manually. Open Road recommends a well mixed, one-to-one volume combination of food and wood chips. When the box is nearly full, it is capped with a layer of finished compost that serves as a passive biofilter. In very sensitive locations, the open end of the aeration pipes can be covered with a biofilter bag to filter odors further. The biofilter bag is a loose mesh bag filled with compost and woodchips... With a 1:1 volume ratio of food and wood chips, each bin holds approximately one-half cubic yard of food. The feedstock (food) is not agitated or mixed once in the bin. Compost is unloaded for curing within one month. When properly loaded, the Hot Box reaches temperatures above 130 F.

Passively aerated bins can take other forms and sizes. As another example, the slightly larger CM Pro container can be used as a passively aerated bin, although it is normally promoted as a forced aeration unit. Similarly, the Hot Box is aerated with fans in some applications. There also are the homemade varieties. For example, some schools and other institutions compost food in backyard-type wooden bins, enclosed within a building. They are managed much like backyard units, and like backyard composters, may not reliably reach high temperatures.

The Hot Box (and its passively aerated counterparts) represents the smallest scale operation. It is suitable for many low volume applications such as schools, individual restaurants and small food service facilities. [And home gardeners, no doubt.]

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Why couldn't you drill 3" holes at the bottom and middle of a garbage bin, aligned on opposite sides, and run perforated PVC pipe horizontally through the holes? Then all you'd have to do would be add greens and browns to the bins and let the passive flow of air aerate the materials.

Has anyone tried this?

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petalpatsy(7b)

This is how most open piles work, in fact, there's no way to stop it. :) It's one of the reasons you hear the 3x3x3 dimension so often, as much bigger and the O2 can't quite make it to the center. My pile is contained by fencing, and bits always fall out. Any minute now, I'm going to build myself a new enclosure of hardware cloth...yup, any minute. Either way, I've no need of perforated PVC. I still turn my little pile just to keep the materials well mixed and speed things up, and keep BSFL from taking over.

    Bookmark   August 7, 2008 at 9:52PM
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jbest123(Zone 5 PA)

I use a passive/active method (dont know what else to call it). My compost bins are adjacent to the garage and I can reach them with my air compressor. There is a copper tube about 3ft long on the end of a blowgun. I will insert it and retract it very slowly on approximately a 6in grid. I will turn a new pile once and when the second heat starts to diminish, I will use the air compressor. It seams to extend the second heat. What I would like to try next is to put a tube on the end of a paint spray gun. Then I could mix a liquid fertilizer with the air for hard to compost browns like corn stalks and fall leaves.

John

    Bookmark   August 8, 2008 at 12:24AM
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Kimmsr(4a/5b-MI)

Any compost pile less than 6 feet wide and 6 feet high will not have a problem with getting enough air inside for the bacteria to have ample amounts to work with, unless there is too much moisture which excludes air. There is no need to spend lots of money buying a composter to do what happens naturally if the material is properly handled from the start, unless this same material is put into a container that does not have enough space for proper air infiltration.

    Bookmark   August 8, 2008 at 7:01AM
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