Rotating Vessel Composter for Small Farms
This project proposed to evaluate the speed and effectiveness of composting using a continuously rotating drum propelled by an elevated water supply.
Many small farms choose not to compost because of the time and labor required to turn the product, says project coordinator Jack Caldicott of Jacyn Lavender and Vegetable Farm in Sequim, Wash. His proposed solution is a continuously rotating drum that would reduce time and labor for composting.
His attempt to fashion a drum 3 feet in diameter and 4 feet long from a piece of culvert pipe required more effort than he’d anticipated. While developing a suitable, reliable, low-cost rotating drum proved a challenge, he has found that the basic principle of using a rotating drum appears to work well in producing the compost quickly and with a quality equal to compost produced in an existing 4-foot cube bin.
The drum was made from a 4-foot section of a double-walled plastic culvert pipe 36 inches in diameter. A plywood disc was attached to one end, and a removable plywood door to the other end with a flap two-thirds up the door to allow for loading the compost material. The drum was mounted on four 6-inch diameter wheels attached to a pallet so it could be rotated.
The initial tests were made with a mixture of horse manure, bedding material and garden waste run through a shredder before being loaded. The loaded drum proved too heavy to turn by hand, so a boat winch was used to rotate the drum daily. The temperature inside reached 160 degrees F. in about 24 hours and stayed between 140 and 160 degrees for three to four days. The compost produced was comparable to that produced by existing 4-foot cube bins.
Because the initial method of mounting the wheels wasn’t strong enough, the composter was rebuilt, again using the boat winch for rotation. Caldicott tried several mixes and all produced good compost except for one that used material previously composted in the bins. That batch failed to heat above 100 degrees F. and had to removed and restarted with material containing more nitrogen.
His second objective, using water as a drive mechanism to rotate the drum, was found to be impractical because of the considerable force required to rotate the loaded drum. So Caldicott developed a system using bicycle parts, a garage door opener and other materials to drive the rotation. Slippage problems and insufficient torque led him to try additional gearing and a larger motor. But that has caused some welds to break, possibly because of excessive friction from homemade bearings.
Undaunted, he continues to seek methods of turning the drum automatically, which currently includes a chain around drum driven by a geared down motor. Screws have been fitted to the drum to act as teeth for the chain. A bicycle gear-change mechanism is being used to take up the slack and guide the chain onto the teeth.
“However,” he says, “I suspect that this will not work reliably, and so I am in the process of trying to locate off-the-shelf worm drive gears together with better bearings that I can use to make a four-wheel drive arrangement.”
While the benefits of compost are well established, the process of making it on a small scale can be arduous and time-consuming, keeping many small farms from composting. A successful rotating composter could reduce the time and labor required, making composting more enticing for small farms.
FARMER ADOPTION AND DIRECT IMPACT
None of the farmers familiar with the project has attempted to emulate the rotating drum practice, but one farmer said, “If you get it working, I want one.” The same farmer said he would prefer to have a composter that’s twice as large as the one being tested in this project.
FUTURE RECOMMENDATIONS OR NEW HYPOTHESES
The project coordinator said he would do more calculations before embarking on such a project and seek advice from someone experienced in drive mechanisms.
DISSEMINATION OF FINDINGS
Because of problems encountered, no official outreach has been conducted so far. However, several small-scale farmers have shown considerable interest in the process.
Jack Caldicott is the only producer directly involved in this project.