In the summer of 2000, the Ontario Waste Diversion Organization (WDO) funded a test in York Region of the operational effectiveness of a new technology to separate film plastic from aerobically composted organic materials. Other financial contributors include The Clorox Company of Canada and the Environment and Plastics Industry Council (EPIC). The findings should be of interest to composting and waste facility managers and operators across the country.
In the early 1990s many yard and waste diversion programs chose clear plastic bags for the curbside collection of source-separated yard waste. The use of bags allows visual inspection of contents by collection staff and is also convenient and cost-effective for residents. As these programs developed a significant challenge arose: the removal of plastic bags from the waste stream.
Since yard waste has seasonal fluctuations in Canada, purchasing equipment or staffing facilities to remove film plastic during peak generation periods can be difficult and expensive. A system that could remove film plastic at the back end of the composting process would avert such problems. (See “Advances in Automated De-Bagging” in the August/September 1999 edition.)
In October 2000, Miller Waste Systems of Markham, Ontario entered into an agreement with Zincot Manufacturing of Dorchester, Ontario to assist in the development of a back-end plastic removal system that uses air to separate film plastic from composted organic material.
Miller Waste owns and operates the Bloomington Yard Waste Composting Facility in Richmond Hill, Ontario and is contracted by York Region to pro-cess all of its municipal yard waste. In addition, Miller Waste also accepts materials from IC&I customers.
Using material from the composting facility as well as from the City of Guelph and the City of Toronto, the Zincot Air separator was put through a series of tests to determine what feedstock the unit could handle and what throughputs could be expected. In addition, the tests helped accumulate better data on the materials separated (for density, moisture content, etc.).
The unit uses an air stream to lift lighter material and separate the heavy organics from the fines and plastic. A cyclone further separates the fines from the air and plastic while a drop box filters the plastic from the air stream. The separator chamber has a 75-horsepower fan.
Co-inventor and president of Zincot, Les Zinn, says, “We received an innovation award years ago, but up until we modified it some critics thought the unit was too small and too expensive.” Mr. Zinn redesigned the unit, using the same principles but increasing the throughput capacity (up to 100 yards per hour) and decreasing the cost.
The new and improved unit was tested for one month on feedstocks that typically result from aerobic composting facilities: “overs” from the screening process, unscreened windrow material and the “unders” from the screening process and the plastic fragments.
The tests showed that the Zincot technology was very effective in removing the film plastic from the “overs.” It was capable of cleaning the film plastic out of the “overs” at throughputs that exceed the existing trommel screen’s capacity. The resulting clean wood product could be re-introduced into the composting feedstocks or be marketed.
Screened “overs” represent approximately 15 to 20 per cent by weight of composted yard waste at the Miller Waste composting facility. Diverting these products from landfill significantly improves the diversion rates at the facility and creates potential revenues from the mulch. In addition, initial testing of the film plastic removed in the process indicates that the material could be utilized by film plastic recycling facilities.
However, the unit encountered difficulties when processing the unscreened windrow material or the “unders” from the trommel screening. The fine compost particles burdened the effectiveness of the air separator and caused build-up on the ductwork and the fan assembly system. These build-ups (even at high duct scour velocities) prevented the continuous operation of the system and the removal efficiency quickly deteriorated.
Mr. Zinn says that much of the test materials was old (up to two years old) and that the results would be different if fresher material was used.
The technology proved effective at removing film plastic from the “overs” of the City of Guelph’s wet composting system. Unfortunately, it is not likely that the resulting product could be marketed as a result of the amount of other contamination that could not be removed through this air separation system, such as rigid plastic and broken glass. (In 2001, Guelph sold over 2,357 tonnes of finished compost at $30 per tonne to local landscapers and nurseries.
The technology removed most of the film plastic from the City of Toronto “overs” at high throughput rates due to the low moisture content. The unscreened windrow material from the City of Toronto also caused operational difficulties.
According to Allan Ramsey, the composting facility manager who continues to use the unit at the Bloomington facility, “It has its limitations, especially in the cold weather, but it works at minus 10 degrees Celsius.”
Last year, the Bloomington facility processed about 27,000 tonnes of compost.
“After the windrows composting,” says Mr. Ramsey, “we use a conventional screener, sort the ‘overs’ and then use the Zincot unit for further separation.”
More research is already underway to study configurations and options to improve the technology’s capability to remove fragments from the “unders” compost and to increase the value and variety of material available to market.
Connie Vitello is editor of this magazine.