September 16, 2009 | General

Sorting C&D Materials For End Markets

C&D materialsBioCycle September 2009, Vol. 50, No. 9, p. 27
Minnesota company processes C&D streams into saleable products, while extending the life of its landfill.
Rhodes Yepsen

DEM-CON Companies has been in the landfill business since the 1960s, starting with Louisville Landfill for municipal solid waste (MSW), located southwest of Minneapolis, Minnesota. In 1985, Dem-Con Landfill was started to accept construction and demolition (C&D) waste materials for the southwestern region of the Twin Cities. Dem-Con Companies has transitioned over the years and now focuses on building end markets for materials that were routinely landfilled. “Our family of companies has expanded several times, and in 1999 we made our first real attempt at C&D recycling, building a facility that was predominately a manual sort operation,” says Jason Haus, CEO of Dem-Con Companies. “Last year we installed a more automated sorting system to achieve higher recovery rates and process higher volumes.”
The C&D landfill has approximately eight million cubic yards of remaining capacity, which was about 20 years worth of disposal space before the recycling equipment was installed. “Our goal was to extend the life of our landfill as long as possible, using proven waste processing equipment,” explains Haus. “We also wanted to sort our waste stream into high quality, salable products. The end markets require high quality materials and without the ability to sell the commodities we segregate, this operation would not be economical.”
finger deck vibratory screen
Incoming material is dumped on the tipping floor, and bulky items are removed. Remaining material enters the new sorting system designed by Erin Recycling. “After being weighed, screened and dumped, the mixed materials are fed onto a steel-belted incline conveyor,” says Haus. “This drops onto the Erin finger deck, a vibratory screen, which was custom-designed to sort into three material sizes. The first is 2-inch minus, which is used as alternate daily cover (ADC) at the landfill. Then it sorts for 2- to 14-inch material, which flows to our B line, with manual picking for wood and aggregate. Overhead belt magnets are used to pull all of the ferrous metals off of these two smaller lines. Finally, 14-inch and above material is sent to our A line, with picking for wood, ferrous and nonferrous metals, cardboard and aggregate.”
The system is designed for growth, with two extra sorting stations. “We’ll begin to use the extra sorting stations for additional materials as soon as an end market becomes apparent, but most likely gypsum will be next,” notes Haus. “However, gypsum recycling has two strikes against it in Minnesota – there are no manufacturing plants locally for turning it back into drywall, and our soils are not acidic or sulfur deficient, thus the gypsum does not provide a lot of value as a soil amendment.”
Electric grinder
The Erin screening system feeds all woody materials free of paint and stain directly into a 400-horsepower electric Rotochopper grinder, which reduces it to 2-inch minus. “The majority of our wood is sold as fuel under contract with energy producers in Minnesota,” explains Haus. “The ground wood is loaded by conveyor into live bottom trailers, with three semi loads going out daily. Minnesota has a strong wood market, so there are other options like animal bedding and landscape mulch.”
Dem-Con reports monthly rates for all recovered and saleable materials, available on its website. “Our recovery rate fluctuates depending on the incoming load compositions, but these statistics are important for contractors and real estate developers interested in achieving LEED Green Building Certification,” says Haus. “In July, our overall recovery rate was almost 75 percent, whereas August was 73 percent. It’s important to note that we only include tonnages of materials that are actually sold to an end market or used as ADC at our own facility. Stockpiles of materials not being processed are not counted in recovery statistics until the material is sold. We believe this is the most accurate way of reporting back to our customers.”
The lack of end markets is the major limiting factor in growing the recovery rate. “For instance, we have been investing in asphalt shingle recycling, purchasing a second Rotochopper grinder to make a product used in hot mix asphalt production,” he explains. “However, the Minnesota Department of Transportation doesn’t currently have a permissive spec for tear-off shingles. This is the only limiting factor holding back Minnesota’s ability to recover shingles, which would keep a large portion of the C&D stream out of the landfill, reduce the need for virgin oils for new asphalt, and result in a lower-cost but high quality product for the consumer. Until more markets develop, we will probably hover around a 70 percent recovery rate.”

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