BioCycle October 2010, Vol. 51, No. 10, p. 43
Mixed waste composting is a component of recycling, resource recovery and landfill operation near Cordoba.
Nora Goldstein

EPREMASA, a regional solid waste company based in Cordoba, Spain, and its affiliated company, Diputación de Cordoba, recently added an enclosed composting component to a 190,000 tons/year “Recycling Park” in Montalban. Epremasa collects municipal solid waste and recyclables from 72 towns around Cordoba, and brings them to its transfer stations within the region. From those points, materials are hauled to the facility in Montalban, which includes a landfill with gas recovery, a materials recycling facility and mixed waste composting. “We process about 400 tons/day, of which about 40 percent is organics, or 160 tons/day,” says Francisco Requena Cruz, who manages the operation.
Households and businesses set out recyclables in yellow bins, which are collected and brought to Montalban for processing. “About 90 percent of that material can be recycled,” adds Requena Cruz. “We recover PET, HDPE, mixed plastic, paper, cardboard, steel, aluminum, glass and textiles. We also are adding a new sorting line only for plastics.”
MSW to be composted is unloaded onto a tipping floor. After oversized items are removed, material is loaded onto a conveyor that feeds a trommel screen. The first portion of the trommel has 90 mm holes. The minus fraction drops onto a conveyor that passes under an electromagnetic separator, then goes out to the composting hall. (Material is not shredded prior to composting.) Overs continue to the next section of the trommel with 190 mm holes to separate out materials for recycling and residuals for disposal.
In 2009, Epremasa installed 13 Biodegma composting modules in an existing covered, but open-sided building, replacing its windrow operation. The composting component enables the company to comply with the national regulations (imposed under the European Union Landfill Directive), which require that organic wastes be stabilized prior to landfill disposal.
The rooves of the Biodegma modules open to facilitate material loading and unloading. The sides, roof and door of the units are made from the GORE Cover semipermeable laminates, attached to an aluminum frame. The GORE fabric serves to control odors and retain moisture in the composting feedstocks. Each module has a capacity of 450 m3. Temperature is controlled via aeration.
“The first stage of composting is 21 days,” says David Pintre, who until recently worked with Biodegma in Spain. “Temperatures of 65° to 70°C are reached in the first three to five days to achieve pathogen kill, and are maintained at that temperature for more than 10 days.”
After three weeks, a module is unloaded and the compost is moved to a large windrow in the center of the covered building for curing for 10 to 15 days. Moisture content is between 40 and 45 percent, and after two weeks is about 30 to 35 percent. “Optimally, the material should stay in the windrow for 6 to 8 weeks,” adds Pintre. “But there is not enough space on the compost floor.”

Compost Screening And Use
The compost is screened through a trommel with 25 mm openings, followed by a vibrating deck screen with 15 mm holes. Overs are used as cover on the adjacent landfill. The compost, which is tested every six months, is applied to olive trees. The final product is about 20 percent of what initially enters the composting system.
In terms of overall recovery from the incoming MSW and recycling streams, about half of what is received at the facility is recycled, about 12 percent is compost, about 20 percent is landfilled and about 18 percent is “mass reduction.” Captured landfill gas runs two engines, one rated at 1.2 MW and the other at 1.4 MW. The Montalban plant also includes an educational area for school groups.