What Is a Materials Recovery Facility (MRF) and How Does It Work?
The materials recovery facility, or MRF, is a key component of residential and commercial single-stream recycling programs. Pronounced as "murf," the MRF is a facility that receives commingled materials and then uses a combination of equipment and manual labor to separate and densify materials in preparation for shipment downstream to recyclers of the particular materials recovered. Materials recovery facilities are alternately known as materials reclamation facilities or multi re-use facilities. Typical materials recovered at MRFs include ferrous metal, aluminum, PET, HDPE, and mixed paper. MRFs include both clean MRFs and dirty MRFs.
Differentiating Between Clean MRFs and Dirty MRFs
A clean MRF can be differentiated from a dirty MRF in that it accepts commingled blue bin material - in other words, recyclable materials that have been separated by households or businesses. A dirty MRF, on the other hand, processes household or commercial trash that has not had trash removed. Dirty MRFs potentially allow for greater recovery in that it can capture material that would have been missed if consumers placed it in the trash rather than the blue bin. The dirty MRF approach can also allow for the recovery of a wider range of materials than a clean MRF. On the other hand, the dirty MRF can require considerably more manual labor for sorting, and can result in the contamination of paper and OCC (old corrugated cardboard.)
The recovery rate of recyclable material from a clean MRF is predictably very high, while the recovery from a dirty MRF is much lower, in the five to 45% range. Dirty MRF material is also much heavier, thanks to organic material in trash. It averages around 350 pounds per cubic yard where organics are not diverted, as opposed to 50 to 100 pounds per cubic yard of blue box material.
How a Materials Recovery Facility Works
MRFs can vary in some respects in terms of technology employed, however, a typical process would include something such as the process described below.
MRFs have customer vehicle scales, and a yard that can accommodate a queue of trucks. Incoming haulers arrive at the MRF and dump the commingled material onto the tipping floor. A front end loader or other bulk material handling equipment then drops into a large steel bin at the start of the processing line. This bin is known as the drum feeder. Inside of the drum feeder, a fast moving drum meters out the commingled material onto the conveyor at a steady rate, while also regulating the density of the material on the conveyor so that it is not packed too tightly together.
From there, material goes to a pre-sort station, where workers standing along the conveyor spot and remove any trash, plastic bags or other mistakenly placed material and separate them for appropriate disposition. Large pieces of plastic or steel, including pipes and other large items, can damage the system or expose workers to risk of injury.
Larger pieces of cardboard are then removed from the mixed material stream, pushed to the top by large sorting disks turning on axles, while heavier material stays beneath. Smaller sets of the disk may then remove smaller pieces of paper. As materials are separated, they are diverted to separate conveyors for accumulation and baling.
Powerful magnets separate steel and tin containers, while an eddy current separator is used to draw aluminum cans and other non-ferrous metals from the remaining co-mingled material. Glass containers can be separated from plastic containers by a density blower, then hammered into the crushed glass, known as cullet.
Remaining plastic containers may be sorted manually by workers on the conveyor line, or increasingly, optical sorters are used to identify different materials and colors. Air classification may be used to separate key plastics such as HDPE and PET.
Separated materials, other than glass cullet, are typically baled, with finished bales weighing in the range of 1000 to 1500 pounds.
MRFs Struggle with Unwanted Materials
Material recovery facilities struggle with a variety of unwanted materials such as plastic bags, large objects, and trash, all of which increase the need for manual sorting, and which increases inefficiencies for MRF operators and ultimately for the communities they serve. Such problems are intensified in the face of declining markets and lower prices for the materials they sell, such as has been experienced in recent years due to tightening import restrictions by China.