MRF

Material Recovery Facility.

is a specialized plant that receives, separates and prepares recyclable materials for marketing to end-user manufacturers. Generally, there are two different types: clean and dirty materials recovery facilities.

Process

Waste enters an MRF when it is dumped onto the tipping floor by the collection trucks. The materials are then scooped up and placed onto conveyor belts, which transports it to the pre-sorting area. Here, human workers remove some items that are not recyclable, which will either be sent to a landfill or an incinerator. Potential hazards are also removed, such as lithium batteries, propane tanks, and aerosol cans, which can create fires. Materials like plastic bags and hoses, which can entangle the recycling equipment, are also removed. From there, materials are transported via another conveyer belt to the disk screen, which separates wide and flat materials like flattened cardboard boxes from items like cans, jars, paper, and bottles. Flattened boxes ride across the disk screen to the other side, while all other materials fall below, where paper is separated from the waste stream with a blower. The stream of cardboard and paper is overseen by more human workers, who ensure no plastic, metal, or glass is present. Newer MRFs or retrofitted ones may use industrial robots instead of humans for pre-sorting and for quality control. Metal is separated from plastics and glass first with electromagnets, which removes ferrous metals. Non-ferrous metals like aluminum are then removed with eddy current separators.

The glass and plastic streams are separated by further disk screens. The glass is crushed into the cullet for ease of transportation. The plastics are then separated by polymer type, often using infrared technology. Infrared light reflects differently off different polymer types; once identified, a jet of air shoots the plastic into the appropriate bin. MRFs might only collect and recycle a few polymers of plastic, sending the rest to landfills or incinerators. The separated materials are baled and sent to the shipping dock of the facility.

Types

Clean

A clean MRF accepts recyclable materials that have already been separated at the source from municipal solid waste generated by either residential or commercial sources. There are a variety of clean MRFs. The most common are single stream where all recyclable material is mixed, or dual stream MRFs, where source-separated recyclables are delivered in a mixed container stream (typically glass, ferrous metal, aluminum and other non-ferrous metals, PET [No.1] and HDPE [No.2] plastics) and a mixed paper stream including corrugated cardboard boxes, newspapers, magazines, office paper and junk mail. Material is sorted to specifications, then baled, shredded, crushed, compacted, or otherwise prepared for shipment to market.

Mixed-waste processing facility (MWPF)/ Dirty MRF

Manual material triage for recycling.

A mixed-waste processing system, sometimes referred to as a dirty MRF, accepts a mixed solid waste stream and then proceeds to separate out designated recyclable materials through a combination of manual and mechanical sorting. The sorted recyclable materials may undergo further processing required to meet technical specifications established by end-markets while the balance of the mixed waste stream is sent to a disposal facility such as a landfill. Today, MWPFs are attracting renewed interest as a way to address low participation rates for source-separated recycling collection systems and prepare fuel products and/or feedstocks for conversion technologies. MWPFs can give communities the opportunity to recycle at much higher rates than has been demonstrated by curbside or other waste collection systems. Advances in technology make today’s MWPF different and, in many respects better, than older versions. 

The percentage of residuals (unrecoverable recyclable or non-program materials) from a properly operated clean MRF supported by an effective public outreach and education program should not exceed 10% by weight of the total delivered stream and in many cases it can be significantly below 5%. A dirty MRF recovers between 5% and 45% of the incoming material as recyclables, then the remainder is landfilled or otherwise disposed. A dirty MRF can be capable of higher recovery rates than a clean MRF, since it ensures that 100% of the waste stream is subjected to the sorting process, and can target a greater number of materials for recovery than can usually be accommodated by sorting at the source. However, the dirty MRF process results in greater contamination of recyclables, especially of paper. Furthermore, a facility that accepts mixed solid waste is usually more challenging and more expensive to site. Operational costs can be higher because it is more labor-intensive.

Wet MRF

A wet materials recovery facility

Around 2004, new mechanical biological treatment technologies were beginning to utilise wet MRFs. These combine a dirty MRF with water, which acts to densify, separate and clean the output streams. It also hydrocrushes and dissolves biodegradable organics in solution to make them suitable for anaerobic digestion.