Treatment Technologies: Shredding

Mechanical treatment to tear waste apart goes by verbs: granulate, pulverizes, shreds, grinds, mixes, agitation, and crushing. These processes can reduce the bulk volume of the waste by 60 percent or more. Waste can be moved through the processing facility with augers, conveyor belts, and other material handling systems.

Mechanical treatment does not kill pathogens or disinfect equipment, but it can reduce waste volume and increase the surface area in preparation of further treatment or disposal. Crushers and milling machines break down solid pieces of waste. Mechanical shattering or splintering of waste can also alter its appearance, which can be useful in lessening the psychological impact of the waste on human observers.

In addition to reducing bulk waste volume, mechanical breakdown increases the surface area of the solid pieces before subsequent chemical or heat treatment. Sometimes the waste is mixed with other material (cement or polymers) but doing so can increase the waste mass, so the engineer in charge should take a hard look at whether mixing waste with an outside agent is worth it.

Mechanical systems can also be an operational headache - things can go wrong and repairs may be needed. Further, mashing or shredding of solid waste can generate dust. If this dust becomes airborne, it can be a workplace hazard and a threat to the environment. That’s why mechanical equipment is often kept in a closed room or under a hood, at slightly lower than ambient air pressure.

Many manufacturers make shredders of some type. Thompsons Register shows over 500 results from a search on “shredder”. Some are intended for paper and cardboard, some for plastic, some for fabric. You should look at the nature of your waste, and work with the manufacturer’s sales engineers to choose what is best for you. Plan for at least 50 percent downtime. In other words, if you have, say 2000 lb/day to treat, choose a shredder that can process 4000 lb/day. Inquire to the manufacturer about warranties and required maintenance. The cost for shredders varies widely from $3000 to $100,000 and more. For a typical processing facility, the cost is under $10K per shredder. Some facilities have a back-up shredder.

Mechanical crushing and deformation is a prime treatment of sharps waste. It also is used in treatment of fabrics.