CBOT sampling protocols

Best Practices in PET Recycling

Sorting Systems: Introduction and Overview

Issue: Due to the increase in commingled curbside collection programs, there is an increased need for reliable and effective sorting systems that separate post-consumer PET plastics from other plastic and non-plastic containers and to remove other contaminants that might be present. PET bottles are separated from other commingled recyclablables and containers at a MRF, before sale to an intermediate processor, PRF, reclaimer or end-user.

Regardless of the actual sorting system design used, it should at a minimum be able to sort out and remove the following materials from acceptable PET bottles and containers for recycling:

· ANY PET BOTTLE WITH A BUILT IN HANDLE

· ANY PET BOTTLE OR CONTAINER THAT IS NOT CLEAR OR TRANSPARENT GREEN

· ANY NON-BOTTLE PET ITEMS SUCH AS SCOOPS, TRAYS, CLAMSHELLS, DRINKING GLASSES, ETC.

· ANY OTHER NON-BOTTLE PLASTICS

· ANY NON-PET PLASTIC BOTTLES

· ANY BOTTLES OR CONTAINERS WITH CONTENTS

· ANY FORM OF PVC PLASTIC

· ANY PLASTIC CONTAINER OR BOTTLE THAT PREVIOUSLY CONTAINED ANY HAZARDOUS OR POTENTIALLY HAZARDOUS MATERIAL (including but not limited to agricultural products, pesticides, herbicides, automotive fluids, medical products -- drugs, IV solutions, flammable, corrosive or reactive liquids, grease and solvents)

There are two generic types of sorting systems used at plastics recycling facilities. These are manual sorting systems and automated sorting systems. Manual systems rely on plant personnel who visually identify and physically sort plastic bottles traveling over a conveyor belt system. Automated systems employ a detection system, or combination of detection systems, that analyze one or more properties of the plastic bottles passing through and automatically sorts these plastics into several categories, either by resin type, color, or both.

The sorting system chosen for a particular facility is a function of several important factors. While cost factors influence system purchasing decisions, sorting system design is primarily a function of incoming plastic quality and level of commingling of plastic containers of different resin types. For example, bales of resin-segregated PET bottles and containers lend themselves to one type of sorting, while bales of two or more commingled plastic container types may require a different approach.

In addition, sorting system design will depend on whether the plastics recycling facility is baling or granulating the plastics they receive from their suppliers. For example, baling operations at MRFs, IPCs or PRFs generally use less expensive and less sophisticated sorting systems than PRFs that debale, sort and granulate incoming bales of plastic into individual resin and color categories for sale to reclaimers and end-users. PRFs that granulate PET plastic bottles and containers often combine manual and automated sorting systems to ensure the highest level of quality control for the regrind they produce.

Regardless of the specific type of plastic recycling facility and the sorting system used, there are several design elements that can be incorporated into a sorting line that will help minimize the presence of contaminants that must be removed either manually or automatically and improve the overall quality of the PET recovered. Whether plastic bottles or containers are entering a facility in loose or baled form, most system designs will feed plastic bottles via an inclined conveyor system to a horizontal conveyor system from which containers will be sorted. A best practice for sorting system design is to install a screening device over which incoming material will pass prior to moving on to the next stage of the sorting process. Screening will remove grit, dirt, broken glass and other non-plastic contaminants and pieces of non-PET plastic bottles that can get trapped inside bottles and potentially contaminate regrind. This can be accomplished by using various commercially available screening devices, such as trommel screens, or vibrating screens (also called “shaker tables”) that the PET bottles and containers pass over before they are discharged onto the sorting line.

In some cases simpler systems can be used, for example, screen tables onto which incoming plastic bottles are placed and then raked across by plant personnel into the feed hopper of the sorting system. Screens can also be installed in the conveyor system where materials drop from one conveyor to another. This design feature can greatly reduce the amount of smaller contaminants that might be difficult to identify and remove later in the sorting process by either manual or automated systems.

Please refer to the specific best practices for manual and automated sorting systems.

These discuss best practices directed towards plastics intermediate processing facilities that are granulating PET plastic bottles and containers for sale to reclaimers or end-users.