Facilities and operation
Waste sorting facilities receive waste from collectors and process this waste in a number of stages. The result is one or more clean material fractions for recycling or further sorting, and a residual component for disposal – typically incineration or land filling.
The configuration of sorting facilities varies from simple manual sorting lines to complex, automated multi-process sorting lines. The sorting process lies at the core of the waste sorting plant, but is supported by a number of pre-input and post-output ancillary processes that enable the smooth running of the facility.
Positive vs. negative sorting
There are two different conceptual approaches to sorting waste: positive sorting and negative sorting. Positive sorting focuses on identifying and removing a desired fraction from the input waste stream (i.e. eddy current which targets specifically non-ferrous materials). Negative sorting focuses instead on identifying and removing a non-desired fraction (i.e. eliminating plastic bottles without the specific polymer properties required). Generally speaking, positive sorting results in a high-quality material product, but at the cost of efficiency, whilst negative sorting tends to be more efficient, although at the cost of quality of the obtained materials.
In practice, waste sorting plants may use both approaches – for example, the manual removal of contamination from the waste at the start of the sorting line (negative sorting) followed by automated removal of material fractions (positive sorting), then another round of manual sorting at the end of the line to remove any residual contaminants (negative sorting) to ensure quality.
Manual versus automatic sorting
There are two technical approaches to sorting waste into individual material streams: manual sorting and automated/mechanical sorting. Configuration of the sorting line is highly dependent upon the incoming waste stream, the purpose of the plant and the market it operates in. In advanced economies, the market structure supports and demands sophisticated technology-based sorting solutions. In emerging economies, lower tech solutions may suffice and are more realistic given labor costs and maintenance programs.
