Recycling by product massive number of types of plastic, they each carry a resin identification code, and must be sorted before they can be recycled. This can be costly; while metals can be sorted using electromagnets, no such 'easy sorting' capability exists for plastics. In addition to this, while labels do not need to be removed from bottles for recycling, lids are often made from a different kind of non-recyclable plastic. To help in identifying the materials in various plastic items, resin identification code numbers 1-6 have been assigned to six common kinds of recyclable plastic resins, with the number 7 indicating any
Pfafstetter Coding System Pfafstetter Coding System The Pfafstetter Coding System is a hierarchical method of hydrologically coding river basins. It was developed by the Brazilian engineer Otto Pfafstetter in 1989. It is designed such that topological information is embedded in the code, which makes it easy to determine whether an event in one river basin will affect another by direct examination of their codes. In the 1950s, Pfafstetter suggested the use of a hierarchical system of coding river basins, later described in a 1989 paper. The method was applied to Brazilian water networks, and has been used in a number of other applications.