Recycling involves using materials which are at the end of their useful lives as the feedstocks for the manufacture of new products. It is differentiated from reuse by the reprocessing and remanufacturing operations.
Within recycling, a further hierarchy can be defined. Primary recycling is the use of recycled products to make the same or similar products. Secondary recycling is the use of recycled materials to make products with less stringent specifications than the original. This allows for downgrading of the material to suit its possibly diminished properties, and hence is of lower value than primary recycling.
All recycling systems must have three major components in order to function. First, they must have a consistent and reliable source of recycled material. Collection of this material is one of the major requirements of this process. Secondly, method for processing the recovered materials into a form suitable for reuse must be in place. Thirdly, markets must exist for the reprocessed materials in an economically viable manner that a recycling system exists.
The very first step should be separation of solid waste at domestic level. The home dustbins can be portioned for the separate collection of paper, glass, metals (tin can, foils), plastics (packing bags, bottles) and everyday putrescible waste matter. A number of recycling centres can be established where citizens will bring bottles, cans, newspapers and other waste separated at home and a number of small industries can process and market the recycled materials.
Paper and Cardboard
Post-consumer waste paper is recovered from solid waste in two ways:
(i) Salvage industry collection of paper boxes, cardboard boxes and office paper from industrial and commercial establishments, government and municipal offices, and private collection of old newspapers.
(ii) Mechanical processing of mixed municipal solid waste in large recovery plant
Recovered paper can very well be used in paper industry for manufacturing paper and paperboard products. However, big paper industries use virgin fibre and secondary industries can use reclaimed paper for their bulk output.
Steel Can
The three major potential markets for old cans are the steel industries, the de-tinning industries and the copper precipitation industry. For stimulating steel can recovery a constant adequate supply of old cans and scrap iron should be maintained. De-tinning industry will have to be established and a sufficient subsidy should be given to these industries to make this process attractive.
Glass
Traditionally, glass was well recycled. For recovery from municipal wastes, glass pieces can be handpicked or mechanically separated where waste undergoes shredding, air classification and other types of separation. Glass can be used as a road paving material or a component of building material.
Plastics
The most difficult operation in recycling is the identification and separation of plastics. Because mixed plastic has few economical uses, plastic recycling is economical only if the different types of plastic are separated from each other. The plastic industry has responded by making most consumer products with a code that identifies the type of plastic that can be recycled are all common products used in everyday life, some of which are listed in Table 6.4.
Three types of plastic are successfully being recycled, the most common being PET bottles. HDPE plastic is used for milk jugs and the bottoms of soft drink bottles. It can be recycled into trashcans and flowerpots. Polystyrene foam is crushed into pellets and turned to plastic lumber for benches and walkways.
Aluminium
Aluminium, particularly cans, is a valuable commodity. By the late 1980s, over 50% of all aluminium cans were recycled. Recycling aluminium saves a tremendous amount of energy. It
takes 95% less energy to produce an aluminium can from an existing one than from ore. Aluminium products that are recycled include siding, gutters, door and window frames and lawn furniture.