An MRF unit, depending on the level of complexity, will consist of a combination of units in varying degrees of mechanization
Pre-sorting: Bulky and contaminated wastes hamper further sorting or processing in the facility; mechanical or manual pre-sorting is essential to separate out these wastes. Manual sorting results in higher labourcosts and lower processing rates. Manual sorters remove bulky waste as the waste passes along a conveyor belt, which carries the pre-sorted waste to the mechanised sorting unit of the facility.
Mechanical sorting: Mechanical processes based on principles of electromagnetics, fluid mechanics, pneumatics, etc. are used to segregate the different waste streams in the pre-sorted waste. Mechanical processes require specialised equipment for segregation of commingled municipal waste. Mechanical sorting typically employs the following processes:
•Screening: Screening achieves an efficient separation of particles into two or more size distributions. Two types of screens are used in MRF centres disc screens and trommels.
•Ferrous metal separation: In the second stage, electromagnets are used for separating heavy ferrous metals from mixed waste.
•Air classification: The residual waste stream is passed through an air stream with sufficient velocity to separate light materials from heavy material, specifically for separating out lightweight plastics and paper from the mixed stream.
•Non-ferrous metal separation: The non-ferrous metal separator segregates zinc, aluminium, copper, lead, nickel, and other precious metal from commingled waste
•Detect and route system: This system separates various grades of paper, plastics, and glass, which are not sorted out in the air classifier.
•Size reduction: Sorted materials after segregation are usually too large for further use or processing; they should be reduced to smaller sizes.
•Baling: Sorted and sized material is baled for further processing or use.
Recyclables separated from mixed waste usually have the lowest quality and might be contaminated by residual waste. In India, the segregation of recyclables from the mixed waste stream is often practiced, not through formal collection systems, but through informal workers (waste pickers).
Any recycling programme depends on two crucial factors:
1.Community awareness and willingness to cooperate,
2.access to markets for segregated materials with acceptable and reliable conditions.
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Urban Infrastructure and Network Study notes for M. plan Sem-III
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