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18-Env-A6 Solid Waste Engineering and Management · December 2014

Question 23 of 29: How Density Separation, Magnetic Separation and Densification Are Accomplished

Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)

Notes on this paper

National Examination, December 2014 — 04-Env-A6 / 18-Env-A6, Solid Waste Engineering and Management. 3 hours duration, closed book, one non-communicating calculator, one letter-sized aid sheet (both sides) permitted. All 29 questions constitute a complete paper (100 marks total).

Reference texts: Tchobanoglous, Theisen & Vigil, Integrated Solid Waste Management: Engineering Principles and Management Issues; Vesilind, Worrell & Reinhart, Solid Waste Engineering; Davis & Cornwell, Introduction to Environmental Engineering (6th ed.); CCME, Guidance Document on Landfill Gas Management; Canadian Environmental Protection Act, 1999.

Note on source parsing

This paper prints marks IN FRONT of the question number on every line (e.g. "5 1. What are the elements…", "4 16. All 29 questions are answered in full.

Question 23: How Density Separation, Magnetic Separation and Densification Are Accomplished (3 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

Density separation is accomplished with an air classifier: a controlled air stream is passed through (or across) a stream of shredded, mixed waste, and the differential drag-to-weight ratio of each particle causes light, low-density material (paper, plastic film, organics) to be carried up/out with the airflow while heavy, dense material (glass, metal, inerts) drops out — separating by density rather than composition per se. Magnetic separation is accomplished with a magnetic drum, overhead belt magnet or magnetic pulley positioned over or beside the waste conveyor, which attracts and lifts out ferrous metal (steel/tin) while non-magnetic material continues along the belt; non-ferrous metals (aluminum) instead require an eddy-current separator. Densification is accomplished by mechanical compaction (a hydraulic baler or compactor) applying pressure to a material (e.g. sorted recyclables, RDF, or MSW itself) to increase its bulk density for more efficient transport, storage or landfilling — typically producing bales or compacted pellets/cubes.