18-Env-A6 Solid Waste Engineering and Management · December 2016
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
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.); Freeze & Cherry, Groundwater; CCME, Guidance Document on Landfill Gas Management; Canadian Environmental Protection Act, 1999.
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.
Five physical properties of municipal solid waste (MSW) that govern its handling, transport and disposal design are: (1) specific weight (density), kg/m³, which differs sharply between as-discarded, collection-truck-compacted and landfill-compacted states, and drives every volume/airspace calculation (see Question 7); (2) moisture content, by wet or dry weight, which affects handling weight, energy content (see Question 16) and leachate generation potential; (3) particle size and size distribution, which governs the effectiveness of mechanical size-reduction, screening and materials-recovery-facility separation equipment; (4) field capacity, the maximum moisture MSW can retain against gravity drainage, which is the controlling parameter in landfill leachate-generation (water-balance) modelling; and (5) permeability (hydraulic conductivity) of compacted waste, which governs both leachate movement through the refuse mass and landfill gas migration.
Each of these is measured through a distinct, standardized field or laboratory procedure rather than assumed from a textbook table: specific weight is measured by weighing a known-volume container of waste at each handling stage; moisture content by oven-drying a representative sample to constant weight and comparing wet and dry masses; particle size distribution by mechanical screening (a stack of graduated sieves); field capacity by column-drainage testing of compacted samples; and permeability by a falling- or constant-head permeameter test on compacted refuse, analogous to a soil hydraulic-conductivity test. Design engineers should treat published "typical value" ranges (e.g. 300–500 kg/m³ loose density) as a starting point only, and confirm the site-specific values through this kind of direct testing wherever the design is sensitive to them — a landfill capacity or leachate-flux calculation is only as reliable as the density or permeability figure it is built on.
