18-Env-A6 Solid Waste Engineering and Management · December 2014
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.); CCME, Guidance Document on Landfill Gas Management; Canadian Environmental Protection Act, 1999.
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 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.
Aerobic composting biologically stabilizes the organic fraction in the presence of oxygen, producing a stable, pathogen-reduced humus-like product (compost) plus CO₂, water and heat. Advantages: relatively simple/low-cost technology, produces a marketable soil amendment, faster stabilization than anaerobic processes, minimal odour if well-aerated. Disadvantages: requires significant land area (windrow systems) or capital (in-vessel systems), needs active management (turning, moisture control) to avoid odour, and does not recover energy.
Anaerobic digestion (AD) biologically stabilizes the organic fraction in the absence of oxygen inside a sealed digester, producing biogas (methane + CO₂) and a digestate. Advantages: recovers energy as biogas (electricity/heat/renewable natural gas), fully enclosed (better odour and emissions control than open composting), smaller footprint per tonne processed. Disadvantages: higher capital cost and technical complexity, digestate still typically requires further stabilization/dewatering, and process can be sensitive to feedstock toxicity (e.g. excess ammonia, heavy metals).
