18-Env-A6 Solid Waste Engineering and Management · May 2013
Question 7 of 17: Factors Influencing Landfill Gas Production
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Notes on this paper
National Examination, May 2013 — 04-Env-A6 / 18-Env-A6, Solid Waste Engineering and Management. 3 hours duration, closed book, one letter-sized aid sheet permitted. All 17 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.
Check: several questions on this paper (Q1, Q13, Q14, Q17) supply an incomplete data set and explicitly invite the candidate to "make and state" assumptions. Every assumed value below is called out where it is introduced and is chosen from standard solid-waste-engineering practice; the governing METHOD, not the specific assumed number, is what the exam is testing.
Question 7: Factors Influencing Landfill Gas Production (4 marks)
Landfill gas production is governed by: moisture content (microbial activity requires water; low moisture retards decomposition); temperature (mesophilic/thermophilic microbial activity rates); waste composition (the biodegradable organic fraction — food and yard waste decompose readily, plastics and inerts do not); oxygen availability/redox state (methanogenesis requires anaerobic conditions, which develop only after the aerobic and acid-formation phases are complete); and pH and age of the refuse (methanogens are pH-sensitive and gas generation follows a characteristic multi-year lag-rise-peak-decay curve).
