Question 9 of 18: Factors Affecting Landfill Gas Production

Question 9: Factors Affecting Landfill Gas Production (6 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.

Landfill gas is generated by anaerobic microbial decomposition of the biodegradable fraction of the waste, so LFG production rate and total yield are governed by whatever controls that microbial activity. Six recognized factors: (1) waste composition — the proportion of readily biodegradable organic material (food waste, paper, yard waste) sets the total gas yield potential; (2) moisture content — water is essential for microbial activity and for transporting nutrients/substrate to the decomposer population, so wetter waste (or leachate-recirculating bioreactor operation) generates gas faster; (3) temperature — anaerobic decomposition is fastest in the mesophilic (roughly 30–35°C) to thermophilic range typically self-sustained within a deep landfill, and production slows markedly in colder climates or shallow/edge cells; (4) pH — methanogenic bacteria are sensitive to pH and are inhibited outside a near-neutral range, which can occur transiently during the acid-formation phase; (5) particle size and density/compaction — finer particle size and adequate (not excessive) compaction increase the surface area available to microbial attack while still permitting moisture movement; and (6) waste age — gas production follows a characteristic multi-phase curve (aerobic, acid-formation, then a peak and gradually declining methanogenic phase), so a landfill's age distribution across its cells governs its instantaneous total gas output.