Question 1 of 18: GHG-Reduction Strategy for Solid Waste

Question 1: GHG-Reduction Strategy for Solid Waste (10 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.

Solid waste GHG emissions arise mainly from methane (CH₄) released by anaerobic decomposition of biodegradable waste in landfills, from combustion of waste and fuel used in collection/haulage, and indirectly from the embodied carbon of materials that are landfilled rather than recovered. An effective municipal strategy attacks all three pathways rather than relying on a single measure.

1. Waste diversion at the top of the hierarchy. The largest, cheapest reduction comes from keeping biodegradable material out of the landfill in the first place: source-separated collection and mandatory organics (food and yard waste) diversion to composting or anaerobic digestion removes the feedstock that would otherwise decompose anaerobically and generate CH₄ — a gas with roughly 25–28× the 100-year global-warming potential of CO₂. Recycling of paper, plastics and metals avoids both landfill CH₄ and the upstream embodied-carbon emissions of virgin material production.

2. Landfill gas capture and beneficial use. For the waste that is still landfilled, an active LFG collection system (extraction wells, header piping, blower/flare station) captures the CH₄ that does form. Flaring converts CH₄ to CO₂ (a 25–28× reduction in CO₂e per unit gas), while LFG-to-energy (engine-generator or direct pipeline injection after upgrading) additionally displaces fossil-fuel generation, giving a double credit. Canadian federal and provincial landfill gas regulations already require collection above a waste-in-place threshold at larger sites — the strategy should meet or exceed that baseline.

3. Residual-fraction management and operations. A well-designed diversion program still leaves a non-recyclable, non-compostable residual; where markets and air-permit conditions allow, waste-to-energy combustion of this residual with energy recovery avoids both future landfill CH₄ generation and an equivalent amount of fossil generation. On the operations side, collection-fleet route optimization and a transition to lower-carbon collection vehicles (compressed natural gas or electric) reduces the Scope 1 emissions of running the system itself, and leachate management/treatment should be sized to avoid uncontrolled N₂O releases.

4. Policy and monitoring. The strategy is only credible with pay-as-you-throw or volume-based user fees to reward diversion, a public reporting program that tracks tonnes diverted and LFG captured against targets, and periodic review against evolving federal methane regulations.