Question 8 of 22: Investigating a Composting Odour Complaint

Question 8: Investigating a Composting Odour Complaint (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.

• Gather background information. Interview site operators and review process records — feedstock composition and C:N ratio, moisture-content logs, turning/aeration frequency, and pile temperature history.
• Conduct a site walk-through / odour survey. Identify which stage (receiving, active composting, curing) and which specific piles are the source, including downwind observations and, if warranted, an odour-intensity survey at the property line.
• Measure key process parameters directly. Pile core temperature profile, oxygen content within the pile, moisture content, and C:N ratio — insufficient oxygen (anaerobic pockets) producing hydrogen sulphide and organic acids is the single most common cause of composting odour.
• Check feedstock balance. Look for excess high-nitrogen, wet feedstock (e.g., food waste) without enough dry, high-carbon bulking agent, which both raises moisture above the optimum range and depresses the C:N ratio.
• Check pile geometry and aeration adequacy. Overly large, compacted or infrequently turned piles restrict oxygen diffusion into the pile core, driving it anaerobic even when the surface looks fine.
• Implement corrective actions. Increase turning frequency or add forced/passive aeration; add bulking agent to raise the C:N ratio and porosity; reduce pile height; improve site drainage to control excess moisture.
• Consider add-on odour control (a biofilter on forced-aeration exhaust, or a buffer of covering material) if source-side corrections alone do not resolve the complaint.
• Follow up. Re-survey odour after corrective action, and set up an ongoing monitoring/complaint-tracking log to confirm the fix is durable.