18-Env-B5 Industrial & Hazardous Waste Management · May 2016
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Reference texts: Nemerow & Dasgupta, Industrial and Hazardous Waste Treatment, 2nd ed.; Metcalf & Eddy, Wastewater Engineering: Treatment and Resource Recovery, 5th ed.; Davis & Cornwell, Introduction to Environmental Engineering, 6th ed.; LaGrega, Buckingham & Evans, Hazardous Waste Management, 2nd ed.; CCME, Guidelines for the Management of Biomedical Waste in Canada (1992); Canadian Environmental Protection Act (CEPA), 1999; Basel Convention on the Control of Transboundary Movements of Hazardous Wastes (1989); Canadian Nuclear Safety Commission (CNSC) regulations on radioactive waste; provincial hazardous waste regulations (e.g. BC's Environmental Management Act and Hazardous Waste Regulation).
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.
(1) Dissolved oxygen concentration — must be maintained above roughly 1–2 mg/L throughout the digester volume or the aerobic biomass shifts to anaerobic/facultative metabolism. (2) Temperature — controls the microbial reaction rate; digestion slows sharply in cold weather and can proceed faster (but with more oxygen demand) at elevated temperature. (3) Solids retention time (SRT) — the sludge must be retained long enough for volatile-solids destruction to reach the target reduction, typically 15–20 days at mesophilic temperature. (4) pH — aerobic digestion performs best near neutral pH; excessive acid production or ammonia release can shift pH outside the favourable range. (5) Volatile-solids (organic) loading rate — an overloaded digester cannot supply enough oxygen per unit of substrate, causing incomplete stabilization and odour.
