18-Env-B5 Industrial & Hazardous Waste Management · May 2013
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 Nuclear Safety Commission (CNSC) regulatory framework and NWMO Adaptive Phased Management; Canadian Environmental Protection Act (CEPA), 1999.
All nineteen questions are compulsory on this paper and are answered in full below.
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.
Biological treatment relies on a healthy, active population of heterotrophic and nitrifying microorganisms, and several classes of industrial contaminants are directly toxic or inhibitory to that population even at relatively low concentrations. Heavy metals — copper, zinc, chromium (particularly hexavalent Cr6+), nickel, cadmium and lead — denature microbial enzymes and disrupt cell membrane function; they are cumulative in activated sludge, so a slug discharge can poison a plant for weeks because the metals partition into the biomass rather than washing straight through. Cyanide (from metal-finishing, electroplating or coke-oven wastewaters) is acutely toxic because it binds directly to the iron in cytochrome oxidase, blocking cellular respiration in the same way it poisons higher organisms — even a few mg/L can severely depress oxygen uptake rate in an activated-sludge system. Phenolic and other chlorinated organic compounds (chlorophenols, halogenated solvents such as TCE/PCE, and high concentrations of free ammonia or sulfide) are similarly inhibitory: phenols denature proteins and disrupt cell membranes, while un-ionized ammonia at elevated pH is directly toxic to nitrifiers specifically, often long before it affects the heterotrophic BOD-removing population.
Because biological toxicity is dose- and acclimation-dependent, a wastewater treatment plant receiving industrial contributions of any of these classes normally requires either pretreatment at the source (precipitation of metals, alkaline chlorination or ozonation of cyanide) or a sewer-use bylaw limiting the discharge concentration, rather than relying on dilution and hoping the biology tolerates the slug.
