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.
Coagulation is considered whenever an industrial wastewater carries fine colloidal or suspended material that will not settle by gravity alone within a practical detention time, because the particles are electrostatically stabilized (typically negatively charged) and repel rather than aggregate. Typical triggers include: a wastewater with significant colour or fine turbidity that gravity settling alone cannot remove (dye-house or pulp-mill effluent); a need to remove dissolved or colloidal metals by hydroxide precipitation ahead of clarification; chemical phosphorus removal, where a coagulant (alum, ferric chloride/sulfate, or lime) precipitates phosphate as an insoluble metal-phosphate floc; treatment of an oily/emulsified wastewater, where coagulation destabilizes the emulsion so oil droplets can coalesce and be removed by flotation or gravity separation; and as a polishing/pretreatment step ahead of filtration or a biological process, where reducing SS and colloidal organic matter improves the performance and protects the media or biomass of the downstream unit. In each case the underlying reason is the same: gravity sedimentation alone is only effective once particles are large enough to settle at a practical rate, and coagulation's role is specifically to convert a stable colloidal suspension into settleable or floatable floc.
