18-Env-B5 Industrial & Hazardous Waste Management · December 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.
Grab samples are taken as a single, discrete sample at one point in time, and are appropriate when: (1) the waste characteristics vary rapidly or unpredictably (batch discharges, slug loads) and an instantaneous value matters more than an average; (2) the parameter itself is unstable and would change during compositing or holding — pH, temperature, dissolved oxygen, residual chlorine, cyanide, sulphide and volatile organics are all classically grab-sampled; (3) a regulatory permit specifies a grab-sample limit for a given parameter; or (4) the discharge itself is intermittent/short-duration, so there is no continuous flow to composite over.
Composite samples (time-proportional or, preferably for variable flow, flow-proportional) combine multiple sub-samples collected over a period (commonly 24 hours) into one representative sample, and are appropriate when: (1) the flow is relatively continuous and the objective is an average characteristic over the period (e.g. mass loading for BOD5/TSS design or sewer-surcharge billing); (2) the parameter is chemically stable over the compositing period; and (3) the regulatory or design objective is explicitly an average (daily mass load) rather than an instantaneous value.
