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.
Four standard laboratory procedures, each measuring organic content on a different basis, are used to characterize industrial wastewater. Biochemical Oxygen Demand (BOD5) measures the oxygen consumed by microorganisms as they biodegrade the organic matter present over a standardized 5-day incubation at 20°C — it estimates the readily biodegradable fraction and is the most directly relevant measure for sizing biological treatment. Chemical Oxygen Demand (COD) measures the oxygen equivalent of essentially all oxidizable material (biodegradable and non-biodegradable) by strong chemical oxidation with dichromate under acidic reflux — it is faster to run (hours vs. days) and captures compounds BOD5 misses, so the COD/BOD5 ratio is itself a useful indicator of biodegradability. Total Organic Carbon (TOC) measures the mass of organic carbon directly, by catalytic combustion (or UV/persulfate oxidation) of the sample followed by infrared detection of the CO2 produced — it is independent of the oxidation state of the carbon and gives a rapid, precise carbon-mass basis useful for regulatory reporting and for cross-checking COD results. Total Oxygen Demand (TOD) measures the oxygen consumed when a sample is completely combusted catalytically at high temperature, converting essentially all organic C, H, N and S to their fully oxidized forms — it is the most complete (and most instrument-intensive) oxygen-demand measure and correlates closely with COD for most industrial wastewaters.
