18-Env-B5 Industrial & Hazardous Waste Management · December 2014
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; provincial Environmental Protection / Hazardous Waste Regulations (e.g. BC's Hazardous Waste Regulation, O.Reg. 347 in Ontario); Montgomery & Runger, Applied Statistics and Probability for Engineers (for Q1–Q5's basic-statistics content).
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.
(i) Inorganic dissolved solids (dissolved salts, hardness, heavy metals) are generally not removable by biological treatment, so removal relies on physical-chemical processes: chemical precipitation (as hydroxides, carbonates or sulphides, for metals and hardness), ion exchange (for selective cation/anion removal, e.g. softening or specific metal recovery), and membrane processes (reverse osmosis, nanofiltration) or evaporation/crystallization for bulk total-dissolved-solids reduction where a very low residual is required. Selection depends heavily on concentration and the specific ionic species — precipitation is economical at higher concentrations of a target metal, while membrane processes are typically reserved for bulk desalination or where multiple dissolved species must be removed together.
(ii) Organic dissolved solids (dissolved BOD/COD-contributing organics) are, by contrast, generally biodegradable and are most economically removed by biological treatment (aerobic or anaerobic, matched to strength as in Question 11); non-biodegradable or refractory organics (e.g. certain synthetic compounds, colour bodies) instead require activated-carbon adsorption, chemical/advanced oxidation (ozone, UV/H2O2), or air stripping (for volatile organics) as physical-chemical polishing steps, either as an alternative to biological treatment or downstream of it to remove the biologically-resistant fraction. The practical design implication is that a stream analysis reporting only "total dissolved solids" is not enough to select a technology — the same TDS number could be almost entirely inorganic salts (pointing toward precipitation or membranes) or almost entirely dissolved organics (pointing toward biological treatment or carbon adsorption), and the correct technology choice depends on which it actually is. A fixed-vs-volatile-solids split on the TDS analysis is a quick, inexpensive screen for this distinction before committing to a more detailed characterization or a treatability study.
