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18-Env-B5 Industrial & Hazardous Waste Management · December 2016

Question 8 of 19: Circumstances for Selecting Chemical Treatment Technology

Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)

Notes on this paper

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 8: Circumstances for Selecting Chemical Treatment Technology (5 marks)

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.

  1. Non-biodegradable/refractory waste — when biological treatment simply cannot break the constituents down, chemical oxidation, precipitation or another chemical route is required instead.
  2. Heavy-metal removal — chemical precipitation (hydroxide or sulphide) is the standard technology to bring dissolved metals (Cr, Ni, Cd, Pb, Zn, Cu) out of solution.
  3. pH adjustment/neutralization — required before discharge, or as a pretreatment step to protect downstream biological treatment from an acidic/alkaline shock.
  4. Presence of toxic or bio-inhibitory compounds — chemical treatment can remove or destroy a compound that would otherwise poison a biological process.
  5. Cyanide destruction or hexavalent-chromium reduction — specific chemical reactions (alkaline chlorination for CN−, sulphite/bisulphite reduction for Cr6+) are needed before conventional treatment can proceed.
  6. Space or retention-time constraints — chemical processes are typically much faster than biological treatment, so they suit sites with limited land/retention time or emergency/intermittent treatment needs.