18-Env-B9 Environmental Chemistry and Microbiology · May 2013
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — May 2013 — 04-Env-B9, Environmental Chemistry/Microbiology. 3 hours duration; closed-book exam (approved Casio or Sharp calculator only). The paper has two sections — Section 1: Chemistry (11 questions, 50 marks) and Section 2: Microbiology (14 questions, 50 marks) — twenty-five questions constitute the complete exam and all are answered below. Total examination mark 100.
Reference texts. Davis & Cornwell, Introduction to Environmental Engineering (6th ed.) (water chemistry, disinfection, water/wastewater microbiology, indicator organisms); Metcalf & Eddy (Tchobanoglous, Stensel, Tsuchihashi & Burton), Wastewater Engineering: Treatment and Resource Recovery (5th ed.) (chemical unit processes, chemical phosphorus precipitation, biomass stoichiometry, activated-sludge microbiology); Guidelines for Canadian Drinking Water Quality (Health Canada); MWH's Water Treatment: Principles and Design (3rd ed.) (chlorine disinfection, contact-tank sizing).
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.
Reclaiming municipal wastewater to potable-quality water requires multiple, independent treatment barriers in series so that no single process failure can compromise the final water quality (the multi-barrier principle). A representative indirect potable reuse (IPR) train, after conventional secondary (biological) treatment, is: microfiltration/ultrafiltration (removes remaining suspended solids, colloids, bacteria, and protozoan cysts) → reverse osmosis (removes dissolved salts, viruses, pharmaceuticals, and most remaining organics down to near-distilled-water quality, producing a concentrate stream requiring separate disposal) → advanced oxidation (UV combined with hydrogen peroxide, destroying trace organic contaminants and providing an additional disinfection barrier) → an environmental buffer (aquifer recharge or reservoir storage, adding retention time, natural attenuation, and public/regulatory confidence before the water re-enters a conventional supply) → a conventional drinking-water treatment plant (coagulation/flocculation/sedimentation/filtration) → final disinfection (chlorine or chloramine) before distribution.
