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.
Mesophilic bacteria — the dominant group in conventional (non-thermophilic) wastewater treatment and most waterborne pathogens — have a characteristic asymmetric growth-rate-versus-temperature curve: growth rate is zero below a minimum temperature ($T_{min}$, roughly 10°C), rises smoothly (and increasingly steeply) with temperature up to an optimum ($T_{opt}$, roughly 37°C, coinciding with the human-body-temperature range that makes mesophiles the medically relevant group), then falls away sharply just past the optimum as rising temperature begins to denature essential enzymes/proteins, reaching zero at a maximum temperature ($T_{max}$, roughly 45°C) only a few degrees above the optimum. The curve is not symmetric: the rise from $T_{min}$ to $T_{opt}$ spans a wide range, while the fall from $T_{opt}$ to $T_{max}$ is compressed into a narrow band.
