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.
Sterilization is the complete destruction or removal of all forms of microbial life, including highly resistant bacterial endospores and viruses — a zero-probability-of-survival standard, achieved by methods such as autoclaving (pressurized steam), dry heat, or gamma irradiation, and normally reserved for laboratory media, medical instruments, and similar critical applications. Disinfection, by contrast, is the selective destruction of pathogenic (disease-causing) organisms to a level that renders water/wastewater safe for its intended use, but does not claim to eliminate every organism present — many non-pathogenic and some resistant organisms (spores, certain protozoan cysts at typical chlorine doses) survive. Water and wastewater treatment always targets disinfection, not sterilization: sterilizing an entire municipal supply is neither necessary for public health nor economically practical.
