18-Env-B9 Environmental Chemistry and Microbiology · May 2017
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — May 2017 — 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 (6 questions, 50 marks) and Section 2: Microbiology (12 questions, 50 marks) — eighteen 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, coagulation, sludge chemistry, disinfection); Metcalf & Eddy (Tchobanoglous, Stensel, Tsuchihashi & Burton), Wastewater Engineering: Treatment and Resource Recovery (5th ed.) (chemical phosphorus precipitation, biomass stoichiometry, activated-sludge microbiology, SRT/F:M); Madigan, Martinko, Bender, Buckley & Stahl, Brock Biology of Microorganisms (14th ed.) (bacterial structure, growth kinetics, microbial physiology); Guidelines for Canadian Drinking Water Quality (Health Canada).
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.
Pathogens surviving outside a host (e.g. in water, wastewater, or soil) rely on several strategies: many bacteria and protozoa form resistant cyst or spore stages (e.g. Giardia cysts, Cryptosporidium oocysts, bacterial endospores) with tough protective walls that resist desiccation, disinfectant exposure, and nutrient starvation for extended periods; some organisms enter a dormant, low-metabolism viable-but-non-culturable (VBNC) state that evades standard culture-based detection while retaining the ability to reactivate; association with particulates or biofilms provides physical shielding from disinfectants (reducing effective disinfectant contact and light penetration for UV); and cooler temperatures and organic-rich environments generally slow the die-off rate by reducing the metabolic/enzymatic degradation processes that would otherwise destroy the organism.
