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.
The biochemical oxygen demand (BOD) test measures the amount of dissolved oxygen consumed by microorganisms as they biologically stabilize (oxidize) the biodegradable organic matter in a water or wastewater sample over a standard incubation period (typically 5 days at 20 °C, BOD₅). It is used because it directly indicates the oxygen-demanding strength of a waste — and therefore its potential to deplete dissolved oxygen and harm aquatic life if discharged untreated — and because it measures only the biodegradable fraction of organic matter (unlike COD, which oxidizes both biodegradable and non-biodegradable material chemically). BOD is used to size and evaluate biological treatment processes, set discharge permit limits, and track treatment-plant performance (percent BOD removal).
