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.
Bacteria are the primary workhorses of biological wastewater treatment: heterotrophic bacteria oxidize organic matter (BOD removal) and autotrophic nitrifiers (Nitrosomonas, Nitrobacter) convert ammonia to nitrate in activated sludge and trickling filters. Fungi can degrade complex/recalcitrant organics (including some xenobiotics that bacteria cannot) and thrive at low pH where bacterial activity is suppressed, but excessive fungal growth (filamentous fungi) is a common cause of poor sludge settleability (bulking) in activated sludge. Algae perform photosynthetic oxygenation of receiving waters and waste stabilization ponds (supplying O₂ to the bacteria that, in turn, supply CO₂ to the algae, a symbiotic loop), but excessive nutrient-driven algal growth (eutrophication) depletes dissolved oxygen when the algae die and decompose, and can produce cyanotoxins in drinking-water sources. Viruses are primarily of concern as pathogens requiring removal/inactivation (Question 13) but bacteriophages are also used as indicator/tracer organisms and in some emerging biological control applications.
