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.
Four chemical unit processes commonly used in wastewater treatment are: (1) chemical precipitation — dosing metal salts (alum, ferric chloride) or lime to precipitate dissolved phosphorus as insoluble Al/Fe/Ca phosphates, applied for tertiary or chemically-enhanced primary phosphorus removal (directly relevant to Q3 and Q5 of this paper); (2) coagulation–flocculation — destabilizing colloidal solids with a coagulant, then gently mixing to build settleable flocs, applied ahead of primary/secondary clarification to boost TSS and BOD₅ capture; (3) disinfection (chemical oxidation) — dosing chlorine, chlorine dioxide or ozone to inactivate pathogenic organisms before discharge or reuse; and (4) neutralization — adjusting pH with acid or base (e.g. lime, sulphuric acid) to bring an industrial or process wastewater within the range required for downstream biological treatment or safe discharge. Ion exchange (softening, ammonia removal) and chemical oxidation for odour/colour control are additional processes sometimes credited.
