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.
Indicator organisms are non-pathogenic (or minimally pathogenic) microorganisms — most commonly total coliforms, faecal coliforms, and E. coli — whose presence in a water sample signals the likely presence of faecal contamination and therefore the possible presence of the actual (harder-to-test-for) pathogens that accompany faecal matter. Their role in sanitary microbiology is practical rather than diagnostic: testing directly for every possible pathogen (bacterial, viral, protozoan) in every sample is impractical and expensive, so a single, easily-cultured, faecally-associated organism present in high numbers in healthy human/animal gut flora is used as a proxy for overall faecal/sanitary risk. A good indicator organism should be present whenever pathogens are present, absent when they are not, survive in the environment at least as long as the pathogens of concern, and be easy and inexpensive to enumerate (e.g. by MPN, Question 9).
