18-Env-B9 Environmental Chemistry and Microbiology · May 2013
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — May 2013 — 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 (11 questions, 50 marks) and Section 2: Microbiology (14 questions, 50 marks) — twenty-five 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, disinfection, water/wastewater microbiology, indicator organisms); Metcalf & Eddy (Tchobanoglous, Stensel, Tsuchihashi & Burton), Wastewater Engineering: Treatment and Resource Recovery (5th ed.) (chemical unit processes, chemical phosphorus precipitation, biomass stoichiometry, activated-sludge microbiology); Guidelines for Canadian Drinking Water Quality (Health Canada); MWH's Water Treatment: Principles and Design (3rd ed.) (chlorine disinfection, contact-tank sizing).
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.
A microbial indicator organism (the coliform group and E. coli being the classic water-quality example) must satisfy several requirements to be a reliable surrogate for pathogen presence: it must be consistently present whenever faecal contamination (and therefore potential pathogens) is present, and absent from unpolluted water; it must be present in numbers proportional to or correlated with the degree of contamination, so its concentration is a meaningful measure of pollution intensity; it must be non-pathogenic itself, so it can be handled and tested safely; it must have survival and resistance characteristics at least equal to, or greater than, the pathogens of concern (so a negative indicator test reliably implies pathogens are also absent, not merely that the more-fragile indicator died first); and it must be easily, reliably, and inexpensively detected and enumerated using standard, reproducible laboratory methods, distinguishable from non-faecal background organisms.
