Diseases Transmitted by Water: 18-Env-B9 Environmental Chemistry and Microbiology, May 2016, Q13

Question 13 of 20: Diseases Transmitted by Water

Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)

Notes on this paper

National Exams — May 2016 — 04-Env-B9, Environmental Chemistry/Microbiology. 3 hours duration; closed-book exam (one 8.5×11" aid sheet, both sides, permitted; any non-communicating calculator permitted). The paper has two sections — Section 1: Chemistry (8 questions, 50 marks) and Section 2: Microbiology (12 questions, 50 marks) — twenty 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, BOD/SRT/F–M); Guidelines for Canadian Drinking Water Quality (Health Canada); MWH's Water Treatment: Principles and Design (3rd ed.) (advanced treatment, UV disinfection, potable reuse).

Section 1: Chemistry (8 questions, 50 marks)

Question 13: Diseases Transmitted by Water (3 marks)

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.

Cholera (bacterium Vibrio cholerae) — acute, severe watery diarrhea and dehydration from ingesting faecally-contaminated water; historically the disease that drove modern sanitary engineering (Broad Street pump, London, 1854).

Typhoid fever (bacterium Salmonella typhi) — a systemic infection (sustained fever, intestinal ulceration) transmitted via water or food contaminated with human faecal matter carrying the organism.

Giardiasis (protozoan Giardia lamblia) — intestinal illness (cramping, diarrhea) from ingesting water containing Giardia cysts, which are highly resistant to standard chlorine disinfection and are a principal driver of filtration requirements in Canadian drinking-water treatment.

Concept & Theory

Topic. Waterborne disease and the faecal–oral transmission route.

Key relations. Infective dose, indicator-organism monitoring (total/faecal coliform, E. coli) as a surrogate for pathogen presence.

Why this works. All three organisms are shed in the faeces of an infected host and survive transmission through water long enough to infect a new host on ingestion, which is exactly the exposure pathway drinking-water treatment (filtration + disinfection) is designed to interrupt.

Common pitfall. Assuming chlorination alone is sufficient protection — Giardia (and Cryptosporidium) cysts/oocysts are highly chlorine-resistant and require physical removal (filtration) as the primary barrier.

Source. Davis & Cornwell, Introduction to Environmental Engineering, ch. 3; Guidelines for Canadian Drinking Water Quality.