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.
1.1 RNA (ribonucleic acid). A single-stranded nucleic acid, built of ribose-sugar nucleotides (A, U, G, C), that translates the genetic code carried by DNA into proteins (messenger, transfer, and ribosomal RNA), and is itself the genome of many viruses.
1.2 Infection. The invasion and multiplication of a pathogenic organism within a host's tissues, which may or may not produce clinical disease depending on the host's immune response and the pathogen's virulence.
1.3 Toxin. A poisonous substance produced by a living organism (bacterial exotoxins secreted by the cell, or endotoxins released from the cell wall — see 1.8) that damages host tissue or disrupts normal physiological function.
1.4 Pathogen. Any microorganism (bacterium, virus, protozoan, helminth) capable of causing disease in a susceptible host.
1.5 Virulence. The degree or intensity of pathogenicity of an organism — its relative capacity to cause disease, often measured as the infective dose required to produce illness in a defined fraction of exposed hosts (e.g. $\text{ID}_{50}$).
1.6 Saprophytes. Organisms that obtain nutrients from dead or decaying organic matter rather than from a living host; the dominant nutritional mode of most environmental/wastewater bacteria responsible for organic-matter stabilization.
1.7 Obligate parasites. Organisms (notably all viruses) that can grow and reproduce only inside a living host cell and cannot be cultured on inert media.
1.8 Endotoxins. Lipopolysaccharide components of the outer membrane of Gram-negative bacterial cell walls, released only when the cell dies/lyses, that can trigger fever and inflammatory response in the host.
1.9 Thermophilic. Describing organisms whose optimum growth temperature is high, roughly 45–70°C (e.g. thermophilic anaerobic digestion), as distinct from mesophilic (see Q4) or psychrophilic organisms.
1.10 Metabolism. The sum of all biochemical reactions occurring within a living cell, comprising catabolism (breakdown of substrate for energy) and anabolism (synthesis of new cell material), which together drive growth and reproduction.
