16-Civ-A3 Elementary Environmental Engineering · Undated paper
Question 5 of 7: Water- & Wastewater-Treatment Plant Configurations
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Notes on this paper
Paper format. National Exams, May 2019 — 16-Civ-A3 Elementary Environmental Engineering. Closed book (one 8.5″×11″ double-sided aid-sheet), 3 hours. Seven problems; any five constitute a complete paper (each 20 marks). All seven are solved here as a study resource.
Reference texts. Davis & Cornwell, Introduction to Environmental Engineering (5th ed.); Mihelcic & Zimmerman, Environmental Engineering: Fundamentals, Sustainability, Design (3rd ed.); Metcalf & Eddy, Wastewater Engineering: Treatment and Resource Recovery (5th ed.); MWH (Crittenden et al.), Water Treatment: Principles and Design (3rd ed.); CCME Canadian Environmental Quality Guidelines; Health Canada Guidelines for Canadian Drinking Water Quality; Impact Assessment Act (Canada, 2019).
Source note. The seven questions and their sub-part mark splits follow the paper’s own Marking Scheme (page 7): 1 (6/6/8), 2 (7/7/6), 3 (8/5/7), 4 (6/7/7), 5 (10/10), 6 (3/3/4 + 3/3/4), 7 (10/10) — each closing to 20 marks. Where a figure ordinate must be read off a plot it is flagged in a check callout.
5(i) — Potable-water treatment train. A conventional surface-water plant removes the listed contaminants in sequence — screening (floatables), coagulation/flocculation/sedimentation (colloids & particulates), filtration (residual particles & pathogens), and disinfection with a clearwell for contact and residual (pathogens; dissolved organics partly via oxidation/adsorption):
Conventional potable-water treatment plant (raw surface water → distribution).
Key operational / monitoring approach for each main unit:
Screening: inspect and clear screens; monitor head-loss across the screen to confirm floatables/debris removal.
Coagulation: control coagulant dose by jar-test / streaming-current (charge neutralization); monitor coagulated-water pH.
Flocculation: control the velocity gradient (G) and tapered mixing energy to grow settleable floc without shearing it.
Sedimentation: monitor surface overflow rate and settled-water turbidity to confirm clarifier performance.
Filtration: monitor filtered-water turbidity (target <0.1–0.3 NTU) and head-loss to schedule backwash — the primary pathogen (e.g. Cryptosporidium) barrier.
Disinfection + clearwell: maintain the required C·t and monitor residual disinfectant leaving the clearwell to ensure inactivation and a distribution-system residual.
5(ii) — Tertiary WWTP for low-nitrogen effluent (TN < 10 mg/L). A biological-nutrient-removal train achieves nitrogen removal by nitrification (aerobic) followed by/preceded by denitrification (anoxic), with tertiary filtration polishing:
Tertiary WWTP with pre-anoxic/aerobic BNR for nitrogen removal.
Engineering function of three main units:
Anoxic zone (denitrification): heterotrophs use nitrate (recycled from the aerobic zone) as the electron acceptor, reducing NO3− to N2 gas while consuming influent BOD as the carbon source — this is the step that actually removes nitrogen from the water.
Aeration basin (nitrification + BOD oxidation): autotrophic nitrifiers oxidize NH4+ to NO3− and heterotrophs oxidize carbonaceous BOD; a long solids-retention time (SRT) is held so the slow-growing nitrifiers are not washed out.
Secondary clarifier: separates the mixed-liquor biomass from the treated water, returning activated sludge (RAS) to maintain the reactor inventory and wasting the excess (WAS) — without reliable solids separation the effluent quality collapses.
Tertiary filtration then removes residual suspended solids (and particulate nitrogen), and disinfection meets the microbial limit before discharge.
