16-Civ-A3 Elementary Environmental Engineering · December 2017
Question 5 of 7: Environmental Principles in Water and Wastewater Treatment
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Notes on this paper
Paper format. National Exams, December 2017 — 16-Civ-A3 Elementary Environmental Engineering. Three hours; closed book with one candidate-prepared 8½ × 11 double-sided aid sheet; approved Casio or Sharp calculator only. Seven problems are printed, each worth 20 marks, and any five constitute a complete paper (maximum 100 marks). All seven are solved here, because the set is intended as a study resource rather than an exam script. Section marks are shown in brackets at the left margin of each question and are reproduced from the final-page Marking Scheme.
Reference texts.
Davis, M.L. & Cornwell, D.A., Introduction to Environmental Engineering, 5th ed., McGraw-Hill — material and energy balances, reactor kinetics, hardness, disinfection, water and wastewater unit processes.
Masters, G.M. & Ela, W.P., Introduction to Environmental Engineering and Science, 3rd ed., Pearson — mass/energy balances on power plants, air-emission estimation, growth–pollution linkages.
Fogler, H.S., Elements of Chemical Reaction Engineering, 5th ed., Prentice Hall — CSTR design and gas-phase stoichiometry with change in total moles.
Canadian context. Answers use the Canadian regulatory frame: the Guidelines for Canadian Drinking Water Quality (GCDWQ) and Canadian Environmental Quality Guidelines (CCME), provincial water and wastewater regulations, the federal Impact Assessment Act / BC Environmental Assessment Act, and the Engineers Canada / EGBC code of ethics whose canons appear in Problem 2(iii).
Question 5: Environmental Principles in Water and Wastewater Treatment (20 marks)
Part (i) — Meeting a doubling demand from a fixed supply (10 marks)
The arithmetic frames the problem: doubling the population while the supply can already only serve half the future population means the system must deliver twice the future service from the same raw water — in effect the per-capita demand must be roughly halved (a factor-of-two gap). No single measure closes that gap, so a combination of demand reduction and supply extension is required.
Technical strategies (engineered):
System-wide leak detection and pressure management. Non-revenue water in older distribution systems is commonly 15–30%; district metering, acoustic leak surveys and pressure control recover a large volume of already-treated water at low cost, directly stretching supply.
Water reuse and demand-offset supply. Reclaim highly treated wastewater for non-potable uses (irrigation, industrial cooling, toilet flushing) or add supply through aquifer storage and recovery / stormwater harvesting, so that potable water is reserved for uses that require it.
Non-technical strategies (policy and behavioural):
Conservation-oriented pricing and metering. Universal metering with an increasing-block tariff gives every household a financial signal to conserve; this alone typically cuts demand 10–20% without lowering living standards.
Efficiency by-laws and public education. Mandate low-flow fixtures and efficient appliances in the building code, restrict discretionary use (lawn watering) in dry periods, and run sustained public-education campaigns so conservation becomes routine.
Together, recovering lost water and cutting per-capita demand through pricing, fixtures and reuse can realistically halve the effective demand, allowing the fixed supply to serve the doubled population while maintaining service levels.
Part (ii) — Tertiary N and P removal schematic (10 marks)
A tertiary plant designed to remove both nitrogen and phosphorus adds three main processes downstream of conventional secondary treatment, as shown.
Tertiary wastewater treatment for nutrient removal: (1) biological nitrification–denitrification for nitrogen, (2) chemical phosphorus precipitation or enhanced biological phosphorus removal (EBPR), and (3) tertiary filtration and disinfection before reuse or discharge.
The three main processes are: (1) biological nitrogen removal by nitrification–denitrification — aerobic bacteria oxidise ammonia to nitrate (nitrification), then anoxic bacteria reduce nitrate to nitrogen gas using influent carbon (denitrification), removing total nitrogen; (2) phosphorus removal — either chemical precipitation by dosing alum or ferric salts to form settleable metal phosphates, or enhanced biological phosphorus removal in which an anaerobic zone selects for organisms that take up phosphorus in excess; and (3) tertiary filtration and disinfection — granular-media or membrane filtration polishes residual suspended solids and particulate phosphorus, followed by UV or chemical disinfection to meet discharge or reuse standards.
Two non-technical principles for lifetime compliance:
Operator training, certification and asset management. Nutrient-removal biology is sensitive; certified operators, documented standard operating procedures and a funded asset-management/renewal plan keep the process in compliance as equipment ages and staff change over the facility's life.
Monitoring, reporting and adaptive governance. A transparent monitoring program with regulatory reporting, adequate operating budget, and a management commitment to act on exceedances (rather than treating the permit limit as optional) sustains compliance decade after decade.
