16-Civ-A3 Elementary Environmental Engineering · May 2017
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Paper format. National Exams, May 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 below.
Reference texts.
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.
Technical strategy 1 — uprate the existing filters. Before building new units, recover hidden capacity in the existing plant: convert conventional rapid sand filters to dual- or tri-media (anthracite/sand/garnet) beds, which allow higher filtration rates at the same head loss, and optimise coagulation (jar-tested coagulant dose, add polymer) so the sedimentation basins carry more solids. Debottlenecking existing basins and adding declining-rate or continuous backwash controls can lift throughput 25–50% at a small fraction of new-plant cost.
Technical strategy 2 — modular, staged expansion. Add capacity in phased increments matched to the 25-year demand curve rather than one oversized build: add a parallel treatment train or package/membrane units as demand grows, and use the existing hydraulic profile. Because a doubling over 25 years is only about 2.8%/yr, staged capital defers most spending and keeps units running near their efficient design point.
Non-technical strategy — demand-side management. The cheapest "new" capacity is the water not used: universal metering with conservation (increasing-block) pricing, an active leak-detection and main-repair program to cut non-revenue water, public conservation education, and efficiency retrofits (low-flow fixtures) can flatten the per-capita demand so a doubled population needs far less than double the plant. This defers or shrinks the required capital expansion outright.
The three main treatment processes of a conventional activated-sludge sewage plant are primary sedimentation (a primary clarifier removing settleable solids), biological aeration (the aeration tank, where the activated-sludge microbial community oxidises dissolved and colloidal organics under supplied air), and secondary clarification (a secondary clarifier separating the biological floc from the treated effluent). Return activated sludge (RAS) is recycled to the aeration tank to maintain the microbial population, and waste activated sludge (WAS) is removed to control sludge age; the clarified effluent is disinfected before discharge.
Non-technical principle 1 — a trained, certified operating staff and preventive-maintenance culture. Biological treatment depends on daily operator judgement (sludge age, RAS/WAS rates, dissolved oxygen). Ensuring provincially certified operators, documented standard operating procedures, and a funded preventive-maintenance program (not run-to-failure) keeps the process stable and equipment serviceable across the 30-year life.
Non-technical principle 2 — asset management and lifecycle funding. A formal asset-management plan — condition assessment, a reserve fund for renewal, and rate-setting that recovers full lifecycle cost — ensures that pumps, blowers and clarifier mechanisms are renewed on schedule rather than deferred, and that regulatory monitoring and reporting are sustained. Good governance and community support (transparent reporting, adequate budgets) underpin reliable long-term operation as much as the hardware does.
