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Monash University
CIV5178 · Advanced Water Treatment

Wastewater Treatment
Plant Design

A full conceptual design for a new secondary treatment plant serving Melton — from flow projections through screening, clarification, disinfection, and sludge handling.

Type
Group Project (4)
Date
May 2025
Lecturer
Prof. Brandon Winfrey
Client (Brief)
Melton City Council
Group project, 4 members. Per the team's final presentation credits, my role covered: introduction and problem framing, all preliminary treatment calculations, all primary treatment calculations, river discharge/dilution analysis, and production of the presentation deck and report formatting/diagrams.

The brief

Melton City Council's Engineering Department needed a conceptual design response for a new secondary wastewater treatment plant. The scope ran the full treatment train — flow and load projections, preliminary screening, primary and secondary treatment, disinfection, and sludge handling — sized for a catchment of 340,000 population equivalent, growing at 1.3% annually over a 25-year design horizon.

340K
Population equivalent
25yr
Design horizon
404.24
ML/day at horizon

Flow and load projections

Present peak flow was calculated at 292.69 ML/day, rising to 404.24 ML/day at the 25-year horizon. Present and future biological pollutant loads were calculated using the Metcalf & Eddy (2014) methodology — the standard reference text for wastewater engineering.

Preliminary treatment — screening

Designed a manually operated secondary coarse screen chamber: 5 screens at 1.2 m each (6 m total width), 10 mm bar spacing, set at a 30° incline. The design was verified against approach velocity (0.3–1.0 m/s), screen velocity, head loss via Bernoulli's equation, and a 50% blockage criterion — the standard check for what happens to hydraulic performance when a screen partially clogs.

Preliminary treatment screen chamber sizing calculations
Preliminary treatment design — coarse screen chamber sizing.

Primary treatment — clarification

4 circular clarifiers, 35.8 m diameter × 5 m depth, 2.1 hour detention time — achieving 35% BOD5 and 50% TSS removal. Weir loading rate came out at 236.6 m³/m/day, comfortably within the acceptable 125–500 range. V-notch weirs and central feed wells were specified for redundancy.

Primary treatment circular clarifier specification
Primary treatment design — circular clarifier specification.

Site selection

Located near Exford Road, adjacent to the Werribee River — chosen for the gravity flow advantage (lower pumping cost over the plant's life) and separation from residential zones.

Site selection map near Exford Road, City of Melton
Site selection — Exford Road catchment, City of Melton.

Disinfection and environmental outcome

Disinfection uses sodium hypochlorite chlorination in an 8,424 m³ contact tank, targeting 0.5–1.0 mg/L residual chlorine over a 30-minute contact time. The design meets EPA Victoria discharge standards (BOD5 ≤ 20 mg/L), with dissolved oxygen recovery modelled at 10.13 km downstream. Sludge production was quantified at 1,664.84 m³/day for downstream thickening and digestion.

Conceptual layout of the proposed WWTP process train
Conceptual layout of the proposed WWTP process train.

Tools & standards