Case 03 · Environmental engineering
Sizing a treatment plant from first principles
An environmental-engineering team needed to turn a manufacturer's effluent specification into a fully sized treatment plant — and be able to defend every number in design review. We built the design system that does it from mass and energy balances, with the governing equation shown behind each figure.
The situation
Estimates are fast. Reviewers want equations.
Sizing a treatment plant means working from the client's effluent characteristics through every stage of the process. Rules of thumb get a number quickly, but they don't survive a design review — and a wrong size is expensive to discover after the order.
What we built
A design computed the way an engineer would check it.
- Mass balances through each stage, from the influent specification to the discharge limit.
- Sludge loads and aeration demand computed from those balances, not estimated.
- Heat and enthalpy duties alongside the biological sizing, so energy and mass are solved together.
- A visible trace: every figure shows the equation and the inputs that produced it.
What was hard
Making it checkable, not just correct.
Every step had to be reviewable. A design reviewer checks the working, not the answer. Showing the governing equation beside each figure mattered more than any screen.
Mass and energy are coupled. Heat and enthalpy duties depend on the same streams as the biological sizing, so they couldn't be bolted on as a separate calculation.
What changed
Design review checks equations, line by line.
- Designs are sized from first principles rather than from the last similar project.
- Changing a client input recomputes the whole design instead of a chain of spreadsheets.
Client name withheld. A reference call can be arranged under NDA.