Water & Wastewater Treatment Workbench

Interactive workspace initializes in your browser. Engineering method, assumptions, validation, and references are available below.

Engineering reference

Water & Wastewater Treatment: theory, method, and sources

This environmental & energy engineering workspace publishes 10 governing equations, 5 stated assumptions, 1 documented boundary, and 2 sources so the numbers it returns can be checked rather than taken on trust.

Calculations run locallyCalculation & source methodology

How this tool works

Ten modules cover clarifier surface overflow rate, detention time, BOD removal kinetics, chlorine dosing and CT disinfection credit, activated sludge food-to-microorganism ratio, solids retention time, oxygen demand, sludge production, and filter loading.

The activated sludge modules use the same MLSS and flow basis, so F/M ratio, SRT, aeration demand, and sludge yield can be evaluated as one consistent process design.

Calculators and topics covered

water
wastewater
treatment
disinfection
clarifier
BOD
activated sludge
SRT
chlorine CT
filter loading

Core equations

\text{surface overflow rate:}\quad SOR = \frac{Q}{A}

\text{detention time:}\quad t = \frac{V}{Q}

\text{first-order BOD removal:}\quad C = C_{0} e^{- kt}

\text{chlorine dose:}\quad \begin{gathered}\text{dose} = \text{demand} + \text{target}\; \text{residual}\\\text{mass} = \text{dose} \times Q\end{gathered}

\text{CT product:}\quad CT = \text{residual} \times \text{contact}\; \text{time},\; \text{compared}\; \text{with}\; the\; \text{target}\; CT

\text{food-to-microorganism ratio:}\quad \frac{F}{M} = \frac{Q \cdot \mathrm{BOD}}{V \cdot MLSS}

\text{solids retention time:}\quad \mathrm{SRT} = \frac{V \cdot MLSS}{Q_{w}\; X_{w} + Q_{e}\; X_{e}}

\text{oxygen demand:}\quad O_{2} = Q \left(\mathrm{BOD}_{in} - \mathrm{BOD}_{\mathrm{out}}\right) \cdot \text{factor}

\text{sludge production:}\quad P_{x} = \frac{Y \cdot Q \left(\mathrm{BOD}_{in} - \mathrm{BOD}_{\mathrm{out}}\right)}{1 + k_{d} \cdot \mathrm{SRT}}

\text{filter loading rate:}\quad v = \frac{Q}{A \cdot run\; \mathrm{hours}}

Method and assumptions

Assumptions

Reactors are treated as completely mixed and at steady state; diurnal and storm flow variation is not modelled.
BOD removal follows first-order kinetics with a single rate constant at the stated temperature.
CT values must be compared against the correct pathogen, temperature, and pH table from the governing regulation.
Activated sludge relationships assume a conventional process without nutrient removal or selector zones.
Yield and decay coefficients are typical literature values and vary with wastewater strength and temperature.

Limitations and design boundaries

Educational screening calculations only. Treatment design and operation require representative testing, current regulations, redundancy, process controls, safety analysis, and qualified professional review.

Sources and references

Primary sources are preferred for ratings, standards, manufacturer data, and externally defined constants.

Source policy

Metcalf & Eddy, Wastewater Engineering: Treatment and Resource Recovery
AWWA and ASCE, Water Treatment Plant Design