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Water and wastewater process calculator
Eight exam-scoped calculators for the numbers operators run every shift, and the exact ones the certification exam tests. Enter your plant values and get the worked result. Every formula is the public physics behind the operator-math trainer, so you can solve a trainer problem by hand and then verify it here.
What can this calculator do?
It computes the pounds formula (chemical feed), chlorine dose from demand and residual, detention time, flow conversions between MGD, GPM, and cubic feet per second, clarifier surface loading, and the activated-sludge process-control set: the food-to-microorganism ratio, the sludge volume index, and sludge age. It is discipline-aware and exam-scoped, not a generic single-purpose widget.
Pounds formula (chemical feed)
lb/day = flow (MGD) x dose (mg/L) x 8.34
Chlorine dose and feed
dose = demand + residual; feed lb/day = MGD x dose x 8.34
Detention time
hours = (volume gal x 24) / flow (gal/day)
Flow conversion
1 MGD = 694.4 GPM = 1.547 cfs
Clarifier surface loading
gpd/sq ft = flow (gpd) / (pi x radius^2)
F:M ratio
F:M = lb BOD/day / lb MLVSS
Sludge volume index (SVI)
SVI = (settled mL/L x 1000) / MLSS (mg/L)
Sludge age
days = lb MLSS in system / lb SS leaving per day
How to use it to study
Work a problem from the operator-math trainer by hand first, then enter the same numbers here to check your result. The point of the certification math is not the calculator, which you may not have on exam day, but knowing the formula and carrying the units and the decimal yourself. This tool is the answer key, not the crutch.
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