Chemical dosing and feed rates
chemical feed rateppm dosingslug dose8.34 formulaproduct strengthlb per day
Feed rate, dose from mass added, slug dose and product strength — converting between ppm, pounds per day and gallons of product.
Chemical Feed Rate (lb/day = mg/L × MGD × 8.34)
Converts a target chemical dose and a plant flow into a mass feed rate, the classic pounds-per-day formula built on water weighing 8.34 lb per gallon.
Chemical Feed Rate from Dose
Chemical feed rate in pounds per day from a ppm dose and a water flow, using the trade density of 8.34 lb per US gallon.
Dose Achieved from Chemical Added
Concentration reached in a system of known volume after adding a measured mass of chemical, at 8.34 lb of water per US gallon.
Product Dose from Active Strength
Converts a required active-ingredient dose into the as-supplied product dose when the drum is only a given percent active.
Pounds of Active Chemical in a Tank
Gives the mass of active chemical held in a storage tank from its volume, the solution's specific gravity and the percent active ingredient.
Closed Loop Slug Dose Volume
Volume of liquid product needed for a one-shot slug dose to hit a target ppm in a closed loop of known volume and product density.
System Volume from Turnover Time
System water volume estimated from the recirculation rate and the measured turnover time — the field method when no drawings exist.
How they fit together
Every one of these is the pounds equation in disguise: lb/day = mg/L × MGD × 8.34, where 8.34 is simply the weight of a US gallon of water in pounds. Turn it around and a known weight of chemical in a known volume gives the dose achieved. A slug dose is the same arithmetic against a system volume rather than a flow, which is how closed loops are treated — you are filling a fixed inventory, not feeding a stream.
Choose by whether the system flows through or recirculates. Continuous flow — potable, wastewater, tower makeup — takes the feed rate form. A closed loop or a batch tank takes the slug form, and its hardest input is the system volume, which is almost never on the drawings; a tracer turnover measurement beats a guess every time. The error that ruins the calculation is forgetting product strength. Twelve and a half percent sodium hypochlorite is 12.5% available chlorine by weight and heavier than water, so a gallon does not deliver 8.34 lb of anything — you need the active pounds, not the product pounds, and mixing the two up is an eightfold error on a 12.5% product. Hypochlorite also degrades in storage, losing meaningful strength in weeks when warm, so dose against a recent titration rather than the label.