Chemical Dose Feed Rate Calculator

The Chemical Dose and Feed Rate Calculator connects three things that have to agree at a treatment plant: the flow being treated, the dose of active chemical you want in it, and the rate at which a real product has to be fed to deliver that dose.

It runs in two directions. Required feed from target dose takes a flow and a dose and reports the product feed rate needed. Achieved dose from actual feed takes the rate your feeder is genuinely running at and reports the dose it is actually delivering - which is the number worth checking after a calibration.

Both directions handle a dry product corrected by its active purity, or a liquid solution corrected by its active concentration, where that concentration can be entered directly or derived from a weight percent and a specific gravity. It reports the active chemical mass rate, the product feed rate in the appropriate form, the applied dose, and optionally how much of a calibrated feeder capacity you are using.

It works in US customary units - MGD, pounds per day, gallons per day - or in metric, using megalitres per day, kilograms per day and litres per day.

Purpose and model boundary

This calculator converts between active-chemical dose and product feed rate for a dry product or liquid solution. It can solve the product rate required for a target dose or calculate the achieved dose from an entered feeder rate, and it can compare the selected rate with a user-entered calibrated capacity.

The calculation is a dimensional mass balance. It does not select a chemical, prescribe a dose, provide a product formulation, or convert a theoretical feed rate into a pump speed or feeder setting.

Inputs and units

• Calculation mode selects required feed from target dose or achieved dose from actual feed.
• Unit system selects US customary or metric values. US flow is MGD, dry rate is lb/day, and liquid rate is US gal/day; metric flow is ML/day, dry rate is kg/day, and liquid rate is L/day.
• Plant flow, Q, and active dose, D, use the same operating period; dose is always mg/L.
• A dry product uses active purity, p, entered as percent by mass.
• A liquid solution uses either active mass per solution volume or weight percent, w, with specific gravity, SG.
• Optional dry-feeder or liquid-pump capacity must be a positive calibrated rate in the selected product and unit basis.

The workbook uses 1 US gal = 3.785411784 L and 1 lb = 0.45359237 kg exactly. Those identities, rather than a rounded operator factor, drive US conversions.

Governing relationships

The workbook first normalizes flow to litres per day:

• US: Q_L/day = Q_MGD x 1,000,000 x 3.785411784;
• metric: Q_L/day = Q_ML/day x 1,000,000.

For a liquid solution, active concentration in kg/L is either

• direct US entry: c = (lb active/US gal) x 0.45359237 / 3.785411784;
• direct metric entry: c = (g active/L) / 1000;
• weight-percent basis: c = (w / 100) x SG x 1 kg/L.

In required-feed mode, active mass is

m_active = Q_L/day x D_mg/L / 1,000,000.

In achieved-dose mode it is

• dry: m_active = dry product kg/day x p/100;
• liquid: m_active = solution L/day x c.

Product rate and dose then follow:

• dry product: m_product = m_active / (p/100);
• liquid solution: V_solution = m_active / c;
• applied dose: D = m_active x 1,000,000 / Q_L/day;
• capacity utilization: u = selected product rate / selected capacity.

Calculation sequence

1. Resolve calculation mode, unit system, product form, liquid-strength basis, and capacity option.
2. Validate only the fields active for those choices; hidden branch inputs are ignored.
3. Normalize flow, product strength, and actual feed to litre/kilogram base units.
4. Calculate active mass, product rate, applied dose, and optional capacity utilization.
5. Convert outputs back to the selected display units.
6. Build the dose-to-product-feed chart from zero through twice the current applied dose (with a minimum chart span of 1 mg/L) and evaluate status.

Outputs and interpretation

Applied dose and active-chemical mass rate are available for both product forms. Dry-product or liquid-solution feed and liquid active concentration appear only when relevant. Calculation interpretation states whether the result is a required rate or an achieved dose. Capacity assessment is not requested, within capacity, at capacity, exceeds capacity, or unavailable.

The reported product rate is theoretical. Calibration, turndown, product condition, and equipment controls determine an actual setting.

Validation and status logic

The workbook evaluates status in this order:

The zero-feed warning precedes capacity warnings. The two 1e-12 capacity tolerances prevent binary rounding alone from changing an at-capacity classification.

Assumptions and limitations

Flow, dose, and feed must share a time basis. Product purity, weight percent, specific gravity, and direct concentration are user-supplied and are assumed representative of the current product, temperature, batch, and aging condition. The weight-percent branch uses the standard 1 kg/L reference-water density relation.

No chemical demand, decay, mixing, reaction efficiency, residual, safety factor, carrier dilution, pump curve, feeder calibration, minimum turndown, redundancy, alarm, chemical compatibility, storage, or regulatory dose limit is modeled. No chemical or vendor database is embedded.

Restrictions and non-computing states

Flow must be positive. Target dose and actual rates may be zero but cannot be negative. Active dry purity and solution weight percent must be greater than zero and no greater than 100. Active concentration and specific gravity must be positive on their active branches. A requested capacity must be positive and use the same product/unit basis as the rate being compared.

The workbook deliberately returns NOT VALID and zero or blank results if otherwise finite inputs overflow derived arithmetic or the authored chart range.

Errors and warnings

This calculator's input rules may reject a value outside its declared range or an unknown dropdown choice before calculation. Workbook NOT VALID is a model refusal for an active submitted state; CHECK is a computed result needing review. A network or calculation-service error is a connection failure and must not be interpreted as a process warning or zero feed.

The workbook implements dose, purity, solution-strength and feeder-capacity relations directly, together with the exact dimensional conversions behind the US mass factor. No product database, vendor formulation table or figure from any publication is reproduced.

• U.S. Environmental Protection Agency. LT1ESWTR Turbidity Provisions Technical Guidance Manual, Appendix C, for the chemical feed, dose, solution-strength, specific-gravity, feeder-rate and percent-capacity relations and the liquid-alum example replayed above. https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=30005ZHV.TXT
• Tennessee Department of Environment and Conservation. Operator Certification Water Treatment Formulas and Conversions, an independent state confirmation of the dose, purity, liquid-concentration and feeder-capacity relations. https://www.tn.gov/content/dam/tn/environment/water/ftc/references/formula-conversions/ftc_op-cert-formula-manual_wt_rev1.pdf
• Pennsylvania Department of Environmental Protection. Drinking Water Operator Training: Corrosion Control and Sequestering, for product-purity and active-ingredient worked examples and the requirement to calibrate feed equipment rather than treat a theoretical capacity as a setting. https://www.pa.gov/content/dam/copapwp-pagov/en/dep/documents/business/water/bureausafedrinkingwater/operatorcertification/training/documents/dw-20_corrosion_control_and_sequestering_wb.pdf
• National Institute of Standards and Technology. Handbook 133, Appendix E: General Tables of Units of Measurement, which fixes the US gallon at exactly 3.785411784 litres and the international pound at exactly 0.45359237 kilograms. https://www.nist.gov/document/14-app-e-14-hb133-finalpdf

Product purity, specific gravity and active concentration must come from the supplier's data sheet for the chemical you are actually feeding. None is shipped here.