Chlorine Dosage & Residual Calculator

ANA›Life Services Authority›National Calculator Authority›Chlorine Dosage & Residual Calculator

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Chlorine Dosage & Residual Calculator

Calculate chlorine dosage, chlorine demand, or residual chlorine for water treatment and disinfection applications.

Calculation Mode

Find Residual (Dosage − Demand) Find Dosage (Demand + Residual) Find Demand (Dosage − Residual)

Chlorine Dosage (mg/L)

Chlorine Demand (mg/L)

Chlorine Residual (mg/L)

Optional: Flow-Based Mass Loading

Flow Rate (MGD — Million Gallons per Day)

Calculate

function chlUpdateMode() { var mode = document.getElementById("chl_mode").value; document.getElementById("chl_dosage_group").style.display = (mode === "dosage") ? "none" : "block"; document.getElementById("chl_demand_group").style.display = (mode === "demand") ? "none" : "block"; document.getElementById("chl_residual_group").style.display = (mode === "residual") ? "none" : "block"; }

function chlCalc() { var resultDiv = document.getElementById("chl_result"); var mode = document.getElementById("chl_mode").value;

var dosageVal = document.getElementById("chl_dosage").value.trim(); var demandVal = document.getElementById("chl_demand").value.trim(); var residualVal = document.getElementById("chl_residual").value.trim(); var flowVal = document.getElementById("chl_flow").value.trim();

var dosage = parseFloat(dosageVal); var demand = parseFloat(demandVal); var residual = parseFloat(residualVal); var flow = parseFloat(flowVal);

var errors = [];

if (mode === "residual") { if (dosageVal === "" || isNaN(dosage) || dosage 0) { resultDiv.innerHTML = "⚠ " + errors.join("⚠ ") + ""; resultDiv.style.display = "block"; return; }

var calcValue, label, html;

if (mode === "residual") { calcValue = dosage - demand; label = "Chlorine Residual"; if (calcValue ⚠ Result is negative (" + calcValue.toFixed(3) + " mg/L). Dosage is less than Demand — increase dosage."; resultDiv.style.display = "block"; return; } } else if (mode === "dosage") { calcValue = demand + residual; label = "Chlorine Dosage"; } else { calcValue = dosage - residual; label = "Chlorine Demand"; if (calcValue ⚠ Result is negative (" + calcValue.toFixed(3) + " mg/L). Residual cannot exceed Dosage."; resultDiv.style.display = "block"; return; } }

html = "" + label + ": " + calcValue.toFixed(3) + " mg/L";

// Flow-based mass loading: lbs/day = concentration (mg/L) × flow (MGD) × 8.34 lb·L/(mg·gal) if (!isNaN(flow) && flowVal !== "" && flow > 0) { var lbsPerDay = calcValue * flow * 8.34; html += "Mass Loading: " + lbsPerDay.toFixed(2) + " lbs/day"; html += "(at " + flow + " MGD flow rate)"; }

// Regulatory context if (mode === "residual" || mode === "dosage") { var res = (mode === "residual") ? calcValue : residual; if (res ⚠ Residual below EPA minimum of 0.2 mg/L for distribution systems (40 CFR 141.72)."; } else if (res >= 0.2 && res ℹ Residual meets EPA minimum (≥0.2 mg/L) but below common target of 0.5 mg/L."; } else if (res ✔ Residual within EPA Maximum Residual Disinfectant Level (MRDL) of 4.0 mg/L."; } else { html += "⚠ Residual exceeds EPA MRDL of 4.0 mg/L for chlorine (40 CFR 141.65)."; } }

resultDiv.innerHTML = html; resultDiv.style.display = "block"; }

// Initialize mode display chlUpdateMode();

#### Formulas Used

Chlorine Residual = Dosage − Demand

Chlorine Dosage = Demand + Residual

Chlorine Demand = Dosage − Residual

Mass Loading (lbs/day) = Concentration (mg/L) × Flow (MGD) × 8.34 lb·L/(mg·gal)

All concentration values are in mg/L (ppm).

#### Assumptions & References

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References

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