Cod Calculator

Theoretical Chemical Oxygen Demand (ThOD) Calculator

function calculateCOD() { var chemicalFormula = document.getElementById("chemicalFormula").value.trim(); var compoundConcentration = parseFloat(document.getElementById("compoundConcentration").value); var resultDiv = document.getElementById("codResult"); if (isNaN(compoundConcentration) || compoundConcentration < 0) { resultDiv.innerHTML = "Please enter a valid positive concentration."; return; } if (chemicalFormula === "") { resultDiv.innerHTML = "Please enter a chemical formula."; return; } // Parse chemical formula for C, H, O, N counts var a = 0, b = 0, c = 0, d = 0; // a=C, b=H, c=O, d=N try { var formulaUpper = chemicalFormula.toUpperCase(); var matchC = formulaUpper.match(/C(\d*)/); if (matchC) a = matchC[1] === "" ? 1 : parseInt(matchC[1]); var matchH = formulaUpper.match(/H(\d*)/); if (matchH) b = matchH[1] === "" ? 1 : parseInt(matchH[1]); var matchO = formulaUpper.match(/O(\d*)/); if (matchO) c = matchO[1] === "" ? 1 : parseInt(matchO[1]); var matchN = formulaUpper.match(/N(\d*)/); if (matchN) d = matchN[1] === "" ? 1 : parseInt(matchN[1]); if (isNaN(a) || isNaN(b) || isNaN(c) || isNaN(d)) { throw new Error("Invalid number in formula."); } } catch (e) { resultDiv.innerHTML = "Error parsing chemical formula. Please ensure it's in the format like C6H12O6."; return; } if (a === 0 && b === 0 && c === 0 && d === 0) { resultDiv.innerHTML = "No C, H, O, or N found in the chemical formula. Please enter a valid organic compound."; return; } // Atomic weights var AW_C = 12.01; var AW_H = 1.008; var AW_O = 16.00; var AW_N = 14.01; var MW_O2 = 32.00; // Calculate Molecular Weight of the compound var compoundMW = (a * AW_C) + (b * AW_H) + (c * AW_O) + (d * AW_N); if (compoundMW a CO2 + (b/2 – 3d/2) H2O + d/2 N2 var molesO2PerMoleCompound = (a + (b / 4) – (c / 2) – (3 * d / 2)); if (molesO2PerMoleCompound < 0) { resultDiv.innerHTML = "The calculated oxygen demand is negative, which indicates the compound is already highly oxidized or the formula is incorrect for this calculation method. Please check the formula."; return; } // Calculate ThOD factor (mg O2 per mg compound) var thodFactor = (molesO2PerMoleCompound * MW_O2) / compoundMW; // Calculate Theoretical COD (ThOD) in mg O2/L var theoreticalCOD = compoundConcentration * thodFactor; if (isNaN(theoreticalCOD)) { resultDiv.innerHTML = "An error occurred during calculation. Please check your inputs."; } else { resultDiv.innerHTML = "Theoretical COD (ThOD): " + theoreticalCOD.toFixed(2) + " mg O₂/L"; } }

Understanding Chemical Oxygen Demand (COD)

Chemical Oxygen Demand (COD) is a crucial environmental parameter used to measure the amount of oxygen required to chemically oxidize organic and inorganic matter in a water sample. It serves as an indicator of water quality and pollution levels, particularly in wastewater treatment and industrial effluents. A higher COD value generally signifies a greater amount of oxidizable pollutants in the water.

What is Theoretical COD (ThOD)?

While COD is typically determined through laboratory analysis, Theoretical Chemical Oxygen Demand (ThOD) provides a calculated estimate based on the known chemical composition of a pollutant. ThOD represents the stoichiometric amount of oxygen required for the complete oxidation of a specific organic compound to its stable end products, usually carbon dioxide (CO₂), water (H₂O), and nitrogen gas (N₂), assuming nitrogen is present.

This calculator uses the following general oxidation reaction for compounds containing Carbon (C), Hydrogen (H), Oxygen (O), and Nitrogen (N):

C_aH_bO_cN_d + (a + b/4 – c/2 – 3d/2) O₂ → a CO₂ + (b/2 – 3d/2) H₂O + d/2 N₂

By knowing the molecular formula and concentration of a specific organic pollutant, we can determine the exact amount of oxygen theoretically needed for its complete breakdown.

How to Use the ThOD Calculator

1. Chemical Formula: Enter the molecular formula of the organic compound. For example, for Glucose, you would enter C6H12O6. The calculator is designed to parse formulas containing Carbon (C), Hydrogen (H), Oxygen (O), and Nitrogen (N).
2. Compound Concentration: Input the concentration of this specific compound in your water sample, typically in milligrams per liter (mg/L).
3. Calculate ThOD: Click the "Calculate ThOD" button to get the theoretical chemical oxygen demand in mg O₂/L.

Example Calculation

Let's calculate the ThOD for a water sample containing 100 mg/L of Glucose (C6H12O6):

• Chemical Formula: C6H12O6 (a=6, b=12, c=6, d=0)
• Compound Concentration: 100 mg/L

Steps:

1. Molecular Weight of Glucose (C6H12O6): (6 × 12.01) + (12 × 1.008) + (6 × 16.00) = 72.06 + 12.096 + 96.00 = 180.156 g/mol
2. Moles of O₂ required per mole of Glucose: (6 + 12/4 – 6/2 – 3*0/2) = (6 + 3 – 3 – 0) = 6 moles O₂
3. ThOD Factor (mg O₂ per mg Glucose): (6 moles O₂ × 32 g/mol O₂) / 180.156 g/mol Glucose = 192 / 180.156 ≈ 1.0657 mg O₂/mg Glucose
4. Theoretical COD: 100 mg/L Glucose × 1.0657 mg O₂/mg Glucose = 106.57 mg O₂/L

This calculator will provide you with this theoretical value, helping you understand the potential oxygen demand of specific pollutants.

Limitations

It's important to note that ThOD is a theoretical value. Actual COD measurements in a lab might differ due to several factors:

• Incomplete Oxidation: Lab methods might not achieve 100% oxidation of all compounds.
• Interfering Substances: Other substances in the sample (e.g., chlorides) can interfere with the COD test.
• Complex Mixtures: Real-world wastewater contains complex mixtures of organic compounds, making a precise ThOD calculation for the entire sample impractical without knowing the concentration of every component.
• Nitrogen Oxidation: This calculator assumes nitrogen is oxidized to N₂. In some COD tests, nitrogen can be oxidized to ammonia or nitrate, which would alter the oxygen demand.

Despite these limitations, ThOD is a valuable tool for understanding the maximum potential oxygen demand of known pollutants and for educational purposes.