function calculateSOUR() {
// 1. Get input values
var doInitial = parseFloat(document.getElementById('sour_do_initial').value);
var doFinal = parseFloat(document.getElementById('sour_do_final').value);
var timeMins = parseFloat(document.getElementById('sour_time').value);
var mlvss = parseFloat(document.getElementById('sour_mlvss').value);
var resultContainer = document.getElementById('sour_result_container');
var resultVal = document.getElementById('sour_final_val');
var ourVal = document.getElementById('sour_our_val');
// 2. Validate inputs
if (isNaN(doInitial) || isNaN(doFinal) || isNaN(timeMins) || isNaN(mlvss)) {
alert("Please enter valid numerical values for all fields.");
return;
}
if (timeMins <= 0) {
alert("Time interval must be greater than zero.");
return;
}
if (mlvss doInitial) {
alert("Final DO should typically be lower than Initial DO for oxygen uptake.");
// Continuing calculation anyway, but result will be negative representing generation (unlikely in this context)
}
// 3. Calculation Logic
// Calculate the drop in Oxygen
var deltaDO = doInitial – doFinal; // mg/L
// Calculate Oxygen Uptake Rate (OUR) in mg/L/min
var ourPerMin = deltaDO / timeMins;
// Convert OUR to mg/L/hr
var ourPerHour = ourPerMin * 60;
// Convert MLVSS from mg/L to g/L for the SOUR standard unit (mg O2/g MLVSS/hr)
var mlvssGramsPerLiter = mlvss / 1000;
// Calculate SOUR
var sourResult = ourPerHour / mlvssGramsPerLiter;
// 4. Display Results
resultContainer.style.display = "block";
// Fix to 2 decimal places
ourVal.innerHTML = ourPerHour.toFixed(2) + " mg/L/hr";
resultVal.innerHTML = sourResult.toFixed(2);
}
What is Specific Oxygen Uptake Rate (SOUR)?
The Specific Oxygen Uptake Rate (SOUR), also known as the oxygen consumption rate or respiration rate, is a critical parameter in wastewater treatment, particularly in activated sludge processes. It measures the amount of oxygen consumed by microorganisms (biomass) per unit of time, normalized by the mass of the solids present.
Unlike the standard Oxygen Uptake Rate (OUR), which only tells you how fast oxygen is depleting in a volume of liquid, SOUR accounts for the concentration of bacteria available to do the work. This makes SOUR a true indicator of the biological activity and health of the biomass.
The SOUR Formula
The calculation involves determining the rate of oxygen depletion and dividing it by the concentration of volatile suspended solids. The standard formula used in this calculator is:
SOUR = (OUR × 60) / (MLVSS / 1000)
Where:
OUR (mg/L/min): (Initial DO – Final DO) / Time in minutes.
MLVSS (mg/L): Mixed Liquor Volatile Suspended Solids (the active biomass).
60: Conversion factor from minutes to hours.
1000: Conversion factor from mg to grams (for solids).
The final unit is expressed as milligrams of Oxygen per gram of MLVSS per hour (mg O2/g MLVSS/hr).
Why Calculate SOUR?
Environmental engineers and plant operators use SOUR for several diagnostic purposes:
Toxicity Assessment: A sudden drop in SOUR may indicate that toxic influent has entered the plant and is inhibiting bacterial respiration.
Process Stability: Consistent SOUR values indicate a stable biological environment.
Sludge Stabilization: In aerobic digestion, a low SOUR value (often below 1.5 mg/g/hr) indicates that the sludge is well-stabilized and ready for disposal (vector attraction reduction).
Food-to-Microorganism Balance: High SOUR values often indicate high organic loading (lots of food), while very low values may indicate endogenous respiration (starvation phase).
Interpreting SOUR Values
While ranges vary based on the specific type of wastewater and treatment phase, general guidelines include:
> 20 mg/g/hr: High organic loading or young sludge age (Log growth phase).