Mixed Liquor Volatile Suspended Solids in mg/L (Required for SOUR calculation)
Calculation Results
Oxygen Depletion:–
OUR (per minute):–
OUR (Oxygen Uptake Rate):–
SOUR (Specific OUR):–
function calculateRespiration() {
// Clear previous errors
var errorDiv = document.getElementById('errorDisplay');
var resultDiv = document.getElementById('resultBox');
var sourRow = document.getElementById('sourRow');
errorDiv.style.display = 'none';
resultDiv.style.display = 'none';
sourRow.style.display = 'none';
// Get Input Values
var doStart = parseFloat(document.getElementById('doStart').value);
var doEnd = parseFloat(document.getElementById('doEnd').value);
var timeElapsed = parseFloat(document.getElementById('timeElapsed').value);
var mlvss = parseFloat(document.getElementById('mlvss').value);
// Validation
if (isNaN(doStart) || isNaN(doEnd) || isNaN(timeElapsed)) {
errorDiv.innerHTML = "Please enter valid numbers for Initial DO, Final DO, and Time.";
errorDiv.style.display = 'block';
return;
}
if (timeElapsed = doStart) {
errorDiv.innerHTML = "Final DO must be less than Initial DO for oxygen uptake.";
errorDiv.style.display = 'block';
return;
}
// Calculations
var doDelta = doStart – doEnd;
// OUR in mg/L/min
var ourMin = doDelta / timeElapsed;
// OUR in mg/L/hr (Standard Unit)
var ourHr = ourMin * 60;
// Display Base Results
document.getElementById('doDeltaResult').innerHTML = doDelta.toFixed(2) + " mg/L";
document.getElementById('ourMinResult').innerHTML = ourMin.toFixed(3) + " mg/L/min";
document.getElementById('ourHrResult').innerHTML = ourHr.toFixed(2) + " mg O₂/L/hr";
// Calculate SOUR if MLVSS is provided
if (!isNaN(mlvss) && mlvss > 0) {
// SOUR Formula: OUR (mg/L/hr) / MLVSS (g/L)
// Convert MLVSS from mg/L to g/L by dividing by 1000
var mlvssGramsPerLiter = mlvss / 1000;
var sour = ourHr / mlvssGramsPerLiter;
document.getElementById('sourResult').innerHTML = sour.toFixed(2) + " mg O₂/g MLVSS/hr";
sourRow.style.display = 'flex';
}
resultDiv.style.display = 'block';
}
How to Calculate Oxygen Uptake Rate (OUR)
The Oxygen Uptake Rate (OUR) is a critical parameter in biological wastewater treatment and cell culture bioprocessing. It measures the rate at which microorganisms consume dissolved oxygen (DO) from their environment. Monitoring OUR provides insight into the metabolic activity, health, and treatment efficiency of the biomass (activated sludge).
The OUR Formula
The calculation is based on the decrease in dissolved oxygen concentration over a specific period of time. The formula typically yields results in mg/L/hr.
OUR = (DOinitial – DOfinal) / Timeelapsed × 60
Where:
DOinitial: The dissolved oxygen concentration at the start of the test (mg/L).
DOfinal: The dissolved oxygen concentration at the end of the test (mg/L).
Timeelapsed: The duration between the two measurements (in minutes).
60: Conversion factor to normalize the rate to "per hour."
Specific Oxygen Uptake Rate (SOUR)
While OUR measures the total oxygen consumption of the liquid volume, the Specific Oxygen Uptake Rate (SOUR) normalizes this value against the amount of biomass present. This allows operators to determine if the bacteria are sluggish or active, regardless of the concentration of solids.
SOUR = OUR / (MLVSS / 1000)
Note: MLVSS (Mixed Liquor Volatile Suspended Solids) is measured in mg/L. We divide it by 1000 to convert it to g/L. The final unit for SOUR is usually mg O₂/g MLVSS/hr.
Step-by-Step Procedure to Measure OUR
Sample Collection: Collect a sample of mixed liquor from the aeration basin. Ideally, this should be done quickly to preserve current biological conditions.
Aeration: Aerate the sample until the Dissolved Oxygen (DO) is high, typically between 6.0 and 8.0 mg/L.
Isolation: Stop aeration and pour the sample into a BOD bottle or a stirred container where no new oxygen can enter (prevent surface re-aeration).
Measurement: Insert a DO probe. Record the DO reading immediately (Time 0) and record it again at regular intervals (e.g., every minute) or after a set duration (e.g., 10 minutes).
Stop Point: Stop the test before the DO drops below 1.0 or 2.0 mg/L, as respiration rates may become oxygen-limited at low concentrations.
Interpreting the Results
In activated sludge systems, the OUR values indicate the load on the system:
High OUR: Indicates a high organic load (high BOD) or very active biomass. This is common at the head of the aeration tank.
Low OUR: Suggests the microorganisms have consumed most of the food (endogenous respiration) or toxic inhibition is occurring.
Stable SOUR: SOUR is often used to predict potential toxicity or shock loads. A sudden drop in SOUR despite constant food supply suggests toxicity.
Typical Ranges
While every plant is different, a conventional activated sludge plant might see OUR values ranging from: