How to Calculate Organic Loading Rate

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Organic Loading Rate (OLR) Calculator

Daily Flow Rate (Q) The volume of influent wastewater per day (m³/day).

Organic Concentration (S) The concentration of BOD or COD (mg/L or g/m³).

Reactor Volume (V) The effective volume of the treatment tank or reactor (m³).

Please enter valid positive numbers for all fields. Volume cannot be zero.

Organic Loading Rate (OLR)

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Total Organic Load

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The Organic Loading Rate (OLR) is a critical parameter in wastewater treatment engineering and anaerobic digestion. It defines the amount of organic matter being fed into a bioreactor or treatment system relative to its volume over a specific time period. Properly calculating and managing the OLR ensures that the biological processes remain stable and efficient.

The Formula

The standard formula for calculating Organic Loading Rate in metric units is:

OLR = (Q × S) / V

Where:

Q = Influent Flow Rate (m³/day)
S = Substrate Concentration, usually COD or BOD (kg/m³). Note: 1 mg/L = 0.001 kg/m³.
V = Reactor Volume (m³)

If your concentration is in mg/L (which is equal to g/m³), you must divide the numerator by 1,000 to convert grams to kilograms. The resulting formula becomes:

OLR (kg/m³/d) = [Flow (m³/d) × Concentration (mg/L)] / [Volume (m³) × 1000]

Why is OLR Important?

Monitoring the OLR is vital for several reasons:

Process Stability: If the loading rate is too high ("shock loading"), bacteria may not be able to break down the organics fast enough, leading to system failure, acidification (in anaerobic digesters), or poor effluent quality.
Efficiency: If the loading rate is too low, the facility is underutilized, meaning the capital investment in the tank volume is not yielding maximum returns.
Microbial Health: A steady OLR supports a healthy biomass population tailored to the specific waste stream.

Step-by-Step Calculation Example

Let's calculate the OLR for a typical activated sludge aeration tank:

Flow Rate (Q): 500 m³/day
BOD Concentration (S): 300 mg/L
Reactor Volume (V): 1000 m³

Step 1: Calculate Total Mass Load
Multiply Flow by Concentration to get the total mass of organics entering the system.
500 m³/d × 300 mg/L = 150,000 g/day
Divide by 1,000 to get kg: 150 kg/day.

Step 2: Divide by Volume
Divide the total load by the reactor volume.
150 kg/day / 1000 m³ = 0.15 kg BOD/m³/day.

Typical OLR Ranges

Different treatment processes operate effectively at different ranges:

Activated Sludge: 0.3 to 0.6 kg BOD/m³/day
Trickling Filters: 0.07 to 0.22 kg BOD/m³/day
Anaerobic Digesters: 1.0 to 5.0 kg COD/m³/day (High-rate systems can go much higher)

function calculateOrganicLoading() { // 1. Get input values by ID var flowRateInput = document.getElementById('flowRate'); var concentrationInput = document.getElementById('concentration'); var volumeInput = document.getElementById('reactorVolume'); var errorDiv = document.getElementById('calcError'); var resultsDiv = document.getElementById('olrResults'); // 2. Parse values var flow = parseFloat(flowRateInput.value); var conc = parseFloat(concentrationInput.value); var vol = parseFloat(volumeInput.value); // 3. Validation if (isNaN(flow) || isNaN(conc) || isNaN(vol) || flow < 0 || conc < 0 || vol <= 0) { errorDiv.style.display = 'block'; resultsDiv.style.display = 'none'; return; } // Hide error if valid errorDiv.style.display = 'none'; // 4. Calculate Total Organic Load (kg/day) // Formula: Flow (m3/d) * Conc (mg/L) / 1000 // Explanation: mg/L is equivalent to g/m3. // m3/d * g/m3 = g/day. // Divide by 1000 to get kg/day. var totalLoadKg = (flow * conc) / 1000; // 5. Calculate OLR (kg/m3/d) // Formula: Total Load (kg/d) / Volume (m3) var olr = totalLoadKg / vol; // 6. Display Results // OLR Result document.getElementById('olrFinal').innerHTML = olr.toFixed(3) + " kg/m³/d"; // Total Load Result document.getElementById('totalLoadFinal').innerHTML = totalLoadKg.toFixed(2) + " kg/day"; // Show results container resultsDiv.style.display = 'block'; }

Organic Loading Rate (OLR) Calculator