How to Calculate Biological Oxygen Demand

Biological Oxygen Demand (BOD) Calculator

function calculateBOD() { var initialDO = parseFloat(document.getElementById('initialDO').value); var finalDO = parseFloat(document.getElementById('finalDO').value); var sampleVolume = parseFloat(document.getElementById('sampleVolume').value); var bottleVolume = parseFloat(document.getElementById('bottleVolume').value); var resultDiv = document.getElementById('bodResult'); if (isNaN(initialDO) || isNaN(finalDO) || isNaN(sampleVolume) || isNaN(bottleVolume) || initialDO < 0 || finalDO < 0 || sampleVolume <= 0 || bottleVolume <= 0) { resultDiv.innerHTML = "Please enter valid positive numbers for all fields."; resultDiv.style.color = '#dc3545'; return; } if (initialDO bottleVolume) { resultDiv.innerHTML = "Wastewater Sample Volume (Vs) cannot be greater than BOD Bottle Volume (Vb). Please check your inputs."; resultDiv.style.color = '#dc3545'; return; } var dilutionFactor = bottleVolume / sampleVolume; var bod = (initialDO – finalDO) * dilutionFactor; resultDiv.innerHTML = "The Biological Oxygen Demand (BOD) is: " + bod.toFixed(2) + " mg/L"; resultDiv.style.color = '#333'; }

Understanding Biological Oxygen Demand (BOD)

Biological Oxygen Demand (BOD) is a crucial water quality parameter that measures the amount of dissolved oxygen consumed by microorganisms during the decomposition of organic matter in a water sample. It is widely used as an indicator of the organic pollution load in wastewater and natural waters.

Why is BOD Important?

High BOD levels indicate a significant amount of organic pollution, which can lead to several environmental problems:

• Oxygen Depletion: As microorganisms consume oxygen to break down organic matter, dissolved oxygen levels in the water decrease. This can be detrimental to aquatic life, such as fish and invertebrates, which need oxygen to survive.
• Eutrophication: High organic loads can contribute to excessive nutrient enrichment, leading to algal blooms and further oxygen depletion when the algae die and decompose.
• Ecosystem Health: BOD is a key metric for assessing the overall health of aquatic ecosystems and the effectiveness of wastewater treatment processes.

How is BOD Measured?

The most common method for measuring BOD is the 5-day BOD (BOD5) test. This involves incubating a water sample, typically diluted with oxygen-saturated dilution water, in a sealed bottle at 20°C for five days. The dissolved oxygen (DO) concentration is measured at the beginning (Initial DO) and at the end (Final DO) of the incubation period. The difference in DO, adjusted for dilution, gives the BOD value.

The BOD Calculation Formula

The formula used to calculate BOD is:

BOD (mg/L) = (DOi – DOf) × (Vb / Vs)

Where:

• DOi: Initial Dissolved Oxygen (mg/L) – The DO concentration of the diluted sample immediately after preparation.
• DOf: Final Dissolved Oxygen (mg/L) – The DO concentration of the diluted sample after 5 days of incubation.
• Vb: BOD Bottle Volume (mL) – The total volume of the BOD bottle (typically 300 mL).
• Vs: Wastewater Sample Volume (mL) – The volume of the undiluted wastewater sample added to the BOD bottle.

Example Calculation:

Let's say you have the following measurements:

• Initial Dissolved Oxygen (DOi) = 8.0 mg/L
• Final Dissolved Oxygen (DOf) = 2.0 mg/L
• Wastewater Sample Volume (Vs) = 6 mL
• BOD Bottle Volume (Vb) = 300 mL

Using the formula:

BOD = (8.0 – 2.0) × (300 / 6)
BOD = 6.0 × 50
BOD = 300 mg/L

This indicates a high organic load in the wastewater sample.