Question

Which parameter is commonly measured to determine the biochemical oxygen demand (BOD) of wastewater?

• A. Nitrate concentration
• B. Ammonia level
• C. Dissolved oxygen
• D. Organic content

Hint:

• BOD measures the amount of oxygen consumed by microbes to decompose organic matter in water.
• The test involves measuring the dissolved oxygen (DO) concentration in a water sample initially and after a period of incubation (e.g., 5 days at 20°C).
• The difference in DO levels (DO$_{initial}$ - DO$_{final}$) represents the oxygen consumed, which is the BOD.
• So, dissolved oxygen is the parameter directly measured to calculate BOD.

Answer 1

The Correct Option is C

To determine the Biochemical Oxygen Demand (BOD) of wastewater, the parameter that is commonly measured is Dissolved oxygen.

Step-by-Step Explanation:

Step 1: Understanding Biochemical Oxygen Demand (BOD)

BOD is a measure of the amount of dissolved oxygen consumed by aerobic microorganisms (like bacteria) as they break down organic matter in a water sample. It's a key indicator of the organic pollution level in water. A higher BOD value indicates more organic pollution and thus a greater demand for oxygen by the microorganisms.

Step 2: The Principle of the BOD Test

The standard BOD test (typically BOD₅, meaning a 5-day test) works on the principle that if there is biodegradable organic matter in the water, microorganisms will consume dissolved oxygen to break it down. By measuring the amount of dissolved oxygen at the beginning and at the end of a specific incubation period (usually 5 days at 20°C in the dark), we can determine how much oxygen has been consumed.

Step 3: The Measurement Process

• Initial Dissolved Oxygen (DO) Measurement: A water sample is taken, and its initial dissolved oxygen concentration is measured.
• Incubation: The sample is then sealed in an airtight bottle and incubated in the dark at a specific temperature (usually 20°C) for a set period (most commonly 5 days). The dark environment prevents photosynthesis by algae, which would produce oxygen and interfere with the measurement.
• Final Dissolved Oxygen (DO) Measurement: After the incubation period, the dissolved oxygen concentration in the same sample is measured again.
• Calculation: The difference between the initial and final dissolved oxygen levels, adjusted for any dilution of the sample, gives the BOD value. This difference represents the amount of oxygen consumed by the microorganisms as they degraded the organic pollutants.

Step 4: Why other options are incorrect:

• Nitrate concentration: While nitrates are important nutrients in wastewater and can indicate pollution, they are not directly measured to determine BOD. Nitrates are related to nitrogenous oxygen demand, which is a separate component of oxygen demand.
• Ammonia level: Ammonia is also a nutrient and can contribute to nitrogenous oxygen demand as it is converted to nitrate, but it's not the direct parameter used for BOD measurement.
• Organic content: While BOD is a measure of the biodegradable organic content, it's not directly measured. Instead, the effect of the organic content (i.e., its oxygen demand) is what is measured through the change in dissolved oxygen. Other tests like Chemical Oxygen Demand (COD) or Total Organic Carbon (TOC) directly measure organic content, but BOD specifically measures the biologically oxidizable organic content via oxygen consumption.

Therefore, the primary and most direct parameter measured to determine BOD is the dissolved oxygen consumed by microorganisms.