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

Biochemical Oxygen Demand (BOD) is a measure of the amount of dissolved oxygen (DO) consumed by aerobic microorganisms while decomposing organic matter present in a water sample, under specific conditions (typically at 20°C for 5 days, known as BOD$_5$). It is an indirect measure of the amount of biodegradable organic pollution in water. The BOD test procedure involves: Option (A) Measuring the initial dissolved oxygen (DO$_i$) concentration in a known volume of the water sample (often diluted). Option (B) Incubating the sample in a sealed, dark bottle at a constant temperature (usually 20°C) for a specified period (usually 5 days). During this time, aerobic microorganisms in the sample consume organic matter and, in doing so, consume dissolved oxygen. Option (C) After the incubation period, measuring the final dissolved oxygen (DO$_f$) concentration in the sample. Option (D) The BOD is then calculated as the difference between the initial and final DO levels, adjusted for any dilution: BOD (mg/L) = (DO$_i$ - DO$_f$) $\times$ Dilution Factor Therefore, dissolved oxygen is the parameter that is directly measured at the beginning and end of the incubation period to determine BOD. Option (a) Nitrate concentration and (b) Ammonia level are forms of nitrogen, which can contribute to nutrient pollution and exert a nitrogenous oxygen demand (NOD) over longer periods, but BOD specifically measures the oxygen consumed for carbonaceous organic matter degradation. Option (d) Organic content is what BOD indicates or estimates (specifically, the biodegradable portion), but it's not the parameter measured to determine BOD. The consumption of dissolved oxygen due to the degradation of organic content is what's measured. \[ \boxed{\text{Dissolved oxygen}} \]