Question

BOD, demand of dissolved oxygen by microbes to disintegrate biologically degradable waste in water, follows:

• A. Zero order kinetics
• B. 1st order kinetics
• C. 2nd order kinetics
• D. 3rd order kinetics

Hint:

BOD half-life: $t_{1/2} = \dfrac{\ln 2}{k}$. First-order means rate $\propto$ remaining substrate concentration.

Answer 1

The Correct Option is B

Step 1: Concept
Kinetics of Biological Oxygen Demand (BOD).

Step 2: Meaning
BOD measures the oxygen consumed by microorganisms when decomposing organic matter in water. First-order kinetics implies the rate of decomposition is proportional to the amount of biodegradable matter remaining.

Step 3: Analysis
The BOD exertion follows first-order kinetics: \[ \frac{dL}{dt} = -k \cdot L \] where $L$ is the remaining BOD and $k$ is the first-order rate constant. The solution is: \[ L(t) = L_0 \, e^{-kt} \] This exponential decay is characteristic of first-order reactions, as the rate is proportional to the concentration of substrate remaining.

Step 4: Conclusion
BOD follows first-order kinetics. Final Answer: (B)