Wastewater metrics in process industries: In the context of chemical process plants, the term BOD (biochemical oxygen demand) is normally used for which type of stream or sample characterisation?

Introduction / Context:
BOD, or biochemical oxygen demand, is a cornerstone metric in environmental engineering. It estimates the amount of dissolved oxygen that microorganisms will consume while degrading biodegradable organic matter in water over a specified incubation period and temperature (commonly 5 days at 20°C for BOD5).

Given Data / Assumptions:

• BOD is discussed within the scope of process industry discharges.
• We compare across solids, gases, and liquid streams.
• Standard laboratory protocols and regulatory frameworks apply.

Concept / Approach:
BOD pertains to oxygen consumption potential in aqueous media; therefore it is inherently a liquid-phase wastewater parameter. It is used to gauge pollution load, size biological treatment units, and demonstrate compliance with discharge permits. It does not characterize gases or dry solids and is distinct from chemical oxygen demand (COD), which chemically oxidizes organics.

Step-by-Step Solution:
Identify the medium: BOD testing requires a water sample with biodegradable organics.Relate to typical applications: influent/effluent monitoring for treatment plants.Select the option that names liquid effluents (wastewater).

Verification / Alternative check:
Design calculations for aeration tanks and secondary clarifiers often start from BOD load (kg/day), confirming its tight linkage to liquid effluents.

Why Other Options Are Wrong:
Solid wastes: measured by moisture, volatile solids, calorific value; BOD is not standard.Gaseous effluents: organics measured as VOCs or TOC in air, not BOD.Boiler feed water: characterized by hardness, silica, dissolved oxygen, not BOD.Stack particulates: measured as PM; BOD is irrelevant.

Common Pitfalls:
Confusing BOD with COD or TOC; assuming any “organic” measure implies BOD irrespective of phase.

Final Answer:
Characterisation of liquid effluents (wastewater)