Which of the following parameters measures both biodegradable and non-biodegradable organic matter in wastewater?

Question

Which of the following parameters measures both biodegradable and non-biodegradable organic matter in wastewater?

1. A. BOD
2. B. COD (Correct answer)
3. C. Alkalinity
4. D. Total nitrogen

Correct Answer

Option B — COD

Detailed Solution & Explanation

The correct answer is COD.

Key Points

• Chemical Oxygen Demand uses a strong chemical oxidant — potassium dichromate in hot, acidic conditions — which attacks almost all organic matter present, whether or not micro-organisms can digest it.
• That is exactly why COD captures both biodegradable and non-biodegradable fractions, while BOD counts only what bacteria will consume in five days.
• Alkalinity measures acid-neutralising capacity and total nitrogen measures a nutrient; neither is a measure of organic matter.

Additional Information

• For any given sample COD ≥ BOD, always. The gap between them is a direct measure of the non-biodegradable (refractory) organic load — a useful diagnostic when deciding whether biological treatment will suffice.
• COD is the practical choice for plant operation because it takes about 3 hours against BOD's 5 days; a five-day answer is useless for adjusting a process today.
• Industrial effluents with persistent synthetic compounds — textile dyes, distillery melanoidins, pharmaceutical residues — show wide BOD-COD gaps and typically need adsorption, advanced oxidation or membranes.
• Total Oxygen Demand (TOD) and Total Organic Carbon (TOC) are instrumental alternatives that measure the carbon content directly and take minutes rather than hours.