Rapid single-parameter assessment of river water pollution: which test provides a quick indication of the oxidisable load without waiting for 5-day incubation?
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ABiochemical Oxygen Demand (BOD5)
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BChemical Oxygen Demand (COD)
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CTotal organic solids
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DDissolved oxygen (DO) only
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EMost probable number of coliforms (MPN)
Answer
Correct Answer: Chemical Oxygen Demand (COD)
Explanation
Introduction / Context:Regulators and operators often need a rapid measure of organic pollution in rivers and effluents. While BOD5 is biologically meaningful, it requires a 5-day incubation. COD offers a fast, laboratory-based oxidation of organics using a strong chemical oxidant, giving a same-day proxy for oxygen demand.
Given Data / Assumptions:
- Sampling is from a river where prompt decisions are needed.
- COD test uses dichromate (or equivalent) under acidic conditions with a catalyst.
- Results approximate the total chemically oxidisable load (often ≥ BOD).
Concept / Approach:COD correlates with BOD for many wastewaters and is favored for process control due to speed. DO alone indicates current oxygen level, not the oxidisable load; total organic solids lack specificity to oxygen demand; MPN indicates fecal contamination, not organic load magnitude.
Step-by-Step Solution:
Select the test that measures oxidisable organics quickly: COD.Note that BOD5 requires 5 days and hence is not 'rapid'.Confirm that COD results help estimate pollutional status promptly.Verification / Alternative check:
Compare COD:BOD ratios; abnormal ratios can signal industrial discharges or poor biodegradability.Why Other Options Are Wrong:
BOD5 is too slow; DO is instantaneous but not a load metric; solids measures are non-specific; MPN relates to pathogens.Common Pitfalls:
Assuming COD always equals BOD; matrix-specific correlations must be established.Final Answer:
Chemical Oxygen Demand (COD)