Identify the correct formula relating theoretical oxygen demand (TOD), biochemical oxygen demand (BOD), and chemical oxygen demand (COD)_______________?
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Answer: B. TOD>COD>BOD
Explanation
Theoretical oxygen demand is the complete stoichiometric oxidation value representing the maximum possible oxygen needed. Chemical oxygen demand measures chemically oxidizable matter which is always less than total theoretical oxidation. Biochemical oxygen demand measures biodegradable matter resulting in the relationship TOD greater than COD greater than BOD. Theoretical oxygen demand is calculated directly from the chemical formula of organic compounds present. Chemical oxygen demand utilizes strong chemical oxidants like potassium dichromate under acidic heated conditions. Biochemical oxygen demand relies on microbial activity over a standard five day incubation period at temperature.
Environmental engineers use these three oxygen demand parameters to characterize wastewater strength and treatability. Comparing COD to BOD helps determine the fraction of industrial versus domestic waste in municipal sewers. Wastewater treatment facility designs depend heavily on understanding these distinct oxygen consumption metrics. Suggesting BOD is higher than COD violates fundamental principles because not all chemicals are biodegradable. Theoretical oxygen demand must always exceed chemical oxygen demand because of complete stoichiometric oxidation limits. Placing biochemical oxygen demand above chemical oxygen demand ignores refractory compounds that resist biological degradation.
- Subject
- Engineering
- Category
- Civil Engineering
- Topic
- —
- Difficulty
- medium
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