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Difficulty: Very hardEnvironmental Pollution: Types, Causes and Control Measures

With reference to water pollution indicators, thermal pollution dynamics, and industrial emission control technologies, which of the following statements are correct?

  1. Biological Oxygen Demand (BOD) measures the amount of dissolved oxygen needed by aerobic organisms to decompose biodegradable organic matter, whereas Chemical Oxygen Demand (COD) measures the oxygen required for chemical oxidation of both biodegradable and non-biodegradable organic pollutants.Answer
  2. Thermal discharge into natural water bodies reduces the solubility of dissolved oxygen while simultaneously increasing the metabolic rates and oxygen demands of aquatic organisms.Answer
  3. C
    Electrostatic Precipitators (ESPs) are primarily deployed in thermal power plants to neutralize gaseous pollutants such as sulfur dioxide (SO2SO_2) and volatile organic compounds (VOCs) through high-voltage ionization.
  4. D
    Cultural eutrophication increases deep-water dissolved oxygen concentrations because algal blooms produce excessive oxygen through surface photosynthesis that diffuses down to the benthic zone.

Answer

The statements distinguishing BOD from COD and describing the dual impact of thermal pollution on dissolved oxygen and metabolic rates are correct.
The statement differentiating BOD and COD correctly highlights that COD includes both chemically degradable refractory compounds and biological organics, making COD higher than BOD. The statement on thermal pollution accurately captures the thermodynamic principle of gas solubility alongside biological metabolic escalation in warmer water.

Step-by-Step Solution

1
Analyze the statement regarding Biological Oxygen Demand (BOD) versus Chemical Oxygen Demand (COD).
BOD measures biodegradable organic fraction via biological oxidation, while COD measures total oxidizable organic content (biodegradable + non-biodegradable) via strong chemical oxidation. Therefore, COD>BODCOD > BOD always holds true for domestic and industrial effluent.
Understanding wastewater quality parameters requires differentiating biological breakdown from chemical breakdown.
2
Evaluate the statement concerning thermal pollution mechanisms in aquatic environments.
Water temperature exhibits an inverse relationship with dissolved oxygen (DO) concentration. Simultaneously, Q10 metabolic principles dictate that higher temperatures increase aquatic animal metabolic rates, compounding oxygen stress.
Thermal pollution creates a synergistic ecological hazard: reduced oxygen availability combined with heightened biological oxygen demand.
3
Evaluate the statement regarding Electrostatic Precipitators (ESPs).
ESPs remove particulate pollutants (fly ash, dust) via high-voltage corona electrodes, not gaseous compounds like SO2SO_2 or VOCs.
Industrial control devices specialize by pollutant phase; gaseous emissions require wet/dry scrubbers or catalytic reactors.
4
Evaluate the statement concerning cultural eutrophication and dissolved oxygen.
Excessive nutrient enrichment causes algal blooms that prevent light penetration. Subsequent decay of dead algae by aerobic bacteria consumes massive amounts of oxygen, producing severe benthic hypoxia.
Eutrophication leads to net oxygen deficit across deeper aquatic zones despite high surface photosynthetic activity.

Key Concept

Wastewater parameters (BOD/COD), thermal pollution mechanics, and air pollution control equipment operating principles
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Topics

Environmental Pollution: Types, Causes and Control Measures