Which statement about temperature effects in wastewater treatment is correct?

Which statement about temperature effects in wastewater treatment is correct?

• A. Cold water holds more dissolved oxygen and slows reactions.
• B. Cold water holds less dissolved oxygen and speeds reactions.
• C. Temperature has no effect on dissolved oxygen or reaction rate.
• D. Cold water decreases the MLSS required to degrade the same amount of BOD.

Answer: (A)

Temperature affects two main things in wastewater treatment: how much oxygen the water can hold and how fast biological processes occur. At lower temperatures, dissolved oxygen solubility increases, so cold water can contain more dissolved oxygen for a given pressure. At the same time, the metabolic and enzymatic activities of microorganisms slow down when it’s cold, so the rate at which bacteria degrade BOD decreases. That combination—more oxygen available but slower treatment activity—fits the statement that cold water holds more dissolved oxygen and slows reactions. The idea that temperature has no effect on dissolved oxygen or reaction rate isn’t correct, since both oxygen solubility and microbial activity are temperature-dependent. Regarding MLSS, colder conditions generally slow microbial processes, often requiring more biomass (MLSS) or longer treatment time to achieve the same BOD removal; claiming that cold water decreases the MLSS needed would be inconsistent with how temperature affects microbial efficiency.

Temperature affects two main things in wastewater treatment: how much oxygen the water can hold and how fast biological processes occur. At lower temperatures, dissolved oxygen solubility increases, so cold water can contain more dissolved oxygen for a given pressure. At the same time, the metabolic and enzymatic activities of microorganisms slow down when it’s cold, so the rate at which bacteria degrade BOD decreases. That combination—more oxygen available but slower treatment activity—fits the statement that cold water holds more dissolved oxygen and slows reactions.

The idea that temperature has no effect on dissolved oxygen or reaction rate isn’t correct, since both oxygen solubility and microbial activity are temperature-dependent. Regarding MLSS, colder conditions generally slow microbial processes, often requiring more biomass (MLSS) or longer treatment time to achieve the same BOD removal; claiming that cold water decreases the MLSS needed would be inconsistent with how temperature affects microbial efficiency.