Texas Wastewater Class B Practice Exam

How is chronic toxicity defined in the context of wastewater treatment?

1. Microorganisms die off entirely

2. Certain microorganisms are inactivated while others continue to work

3. There's no effect on biological processes

4. It improves overall treatment efficiency

The correct answer is: Certain microorganisms are inactivated while others continue to work

Chronic toxicity in the context of wastewater treatment refers to the long-term effects of toxic substances on the organisms in the treatment process. When certain microorganisms are inactivated, it indicates that those specific organisms are negatively impacted by toxic constituents in the wastewater. However, the fact that other microorganisms continue to work highlights how chronic toxicity does not result in a total die-off, allowing some biological processes to persist. This scenario can lead to imbalances in the treatment system, as the inactivation of crucial species may impact the overall treatment efficiency and stability. The other choices do not accurately capture the concept of chronic toxicity. A total die-off of microorganisms would indicate acute toxicity rather than chronic. A scenario where there is no effect on biological processes contradicts the very definition of chronic toxicity. Lastly, if chronic toxicity were to improve overall treatment efficiency, it would be a misguided interpretation of the effects of toxic substances, as these are typically detrimental to the wastewater treatment process.