Massachusetts Wastewater Practice Exam

When is the use of nitric acid necessary in wastewater treatment?

1. Neutralizing pH.

2. As a preservative for heavy metal samples.

3. As an oxidizing agent in detoxification.

4. For odor control.

The correct answer is: As a preservative for heavy metal samples.

The use of nitric acid in wastewater treatment is primarily relevant when considering the analysis of heavy metal samples. In this context, nitric acid serves as an effective preservative, ensuring that the samples remain representative of their original state for accurate analysis. Heavy metals can precipitate or change form if not properly preserved, leading to inaccurate test results. By acidifying the samples with nitric acid, the metals remain in solution and prevent microbial growth, which could alter their composition. In contrast, while nitric acid has other applications, options related to odor control or detoxification might involve different chemicals or approaches better suited for those purposes. For instance, neutralizing pH typically requires the use of bases for alkaline conditions or acids for acidic conditions, but not primarily nitric acid unless adjusting for specific metal contaminants. Each choice highlights the multifunctionality of chemicals in wastewater treatment processes while pinpointing the precise role of nitric acid specifically in preserving heavy metal samples for accurate analysis.