Tennessee Wastewater Operator Practice Exam

When are digested solids considered to be stabilized?

1. After two weeks of digestion

2. When they smell pleasant

3. When they meet requirements in the 503 regulations

4. Once they achieve a low moisture content

The correct answer is: When they meet requirements in the 503 regulations

Digested solids are considered to be stabilized when they meet the requirements detailed in the 503 regulations. These regulations, established by the Environmental Protection Agency (EPA), set specific criteria for the treatment and use of biosolids to ensure they are safe for land application and do not pose a risk to public health or the environment. Stabilization reduces pathogens and decreases the potential for odor, attracting vermin, and other issues. Meeting the 503 regulations ensures that the treated biosolids undergo sufficient biological, chemical, or thermal processes to achieve the necessary stability and safety standards. Thus, compliance with these regulations is the key determinant for considering digested solids as stabilized. Other options would not adequately define stabilization. Simply waiting two weeks may not provide sufficient treatment; a pleasant smell does not necessarily indicate safety or stability; and low moisture content alone doesn't ensure that the solids are free from harmful pathogens or contaminants, which are central considerations in the 503 regulations.