California Wastewater Treatment Operator Practice Exam 2025 – 400 Free Practice Questions to Pass the Exam

The correct answer, volatile solids, refers specifically to the portion of organic solids that are present in a sample of wastewater. Volatile solids are determined through a process that involves igniting a sample at high temperatures, which causes the organic material to vaporize. This measurement helps identify the organic content of the solids, indicating the potential for biological decomposition and the availability of nutrients for microorganisms in the treatment process.

In contrast, total solids encompasses both organic and inorganic solids. It does not specifically reflect the organic fraction. Total suspended solids, while also related to solids in the water, includes both volatile (organic) and non-volatile (inorganic) material suspended in the liquid. Settleable solids refers to the portion of solids that can be removed by sedimentation, and while they may include organic matter, they do not specifically quantify or focus on organic solids alone. Therefore, volatile solids is the term that directly aligns with the concept of organic solids in the context of wastewater treatment.