Texas Wastewater Class B Practice Exam

Total Dissolved Solids (TDS) refers to the sum of all inorganic and organic substances present in water that are capable of passing through a filter, which typically has a pore size of 2 micrometers. Because of their small size, TDS includes a wide variety of materials, such as minerals, salts, and some organic compounds, which remain dissolved in the water.

The correct characterization of TDS as solids that cannot be filtered out is based on their nature; they exist in a dissolved state and therefore cannot be separated from water by standard filtration methods.

In contrast, solids that are easily filtered or can be settled are typically larger particles or suspended solids, which do not contribute to TDS. Similarly, solids that float on water pertain to specific materials that are less dense than water, and again, these are not representative of TDS, as they do not remain dissolved. Therefore, considering the fundamental properties of TDS, the chosen answer accurately reflects their characteristics in wastewater treatment contexts.