Total suspended solids (TSS) are defined as...

• A. Solids in wastewater that can be removed readily by standard filtering procedures in a laboratory and reported as milligrams per liter.
• B. Solids that are dissolved in wastewater.
• C. Microorganisms in wastewater.
• D. The total solids in wastewater measured by gravity.

Answer: (A)

Total suspended solids are the portion of solids in wastewater that can be removed by filtration. In practice, you pass a known volume of water through a standard filter; the material retained on the filter is dried and weighed, and the result is reported as milligrams per liter. This definition highlights the difference between what stays suspended (and thus is capturable by a filter) versus what is dissolved and passes through the filter.

Dissolved solids, by contrast, pass through the filter and are measured by a different approach, so they’re not part of TSS. Microorganisms can be part of what’s present in suspension, but the term TSS is about the physical ability to be retained by filtration, not about identifying specific organisms. The idea of measuring solids by gravity isn’t how TSS is defined or determined—TSS relies on filtration, not a gravity-based method.