What do we call a solid that cannot be filtered from wastewater?

The term that best describes a solid that cannot be filtered from wastewater is total dissolved solids. This category includes substances that are dissolved in water, making them unable to be physically separated by conventional filtration methods. Total dissolved solids primarily consist of organic and inorganic materials, minerals, and salts that remain dissolved in the water column, contributing to the overall turbidity and chemical composition of the wastewater.

In contrast, total suspended solids represent materials that can be filtered out of wastewater, as they remain in suspension and are not dissolved. Residual solids typically refer to the leftover material after treatment processes but do not exclusively delineate solids based on their ability to be filtered. Insoluble solids may imply elements that do not dissolve in water but may still be removable through filtration. Therefore, total dissolved solids is the precise term for solids that cannot be filtered from wastewater due to their dissolved state.