* Solutions are homogeneous mixtures where the components are evenly distributed at a molecular level. They have a uniform composition throughout.

* Heterogeneous mixtures have components that are not evenly distributed. You can often see the different parts of the mixture.

Sewage contains a wide range of substances, including:

* Solids: Feces, toilet paper, food scraps, grit, etc.

* Liquids: Urine, water, fats, oils, etc.

* Dissolved substances: Salts, minerals, detergents, etc.

These components do not dissolve fully in water, creating a mixture where different phases (solid, liquid, and possibly even gas) are visible.

Think of it this way: If you stir a spoonful of sand into a glass of water, you can still see the sand particles. The sand doesn't dissolve; it just gets suspended in the water. Sewage is similar in that it contains many undissolved particles.