The layer of gases surrounding the earth.

To soak up or take in.

Containing an excess of acids, or hydrogen ions (H+) Having a pH less than 7. The opposite of basic. A lemon is acidic.

Sludge floc produced in raw or settled sewage by the growth of bacteria and other organisms in the presence of dissolved oxygen.

A biological sewage treatment process in which a mixture of sewage and activated sludge is agitated and aerated. Activated sludge separates from the treated sewage by settling and is disposed of or returned to the process as needed. The treated wastewater overflows to the next treatment stage.

Contact between air and a liquid by diffusion or mechanical mixing.

Bacteria which require oxygen for their growth.

A gel-like substance containing nutrients used for growing bacteria for study.

Also referred to as basic. Having a pH greater than 7. The opposite of acid. i.e. Dishwashing detergent

A chemical which combines with chlorine in the water treatment process to form chloramine, a long-lasting disinfectant.