Glossary of Wastewater-related Terms

Advanced Primary Treatment
During wastewater treatment at the Granite City Regional Wastewater Treatment Plant, ferric chloride and organic polymers are added to the sedimentation tanks to help waste particles bond together in large enough masses to settle out.

Nutrient-rich, organic material generated from household waste, removed during the treatment process. Once digested and dewatered, the material, called Biosolids, can be beneficially recycled.

BOD (Biological Oxygen Demand)
Rate at which organisms use oxygen in water and wastewater.

Co-production of electrical and thermal energy, also called combined heat and power (CHP).

Process by which organisms break down sludge, creating as by-products methane gas, carbon dioxide, solid organic material and water. (Aerobic digestion takes place in the presence of oxygen and anaerobic digestion takes place with the absence of oxygen.)

Final step in the tertiary wastewater treatment process, when chlorine or sodium hypochlorite is added to the treated wastewater to kill disease-causing organisms. Ultraviolet light is another means of disinfection.

"Cleaned" wastewater which flows out of a treatment plant.

Grit Chamber
Tank in which the flow of wastewater is slowed, allowing heavy solid materials such as pebbles, sand, coffee grounds and eggshells to sink to the bottom.

Area of treatment plant where influent begins treatment.

Untreated wastewater when it flows into a treatment plant.

Influent Screens
First step in the wastewater treatment process. The screen consists of bars between ¾ inch and 3 inches apart. Wastewater is allowed to pass through the bars, but large solid objects such as rocks, cans, plastic bags and sticks are stopped.

Million Gallons per Day - 694.4 gallons per minute.

Raw sewage
Untreated wastewater.

Reclaimed water
Product produced by tertiary treatment of wastewater.

Run off
Rainfall or other water that is not absorbed into the soil and drains off the street or land. This runoff moves through the Storm Drain system, not the sewerage system.