Glossary of Wastewater-Related Terms

Advanced Primary Treatment - During wastewater treatment at the Point Loma 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.

Biosolids - 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.

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

Digestion - 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.)

Disinfection - 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.

Effluent - "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.

Headworks - Area of treatment plant where influent begins treatment.

Influent - 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.

MGD - Million Gallons per Day - 694.4 gallons per minute.

Modified Permit (also known as a "Waiver") - Permit granted by the U.S. Environmental Protection Agency which allows the Point Loma Wastewater Treatment Plant to operate at an Advanced Primary Level rather than a Secondary Treatment level. The Modified Permit was first granted in 1994 and renewed in 2002 and 2010.

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.

Scum - Floatable material in wastewater made up of mainly fats, cooking oil and grease which are skimmed off during the treatment process.

Secondary Treatment - Second stage of wastewater treatment that uses biological process in which bacteria consume organic matter, then settle out as sludge.

Sedimentation - Process by which solid material settles out of a liquid. Sludge settles out of wastewater in sedimentation tanks.

Sewage (or wastewater) - The used water and added waste of a community which is carried away by drains and sewers.

Sewerage - A system of sewers; the removal of waste materials by means of a sewer system.

Sludge - The solid waste material which settles out in the wastewater treatment process.

Storm Drain - A pipeline or channel system that carries surface water and/or runoff to public waters, but does not feed into sewer system.

Tertiary Treatment - The use of filtration to remove microscopic particles from wastewater that has already been treated to a Secondary Level. Anthracite coal is the filter medium used by the Public Utilities Department Wastewater Branch.

TSS - Total Suspended Solids - Solids in water that can be trapped by a filter. TSS can include a wide variety of material, such as silt, decaying plant and animal matter, industrial wastes, and sewage.

Waiver - See Modified Permit