FAQ and Glossary

ACTIVATED SLUDGE

Sludge particles produced in wastewater by growth of organisms in aeration tanks. The term “activated” is based on the fact that particles are inundated with bacteria, fungi and protozoa.

ACTIVATED SLUDGE PROCESS

A biological wastewater treatment process that speeds up waste decomposition. When activated sludge is added to wastewater, it is aerated and agitated for a set amount of time, then allowed to settle out by sedimentation.

AEROBIC

Condition where oxygen is present.

ANAEROBIC

Condition where oxygen is absent (or sufficiently depleted).

ATP TEST

ATPs (adenosine triphosphate) are molecules found in and around living cells. ATP test rapidly measures actively growing micro-organisms by detecting ATP.

BOD

Biological Oxygen Demand. The measure of oxygen used by microorganisms to decompose water, BOD is a test used by wastewater treatment plants as a measure of the oxygen-depletion effect of a waste contaminant. The 5-day BOD is the universally-accepted standard used to measure relative pollution effect. It measures the amount of dissolved oxygen consumed by biochemical oxidation of waste contaminants over a 5-day period. [BOD and COD lab tests are both used as wastewater quality indicators to determine if specific wastewater will have a significant adverse effect on fish or aquatic plant life.]

BULKING

Sludge bulking occurs when the sludge does not settle properly and fails to separate out in the sedimentation tanks. Bulking is primarily caused by the growth of filamentous bacteria.

FILAMENTOUS BACTERIA

The long solid strands that result during sludge bulking. Similar to floc, filamentous bacteria have much greater volume and surface area than conventional floc and are very slow to settle.

FLOCCULATION

Process of agitating wastewater to induce the small suspended particles to join together into heavier particles (termed “floc”) so they settle out.

MIXED LIQUOR (MLSS)

Activated sludge mixed with raw wastewater

RBC

Rotating Biological Contactor is a biological process used in a secondary wastewater treatment plant. The RBC process uses 3-4m plastic disks mounted on a motorized shaft. When partially submerged in the pretreated wastewater, the RBC shaft is rotated so the disk continually introduces oxygen into the wastewater along with a biological medium. Most RBC designs include a minimum of 4 or 5 module sets (in parallel or in a series) to obtain the desired nitrification of wastewater.

SEDIMENTATION

In wastewater treatment, a sedimentation basin (settling basin or clarifier) is a large tank with a slow waterflow that allows floc to settle at the bottom. Normally, the sedimentation basin is located near the flocculation basin – as long distance transfer could cause the floc to break up. The amount of floc that settles out of the water depends on the basin’s depth and the amount of time retained in the basin.

SLUDGE

The solids that settle out during wastewater treatment processing.

SUPERNATANT

The liquid that is removed from settled sludge. It commonly refers to the liquid between the sludge on the bottom of the tank and the scum on the surface.

ULTRAVIOLET DISINFECTION

UV Light is used to ensure water is free from harmful organisms. When UV light is exposed to the water, the DNA (in any living matter within the water) absorbs the light. UV light cross-bonds with the DNA structure causing it to vibrate to the point of rupture and quickly ceasing normal cell functions. Ultra Violet (UV) light is now a standard practice in most municipal wastewater treatment processes.