Environmental Engineering Reference
In-Depth Information
Biochemical oxygen demand (Bod)—
A measure of the amount of food
available to the microorganisms in a particular waste. It is mea-
sured by the amount of dissolved oxygen used up during a specific
time period (usually 5 days, expressed as BOD
5
).
Biodegradable—
From
degrade
(“to wear away or break down chemi-
cally”) and
bio
(“by living organisms”). Put it all together, and you
have a “substance, usually organic, which can be decomposed by
biological action.”
Bulking—
A problem in activated sludge plants that results in poor
settleability of sludge particles.
Coning—
A condition that may be established in a sludge hopper dur-
ing sludge withdrawal when part of the sludge moves toward the
outlet while the remainder tends to stay in place; development of a
cone or channel of moving liquids surrounded by relatively station-
ary sludge.
decomposition—
Generally, in waste treatment, refers to the chang-
ing of waste matter into simpler, more stable forms that will not
harm the receiving stream.
diffused air aeration—
A diffused-air-activated sludge plant takes air,
compresses it, then discharges the air below the water surface to
the aerator through some type of air diffusion device.
diffuser—
A porous plate or tube through which air is forced and
divided into tiny bubbles for distribution in liquids. Commonly
made of carborundum, aluminum, or silica sand.
dissolved oxygen (do)—
Atmospheric oxygen dissolved in water or
wastewater.
Note:
The typical required DO for a well-operated activated sludge plant
is between 2.0 and 2.5 mg/L.
facultative—
Facultative bacteria can use either molecular (dissolved)
oxygen or oxygen obtained from food materials. In other words, fac-
ultative bacteria can live under aerobic or anaerobic conditions.
filamentous bacteria—
Organisms that grow in thread or filamentous
form.
food-to-microorganisms (f/m) ratio—
A process control calculation
used to evaluate the amount of food (BOD or COD) available per
pound of mixed liquor volatile suspended solids (MLVSS). This may
be written as an F/M ratio:
Food
Microorganisms
BOD(lb/day)
MLVSS (lb)
F
low(MGD)
× ×
))MLVSS (mg/L)
BOD(mg/L)8.34lb/gal
=
=
Volume (MG
×
×
8.34 lb/gal
fungi—
Multicellular aerobic organisms.
gould sludge age—
A process control calculation used to evaluate the
amount of influent suspended solids available per pound of mixed
liquor suspended solids (MLSS).
