Dissolved air flotation (DAF): One of the dissolved gas flotation (DGF) processes
when air is used for the generation of gas bubbles. See dissolved gas flotation
(DGF).
Dissolved gas flotation (DGF): It is a process involving pressurization of gas at
25–95 psig for dissolving gas into water and subsequent release of pressure
(to one atm) under laminar flow hydraulic conditions for generating extremely
fine gas bubbles (20–80 microns) which become attached to the impurities to be
removed and rise to the water surface together. The impurities or pollutants to be
removed which are on the water surface are called float or scum which are
scooped off by sludge collection means. The clarified water is discharged from
the flotation clarifier’s bottom. The gas flow rate is about one percent of influent
liquid flow rate. The attachment of gas bubbles to the impurities can be a result of
physical entrapment, electrochemical attraction, surface adsorption, and/or gas
stripping. The specific gravity of the bubble-impurity agglomerate is less than
one, resulting in buoyancy or non-selective flotation (i.e., Save-All).
Dissolved oxygen (DO): Molecular oxygen dissolved in water or wastewater.
Enhanced biological phosphorus removal (EBPR): The process of phosphorus
removal in wastewater that relies on the proliferation and selection of a microbiological population capable of storing phosphorus in excess of their normal
growth requirements. Also called biological nutrient removal (BNR).
Eutrification: Nutrient over-enrichment of a body of water, causing increased
growth of algae and rooted aquatic plants.
Extended aeration activated sludge process: A long aeration time (over 18 hours
DT) is employed in an extended aeration system. It is applicable only to small
wastewater treatment plants of less than 3785 m
3 /day or 1.0 MGD. Normally no
primary clarifier is provided, and no exercise of optimum return sludge control is
attempted although the return activated sludge (RAS) flow is about 75% to 100%
of plant flow. The objective is to simplify the process both in construction and in
operation. Sludge production is very small because of prolonged endogenous
oxidation, which minimizes the problem of sludge treatment and disposal. The
aeration effluent’s sludge normally has an inferior settling characteristic. Therefore, a secondary flotation clarifier is better for an extended aeration plant.
Fermentation: The process in which bacteria degrades organic matter under anaerobic conditions, such as in a collection system, primary clarifier, anaerobic
selector, or fermenter tank.
Filamentous organism: Microorganisms, such as bacterial, algal, or fungal species
that grow in thread-like colonies, or a biological mass that may interfere with
settling in clarifiers or may interfere with drainage through a filter.
Filtration: It is usually a granular medial filtration process which involves the
passage of wastewater or water through a bed of filter media with resulting
deposition of suspended solids. Eventually the pressure drop across the bed
becomes excessive, or the ability of the bed to remove suspended solids is
impaired. Cleaning is then necessary to restore operating head and effluent
quality. The time in service between cleanings is termed the filter run time or
3 Biological Processes
145
when air is used for the generation of gas bubbles. See dissolved gas flotation
(DGF).
Dissolved gas flotation (DGF): It is a process involving pressurization of gas at
25–95 psig for dissolving gas into water and subsequent release of pressure
(to one atm) under laminar flow hydraulic conditions for generating extremely
fine gas bubbles (20–80 microns) which become attached to the impurities to be
removed and rise to the water surface together. The impurities or pollutants to be
removed which are on the water surface are called float or scum which are
scooped off by sludge collection means. The clarified water is discharged from
the flotation clarifier’s bottom. The gas flow rate is about one percent of influent
liquid flow rate. The attachment of gas bubbles to the impurities can be a result of
physical entrapment, electrochemical attraction, surface adsorption, and/or gas
stripping. The specific gravity of the bubble-impurity agglomerate is less than
one, resulting in buoyancy or non-selective flotation (i.e., Save-All).
Dissolved oxygen (DO): Molecular oxygen dissolved in water or wastewater.
Enhanced biological phosphorus removal (EBPR): The process of phosphorus
removal in wastewater that relies on the proliferation and selection of a microbiological population capable of storing phosphorus in excess of their normal
growth requirements. Also called biological nutrient removal (BNR).
Eutrification: Nutrient over-enrichment of a body of water, causing increased
growth of algae and rooted aquatic plants.
Extended aeration activated sludge process: A long aeration time (over 18 hours
DT) is employed in an extended aeration system. It is applicable only to small
wastewater treatment plants of less than 3785 m
3 /day or 1.0 MGD. Normally no
primary clarifier is provided, and no exercise of optimum return sludge control is
attempted although the return activated sludge (RAS) flow is about 75% to 100%
of plant flow. The objective is to simplify the process both in construction and in
operation. Sludge production is very small because of prolonged endogenous
oxidation, which minimizes the problem of sludge treatment and disposal. The
aeration effluent’s sludge normally has an inferior settling characteristic. Therefore, a secondary flotation clarifier is better for an extended aeration plant.
Fermentation: The process in which bacteria degrades organic matter under anaerobic conditions, such as in a collection system, primary clarifier, anaerobic
selector, or fermenter tank.
Filamentous organism: Microorganisms, such as bacterial, algal, or fungal species
that grow in thread-like colonies, or a biological mass that may interfere with
settling in clarifiers or may interfere with drainage through a filter.
Filtration: It is usually a granular medial filtration process which involves the
passage of wastewater or water through a bed of filter media with resulting
deposition of suspended solids. Eventually the pressure drop across the bed
becomes excessive, or the ability of the bed to remove suspended solids is
impaired. Cleaning is then necessary to restore operating head and effluent
quality. The time in service between cleanings is termed the filter run time or
3 Biological Processes
145