Digging depth, dredging It is the maximum design depth from which the dredge
can excavate material, which is usually stated as a measurement from water level
and typically expressed in feet or meters.
Digital Elevation Model (DEM) It is a terrain elevation data provided in
digital form.
Digitize It is an action to encode map features as x,y coordinates in digital form.
Lines are traced to define their shapes. This can be accomplished either manually
or by use of a scanner.
Disinfection Potable water disinfection is used in an attempt to destroy all pathogenic agents in drinking water for public health protection. Wastewater disinfection is used in an attempt to destroy pathogenic agents in a wastewater stream and
protect the best uses of the receiving stream or groundwater. Environmental
disinfection is used in an attempt to destroy pathogenic agents in rooms, houses,
swimming pools, buildings, restaurants, streets, parks, etc., to prevent the spread
of pathogenic agents, such as pathogenic bacteria and Coronavirus in the environment. Typical disinfection techniques used include chlorine (gas), sodium
hypochlorite (liquid), bromine (gas), bromine dioxide (gas), UV (light), ozone
(gas), and cationic surfactant (water-soluble solid).
Disinfection The process designed to kill or inactivate most microorganisms in
wastewater, including essentially all pathogenic (disease-causing) bacteria. There
are several ways to disinfect, with chlorination being the most frequently used in
water and wastewater treatment plants.
Dispersion A uniform and maximum separation of extremely fine particles, often
of colloidal size.
Dissolved air flotation (DAF) One of dissolved gas flotation (DGF) processes
when air is used for generation of gas bubbles. See dissolved gas flotation (DGF).
Dissolved gas flotation (DGF) It is a process involving pressurization of gas at
25 to 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 are on the water surface and 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
1, resulting in buoyancy or nonselective flotation (i.e., Save-All).
Dissolved oxygen (DO) Molecular (atmospheric) oxygen dissolved in water or
wastewater.
Distilled water Water that has been purified by distillation (boiling the water off as
steam and condensing it back to a liquid, leaving the impurities behind). Having
been boiled, it is also sterile.
Dredge mining It is a practical means for extracting submerged sand, gravel, sand,
iron ore, coal, fine tailings, and other minerals. Mining with a dredge is an
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can excavate material, which is usually stated as a measurement from water level
and typically expressed in feet or meters.
Digital Elevation Model (DEM) It is a terrain elevation data provided in
digital form.
Digitize It is an action to encode map features as x,y coordinates in digital form.
Lines are traced to define their shapes. This can be accomplished either manually
or by use of a scanner.
Disinfection Potable water disinfection is used in an attempt to destroy all pathogenic agents in drinking water for public health protection. Wastewater disinfection is used in an attempt to destroy pathogenic agents in a wastewater stream and
protect the best uses of the receiving stream or groundwater. Environmental
disinfection is used in an attempt to destroy pathogenic agents in rooms, houses,
swimming pools, buildings, restaurants, streets, parks, etc., to prevent the spread
of pathogenic agents, such as pathogenic bacteria and Coronavirus in the environment. Typical disinfection techniques used include chlorine (gas), sodium
hypochlorite (liquid), bromine (gas), bromine dioxide (gas), UV (light), ozone
(gas), and cationic surfactant (water-soluble solid).
Disinfection The process designed to kill or inactivate most microorganisms in
wastewater, including essentially all pathogenic (disease-causing) bacteria. There
are several ways to disinfect, with chlorination being the most frequently used in
water and wastewater treatment plants.
Dispersion A uniform and maximum separation of extremely fine particles, often
of colloidal size.
Dissolved air flotation (DAF) One of dissolved gas flotation (DGF) processes
when air is used for generation of gas bubbles. See dissolved gas flotation (DGF).
Dissolved gas flotation (DGF) It is a process involving pressurization of gas at
25 to 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 are on the water surface and 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
1, resulting in buoyancy or nonselective flotation (i.e., Save-All).
Dissolved oxygen (DO) Molecular (atmospheric) oxygen dissolved in water or
wastewater.
Distilled water Water that has been purified by distillation (boiling the water off as
steam and condensing it back to a liquid, leaving the impurities behind). Having
been boiled, it is also sterile.
Dredge mining It is a practical means for extracting submerged sand, gravel, sand,
iron ore, coal, fine tailings, and other minerals. Mining with a dredge is an
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M.-H. S. Wang and L. K. Wang