9 Recent Advances in Biological Waste Treatment
Processes
Dissolved gas flotation (DGF) 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 air flotation (DAF) is one of the
dissolved gas flotation (DGF) processes when air is used for the generation of gas
bubbles. DGF or DAF is highly efficient for clarification of both water or wastewater
[101, 130–160].
The first wave of evolutionary development in potable water treatment has been
replacement of sedimentation clarifiers with dissolved air flotation (DAF) clarifiers
using commercial DAF products, such as Supracell, Sandfloat, Clari-DAF,
AquaDAF, KAMWT, etc. [101, 131, 141, 155–160]. This evolution has been
extremely successfully. The largest city in the world, New York City, has adopted
DAF for potable water treatment. The readers are referred to the Glossary section for
all technical terms and commercial product names.
The second wave of evolutionary development in wastewater treatment has
started [130, 132–140, 142–154]. Typical examples are shown in Fig. 3.21
(A suspended-growth activated sludge system uses primary flotation clarification
and secondary flotation clarification) and Fig. 3.22 (An attached-growth trickling
filter system uses primary flotation clarification and secondary flotation clarification)
[101, 157], in which traditional primary sedimentation clarification is replaced by
primary flotation clarification and traditional secondary sedimentation clarification is
replaced by secondary flotation clarification.
A few newly developed biological processes are listed below:
1. Innovative biological wastewater treatment system: It normally includes
(a) preliminary treatment units (i.e., screen, comminutor, grit chamber, etc. for
the removal of sand, gravel, cinders, coffee grounds, small stones, cigarette filter
tips, logs, cans, and other large-sized unwanted materials from raw wastewater),
(b) primary flotation clarification for removing mainly total suspended solids
from preliminary effluent, (c) secondary biological treatment units (such as
activated sludge aeration or equivalent plus secondary flotation clarification) for
removing dissolved organic/inorganic pollutants from primary effluent, and
(d) tertiary treatment plant units (i.e., filtration, granular activated carbon
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L. K. Wang et al.
Processes
Dissolved gas flotation (DGF) 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 air flotation (DAF) is one of the
dissolved gas flotation (DGF) processes when air is used for the generation of gas
bubbles. DGF or DAF is highly efficient for clarification of both water or wastewater
[101, 130–160].
The first wave of evolutionary development in potable water treatment has been
replacement of sedimentation clarifiers with dissolved air flotation (DAF) clarifiers
using commercial DAF products, such as Supracell, Sandfloat, Clari-DAF,
AquaDAF, KAMWT, etc. [101, 131, 141, 155–160]. This evolution has been
extremely successfully. The largest city in the world, New York City, has adopted
DAF for potable water treatment. The readers are referred to the Glossary section for
all technical terms and commercial product names.
The second wave of evolutionary development in wastewater treatment has
started [130, 132–140, 142–154]. Typical examples are shown in Fig. 3.21
(A suspended-growth activated sludge system uses primary flotation clarification
and secondary flotation clarification) and Fig. 3.22 (An attached-growth trickling
filter system uses primary flotation clarification and secondary flotation clarification)
[101, 157], in which traditional primary sedimentation clarification is replaced by
primary flotation clarification and traditional secondary sedimentation clarification is
replaced by secondary flotation clarification.
A few newly developed biological processes are listed below:
1. Innovative biological wastewater treatment system: It normally includes
(a) preliminary treatment units (i.e., screen, comminutor, grit chamber, etc. for
the removal of sand, gravel, cinders, coffee grounds, small stones, cigarette filter
tips, logs, cans, and other large-sized unwanted materials from raw wastewater),
(b) primary flotation clarification for removing mainly total suspended solids
from preliminary effluent, (c) secondary biological treatment units (such as
activated sludge aeration or equivalent plus secondary flotation clarification) for
removing dissolved organic/inorganic pollutants from primary effluent, and
(d) tertiary treatment plant units (i.e., filtration, granular activated carbon
136
L. K. Wang et al.