Page 58 - GRIHA Manual Volume IV - Introduction to National Rating System
P. 58
Building planning and construction 49
chemical, and biological means. The individual methods usually are classified as physical unit
processes, chemical unit processes, and biological unit processes. These operations and processes
are often found to occur in a variety of combinations in treatment systems; however, it is good to
understand the scientific basis separately as the principles remain the same.
Physical unit operations
Treatment methods in which the application of physical forces predominates are known as physical
unit operations. The impurities are removed physically by screening, sedimentation, filtration,
flotation, absorption or adsorption or both, centrifugation, and so on.
Chemical unit operations
Treatment methods in contaminants are removed by adding chemicals or by other chemical
reactions. Precipitation, gas transfer, adsorption, and disinfection are the most common examples
under this category. In chemical precipitation, treatment is done by producing a chemical precipitate
that settles down. Adsorption involves the removal of specific compounds from the wastewater on
solid surfaces using the forces of attraction between bodies.
Biological unit operations
In this, the removal of contaminants is brought about by biological activity. Biological treatment
is used primarily to remove the biodegradable organic substances (colloidal or dissolved) in
wastewater. These operations are broadly classified as aerobic, anaerobic systems, and waste
stabilization pond system, which is a combination of the two.
a) Aerobic systems
These could be aerobic fixed film or aerobic dispersed growth systems. In these treatment systems,
a solid medium is provided to which the micro-organisms can attach themselves and develop a
biological film or the micro-organisms are grown in a reactor to encourage growth and enable
contact with the organic part of the waste. The earliest form of attached growth treatment process
was the biological filter of which many variants have been developed over time, such as Rotating
Biological Contractors (RBCs), and Biological Aerated Filters (BAF). Examples of aerobic dispersed
growth systems are Activated Sludge (conventional, high-rate, extended aeration) Systems,
Oxidation ditches, and so on.
b) Anaerobic systems
In anaerobic systems, the decomposition of organic matter takes place under anaerobic condition
in various waste disposal systems, such as septic tanks, aqua privies, biogas units, sludge digestion
plants, and so on. It is in the design and operation of sludge digester and biogas units that serious
attempts have been made to harness the high resources recovery potential of the anaerobic
decomposition process.
c) Waste stabilization ponds (WSP)
It is a combination of both aerobic and anaerobic systems. Major types of such ponds are anaerobic
ponds, facultative ponds, maturation ponds, and aerated lagoon. Various combinations of these
ponds are used for the treatment of wastewater.
chemical, and biological means. The individual methods usually are classified as physical unit
processes, chemical unit processes, and biological unit processes. These operations and processes
are often found to occur in a variety of combinations in treatment systems; however, it is good to
understand the scientific basis separately as the principles remain the same.
Physical unit operations
Treatment methods in which the application of physical forces predominates are known as physical
unit operations. The impurities are removed physically by screening, sedimentation, filtration,
flotation, absorption or adsorption or both, centrifugation, and so on.
Chemical unit operations
Treatment methods in contaminants are removed by adding chemicals or by other chemical
reactions. Precipitation, gas transfer, adsorption, and disinfection are the most common examples
under this category. In chemical precipitation, treatment is done by producing a chemical precipitate
that settles down. Adsorption involves the removal of specific compounds from the wastewater on
solid surfaces using the forces of attraction between bodies.
Biological unit operations
In this, the removal of contaminants is brought about by biological activity. Biological treatment
is used primarily to remove the biodegradable organic substances (colloidal or dissolved) in
wastewater. These operations are broadly classified as aerobic, anaerobic systems, and waste
stabilization pond system, which is a combination of the two.
a) Aerobic systems
These could be aerobic fixed film or aerobic dispersed growth systems. In these treatment systems,
a solid medium is provided to which the micro-organisms can attach themselves and develop a
biological film or the micro-organisms are grown in a reactor to encourage growth and enable
contact with the organic part of the waste. The earliest form of attached growth treatment process
was the biological filter of which many variants have been developed over time, such as Rotating
Biological Contractors (RBCs), and Biological Aerated Filters (BAF). Examples of aerobic dispersed
growth systems are Activated Sludge (conventional, high-rate, extended aeration) Systems,
Oxidation ditches, and so on.
b) Anaerobic systems
In anaerobic systems, the decomposition of organic matter takes place under anaerobic condition
in various waste disposal systems, such as septic tanks, aqua privies, biogas units, sludge digestion
plants, and so on. It is in the design and operation of sludge digester and biogas units that serious
attempts have been made to harness the high resources recovery potential of the anaerobic
decomposition process.
c) Waste stabilization ponds (WSP)
It is a combination of both aerobic and anaerobic systems. Major types of such ponds are anaerobic
ponds, facultative ponds, maturation ponds, and aerated lagoon. Various combinations of these
ponds are used for the treatment of wastewater.
