Page 59 - GRIHA Manual Volume IV - Introduction to National Rating System
P. 59
50 Griha Manual: Volume 4
Wastewater treatment stages
a. Primary treatment
This stage is used for removing suspended solids, odour, colour, and to neutralize the high or low
pH. This stage exploits the physical or chemical properties of the contaminants and removes the
suspended and floating matter by screening, sedimentation, floatation, filtration, and precipitation.
b. Secondary treatment
This stage involves biological process of stabilizing and rendering very fine, harmless suspended
matter and solids that remain after the primary treatment. In biological treatment, organic matter
is stabilized by bacteria using processes, such as stabilization ponds, trickling filter, oxidation ditch,
and activated sludge, which is then followed by sedimentation of biomass (sludge).
c. Tertiary or advanced treatment
Usually, the primary and secondary treatment is sufficient to meet the wastewater effluent
standards. However, advanced wastewater treatment is required for high-level removal of specific
pollutants, such as nitrogen or phosphorus, further removal of suspended solids, toxic substances,
biological oxygen demand (BOD), and so on, which cannot be removed by conventional secondary
treatments.
d. Disinfection
At this stage, disinfection is done to remove micro-organisms to eliminate or reduce the possibility
of disease when the flow is discharged.
e. Sludge treatment
Wastewater treatment generates sludge as one of the by-products. Sludge should ideally be further
treated for final disposal. There are primarily six stages involved in sludge treatment. They are as
follows.
1. Concentration/thickening: Separating as much water as possible by centrifuge, gravity floatation,
and clarifier.
2. Stabilization: Converting the organic solids to more refractory (inert) forms so that they can be
handled or disposed.
3. Digestion: Using biochemical methods to reduce volume as well as recover methane in anaerobic
process.
4. Conditioning: Treating the sludge with chemicals or heat so that the water can be readily
separated.
5. Dewatering: Separating water by subjecting the sludge to vacuum, pressure or drying.
6. Reduction: Converting the solids to a stable form by wet oxidation or incineration.
Table 2 further elaborates on the different types of treatment uses and contaminants removed
from the wastewater.
Wastewater treatment stages
a. Primary treatment
This stage is used for removing suspended solids, odour, colour, and to neutralize the high or low
pH. This stage exploits the physical or chemical properties of the contaminants and removes the
suspended and floating matter by screening, sedimentation, floatation, filtration, and precipitation.
b. Secondary treatment
This stage involves biological process of stabilizing and rendering very fine, harmless suspended
matter and solids that remain after the primary treatment. In biological treatment, organic matter
is stabilized by bacteria using processes, such as stabilization ponds, trickling filter, oxidation ditch,
and activated sludge, which is then followed by sedimentation of biomass (sludge).
c. Tertiary or advanced treatment
Usually, the primary and secondary treatment is sufficient to meet the wastewater effluent
standards. However, advanced wastewater treatment is required for high-level removal of specific
pollutants, such as nitrogen or phosphorus, further removal of suspended solids, toxic substances,
biological oxygen demand (BOD), and so on, which cannot be removed by conventional secondary
treatments.
d. Disinfection
At this stage, disinfection is done to remove micro-organisms to eliminate or reduce the possibility
of disease when the flow is discharged.
e. Sludge treatment
Wastewater treatment generates sludge as one of the by-products. Sludge should ideally be further
treated for final disposal. There are primarily six stages involved in sludge treatment. They are as
follows.
1. Concentration/thickening: Separating as much water as possible by centrifuge, gravity floatation,
and clarifier.
2. Stabilization: Converting the organic solids to more refractory (inert) forms so that they can be
handled or disposed.
3. Digestion: Using biochemical methods to reduce volume as well as recover methane in anaerobic
process.
4. Conditioning: Treating the sludge with chemicals or heat so that the water can be readily
separated.
5. Dewatering: Separating water by subjecting the sludge to vacuum, pressure or drying.
6. Reduction: Converting the solids to a stable form by wet oxidation or incineration.
Table 2 further elaborates on the different types of treatment uses and contaminants removed
from the wastewater.
