STP stands for Sewage Treatment Plant. The Central Public Works Department (CPWD) in India has developed its own set of specifications and guidelines for STP construction and operation.
Some of the key aspects covered in the CPWD specifications for STP include:
Site Selection and Planning - This includes selecting an appropriate site for the STP, planning the layout of the STP, and ensuring adequate space for future expansion.
Design and Construction - This includes designing and constructing the various components of the STP, such as screens, grit chambers, sedimentation tanks, aeration tanks, clarifiers, and disinfection units. The specifications also cover the materials to be used for construction, quality control measures, and safety precautions.
Operation and Maintenance - This includes guidelines for operating and maintaining the STP, including daily checks, regular maintenance activities, and record keeping. The specifications also cover the training of operators and the handling of sludge generated by the STP.
Testing and Commissioning - This includes guidelines for testing and commissioning the STP, including the performance of various tests to ensure that the STP meets the required standards.
It's important to note that the CPWD specifications and guidelines for STP are specific to India and may differ from other countries' standards. It's always recommended to consult with qualified professionals and adhere to the relevant codes and standards when designing, constructing, and operating STPs in India.
Working Principle of STP
The working principle of STP as per CPWD involves several stages of treatment to purify sewage and make it suitable for reuse or discharge into the environment. The CPWD STP design follows the following process:
Preliminary Treatment: In this stage, the wastewater is screened to remove large objects such as plastic bags, bottles, and other debris that could damage the treatment equipment.
Primary Treatment: In this stage, the wastewater is allowed to settle in a tank, and solids settle to the bottom. The settled solids, also called sludge, are then removed and sent to the sludge handling unit for further treatment.
Secondary Treatment: This stage involves the use of biological processes to further treat the wastewater. The wastewater is sent to an aeration tank where microorganisms are added to break down the organic matter in the water.
Tertiary Treatment: In this stage, the water is disinfected using chemicals such as chlorine to kill any remaining bacteria and viruses. The water is then polished using a sand filter to remove any remaining solids.
Sludge Handling: The sludge that is removed from the primary treatment tank is sent to a sludge handling unit for further treatment. The sludge is thickened and dewatered, and the resulting sludge cake can be used as fertilizer or disposed of in an environmentally friendly manner.
Overall, the CPWD STP design aims to provide a cost-effective and efficient way to treat sewage and protect the environment by removing harmful pollutants from wastewater before it is discharged or reused.
The STP or Sewage Treatment Plant as per CPWD, involves several stages
of treatment to purify sewage for reuse or discharge. The process
includes preliminary treatment, primary treatment, secondary treatment,
tertiary treatment, and sludge handling. The preliminary treatment
removes large objects, primary treatment settles solids, secondary
treatment uses biological processes, tertiary treatment disinfects the
water, and sludge handling thickens and dewatered the sludge. The CPWD
STP design aims to provide a cost-effective and efficient way to treat
sewage and protect the environment by removing harmful pollutants from
wastewater before it is discharged or reused.
STP Equipment's:
Some of the common equipment used in a Sewage Treatment Plant (STP) are:
Bar Screen: This is a mechanical equipment that removes large objects and debris from the wastewater.
Grit Chamber: This equipment removes sand, gravel, and other heavy materials that settle in the wastewater.
Primary Clarifier: This is a tank where wastewater is allowed to settle, and solids (sludge) are removed.
Aeration Tank: This is a tank where wastewater is treated with microorganisms that break down organic matter.
Secondary Clarifier: This is a tank where the treated water is allowed to settle, and remaining solids (sludge) are removed.
Sand Filter: This equipment removes remaining solids from the treated water.
Disinfection Unit: This equipment disinfects the water using chemicals such as chlorine to kill any remaining bacteria and viruses.
Sludge Drying Beds: These are used to dewater the sludge before it is disposed of.
Sludge Digesters: These are tanks where sludge is broken down by microorganisms to produce methane gas.
Screw Press: This equipment dewater the sludge using a screw mechanism.
Ultraviolet disinfection system: This equipment uses UV light to disinfect the water.
These are some of the common equipment used in a Sewage Treatment Plant (STP), and the specific equipment used depends on the type and size of the plant.
Various Pumps used in STP:
There are several types of pumps used in Sewage Treatment Plants (STPs) to transport wastewater and sludge. Some of the common pumps used in STPs are:
Centrifugal Pumps: These pumps are commonly used to transfer raw wastewater and treated water between different stages of the treatment process. They are also used to move sludge and other fluids throughout the plant.
Positive Displacement Pumps: These pumps are used to transport thick or viscous sludge that cannot be transported by centrifugal pumps. Positive displacement pumps can handle higher pressures and can be used to move sludge through long pipelines.
Submersible Pumps: These pumps are used to lift raw wastewater from the influent chamber to the headworks or preliminary treatment stage. They are also used in the aeration tank to provide oxygen to the microorganisms that break down organic matter.
Air Operated Diaphragm Pumps: These pumps are used to move sludge from the sludge digesters to the sludge dewatering unit. They are also used in the chemical dosing process to add chemicals to the water for disinfection.
Screw Pumps: These pumps are used to move thick or viscous sludge, and they can handle high pressures and flow rates. Screw pumps are commonly used in sludge dewatering and thickening processes.
Progressive Cavity Pumps: These pumps are used to transport thick sludge and slurry with high solid content. They can handle highly abrasive and corrosive materials and are commonly used in the dewatering and thickening processes.
The specific type of pump used in a STP depends on the specific application, flow rate, head, and other factors.
Testing of STP
The testing of a Sewage Treatment Plant (STP) is an important step to ensure that the plant is operating efficiently and effectively. Here are some common tests performed on a STP:
Flow Test: This test measures the flow rate of wastewater entering and leaving the plant. It is important to ensure that the plant is able to handle the peak flow rates and that the treatment process is not overloaded.
Chemical Oxygen Demand (COD) Test: This test measures the amount of organic matter in the wastewater. It is an indicator of the effectiveness of the treatment process and the amount of oxygen required for the biological processes.
Total Suspended Solids (TSS) Test: This test measures the amount of solid material in the wastewater. It is an important indicator of the performance of the primary and secondary treatment processes.
pH Test: This test measures the acidity or alkalinity of the wastewater. It is important to maintain the pH within a certain range for the microorganisms to function properly.
Dissolved Oxygen (DO) Test: This test measures the amount of oxygen dissolved in the wastewater. It is important to maintain a certain level of dissolved oxygen in the aeration tank for the microorganisms to function properly.
Chlorine Residual Test: This test measures the amount of residual chlorine in the treated water. It is important to ensure that the disinfection process is effective and that the water is safe for reuse or discharge.
Sludge Volume Index (SVI) Test: This test measures the settleability of the sludge. It is important to ensure that the sludge can settle properly in the clarifier and does not interfere with the treatment process.
These are some common tests performed on a STP to ensure that the plant is operating efficiently and effectively. The frequency and scope of the tests may vary depending on the size and complexity of the plant, as well as regulatory requirements.
STP water test as per CPWD
The Central Public Works Department (CPWD) of India follows various tests and standards for the water quality of Sewage Treatment Plants (STPs). The water tests for STPs are carried out to ensure that the treated water meets the required quality standards before it is discharged into the environment or reused.
Here are some of the tests that CPWD typically conducts for the water quality of STPs:
pH: The pH of the treated water should be between 6.5 and 8.5, as per the CPWD guidelines.
Biological Oxygen Demand (BOD): BOD is the amount of oxygen required by microorganisms to break down organic matter in the water. The BOD level of the treated water should be less than 30 mg/l, as per CPWD guidelines.
Chemical Oxygen Demand (COD): COD is the amount of oxygen required to chemically oxidize the organic matter in the water. The COD level of the treated water should be less than 250 mg/l, as per CPWD guidelines.
Total Dissolved Solids (TDS): TDS is the total amount of inorganic and organic substances that are dissolved in the water. The TDS level of the treated water should be less than 500 mg/l, as per CPWD guidelines.
Total Suspended Solids (TSS): TSS is the total amount of solid particles that are suspended in the water. The TSS level of the treated water should be less than 30 mg/l, as per CPWD guidelines.
Coliform Count: Coliforms are a group of bacteria that are commonly found in sewage. The treated water should not contain any coliforms, as per CPWD guidelines.
These tests are conducted periodically as per CPWD guidelines to ensure that the STP is functioning effectively and the treated water meets the required quality standards.
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