STP Plant Q&A (STP)
Question: What is STP ?
Answer:
STP stands for Sewage Treatment Plant.
It is a facility that receives wastewater from domestic, commercial, and industrial buildings and removes harmful substances from it.
After treatment, the clean water can be safely discharged into rivers, canals, or reused for purposes like gardening.
The main goal of an STP is to protect the environment and promote water reuse.
Question: What is the full form of ACF & purpose of use ?
Answer:
The full form of ACF is Activated Carbon Filter.
It is used in water treatment plants to remove organic compounds and free chlorine from water.
Activated carbon filters work by adsorbing impurities onto the surface of the carbon media. This process helps improve water quality and protects downstream equipment from damage.
Question: What is the full form of MGF & purpose of use ?
Answer:
The full form of MGF is Multi Grade Filter.
Multi Grade Filters are used in water and wastewater treatment to remove suspended solids, dust, and dirt from water. They contain multiple layers of different filter media to enhance the filtration process.
This helps improve water clarity and protects downstream equipment from clogging and damage.
Question: What is water treatment plant ?
Answer:
A Water Treatment Plant (WTP) is a facility designed to purify water by removing contaminants, impurities, and harmful substances to make it suitable for specific uses- such as drinking, industrial processes, or safe discharge into the environment.
Water treatment plants play a crucial role in ensuring public health and environmental protection.
Question: What is the use of softener ?
Answer:
A softener is a device used for water softening, which removes hardness-causing ions from water.
It mainly eliminates calcium and magnesium ions that make water hard. This process helps prevent scale buildup in pipes, boilers, and appliances.
Using a softener improves water quality and extends the lifespan of plumbing systems.
Question: Function of filter feed pump ?
Answer:
The function of a filter feed pump is to supply water to the filters in a treatment plant.
It ensures a steady and controlled flow of water to the filtration units for effective operation. Maintaining proper pressure and flow is essential for optimal filter performance.
A reliable filter feed pump helps achieve consistent water quality during the treatment process.
Question: What is the treatment cycle in STP ?
Answer:
The treatment cycle in an STP (Sewage Treatment Plant) involves several key stages.
It typically includes the screen bar chamber, oil & grease (O&G) chamber, equalization tank, MBBR tank, tube settler tank, clear water tank, filters, and treated water tank.
Each stage is designed to remove specific contaminants and improve the quality of wastewater.
This systematic process ensures that the treated water is safe for discharge or reuse, such as for gardening.
Question: Source of water to the building ?
Answer:
The main source of water to a building is typically the wastewater generated within the building itself.
This wastewater comes from various activities such as bathing, washing, cleaning, and other domestic uses.
It is collected through a network of drainage pipes and directed to the sewage treatment plant (STP) for processing.
Proper management of this wastewater is essential for environmental protection and water reuse.
Question: What is the purpose of backwash the filter ?
Answer:
The purpose of backwashing a filter is to remove trapped debris, contaminants, and accumulated particles from the filter media.
During normal operation, filters collect dirt and impurities from water or other fluids. Over time, this buildup reduces the filter's efficiency and flow rate.
Backwashing reverses the flow of fluid through the filter, flushing out the collected debris and restoring the filter's performance.
Question: What is COD ?
Answer:
COD stands for Chemical Oxygen Demand. It is a measure of the amount of oxygen required to chemically oxidize organic and inorganic matter in water.
COD is used to assess the level of pollution in wastewater and surface water. A lower COD value indicates cleaner water.
Typical acceptable range for treated wastewater is below 250 mg/L, depending on local environmental regulations.
Question: What is BOD ?
Answer:
BOD stands for Biochemical Oxygen Demand (also called Biological Oxygen Demand).
It measures the amount of oxygen required by microorganisms to break down organic matter in water over a specific period, usually 5 days at 20°C.
BOD is an important indicator of water quality and pollution levels. For treated wastewater, the acceptable BOD range is typically around 30 mg/L or lower, depending on environmental standards and discharge regulations.
Question: What is TDS ?
Answer:
TDS (Total Dissolved Solids) refers to the combined content of all inorganic and organic substances dissolved in water, including minerals, salts, and metals.
It is an important parameter for assessing water quality, especially in drinking water and industrial applications. High TDS levels can affect the taste, hardness, and safety of water.
For general water use, the acceptable TDS range is typically below 2100 mg/L, but for drinking water, the recommended limit is usually below 500 mg/L, depending on local standards.
Question: What is the purpose of the Screen Bar Chamber in an STP? Answer: The screen bar chamber is the first stage of the STP. Its primary purpose is to remove large floating objects such as plastic bottles, rags, paper, and sticks from the incoming sewage. By catching these large solids at the entry, it protects downstream pumps and equipment from clogging or mechanical damage.
Question: Why is the Oil and Grease (O&G) Chamber necessary?
Answer: The O&G chamber uses the principle of gravity to separate oil, fat, and grease from the wastewater. Since oil is lighter than water, it floats to the surface where it is skimmed off. Removing oil is critical because it can coat the media in biological tanks (like MBBR), preventing microorganisms from receiving oxygen and effectively "suffocating" the treatment process.
Question: What is the function of the Equalization (EQ) Tank?
Answer: The EQ tank acts as a buffer. Sewage flow into a building is not constant; it peaks in the morning and evening. The equalization tank collects this variable flow and allows the plant to pump a constant, steady volume of water into the treatment tanks. This prevents the biological system from being "shocked" by sudden surges of water.
Question: What is MBBR technology?
Answer: MBBR stands for Moving Bed Biofilm Reactor. It uses small plastic carriers (media) that circulate in an aerated tank. These carriers provide a large surface area for helpful bacteria to grow. As the media moves through the sewage, the bacteria "eat" the organic pollutants. MBBR is popular because it is compact and can handle higher loads than traditional systems.
Question: What is the role of the Air Blower in an STP?
Answer: The air blower provides a continuous supply of oxygen to the aeration tanks (like MBBR or SBR). This oxygen is essential for aerobic bacteria to survive and break down organic matter (BOD). Additionally, the air from the blowers keeps the MBBR media in constant motion, ensuring it mixes thoroughly with the sewage.
Question: What is the purpose of a Tube Settler Tank?
Answer: The Tube Settler is used for clarification after biological treatment. It contains inclined plastic tubes (lamella) that increase the effective settling area. As water flows upward through the tubes, the heavy biological solids (sludge) settle on the tube surfaces and slide down to the bottom, while clear water flows out from the top.
Question: What is "Activated Sludge" and "RAS"?
Answer: Activated Sludge is the mass of microorganisms used to treat sewage. RAS (Return Activated Sludge) is the process of pumping a portion of the settled sludge from the clarifier back into the aeration tank. This ensures a high concentration of "hungry" bacteria is always available to treat the incoming raw sewage.
Question: What is SBR (Sequential Batch Reactor) technology?
Answer: SBR is a "fill-and-draw" batch treatment system. Unlike MBBR, which is a continuous flow process, SBR performs all treatment steps—aeration, settling, and decanting—in a single tank in a timed sequence. It is highly efficient and often requires less space than traditional systems.
Question: What is the function of the Sludge Holding Tank and Filter Press?
Answer: The sludge holding tank collects the excess waste sludge produced during treatment. A Filter Press or Sludge Drying Bed is then used to remove water from this sludge. The result is a solid "sludge cake" that can be used as manure for gardening, while the separated water is sent back to the equalization tank for re-treatment.
Question: What is the "F/M Ratio" in STP operation?
Answer: The F/M Ratio stands for Food-to-Microorganism ratio. It is a calculation used to balance the amount of incoming organic matter (food) with the amount of bacteria (microorganisms) in the system. If the ratio is too high, the bacteria can't keep up; if it's too low, the bacteria may die off. Maintaining this balance is key to achieving low BOD levels.
Question: What is "MLSS" and why is it monitored?
Answer: MLSS stands for Mixed Liquor Suspended Solids. It represents the total concentration of solids (mostly bacteria) in the aeration tank. Operators monitor MLSS to ensure there is enough biological mass to treat the sewage. Typical MLSS values for an MBBR or Activated Sludge plant range from 2000 to 5000 mg/L.
Question: How does Chlorine Dosing work in an STP?
Answer: After filtration, the water is dosed with chlorine (usually sodium hypochlorite) in a "Chlorine Contact Tank." This kills any remaining pathogens or bacteria before the water is reused for gardening or flushing. It ensures the water is safe for human contact and prevents the growth of algae in storage tanks.
Question: What is the purpose of the Treated Water Tank?
Answer: The treated water tank is the final storage point. Water here has passed through biological treatment, settling, and dual-media filtration (MGF/ACF). This water is now clear, odorless, and safe. It is typically pumped from here to the building's flushing line or gardening sprinklers.
Question: What does it mean if the STP aeration tank is producing excessive white foam?
Answer: Excessive white foam usually indicates "Young Sludge" or a high F/M ratio, often caused during the initial startup of the plant or if a large amount of detergent (soap) has entered the system. It can be managed by adjusting the sludge wasting rate or using anti-foaming agents.
Question: Why is the treated water coming out cloudy or turbid?
Answer: Cloudy water can be caused by several factors:
Over-aeration: Breaking up the floc particles.
Filter Failure: The MGF or ACF media may need replacement or a longer backwash.
Low MLSS: Not enough bacteria to settle properly in the tube settler.
Question: What is the cause of "Rotten Egg" smell (H2S) in an STP?
Answer: A rotten egg smell indicates Anaerobic conditions, meaning there is a lack of oxygen. This usually happens if the air blowers are turned off for too long or if the sewage has become stagnant in the equalization tank. Increasing aeration usually solves this problem.