Water pollution from untreated sewage and industrial waste is a health and environmental hazard. Rapid industrialisation and urbanisation have compounded the problem. The Central Pollution Control Board reported an estimated 72,368 MLD of sewage generated from urban areas, with a treatment capacity of 31,841 MLD. Sewage water treatment plants protect rivers and the environment by treating wastewater before it is released. In this blog, we explore different types sewage treatment plants used in industry.
We have already covered some types of sewage treatment plants here.
Rotating disc plants
A rotating biological contractor (RBC) or rotating disc plant uses a series of parallel rotating discs to treat sewage water. Pre-treated water enters the RBC.
The discs, made of plastics like polyethene, PVC, or expanded polystyrene, are mounted on a motor-driven shaft and spin slowly at 2 to 5 rotations per minute (rpm) inside a tank. A layer of microorganisms or bacteria called biofilm grows on the discs.
As the shaft rotates, the discs submerge approximately 40% in water. The biological growth, or bacteria, attaches to the discs and feeds off the organic matter (BOD5) in the sewage water. Acting like paddles, the discs churn the wastewater, bringing it into contact with the air, which further breaks down the pollutants and removes excess solids from the biofilms.
| Advantages | Disadvantages |
|---|---|
| High quality of effluent (both BOD and nutrients) | Continuous energy is required. |
| Short contact period | High investment, operational, and maintenance costs. |
| Low space requirement | Odour problems |
| Relatively silent compared to other treatment methods. | The treatment facility must be protected against sunlight, wind, rain, and freezing weather. |
| Low quantities of sludge | Requires skilled operator |
Submerged Aerated Filter (SAF)
The submerged aerated filter (SAF) uses a neutral buoyancy plastic media to remove pollutants. It comprises a containment tank filled with plastic media and an aeration system. Wastewater flows through the 1 to 4 m deep media bed, where beneficial bacteria (biofilm) grow and break down organic matter present in the wastewater. The plant has 1 to 4 m deep filter bed media.
How it Works:
- Pre-treatment: Wastewater typically undergoes some pre-treatment, such as settling, to remove a significant portion of suspended solids before entering the SAF. This helps prevent clogging of the media.
- Wastewater Flow: Pre-treated wastewater flows upwards through the submerged media bed.
- Biofilm Action: The plastic media provides a large surface area for the biofilm to grow and thrive. These microorganisms consume organic matter in the wastewater, breaking it into simpler compounds.
- Aeration: Diffuser systems, either at the bottom of the tank or along the reactor walls, continuously pump air into the water. This aeration process provides the oxygen necessary for the biofilm to function effectively.
- Solids Removal: As the wastewater flows through the media bed, some suspended solids and colloids get trapped and adsorbed by the biofilm.
| Advantages | Disadvantages |
|---|---|
| Does not require a large treatment area | High energy demand |
| No sludge recirculation | Reactors can clog if primary treatment is not done. |
| Can handle higher loads | Requires trained operator |
| Simple installation | Media can clog from FOG (fats, oil, and grease) |
| Sludge output is low and stable | |
| Can reduce BOD by 95 to 98% |
Suspended Media Filter (SMF)
How they work:
- Filtration Process: Water containing suspended solids enters the SMF and passes through the specialised media bed. This media has a specific pore size, allowing water to pass freely while capturing larger particles like sand, silt, and other debris. As the filtration process continues, the media bed accumulates these captured solids.
- Maintaining Efficiency: Over time, the accumulation of solids within the media bed can increase the pressure required to push water through the filter. SMF systems have an automatic backwashing mechanism to maintain optimal performance.
- Automatic Backwashing: The backwash cycle initiates when the pressure drop reaches a pre-set level or a specific time interval has elapsed. This process essentially reverses the flow of water within the filter. The system pushes clean water backwards through the media bed, dislodging the trapped solids and flushing them out. This ensures the media bed remains clean and allows the filter to function efficiently for effective filtration.
| Advantages | Disadvantages |
|---|---|
| High filtration efficiency can remove solids up to 5 microns | The water needs pre-treatment |
| Automatic operations | Limited filtration size |
| Versatile systems can be used in power generation, chemical processing, pharmaceuticals, and cooling tower systems | Media needs periodic replacement |
| Compact design | |
| Low maintenance |
Non-Electric Filter
Non-electric sewage water treatment is a sustainable and eco-friendly alternative to traditional water treatment plants. This eco-friendly approach utilizes the power of naturally occurring bacteria and a unique filtering media to achieve effective treatment.
How it Works:
- Natural Bacteria: At the heart of this system lies the principle of aerobic bacteria. These microscopic organisms thrive on oxygen and consume organic pollutants, converting them into simpler compounds.
- Coconut Coir Filtration: The biofilter employs a patented filtering media made from recycled coconut husk fragments. This natural material provides a large surface area for the beneficial bacteria to grow and adhere.
- Passive Aeration: The system relies on natural air currents to passively aerate the wastewater. This eliminates the need for electricity-powered pumps or blowers required in conventional treatment plants.
| Advantages | Disadvantages |
| Zero energy operation | Filter media requires periodic replacement |
| Silent and odourless | Limited applications |
| Compliant to stringent European standard |
Trickling Filters
A trickling filter is a traditional and well-established method for treating wastewater. It utilizes a fixed bed of media, like rocks, gravel, or plastic, over which wastewater flows downward. This environment fosters the growth of a layer of beneficial bacteria and other microorganisms forming a slimy layer called a biofilm.
How it Works:
- Wastewater Distribution: Settled sewage first enters the system and is distributed evenly over the top of the media bed through rotating arms or perforated pipes.
- Biofilm Action: As the wastewater trickles down through the media, it comes in contact with the biofilm. These microorganisms act as tiny decomposers, breaking down organic pollutants and contaminants present in the wastewater.
- Oxygen Supply: Air naturally flows up through the gaps in the media, providing the necessary oxygen for the aerobic bacteria in the biofilm to function effectively.
- Biofilm Maintenance: Over time, the biofilm layer can thicken. Pieces may slough off and get carried away with the treated effluent.
| Advantages | Disadvantage |
|---|---|
| Simple and robust design | Large land requirement |
| Energy efficient | Potential for clogging |
| Wide applications | Can generate unpleasant odours |
| Effective treatment | Efficiency can go down in cold climates. |
| Can handle fluctuations |
Leading Sewage Treatment Plant Vendors on our platforms
Capital Construction Pvt.ltd.
Capital Construction Pvt. Ltd., established in 2004 in Indore, is a verified vendor specializing in the supply, installation, erection, and commissioning of STP (Sewage Treatment Plants), among other construction services. With a robust team of 200 employees and certifications in ISO 9001, 14001, and 45001, they serve a variety of industries, including pharmaceuticals, food processing, and energy. Key clients include Vedanta, Lupin, and P&G, with notable projects such as a 200 TPD industrial gases plant for Inox Air Products.
Armstrong International Private Limited
Armstrong International Private Limited, based in Kancheepuram, specializes in the design, supply, and maintenance of STP (Sewage Treatment Plants) along with a wide array of industrial equipment. Established in 2007, the company serves key sectors such as Power & Energy, Pharmaceuticals, and Food Processing. With a workforce of 600 and ISO 9001:2015 certification, they cater to major clients, including Sanofi, ITC, and Dr. Reddy’s. Their extensive service capabilities ensure efficient and sustainable solutions for complex industrial needs.
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