Sewage Treatment Plant (STP)
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A Sewage Treatment Plant (STP) is a complete and scientifically engineered system used to purify wastewater and make it suitable for reuse in applications such as gardening, agriculture, flushing, and other non-potable purposes. The quality standards for treated sewage water are strictly regulated by the Pollution Control Board, making STPs mandatory in most industries, residential complexes, housing colonies, and commercial buildings. Modern STPs are equipped with high-precision equipment, automation, and advanced treatment technologies to ensure consistent performance and environmental compliance.
STP is often confused with ETP (Effluent Treatment Plant), but there is a clear distinction between the two. While an ETP is mainly used to treat industrial wastewater containing chemicals and process residues, an STP is specifically designed to treat domestic sewage and mixed effluents from residential and commercial sources. The working principle of an STP is based on controlled aeration that promotes the growth of beneficial bacteria, which naturally break down organic waste and harmful pollutants. The objective is to produce significantly cleaner, eco-friendly water that is safe for discharge or reuse.
Depending on capacity and design, a sewage treatment plant can serve a single commercial facility or an entire residential community. The treatment process is carried out in multiple stages—primary, secondary, biological, and tertiary—each playing a critical role in removing solids, organic load, pathogens, and residual impurities. In Bangladesh, MHT Filtration stands as one of the leading sewage treatment plant service providers, working successfully in collaboration with various organizations to enhance wastewater quality and promote sustainable water recycling.
How Does a Sewage Treatment Plant (STP) Work?
A Sewage Treatment Plant (STP) works through a step-by-step purification system that removes physical waste, organic pollutants, and harmful microorganisms from wastewater, making it safe for discharge or reuse. The entire process is divided into well-defined treatment stages, each with a specific role in improving water quality.
1. Primary Treatment – Physical Separation
In the first stage, raw sewage enters the STP and passes through screening units where large materials like plastics, cloth, stones, and solid debris are removed. After screening, the wastewater flows into a grit chamber where heavy sand and grit settle at the bottom. It then enters a primary settling tank (clarifier) where suspended solids and sludge gradually settle, reducing the initial pollution load of the water.
2. Secondary Treatment – Biological Breakdown
This is the most critical stage of the STP. The partially treated water is transferred into aeration tanks where air is supplied continuously. This oxygen supports the growth of beneficial bacteria that consume dissolved organic waste. These microorganisms convert harmful pollutants into harmless by-products like carbon dioxide, water, and biomass. The water then passes into a secondary clarifier where the biological sludge settles, and clear treated water flows forward.
3. Tertiary Treatment – Advanced Purification
In this advanced stage, the water is filtered through sand, carbon, or membrane systems to remove any remaining fine particles. Disinfection is then carried out using chlorine, ultraviolet (UV) light, or ozone to destroy harmful bacteria and viruses. This ensures the treated water meets safety and environmental reuse standards.
4. Sludge Treatment & Disposal
The sludge collected from the primary and secondary clarifiers is thickened, dewatered, and safely disposed of or reused as manure after proper treatment. This step prevents environmental contamination and supports waste-to-resource practices.
Key Benefits of a Sewage Treatment Plant (STP)
✅ Protects the environment from water pollution
✅ Prevents contamination of groundwater
✅ Enables reuse of treated water
✅ Reduces health risks and bad odors
✅ Ensures compliance with environmental laws
✅ Saves fresh water resources
✅ Supports sustainable water management
A Sewage Treatment Plant (STP) is widely used in:
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Residential buildings and housing projects
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Hospitals and healthcare centers
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Hotels, resorts, and restaurants
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Shopping malls and commercial complexes
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Industrial plants and factories
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Educational institutions
Why Are Sewage Treatment Plants (STP) Necessary in Bangladesh?
1. Rapid Urbanization & Population Growth
Cities like Dhaka, Chattogram, and Narayanganj generate massive volumes of wastewater every day. Without STP, this untreated sewage directly pollutes rivers and low-lying areas.
2. Protection of Public Health
Untreated sewage spreads deadly diseases such as cholera, diarrhea, typhoid, and hepatitis. STP removes harmful bacteria, viruses, and pathogens, keeping communities safe.
3. River & Environmental Protection
Major rivers like Buriganga, Turag, Shitalakshya, and Karnaphuli are heavily polluted by raw sewage. STP helps prevent:
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Fish death
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Water toxicity
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Ecosystem destruction
4. Safe Water Reuse
Treated water from STP can be reused for:
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Gardening
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Landscaping
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Industrial cooling
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Cleaning purposes
5. Legal & Regulatory Compliance
Bangladesh Environment Conservation Rules (ECR) require:
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Industries, housing projects, hospitals, and commercial buildings to install STP
Non-compliance can lead to legal penalties and project shutdowns.
6. Support for Sustainable Development
STP is essential for:
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Smart cities
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Eco-friendly housing
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Green industrial zones
It directly supports SDG-6 (Clean Water & Sanitation).
7. Prevention of Groundwater Contamination
Raw sewage seeps into soil and contaminates underground water sources, making tube-well water unsafe. STP prevents this silent long-term threat.
FAQs about Sewage Water Treatment Plant
What is Sewage?
Sewage is wastewater that comes from homes, industries, and other places, containing waste materials, dirt, and harmful substances.
What is Sewage Treatment Plant?
A Sewage Treatment Plant (STP) is a system used to treat wastewater coming from homes, industries, and commercial areas. It removes solid waste, harmful chemicals, and disease-causing germs through physical, chemical, and biological processes. After treatment, the water becomes safe for discharge into the environment or for reuse in gardening and other purposes.
What is the Sewage Treatment Plant Purposes?
Sewage treatment plants provide a service that is vital to the environment and public health by collecting, treating, and discharging wastewater. Sewage will leak into the environment and contaminate ecosystems if it is not properly treated.
What are sewage treatment’s five stages?
1. Preliminary Treatment – Removes large objects like plastic, stones, and rags.
2. Primary Treatment – Separates solid waste by settling in tanks.
3. Secondary Treatment – Uses bacteria to break down organic waste.
4.Tertiary Treatment – Further cleans water by removing chemicals and nutrients.
5. Disinfection – Kills remaining germs using chlorine, UV, or ozone.
How does an STP plant work?
A Sewage Treatment Plant (STP) works by passing dirty wastewater through several treatment steps to make it safe for discharge or reuse. First, large waste like plastic and rags are removed through screening. Then, in primary treatment, heavy solids settle at the bottom of tanks. After that, in secondary treatment, helpful bacteria break down organic waste using oxygen in aeration tanks. Next, tertiary treatment further cleans the water by removing fine impurities and chemicals. Finally, the water is disinfected using chlorine, UV, or ozone to kill harmful germs before it is released or reused.
How is the wastewater treatment process referred to?
Sewage or wastewater treatment refers to the process of treating wastewater.
ABOUT MHT FILTRATION LIMITED
MHT Filtration Ltd. is Bangladesh’s first and leading water technology company. Since 2017, we've been dedicated to providing complete water treatment solutions and guaranteeing access to clean, safe water nationwide through our range of premium imports like RO membranes, purifiers, and industrial pumps.