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Sewage Treatment Plant

A Sewage Treatment Plant (STP) is a wastewater treatment system specifically designed to purify domestic wastewater. Its primary goal is to ensure that the treated water is safe for environmental release, mitigating the harmful effects of sewage.

We offer design, erection and commissioning of STP(s) starting from 10KL per day.

We provide custom STP solutions in two main forms:

  1. Civil Construction STP: This type of STP integrates seamlessly with existing infrastructure, offering robustness and durability.
  2. Packaged STP: Available in Fiber Reinforced Plastic (FRP) / Mild Steel (MS) constructions, these compact and portable units are pre-fabricated and ready for quick installation.
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Choose the best option that suits your needs, whether you prefer the permanence of civil construction or the convenience of a packaged solution.

How to choose a Right STP? click on the link to know more

How does a STP works?

The STP operates at multiple levels, employing physical, chemical, biological, and membrane processes to treat wastewater. There are four stages of treatment: Preliminary, primary, secondary and tertiary.

Preliminary treatment in a Sewage Treatment Plant (STP) involves the initial steps to remove large and heavy materials from the wastewater. This typically includes:

  1. Screening: Removing large debris / solid materials like tree branches, bottles, and plastic wrappers using screens.
  2. Grit Removal: Allowing sand, gravel, and other heavy particles to settle out by reducing the flow velocity.
  3. Flow Measurement and Control: Assessing and managing the flow rate to ensure efficient treatment downstream.

Primary Treatment focuses on eliminating solid materials and lowering pollution levels. The aim is to prepare the water for further treatment and to decrease the Biochemical Oxygen Demand (BOD) and Total Suspended Solids (TSS) in the sewage.

  1. Equalization: The main objective of this process is to maintain a pH range of 6 to 9, which is essential for the proper functioning of the different processing units within the STP system.
  2. Coagulation: It is a process where coagulants are added to quickly settle tiny solid particles in a sewage into larger masses, allowing for their removal through sedimentation and filtration.
  3. Sedimentation: Sewage is held in large settling tanks where heavier solids settle at the bottom as sludge.

Primary Clarifiers are equipped with devices that remove floating solids from the surface and large solid masses that settle at the bottom of the tank.

Secondary treatment aims to eliminate suspended solids and residual organic matter from the primary treated sewage using biological processes. Secondary treatment usually aims to reduce upto 90% of BOD in sewage.

  1. Biological treatment:  is a common method that uses microorganisms to remove organic matter and pollutants from sewage.
  2. Aerobic: Uses oxygen to break down organic matter. This is the more common method and can be further classified as suspended growth or attached growth. 

Activated Sludge Process (ASP) click on the link to know more
Moving Bed Bio Reactor (MBBR) click on the link to know more
Membrane Bio Reactor (MBR) click on the link to know more
Sequencing Batch Reactor (SBR) click on the link to know more

  • Anaerobic: Functions in oxygen-deprived conditions and is often used for high-strength organic Sewage. Anaerobic digestion produces biogas as a byproduct. 

Up-flow Anaerobic sludge blanket (UASB) click on the link to know more

  • Secondary clarifier: It is a unit operation in sewage treatment plants that separates solids from biologically treated sewage. The wastewater-sludge mixture flows into the secondary clarifier where the sludge settles. The clear water is then directed to next stage of treatment and the sludge is returned to the biological reactor.

Tertiary treatment is the final stage in the wastewater treatment process, ensuring that the waste quality meets required standards before it is recycled, reused, or discharged into the environment.

  1. Disinfection: Wastewater is disinfected to destroy or inactivate disease-causing organisms. Here are some methods:
  2. Chlorination: Uses chlorine to kill bacteria and control organisms; cost-effective and Odor-eliminating.
  3. Ultraviolet (UV) Radiation: Inactivates bacteria and viruses by altering their DNA; effective for small wastewater flows.
  4. Ozone: Attacks microbes using ozone molecules and hydroxyl radicals.

2.   Filtration: Uses semi-permeable membranes to remove contaminants from the water. The membranes allow water molecules to pass through, but block contaminants. Different types of membrane filtration include microfiltration, ultrafiltration, nanofiltration, Reverse Osmosis.

  • Ultra-filtration: UF uses a semipermeable membrane with pores ranging from 0.01 to 0.1 microns. The membrane blocks particles larger than a specific size, removing bacteria, viruses, and other contaminants. click on the link to know more
  • Nano-filtration: NF uses semi-permeable membranes to remove the particles that are about 1 nanometre in size. They remove contaminants from sewage, including ions and organic substances.
  • Recycle RO (Reverse Osmosis): A Reverse Osmosis plant can further eliminate dissolved solids from the sewage, allowing the water to be reused. click on the link to know more