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Small STP Plant - STP Plant - Kelvin India
Small STP Plant

Small STP Plant

Small STP Plant

Small STP Plant: A sewage treatment plant, also known as a wastewater treatment plant, is a facility designed to remove contaminants from the water that flows through our drains and toilets. It plays a crucial role in preventing pollution and protecting public health.

At its core, a Small STP Plant works by using various physical, chemical, and biological processes to treat wastewater before it is released back into the environment. The process involves several stages that work together seamlessly to clean the water.

How does the Small STP Plant Work?

Preliminary Treatment:

  • Wastewater from homes, industries, and businesses enters the treatment plant through pipes.
  • Large objects, such as sticks, rags, and debris, are removing using screens or bar racks to prevent clogging and damage to downstream equipment.
  • Grit chambers are using to allow heavy inorganic materials like sand and gravel to settle out.

Primary Treatment:

  • The partially screened wastewater, also known as influent, enters large sedimentation tanks or clarifiers.
  • The flow of the water slows down, allowing larger suspended solids to settle at the bottom as sludge.
  • The relatively clear water at the top, called effluent, moves on to the next stage.

Secondary Treatment (Biological Treatment):

  • Effluent from primary treatment is introducing to a biological treatment process, that uses microorganisms to break down organic matter and pollutants.
  • There are several methods for secondary treatment, such as the activated sludge process, trickling filters, and rotating biological contactors.
  • In the activated sludge process, wastewater is mixing with a mixture of microorganisms in aeration tanks. Oxygen is provided to support the growth of these microorganisms, which consume the organic matter.
  • In trickling filters and rotating biological contactors, wastewater flows over a medium that supports the growth of microorganisms. These microorganisms also consume organic matter and pollutants.

Tertiary Treatment (Advanced Treatment):

  • Depending on local regulations and water quality standards, some sewage treatment plants include a tertiary treatment stage.
  • Tertiary treatment processes further remove nutrients, fine suspended particles, and other contaminants that may not have been fully removing during primary and secondary treatment.
  • Common methods include sand filtration, chemical coagulation, and advanced biological processes like membrane bioreactors.


  • After tertiary treatment, the treated water may still contain harmful pathogens and bacteria.
  • Disinfection is carring out to kill or deactivate these pathogens before the water is discharging into the environment.
  • Common disinfection methods include chlorination, ultraviolet (UV) irradiation, and zonation.

Sludge Treatment:

  • Sludge generating from primary and secondary treatment processes is treating separately.
  • Sludge may undergo anaerobic or aerobic digestion to reduce its volume, stabilize its content, and produce biogas (methane) as a byproduct.
  • Dewatering processes, such as mechanical presses or centrifuges, remove excess water from the sludge to make it more manageable for disposal or beneficial reuse.

Effluent Discharge or Reuse

  • The treated water (effluent) is typically released into natural water bodies, such as rivers or oceans, after meeting the required quality standards.
  • In some cases, the treated water can be further treated to meet higher standards and used for non-potable purposes like irrigation, industrial processes, or groundwater recharge.

The Different Types of Small STP Plant

Activated Sludge Process (ASP):

This is one of the most widely used biological treatment methods. It involves aeration tanks where microorganisms break down organic matter in the wastewater. The treated water is then separated from the activated sludge before discharge.

Extended Aeration System:

Similar to ASP, extended aeration systems also use aerobic microorganisms to treat wastewater. They provide an extended contact time between wastewater and microorganisms, resulting in highly efficient treatment.

Sequential Batch Reactor (SBR):

SBR systems operate in batches, where wastewater is added to a reactor tank, treated, and then discharged. They offer flexibility in handling variable wastewater loads and are suitable for small-scale applications.

Membrane Bioreactor (MBR):

MBR combines biological treatment with membrane filtration. It uses a membrane barrier to separate treated water from activated sludge, producing high-quality effluent suitable for reuse or discharge.

Rotating Biological Contactor (RBC):

RBC systems consist of rotating discs or media where microorganisms attach and degrade organic matter in wastewater. They are compact and suitable for decentralized wastewater treatment.

Trickling Filter System:

In trickling filter systems, wastewater is distributed over a media bed where microbial growth occurs. As wastewater trickles through the media, organic pollutants are removed by microbial action.

Constructed Wetlands:

This is a natural treatment system where wastewater flows through shallow ponds or wetland areas planted with vegetation. The plants and microorganisms in the wetland help in biological degradation and nutrient removal.

Anaerobic Digestion Systems:

Anaerobic STPs utilize anaerobic bacteria to break down organic matter in the absence of oxygen. They are effective in treating high-strength organic waste and producing biogas as a by product.

Chemical Treatment Plants:

Some small STPs incorporate chemical treatment processes such as coagulation, flocculation, and disinfection using chemicals like chlorine or ultraviolet (UV) light to treat wastewater.

Electrocoagulation Systems:

These systems use an electrical current to destabilize contaminants in wastewater, allowing for easier removal through settling or filtration processes.

How to Choose the Right Sewage Treatment Plant for Your Home

Choosing the right sewage treatment plant for your home is an important decision that can have long-term implications for you and the environment. With so many options available in the market, it can be overwhelming to determine which one is best suited for your needs. However, with a little research and consideration of key factors, you can make an informed choice.

Consider the size of your household and its wastewater generation. A smaller household may require a compact system, while larger households might need a more robust solution. Next, assess the space available on your property for installation. Different treatment plants have different spatial requirements.

Additionally, consider local regulations and permits required for installing a sewage treatment plant. Some areas may have specific guidelines or restrictions regarding their use.

Another crucial factor to consider is the maintenance requirements and costs associated with each type of sewage treatment plant. Some systems require regular servicing and upkeep, while others are more low maintenance.


Small sewage treatment plants (STPs) offer a range of options for efficiently treating wastewater in various settings. The choice of STP plant type depends on factors such as wastewater volume, characteristics, space availability, budget, and regulatory requirements.

Choosing the right small STP plant requires careful consideration of these factors and may benefit from consulting with wastewater treatment experts to ensure optimal performance, compliance, and cost-effectiveness.

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