STP Plant

STP Plant

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 sewage treatment 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 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 Sewage Treatment Plants

Conventional Activated Sludge Process: This is the most widely used method, where sewage is mixed with a microbial culture called activated sludge. The sludge breaks down organic matter through aeration and sedimentation processes.

2. Extended Aeration System: Like the conventional activated sludge process, this system provides longer aeration times for better treatment efficiency.

3. Sequential Batch Reactor (SBR): In this type of plant, wastewater goes through distinct treatment stages in separate tanks or chambers.

4. Membrane Bioreactor (MBR): MBR systems use membranes to filter out bacteria, viruses, and other contaminants from the wastewater.

5. Rotating Biological Contactor (RBC): RBC systems have rotating discs covered in microorganisms that break down pollutants as they meet them.

6. Constructed Wetlands: These natural systems use aquatic plants and microbes to treat wastewater by mimicking natural wetland 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.


Sewage treatment plants are designing to remove contaminants from wastewater before it is discharging back into the environment or reused for various purposes. The process involves several stages, including primary, secondary, and tertiary treatments, each targeting different types of pollutants.

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