How Sewage Treatment Plant works?

What is STP?

Estimates vary, but an average each person uses approximately 100-150 Liters of fresh water per day, for indoor house applications such as cooking, Body cleansing, cleaning of clothes & kitchen utensils, toilet flushing etc. But What Happens to this dirty water when it leaves from our area of applications?

This wastewater is drained through the pipeline systems and then enters the common sewerage system where it gets treated. We called this system as Sewage Treatment Plants aka STP.

So, a STP is designed for treating wastewater which generates from Houses, commercial buildings, colony, apartments, or Industrial units. Sometimes this wastewater fed together with rainwater that accumulate on sealed surfaces such as streets or roofs.


How it works?

Essentially, a sewage treatment plant operates by circulating air to encourage the growth of bacteria to break down sewage. The goal being to deliver much cleaner, more environmentally friendly effluent.

Years ago, when sewage was dumped into waterways, a natural process of purification began. First, the sheer volume of clean water in the stream diluted wastes. Bacteria and other small organisms in the water consumed the sewage and other organic matter, turning it into new bacterial cells, carbon dioxide and other products. Today’s higher populations and greater volume of domestic and industrial wastewater require that communities give nature a helping hand. The basic function of wastewater treatment is to speed up the natural processes by which water is purified.

There are two basic stages in the treatment of wastes, primary and secondary, which are outlined here.


In the primary stage, solids are allowed to settle and removed from wastewater.

The secondary stage uses biological processes to further purify wastewater. Sometimes, these stages are combined into one operation.


Primary Treatment- As sewage enters a plant for treatment, it flows through a screen / Grit chamber, which removes large floating objects such as rags and sticks that might clog pipes or damage equipment. After sewage has been screened, it passes into a grit chamber, where pieces of threads, plastics, sand, and small stones settle to the bottom. Then these solids are minute particles that can be removed from sewage in a sedimentation tank. Over the years, primary treatment alone has been unable to meet many communities’ demands for higher water quality. To meet them, cities and industries normally treat to a secondary treatment level, and in some cases, also use advanced treatment to remove nutrients and other contaminants.


Secondary Treatment- The secondary stage of treatment removes about 85-90 percent of the organic matter in sewage by making use of the bacteria in it.


How helpful bacteria are? 

After the sewage leaves the settling tank in the primary stage, it is pumped into an aeration tank, where it is mixed with air and sludge loaded with bacteria and allowed to remain for several hours. During this time, the bacteria break down the organic matter into harmless by-products.

The bacteria and fungi have the task of metabolizing organic components in the wastewater into its individual parts. This process is called biological nutrient removal. Oxygen-rich and oxygen poor areas providing optimal conditions for breaking down all carbon and phosphate compounds and urea from the urine.

The secondary clarifier is used again for sedimentation. Here, bacterial flakes and other components that have no place in clean water sink to the bottom of the tank. In the end, the clarified water is returned to the natural water cycle, usually lakes or streams.

Very modern sewage treatment plants have additional treatment stages for further phosphorus elimination or the killing of pathogens. Bacterial flakes and sludge are processed into gas in digestion towers and in many cases are used to supply the sewage plant with energy.

To complete secondary treatment, effluent from the sedimentation tank is usually disinfected with chlorine before being discharged into receiving waters. Chlorine is fed into the water to kill pathogenic bacteria, and to reduce odor. Done properly, chlorination will kill more than 99 percent of the harmful bacteria in an effluent.


Advantages of a sewage treatment plant

  • Reliable and unlikely to encounter problems with only regular maintenance.
  • Can be installed even on challenging or compact sites.
  • Cost-effective over time, with only installation, power, and maintenance to pay for
  • Skid mounted systems to avoid civil works and to upgrade capacity easily.
  • Mobilized units, can shift to another unit.
  • Plug and play model using Skid mounted systems.


Disadvantages of a sewage treatment plant

  • The plant needs a constant supply of electricity to run.
  • Will require professional maintenance annually, and in the unlikely event of problems.
  • Design and installation of the system needs to be undertaken professionally.
  • Treated effluent have very limited applications.

As you can see, the biggest disadvantage of having a STP is that you are relying heavily on maintenance from a professional company. This means that you will have to wait for any problems, however unlikely they are, to be resolved, and makes choosing the supplier of the service absolutely crucial.

With ROSERVE, you can not only rely of Design, Installation, regular operation & Maintenance but also can benefit from our unique OPEX solutions.

 The advantages with ROSERVE are:

  • No capital Investment.
  • Advance treatment system with facility of upgradation in technologies.
  • Plug and Play model can save your time.
  • Skid mounted and containerized units to save lots of civil costs and ease of moveability from one site to another as and when required.
  • Using RO system can recycle treated effluent for the applications such as cleaning, washing, flushing, and gardening.

Here at ROSERVE, we’re not only ready and waiting to take your call and discuss your options and queries, we’re also dedicated to ensuring that your sewage treatment is reliable at all times. To learn more about the installation or maintenance of a sewage treatment system on your site, give us a call today on +91 22 67049000 or send your enquiry on