Sewage Treatment Plant (STP)

Sewage Treatment Plant

In general, a sewage treatment plant works by moving air to promote the development of bacteria that decompose waste. Delivering significantly cleaner, more environmentally friendly wastewater is the aim. There are some significant differences, but the process is comparable to that of a typical septic tank. Depending on its size, sewage treatment plants can handle the waste from a single business property or a large number of residential area.

City Water Purifier collaborating successfully with to improve the quality of wastewater for recycling, sewage treatment plants use primary, secondary, or biological, and tertiary treatment processes.

There is waste water produced when infrastructure develops and water is used for various reasons such as domestic and commercial.

The process of eliminating impurities from wastewater, especially domestic sewage, is known as sewage treatment. To remove these impurities and generate ecologically safe treated wastewater, it uses physical, chemical, and biological processes (or treated effluent). Sewage sludge is a semi-solid waste or slurry produced as a by-product of sewage treatment that requires additional treatment before being appropriate for disposal or land application.

What Are The Sewage Treatment Stages?

A sewage treatment plant and a septic tank are both generally built in very similar ways. Sewage enters the first chamber of the sewage treatment plant from the property being served, much like a septic tank. Here, the water rests until sediments have accumulated on the tank’s bottom and grease, oil, and scum have floated to the top.

Sewage treatment plants and septic tanks differ in that the liquid moves into a second chamber when the separation process is complete. An air pump is installed in this chamber to move air around the space and promote the development of aerobic bacteria. By assisting in the breakdown of the water’s pollutants, this bacteria successfully cleans the water.

A final settlement tank serves as the sewage treatment plant’s ultimate stage. Before the wastewater is released into a soakaway or watercourse, this final tank enables any remaining solids to fall to the bottom of the tank.

Wastewater can be released into the environment when the treatment procedure is finished and it has been treated as fully as possible. Sewage treatment plants differ from wastewater treatment facilities in one important regard. While you need an Environment Agency Consent to Release to discharge effluent from a septic tank into a soakaway for additional treatment in the ground, you can discharge your wastewater directly from your treatment plant into nearby water sources. This is a result of the treatment procedure’ significantly improved effluent quality.

Technology Used

  • ASP: Activated Sludge Process
  • MBBR: Moving Bed Bioreactor
  • SAFF: Submerged Aerated Fixed Film
  • SBR: Sequential Bioreactor
  • MBR: Membrane Bio-Reactor
  • SBR: Sequential Bioreactor


Process of a Sewage Treatment Plant

Sewage can be treated by constructing a sewage treatment plant (STP) with three stages: primary, secondary, and tertiary.

Primary Treatment

Sewage water is first permitted to travel through screens or a grit chamber in a sewage treatment facility, where big solids are removed. The suspended solids settle down after aeration/mixing in a tank and then primary sedimentation. The inclusion of a coagulant as a primary treatment tries to remove grits, coarse solids, oil, and grease, if any are present.

Biological or Secondary Treatment

Through biological processes, this stage transforms organic waste in sewage into stable forms, resulting in secondary sedimentation. Trickling filters and the activated sludge technique are two common approaches.

An enclosed tank with a bed of bricks and a layer of microorganisms makes up trickling filters. The effluent is pumped into the tank through an intake and then sprinkled over the bed layer. Microbial activities oxidize the organic matter in the effluent, resulting in fine solids removal, sludge formation, and effluent with fewer organic solids.

Tertiary Treatment

The wastewater is subsequently treated with UV radiation or chlorination for tertiary treatment/disinfection. Other technologies for this step of treatment, such as sand filters and reverse osmosis, may be employed instead, depending on the type of sewage and the effluent from secondary treatment.

In some countries, the word “sewage treatment plant” (or “sewage treatment works”) has been superseded by the term “wastewater treatment plant.”

Sewage can be treated near to the source of the sewage, which is known as a “decentralized” or “on-site” system (in septic tanks, biofilters, or aerobic treatment systems). Alternatively, sewage can be collected and delivered to a municipal treatment facility via a network of pipes and pump stations. A “centralized” system is what this is referred to as (see also sewerage and pipes and infrastructure).


Waste from residential, institutional, commercial, and industrial organizations is referred to as sewage. The sewage is treated at the STP facility to make it safe for disposal, agricultural use, or home usage in toilets, among other things. Organic and inorganic pollutants are typically found in large quantities in sewage. Before sewage may enter any water body, it must be treated. If sewage is allowed to enter water sources without being treated, it will contaminate them; therefore, it is critical to properly treat sewage before releasing it into rivers or other water sources.

Sewage Treatment Plant

Primary Treatment Areas in an STP Plant

Wastewater is run through a screen in primary treatment to remove any big objects suspended in the water. The water then passes through a grit chamber, where the grit is removed. Sand, gravel, eggshells, bone pieces, seeds, and other items make up grit. To decrease heavy deposits in aeration tanks, digesters, channels, and conduits, grit treatment is required. The principal settling tanks are the next step. Solids sink down due to gravity and are collected as sludge from the bottom of these tanks, which are usually huge in size. In the meantime, the oil floats to the top and is skimmed off. It is estimated that 50-60% of the suspended solids will be eliminated, and the five-day biological oxygen consumption would be reduced by 30-40%.

Subsequent Treatment

The second stage of wastewater treatment is secondary treatment. Suspended solids, colloidal particles, oil, and grease are removed during the initial treatment. The wastewater is then subjected to a second biological treatment to eliminate any remaining organic debris.


Biodegradable soluble pollutants like sugar, fat, detergent and food waste are consumed by indigenous and aquatic microorganisms such as bacteria and protozoa. These processes are temperature sensitive, and the rate of biological reactions increases as the temperature rises.

Secondary treatment is separated into two types of procedures: 1. Aerobic Treatment – Aerobic wastewater treatment is a biological treatment that breaks down organic materials and removes other contaminants such as nitrogen and phosphorus using oxygen. In most cases, aerobic treatment is used in sewage treatment.

Anaerobic Treatment — Anaerobic treatment is a procedure in which microorganisms break down wastewater or materials without the use of dissolved oxygen. Anaerobic bacteria, on the other hand, can and will use oxygen from the oxides put into the system or from organic material in the effluent.

Treatment in the Final Stage

Tertiary treatment, often known as an advanced treatment, is the third step of wastewater treatment. The burden of nitrogen and phosphorus in the water is removed during tertiary treatment. Filtration, ion exchange, activated carbon adsorption, electrodialysis, nitrification, and denitrification are some of the processes involved.

The properties of effluent after secondary treatment and the type of water required at the end of the treatment determine the treatment options in tertiary treatment. If we need potable water, for example, filtration and disinfection are used to handle wastewater.


Sewage Treatment and Reuse Plants for

  • Hotels
  • Hospitals
  • Residential
  • Commercial Complexes
  • Shopping Centers
  • Institutions of Higher Learning
  • Units of production

Why Are Sewage Treatment Plants (STP) Necessary?

Getting linked to the main sewage system should be the first consideration for anyone organizing a new development. They are often the most affordable and dependable way to handle your wastewater. It’s not always possible to get a mains sewer connection, though. In some cases, it may not be possible to have your property serviced by a mains sewer due to the distance from the closest sewer or the nature of the land. Sewage treatment plants and other options can help with that. A sewage treatment plant may be put practically anywhere as long as there is an electrical connection, thanks to the way they work.

Benefits of a Sewage Treatment Plant (STP)

  • Reliable, unlikely to experience issues, and simply requires routine maintenance
  • Installation is possible even on difficult or small places.
  • Cost-effective over time, requiring only payment for installation, power, and maintenance

Disadvantages of a Sewage Treatment Plant (STP)

  • To operate, the plant requires a constant supply of electricity.
  • Will need yearly maintenance from professionals, and in the odd occasion that issues arise.

Professional design and installation of the system are required.

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