Sewage Treatment Plant and Process

Sewage treatment is the multi-step process that filters wastewater before it is released into water bodies or is reused on the land for irrigation. The wastewater treatment helps to remove the pollutants and kill disease-causing pathogens. The sewage treatment process involves physical, chemical, and biological procedures to remove these contaminants and produce environmentally safe treated wastewater.

Sewage treatment has three stages, primary (solid removal), secondary (bacterial decomposition), and tertiary (extra filtration to remove impurities from sewage). In this article, we will learn about the sewage treatment process, sewage treatment plants, and the environmental impact of sewage treatment.

What is Sewage Treatment?

Sewage treatment is the process of removing contaminants/ pollutants from wastewater, mainly from household sewage. Sewage is the wastewater discharged from residences, workplaces, and industries that contains human waste, domestic trash, and other impurities. This wastewater treatment process helps to prevent water pollution and protect public health and the environment.

Sewage Treatment Plant

A sewage treatment plant is a facility designed to treat wastewater from residential, commercial, and industrial sources. Its main objective is to eliminate impurities and produce treated wastewater/effluent and solid waste/sludge suitable for discharge or recycling back into the environment. Sewage treatment process usually include physical, chemical, and biological processes to remove pollutants, including solids, organic matter, nutrients, and pathogens, before the treated water is released into waterbody or reused for irrigation.

Sewage Treatment Process

Sewage treatment aims at the elimination of contaminants from sewage, to produce an effluent that is suitable to be discharged into waterbody, thereby preventing water pollution.

Preliminary Treatment

Screening, grinding and separating large solids and debris from wastewater is the first and foremost stage in wastewater treatment. Upon arrival to the sewer system, the wastewater is sent through a bar screen, which removes large solid objects such as sticks, large food particles, sand, rags, gravel etc. All the gathered debris from the bar screen and grit tank is usually disposed of at a sanitary landfill.

Primary Treatment

It is the second step in wastewater treatment. It allows for the physical separation of solids and greases from the wastewater. The screened wastewater flows into sedimentation tanks where gravity pushes solids to the bottom and oils and greases to float to the top of the tank. Solids are drawn off the bottom, and grease is skimmed off the top and sent on to be treated as sludge/slurry. The clarified wastewater flows on to the next stage of wastewater treatment. Clarifiers and septic tanks are generally used for the purpose of primary treatment.

Secondary Treatment (Biological Treatment)

It is the biological treatment stage where microorganisms are mixed with wastewater that breaks down organic pollutants present in wastewater. Naturally occurring microorganisms are cultivated and feed on the pollutants in the wastewater. Organic matter is consumed and ammonia is converted to nitrate. Three methods are used for Secondary treatment, Suspended film, Fixed film and Lagoon systems.

A. Activated Sludge/Suspended Film Systems

Here, wastewater is mixed and aerated with microorganisms. The clarified wastewater becomes hazy as microorganisms are poured into the sewage. For several hours, mixers and aerators stir the wastewater-microbe mixture as the organic matter and ammonia is consumed. Then, the microorganisms are removed from the wastewater by allowing the mixture to flow to a settling tank. The microbes sink to the tank bottom, are collected and are returned to the mixing tank. The clear, treated wastewater flows out of the tank to the tertiary stage of treatment.

B. Trickling filters/ Fixed Film Systems

Wastewater is sprayed over rocks, sand or even small bits of plastic that are covered with a thin, microscopic film of microorganisms. As the wastewater flows over the microbial film, organic matter and ammonia are consumed.

C. Lagoon Systems

Large, shallow ponds collect and hold wastewater for months where naturally occurring microorganisms consume the organic matter and stabilize the wastewater. Lagoon systems may be naturally aerated or be equipped with a mechanical aerator to gently stir the wastewater in order to promote good interaction between the microorganisms and the pollutants.

Energy Generation

Sewage treatment plants can generate energy through various processes such as Biogas Production, Combined Heat and Power (CHP) system (also known as cogeneration), Heat Recovery, Hydroelectric Generation, Solar Power and Wind Power.

Energy generation from sewage treatment plants can help offset operational energy costs and reduce greenhouse gas emissions associated with conventional energy sources.

Odor Control

Odor control in sewage treatment plants is important to reduce nuisance odors that can impact surrounding communities. Some common methods used for odor control are:

• Chemical Scrubbers: They use a chemical solution to neutralize odorous gases. The gases are passed through the solution, where they react with the chemicals and are converted into non-odorous compounds.
• Biological Filters: They use microorganisms to break down odorous compounds in the air. The filters contain a media that provides a habitat for the microorganisms to grow and thrive.
• Activated Carbon Adsorption: Activated carbon is very effective at adsorbing odorous gases. Air is passed through a bed of activated carbon, where the odorous compounds are adsorbed onto the surface of the carbon particles.
• Ozone Treatment: Ozone is a powerful oxidizing agent that can effectively neutralize odorous compounds. Ozone treatment systems generate ozone gas, which is injected into the air stream to oxidize odorous compounds.

Environmental Impact of Sewage Treatment

There are a number of environmental impacts to wastewater treatment, both positive and negative.

Positive Aspects

• Water Quality Improvement: Sewage treatment plants eliminates harmful contaminants from wastewater, thereby improving the quality of water bodies into which the treated effluent is released.
• Ecosystem Protection: Sewage treatment contributes to the protection of aquatic ecosystems and the organisms that depend on them by lowering the quantity of contaminants that enter rivers, lakes, and seas.
• Public Health: Proper treatment of sewage helps prevent the spread of waterborne diseases, hence contributes to the protection of public health.

Negative Aspects

• Energy Consumption: Sewage treatment plants require energy to operate mainly for pumping, aeration, and treatment processes. This leads to greenhouse gas emissions and other environmental impacts associated with energy production.
• Chemical Use: Some treatment processes require the use of chemicals, such as chlorine or ferric chloride, which can have environmental impacts.
• Sludge Disposal: Sewage treatment generates sludge, which must be treated and disposed of appropriately. Improper disposal can lead to adverse effect on environment.

Conclusion – Sewage Treatment

In conclusion, sewage treatment plays a crucial role in protecting public health and the environment by removing pollutants from wastewater before it is discharged into water bodies or reused. Sewage treatment plants help improve water quality, protect aquatic ecosystems, and prevent the spread of waterborne diseases. The Sewage treatment process involves

FAQs on Sewage Treatment

What are the 4 Types of Sewage Treatment?

The four main types of sewage treatment are: Primary, Secondary, Tertiary and Advanced Treatment.

What are the Sewage Treatment Method?

Sewage treatment methods include primary treatment (which separates solids from wastewater), and secondary treatment (removes organic matter), and biological processes (removes pathogens).

Why is Sewage Treatment Important?

Sewage treatment is important because untreated sewage contains harmful disease-causing pathogens and it can also contaminate water bodies.

Is STP Water Safe?

Yes. If the treated water is intended for reuse, such as for irrigation or even drinking water, it may require tertiary treatment.

Why is Chlorine used in Sewage Treatment?

Chlorine is a powerful disinfectant that can effectively kill a wide range of pathogens, including bacteria, viruses, and parasites, that may be present in sewage.

What is pH in Sewage Treatment Plant?

The optimal pH range for most sewage treatment processes is typically between 6.5 and 8.5.

What is the Importance of Sewage Treatment?

Sewage treatment is important as it protects public health and the environment by removing pollutants and pathogens from wastewater before it is discharged back into water bodies, preventing contamination and promoting ecosystem health.