Discovering what is produced during wastewater treatment: A comprehensive guide

Wastewater treatment is one of the most important processes in modern society. It’s a crucial aspect of ensuring that our environment is clean and healthy for both people and wildlife. However, most of us don’t give wastewater treatment a second thought. We just turn on the tap and expect clean water to come out. But what exactly happens during wastewater treatment? What do we end up with after all the cleaning is done?

Well, wastewater treatment produces a lot of things! First and foremost, it produces clean water that can be released back into the environment. This is an essential output, as it helps to maintain the delicate balance of our ecosystems. In addition to clean water, wastewater treatment facilities also produce biosolids, which are nutrient-rich organic materials that can be used as fertilizer. Biosolids are an excellent way to reduce waste while also enriching soil and promoting plant growth.

Finally, wastewater treatment produces energy! This might come as a surprise, but it’s true. During the treatment process, large amounts of methane gas are produced. This gas can be captured and used to generate electricity, which is then used to power the treatment facility and, in some cases, even sold back to the grid. It’s a win-win for everyone involved: the environment benefits from reduced methane emissions, the facility saves on energy costs, and the surplus energy generated can be used by others. All in all, wastewater treatment is incredibly important, and its benefits are far-reaching.

Sewage Treatment Plant Overview

Sewage treatment plant is an essential infrastructure that helps to purify wastewater. It is designed to remove impurities, contaminants, and pollutants from sewage to make it safe for disposal or reuse. The process of wastewater treatment involves several stages that work together to eliminate harmful substances from the water.

Stages of Wastewater Treatment

  • Preliminary Treatment: This stage involves removing large debris, such as tree branches, bottles, and plastics, from the wastewater. Screening devices, such as grates and screens, are used for this process. Once removed, the debris is either disposed of in landfills or incinerated.
  • Primary Treatment: In this stage, the sewage is held in large tanks, allowing the solids to settle to the bottom while the liquid stays at the top. The settled solids are then removed and treated separately.
  • Secondary Treatment: In the secondary treatment, the wastewater goes through a biological process known as aeration. This stage involves pumping air into the wastewater to provide oxygen for the bacteria to break down organic matter. After this process, additional settling takes place to remove the bacteria and other waste products that have been created.

Tertiary Treatment

The tertiary treatment is an additional purification process that is used to remove any remaining suspended and dissolved particles through advanced filtration and disinfection. This process utilizes chemicals, such as chlorine, to kill any remaining bacteria and viruses in the water. The water is then disinfected and dechlorinated before it is released back into the environment or reused for other purposes.


Wastewater treatment is a crucial process in society that provides clean water to sustain life and promote a healthy environment. The sewage treatment plant plays a vital role in ensuring that the water discharged from homes, businesses, and industries meets safety standards. The entire process involves removing impurities and pollutants from the water through various stages to make it safe for disposal or reuse. The final product of wastewater treatment is clean and safe water that can be used for irrigation, industrial processes, and even drinking water with additional treatment.

Stage of Wastewater TreatmentPurpose
Preliminary TreatmentRemove large debris from the wastewater
Primary TreatmentSeparate solids from the liquid
Secondary TreatmentBiological process to break down organic matter
Tertiary TreatmentRemove remaining particles and disinfect the water before release or reuse

As shown in the table above, each stage of wastewater treatment has a specific purpose that plays an essential role in cleaning and purifying the wastewater.

Primary Treatment

Primary treatment is the first stage in the wastewater treatment process, where physical and mechanical processes are used to remove large objects and particles from the wastewater. These processes aim to remove solid waste materials from incoming wastewater before it can move to further treatment processes. The major processes employed in primary treatment include screening, grinding, sedimentation, and flotation.

  • Screening: The first step in primary treatment involves screening to remove large objects like plastic bags, rags, and other debris that may cause problems for downstream processes. The wastewater is passed through screens with different gap sizes to catch all large materials. Once removed, these materials are either sent to landfill or incinerated.
  • Grinding: Once large materials have been removed from the wastewater, it moves on to a grinding process. This involves shredding all the physical material that cannot be separated easily in screening using a grinding machine.
  • Sedimentation and Flotation: After screening and grinding, the wastewater moves on to sedimentation and flotation processes, where it undergoes gravity processes that allow denser waste materials to sink to the bottom of a tank and floatable materials to move to the surface. Sedimentation uses gravity while flotation uses chemicals like aluminum sulfate and ferric chloride to make the pollutants clump together and float on the surface. The floating materials are then skimmed or pumped off, and the settled materials are removed as sludge.

Sludge Treatment

One byproduct of primary treatment is sludge, which is mostly composed of the aforementioned materials such as biodegradable matter, grit, and heavy metals. It is a semi-solid byproduct that has the potential to emit noxious gases and cause foul odors from its decay over time, which makes it important that it is treated before disposal. Sludge treatment includes several processes like digestion, thickening, and dewatering, all of which aim to reduce the overall volume of sludge and further remove impurities.

Sludge Treatment ProcessDescription
DigestionThis is a biological process where microorganisms decompose organic matter such as bacteria, viruses, and protozoa, in an anaerobic reactor. This process reduces the volume of sludge and removes many impurities. During digestion, methane gas is produced and is captured for energy generation, which is used to power some wastewater treatment plants.
ThickeningThis process involves increasing the solids concentration in sludge by removing water through gravity thickening, dissolved air flotation, or centrifuge. The resulting sludge is then easier to dewater.
DewateringAfter thickening, the final step in sludge treatment is dewatering. This process removes as much of the remaining water as possible to reduce the volume of sludge that needs to be disposed of or incinerated. Methods for dewatering include belt presses, centrifuges, and filter presses.

Overall, primary treatment is an essential part of the wastewater treatment process that helps to remove substances that could potentially clog pipes and damage the more sensitive systems that are involved in the downstream processes.

Secondary Treatment

After primary treatment, wastewater is then subjected to secondary treatment to further reduce pollutants before being discharged into bodies of water. Secondary treatment focuses on removing suspended and dissolved solids, organic matter, and nutrients through physical, biological, and chemical processes. Here are the three main methods of secondary treatment:

  • Activated Sludge Process: In this process, wastewater is mixed with a microbial culture that breaks down organic matter in the presence of oxygen. The mixture is aerated to provide the microbes with sufficient oxygen, and the resulting sludge settles to the bottom of a tank while the treated water is discharged or further treated. The settled sludge is usually taken to a digester for further processing and/or disposal.
  • Biofiltration/Trickling Filter: In this process, wastewater is sprayed onto a bed of plastic or ceramic media that provides a surface for attached microbial communities. Oxygen is supplied through natural means or aeration, and the organic matter is degraded by the microbes. The treated water is then collected and further processed or discharged. The media can be cleaned and reused multiple times.
  • Oxidation Ditches: In this process, wastewater is circulated in a channel or oval-shaped tank where it is mixed with a microbial culture that degrades organic matter in the presence of oxygen. The water is then discharged or further treated, and the resulting sludge settles to the bottom of the tank for processing and/or disposal.

Nutrient Removal

In some cases, wastewater may need to undergo additional processes to remove nutrients, such as nitrogen and phosphorus, that can harm aquatic ecosystems. Nutrient removal can be accomplished through two main methods: biological and chemical.

Biological nutrient removal relies on specialized microbial cultures that can remove nitrogen and/or phosphorus from wastewater by converting them to gaseous compounds that can be released into the atmosphere. This can be achieved through modifications to the activated sludge process or other biological treatment methods.

Chemical nutrient removal involves adding chemicals, such as alum, iron salts, and lime, to wastewater to precipitate or adsorb the nutrients. The resulting compounds are then removed through settling or filtration. Chemical nutrient removal is often used in conjunction with biological methods for optimal results.

ProcessN Removal EfficiencyP Removal Efficiency
Activated Sludge65-85%10-40%
Biofiltration/Trickling Filter40-75%10-30%
Oxidation Ditch65-85%15-50%

The table above shows the typical nutrient removal efficiencies for each of the three main methods of secondary treatment.

Tertiary Treatment

After primary and secondary treatments, the wastewater still contains small amounts of dissolved and suspended pollutants, such as nitrogen and phosphorus compounds, heavy metals, and pathogens. Tertiary treatment is the stage that removes these remaining impurities and makes the water suitable for discharge into natural watercourses or for reuse.

  • Filtration: One of the most common methods for tertiary treatment is filtration, which involves passing the water through various physical, biological, or chemical filters to remove remaining pollutants. Sand filters, activated carbon filters, and ultrafiltration membranes are some of the commonly used filters.
  • Disinfection: This process is carried out after filtration to remove any remaining pathogens like bacteria, viruses, and protozoa. The most common disinfection methods are chlorination, ozonation, and ultraviolet (UV) radiation. Chlorination involves adding chlorine to the water to kill bacteria, while ozonation is the process of introducing ozone to oxidize and disinfect. UV radiation, on the other hand, damages the genetic material of the pathogens, rendering them unable to reproduce.
  • Nutrient Removal: Nutrient removal is a critical process in wastewater treatment to prevent the excess growth of algae and other aquatic plants in natural water bodies. High levels of nutrients like nitrogen and phosphorus in wastewater lead to eutrophication and degrade water quality. Common ways to remove nutrients are biological nitrogen and phosphorus removal in which specific bacteria and microorganisms are used to break down nitrogen and phosphorus compounds into harmless gases.

Once the tertiary treatment is complete, the water quality is usually improved enough to meet local regulatory requirements and can be discharged into the environment or reused.

The table below shows the typical removal efficiencies achieved through tertiary treatment processes:

Tertiary Treatment ProcessRemoval Efficiencies (%)
Sand Filtration60-90
Activated Carbon Filtration70-90
Biological Nitrogen Removal90-95
Biological Phosphorus Removal80-95
UV Radiation99.9

Tertiary treatment is a crucial step in wastewater treatment, as it not only improves the quality of water for discharge or reuse, but also protects the environment, public health, and ecosystem.

Sludge and Biosolids Production

Sludge and biosolids are the byproducts produced during the wastewater treatment process. Sludge refers to the solids that settle at the bottom during the primary and secondary stages of treatment, while biosolids are the treated and stabilized organic solids that are generated from sludge.

The amount of sludge produced during wastewater treatment varies depending on the quality and quantity of influent wastewater, treatment processes used, and the efficiency of the equipment. On average, 0.4 to 0.5 kilograms of sludge are produced per cubic meter of wastewater treated.

  • Primary Sludge – This is the sludge that forms during the primary treatment process. It is composed of larger particles such as sand, grit, and organic matter.
  • Secondary Sludge – This type of sludge is generated during the biological treatment process. It contains smaller particles such as microorganisms, bacteria, and organic matter.

The sludge generated during the treatment process needs to be treated further to make it safe for disposal and reuse. This is where biosolids production comes in.

Biosolids are the stabilized organic solids that are generated from the treated sludge. To produce biosolids, the sludge is first treated with chemicals or heat to kill any pathogens present in it. This is followed by a process of dewatering to remove the excess water and produce a solid material that meets the regulatory standards for land application or landfills.

Once stabilized, biosolids can be used as a valuable resource for agriculture, horticulture, mine reclamation, and other land restoration purposes. Biosolids contain essential nutrients such as nitrogen, phosphorus, and potassium that are beneficial for plant growth and can enhance soil quality.

Sludge Treatment ProcessBiosolids Treatment Process
Primary TreatmentStabilization
Secondary TreatmentDewatering
Chemical TreatmentTesting and Monitoring

In conclusion, sludge and biosolids production is an integral part of the wastewater treatment process. While sludge is just a byproduct of the treatment process, biosolids are a valuable resource that can be reused for land application and restoration purposes, bringing economic and environmental benefits.

Effluent quality

Effluent quality refers to the characteristics of the water that is discharged from a wastewater treatment plant. The goal of wastewater treatment is to produce water that can be safely released into the environment without causing harm to human health or the ecosystem. To achieve this goal, wastewater treatment plants use several processes to remove pollutants and contaminants from the water.

  • Primary treatment: During primary treatment, large particles and solids are removed from the water through sedimentation. This process reduces the organic load of the water, making it easier to treat in later stages.
  • Secondary treatment: Secondary treatment is a biological process that removes dissolved and suspended organic matter from the water. This is achieved through the use of microorganisms that consume the organic matter and convert it into harmless byproducts such as carbon dioxide and water.
  • Tertiary treatment: Tertiary treatment is the final stage of the wastewater treatment process. This process removes any remaining contaminants from the water, such as phosphorus and nitrogen, that can contribute to eutrophication and harm aquatic life. Tertiary treatment may involve filtration, chemical treatment, or the use of ultraviolet light to disinfect the water.

Once the wastewater treatment process is complete, the quality of the effluent is measured to ensure that it meets the required standards. The quality of the effluent is typically measured using several parameters, including:

  • Biochemical Oxygen Demand (BOD): This parameter measures the amount of oxygen required by microorganisms to break down the organic matter in the water. A lower BOD indicates that the water is less polluted and has a lower organic load.
  • Total Suspended Solids (TSS): This parameter measures the amount of suspended solids in the water. A high TSS indicates that the water contains a high amount of pollutants and contaminants.
  • pH: The pH level of the water is an important parameter that affects the health of aquatic organisms and the overall aquatic ecosystem. Wastewater treatment plants aim to neutralize the pH of the water to prevent any harmful effects on the environment.
BOD10-30 mg/L
TSS30-40 mg/L

Effluent quality is an important consideration for wastewater treatment plants, as well as for regulatory agencies that oversee water quality standards. By producing high quality effluent, wastewater treatment plants can protect human health and the environment, and support a sustainable future.

Environmental and Health Benefits of Wastewater Treatment

Wastewater treatment is a process that cleanses wastewater to make it safe for discharge into the environment. This process involves physical, biological, and chemical treatment to remove pollutants and contaminants from wastewater. Wastewater treatment provides many environmental and health benefits, which include:

  • Environmental Protection: Wastewater treatment plays a crucial role in protecting the environment. By treating wastewater, harmful substances, such as chemicals, heavy metals, and other pollutants, are removed from the water before being released back into the environment. This ensures that the waterways and aquatic life are protected from contamination and pollution.
  • Resource Conservation: In addition to protecting the environment, wastewater treatment also conserves natural resources. Treated wastewater can be reused for irrigation, industrial processes, and other non-potable purposes. This reduces the demand for freshwater resources and helps conserve and manage our water resources.
  • Health Protection: Wastewater treatment also protects public health by reducing the spread of disease-causing organisms. Untreated wastewater can contain harmful pathogens that can cause illnesses such as cholera, dysentery, typhoid, and hepatitis A. Wastewater treatment removes these pathogens, making wastewater safe for disposal.

In addition to the benefits listed above, wastewater treatment also provides economic benefits. By treating and reusing wastewater, resources are conserved, and costs associated with the production and distribution of freshwater are reduced.

The Wastewater Treatment Process

The wastewater treatment process consists of three main stages: primary treatment, secondary treatment, and tertiary treatment.

  • Primary Treatment: In this stage, physical processes are used to remove large particles and debris from the wastewater. This can include screening, sedimentation, and flotation to remove grit, sand, and other solids.
  • Secondary Treatment: In this stage, biological processes are used to remove dissolved and suspended organic matter from the wastewater. This is done through aeration and the use of microorganisms, which break down the organic matter into carbon dioxide and water.
  • Tertiary Treatment: In this stage, chemical and physical processes are used to remove any remaining contaminants and pollutants from the wastewater. This may include disinfection, filtration, and nutrient removal.

The treated wastewater can then be discharged into the environment or treated further for reuse in non-potable applications.


Wastewater treatment plays a critical role in safeguarding the environment and protecting public health. By removing contaminants and pollutants from wastewater, it ensures that the waterways are protected from contamination and pollution. In addition, wastewater treatment conserves natural resources and provides economic benefits by reducing the demand for freshwater and reducing costs associated with water production and distribution. Overall, wastewater treatment is an essential process that provides numerous benefits and helps to create a more sustainable future.

FAQs About What is Produced During Wastewater Treatment

1. What is produced after primary treatment of wastewater?

After primary treatment, effluent is produced which is a semi-clear liquid that contains suspended solids but no organic matter.

2. What is produced after secondary treatment of wastewater?

After secondary treatment, an effluent is produced which is of high quality and can be released into rivers or bodies of water. The sludge is produced that is rich in nutrients, which can be recycled as fertilizers.

3. What are biosolids?

Biosolids are a byproduct of wastewater treatment and consist of organic matter that has been treated to stabilize it for safe use as a fertilizer or soil amendment.

4. How are biosolids used?

Biosolids can be used as a fertilizer for crops and gardens, in landfills as a soil cover, or for energy production.

5. What is methane gas?

Methane gas is a byproduct of anaerobic digestion, a process that breaks down organic matter into simpler compounds. It is a valuable source of renewable energy that can be used to power homes and businesses.

6. How is methane gas produced during wastewater treatment?

Methane gas is produced during the anaerobic digestion of sludge, a process that occurs after secondary treatment.

7. What is the economic value of methane gas produced during wastewater treatment?

Methane gas produced during wastewater treatment has an economic value as an energy source that can be used to reduce energy costs.

Closing Thoughts

Now that you have learned more about the products of wastewater treatment, you can see how this process is essential to protecting our environment. Remember to thank your local wastewater treatment plant and be mindful of the products they produce. Thank you for reading and visit us again for more information.