Waste wastewater treatment refers to the process of cleaning water that is no longer fit for use due to contamination from domestic, industrial, or agricultural sources. Wastewater typically contains organic and inorganic compounds that must be carefully removed before the water can be safely reused or returned to the environment.
Because this is a complex task, waste wastewater treatment is carried out in three stages: primary, secondary, and tertiary treatment, with each stage focusing on a different aspect of removing contaminants and improving water quality.
What Is Waste Wastewater Treatment?
Waste wastewater treatment plays a critical role in protecting freshwater resources by removing harmful pollutants such as metals, debris, microorganisms, and biological waste before water is discharged into surface water or groundwater. The treatment process uses specialized equipment to eliminate or reduce contaminants so the water meets environmental and safety standards.
Wastewater treatment has been used for decades to help prevent pollution and protect ecosystems. From an environmental perspective, effective treatment methods ensure that harmful chemicals and biological contaminants are safely removed, helping preserve water quality for people, plants, and wildlife.
Types of Waste Wastewater Treatment Systems
Different waste wastewater treatment systems are designed to handle specific sources of wastewater depending on whether it comes from homes, industries, or commercial facilities.
Sewage Treatment Plants (STP)
This treatment method involves the following steps: infiltration, grit removal, primary sedimentation tank, secondary sedimentation tank, and secondary clarification. This process is used to treat domestic wastewater and commercial waste.
Effluent Treatment Plants (ETP)
This method uses the same process as STPs but uses more advanced technology resulting in the effluent having a lower BOD (biological oxygen demand) level.
Common and Combined Effluent Treatment Plants (CETP)
This type of wastewater treatment is for small businesses that are required to process their wastewater before releasing it into the water bodies but can’t afford to do so. CEPTs allow small industrial businesses to pool their wastewater with other businesses like them and divide the cost of treating wastewater to save their resources and the environment.
Activated Sludge Plants (ASP)
This involves creating a highly concentrated sludge with activated sludge, which is mixed with air and septic tanks to cause oxidation and breakdown of organic matters.
Primary Stage of Waste Wastewater Treatment
The primary stage of waste wastewater treatment focuses on removing large solids, settleable materials, and floating debris using mechanical and biological processes.
The first stage of wastewater treatment is done in a series of tanks and clarifiers. The clarification process involves the removal of 50 to 90 percent of solids and floatable materials from wastewater.
Solids removal relies on providing the right conditions for biochemical, physical, and other natural processes to remove solid matter. The basic aim of primary wastewater treatment is to stop human health hazards, protect freshwater ecosystems and preserve the quality of receiving waters.
This is achieved by screening (large solids removal), sedimentation (settling of heavy materials) or skimming (floaters or light materials), grit removal, chemical precipitation, biological treatment (sewage sludge settled on the bottom), flocculation (clumping of particles to form bigger particles) and disinfection.
Stages of Waste Wastewater Treatment
Waste wastewater treatment is the process of cleaning contaminated water before it is discharged back into waterways or reused as a reclaimed water source.
This process is carried out in three main stages—primary, secondary, and tertiary treatment—each designed to remove different types of pollutants and improve overall water quality.
Secondary Stage of Waste Wastewater Treatment
The secondary stage of waste wastewater treatment focuses on removing dissolved and suspended organic matter that remains after primary treatment. During this stage, wastewater is held in treatment tanks where biological processes help break down organic contaminants.
In some treatment systems, the water is allowed to settle so that remaining particles such as grit and organic matter can separate before moving on to further treatment.
The purpose of the secondary stage is to remove suspended solids, settleable particles, dissolved chemicals, and other pollutants that were not fully eliminated during primary treatment.
Secondary treatment removes these contaminants using three main biological methods: biofiltration, aeration, and oxidation ponds.
Biofiltration:
Biofiltration uses porous materials such as sand filters or trickling filters to remove residual sediment from wastewater. Organic matter is broken down into carbon dioxide and water through biological activity.
Aeration:
Aeration involves diffusing air into wastewater to support microorganisms that break down pollutants. This process typically takes several hours and significantly improves water quality.
Oxidation Ponds:
Oxidation ponds are nutrient-rich ponds or reservoirs where wastewater is naturally treated over time. As the water flows through these ponds, organic compounds are broken down before the water is discharged into the environment.
Tertiary Stage of Waste Wastewater Treatment
The tertiary stage of waste wastewater treatment follows primary and secondary treatment and focuses on removing remaining contaminants to improve water quality. While the earlier stages remove large solids and organic matter, tertiary treatment targets dissolved chemicals, nutrients, and microorganisms to make the water safe for discharge or reuse.
This stage includes advanced processes that further improve the quality of treated wastewater, allowing it to be safely returned to the natural environment or reused for non-potable purposes.
Common tertiary treatment processes include activated carbon filtration, advanced oxidation processes, ozone injection, and reverse osmosis, all of which help remove trace contaminants and improve overall water quality.
In many systems, tertiary wastewater treatment includes two final steps: disinfection and dechlorination, which help ensure treated water is safe for release into the environment.
Disinfection:
During disinfection, chemical disinfectants such as chlorine are used to eliminate harmful bacteria and microorganisms. This step helps reduce health risks and improve water safety before discharge or reuse.
Dechlorination:
Dechlorination involves removing excess chlorine from treated water, often using compounds such as sodium bisulfite. This is important because residual chlorine can be harmful to aquatic life and degrade water quality.
Once wastewater completes the tertiary stage of treatment, it meets environmental standards and can be safely discharged or reused without negatively impacting ecosystems when properly managed.
How Wastewater Treatment Is Completed
Waste wastewater treatment is completed once water has successfully passed through the primary, secondary, and tertiary stages, with each step removing specific contaminants and improving overall water quality.
During primary treatment, large solids and debris are removed. Secondary treatment then breaks down dissolved and suspended organic matter using biological processes. Finally, tertiary treatment removes remaining chemicals, nutrients, and microorganisms through advanced filtration and disinfection.
Once these stages are complete, treated wastewater meets environmental and regulatory standards. The water can then be safely discharged into rivers, lakes, or groundwater, or reused for approved non-potable applications, depending on local regulations and treatment goals.
Completing wastewater treatment in this structured way helps protect public health, preserve freshwater ecosystems, and reduce pollution in the environment.
FAQs About Waste Wastewater Treatment
What is waste wastewater treatment?
Waste wastewater treatment is the process of removing contaminants from used water so it can be safely reused or returned to the environment.
What are the three stages of waste wastewater treatment?
The three stages are primary treatment, secondary treatment, and tertiary treatment, each designed to remove different types of pollutants.
Why is tertiary wastewater treatment important?
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