The Main Stages of a Wastewater Treatment Plant Process
2025-04-29
Preliminary Treatment
- Screens: Mechanical or manual screens intercept larger solid debris in the wastewater, such as branches and plastic bottles, to prevent them from clogging the downstream equipment.
- Grit chamber: Using gravity, inorganic particles such as sand settle to the bottom of the chamber, reducing abrasive wear on the downstream treatment equipment.
Biological Treatment
- Aerobic treatment: Common processes include the activated sludge process and the biofilm process. In the activated sludge process, air is blown into the aeration tank so that the wastewater and activated sludge mix and contact thoroughly, allowing aerobic microorganisms to break down the organic matter in the wastewater. In the biofilm process, microorganisms attach to the surface of a media to form a biofilm, and as the wastewater flows across the biofilm the organic matter is broken down by the microorganisms.
- Anaerobic treatment: Under oxygen-free conditions, anaerobic microorganisms convert the organic matter in the wastewater into gases such as methane and carbon dioxide. This process is commonly used to treat high-strength organic wastewater.
Secondary Clarifier
After biological treatment, the wastewater enters the secondary clarifier for solid-liquid separation. Microbial flocs such as activated sludge settle to the bottom of the tank, while the supernatant is discharged as treated water. A portion of the settled sludge is returned to the biological treatment unit to maintain the microbial population, and the surplus sludge must be processed and disposed of.
Tertiary (Advanced) Treatment
Depending on the required effluent quality, advanced treatment may be applied. For example, a filtration process can further remove suspended solids from the water; activated carbon adsorption can remove trace organic compounds, color, and similar contaminants; and a disinfection process can kill pathogenic microorganisms in the water. Common disinfection methods include chlorine disinfection and UV disinfection.
Sludge Treatment
The surplus sludge typically contains large amounts of organic matter, microorganisms, and pathogens. It is generally thickened first to reduce its moisture content, then stabilized through methods such as anaerobic digestion or aerobic composting to break down the organic matter and reduce the sludge's volume and odor. Finally, after dewatering, the sludge can be landfilled, incinerated, or recovered as a resource, for instance as fertilizer.
- Screens: Mechanical or manual screens intercept larger solid debris in the wastewater, such as branches and plastic bottles, to prevent them from clogging the downstream equipment.
- Grit chamber: Using gravity, inorganic particles such as sand settle to the bottom of the chamber, reducing abrasive wear on the downstream treatment equipment.
Biological Treatment
- Aerobic treatment: Common processes include the activated sludge process and the biofilm process. In the activated sludge process, air is blown into the aeration tank so that the wastewater and activated sludge mix and contact thoroughly, allowing aerobic microorganisms to break down the organic matter in the wastewater. In the biofilm process, microorganisms attach to the surface of a media to form a biofilm, and as the wastewater flows across the biofilm the organic matter is broken down by the microorganisms.
- Anaerobic treatment: Under oxygen-free conditions, anaerobic microorganisms convert the organic matter in the wastewater into gases such as methane and carbon dioxide. This process is commonly used to treat high-strength organic wastewater.
Secondary Clarifier
After biological treatment, the wastewater enters the secondary clarifier for solid-liquid separation. Microbial flocs such as activated sludge settle to the bottom of the tank, while the supernatant is discharged as treated water. A portion of the settled sludge is returned to the biological treatment unit to maintain the microbial population, and the surplus sludge must be processed and disposed of.
Tertiary (Advanced) Treatment
Depending on the required effluent quality, advanced treatment may be applied. For example, a filtration process can further remove suspended solids from the water; activated carbon adsorption can remove trace organic compounds, color, and similar contaminants; and a disinfection process can kill pathogenic microorganisms in the water. Common disinfection methods include chlorine disinfection and UV disinfection.
Sludge Treatment
The surplus sludge typically contains large amounts of organic matter, microorganisms, and pathogens. It is generally thickened first to reduce its moisture content, then stabilized through methods such as anaerobic digestion or aerobic composting to break down the organic matter and reduce the sludge's volume and odor. Finally, after dewatering, the sludge can be landfilled, incinerated, or recovered as a resource, for instance as fertilizer.