1. Classification by Treatment Mechanism
According to the principles and mechanisms applied during treatment, wastewater treatment methods can be classified into four main categories:
1.1 Physical Treatment Methods
Physical treatment removes suspended solids, floating matter, and oil through physical processes without changing the chemical nature of pollutants. It is commonly used in the pretreatment stage.
Main methods include:
Sedimentation
Filtration
Oil Separation
Dissolved Air Flotation (DAF)
Centrifugal Separation
Magnetic Separation
1.2 Chemical Treatment Methods
Chemical treatment involves the addition of chemical agents to induce chemical reactions that transform or remove pollutants.
Main methods include:
Coagulation and Sedimentation
Neutralization
Oxidation–Reduction
Chemical Precipitation
1.3 Physicochemical Treatment Methods
Physicochemical methods combine physical and chemical mechanisms and are typically applied to remove dissolved or refractory pollutants.
Main methods include:
Adsorption
Ion Exchange
Extraction
Air Stripping
Steam Stripping
1.4 Biological Treatment Methods
Biological treatment utilizes microbial metabolism to degrade organic pollutants and represents the core process in wastewater treatment systems.
Main processes include:
Activated Sludge Process
Biofilm Process
Anaerobic Treatment Processes
Biological Nitrogen and Phosphorus Removal Processes
2. Classification by Water Quality and Effluent Reuse Purpose
Based on influent characteristics and the final destination of treated water, wastewater treatment is commonly divided into primary, secondary, and tertiary treatment.
2.1 Primary Treatment (Pretreatment and Mechanical Treatment Stage)
Primary treatment mainly relies on physical processes to remove large suspended solids, grit, and floating materials, providing stable conditions for subsequent treatment stages.
Typical units include:
Coarse and Fine Screens
Grit Chambers
Primary Sedimentation Tanks
Flotation Tanks
Equalization Tanks
2.2 Secondary Treatment (Main Biological Treatment Stage)
Secondary treatment is the core stage of wastewater treatment, primarily aimed at removing dissolved organic pollutants through biological processes.
Common processes include:
Activated Sludge Process
CASS Process
A²/O Process
A/O Process
SBR Process
Oxidation Ditch
Hydrolysis–Acidification Tank
2.3 Tertiary Treatment (Advanced Treatment and Water Reuse Stage)
Tertiary treatment focuses on removing nutrients, refractory organic compounds, and trace pollutants to control eutrophication or enable water reuse.
Common technologies include:
Advanced Catalytic Oxidation
Biological Aerated Filters (BAF)
Fiber Filters
Activated Sand Filtration
Reverse Osmosis (RO)
Membrane Treatment Technologies
For reclaimed water reuse systems, disinfection tanks are typically required to ensure hygienic safety. Common disinfection methods include:
Ultraviolet (UV) Disinfection
Ozone Disinfection
Chlorine Dioxide Disinfection