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Wastewater treatment methods can be divided into four major categories based on their working principles: physical methods, chemical methods, physicochemical methods, and biological methods. A. Physical methods: These utilize physical forces to separate suspended solids and emulsions from wastewater. Common methods include gridding, screening, centrifugation, clarification, filtration, and oil separation. B. Chemical method: Utilizing chemical reactions to remove dissolved substances or colloidal substances from water. Common methods include neutralization, precipitation, redox reactions, catalytic oxidation, photocatalytic oxidation, microelectrolysis, electrolytic flocculation, incineration, etc. C. Physicochemical methods: Utilize physicochemical processes to remove dissolved substances or colloidal substances from water. Common methods include coagulation, flotation, adsorption, ion exchange, membrane separation, extraction, stripping, venting, evaporation, crystallization, and incineration. D. Biological treatment method: Utilizing the metabolic activities of microorganisms to convert organic pollutants and inorganic microbial nutrients in wastewater into stable, harmless substances. Common methods include activated sludge process, biofilm process, anaerobic biological digestion, stabilization ponds, and wetland treatment. Biological treatment methods are classified into aerobic treatment (such as the activated sludge process and biofilm process) and anaerobic treatment (various anaerobic digestion methods), depending on whether oxygen is supplied. Wastewater treatment can be divided into three categories based on the degree of treatment: primary, secondary, and tertiary treatment. A. Primary treatment: Removal of suspended solids and oil pollutants in a stratified or emulsified state from wastewater. Various treatment units from physical treatment methods are commonly used. Primary treatment belongs to pretreatment. B. Secondary treatment: This involves removing organic pollutants in colloidal and dissolved forms from wastewater. Generally, industrial wastewater meets the discharge standards after undergoing secondary treatment. C. Tertiary treatment: Further removes pollutants that were not eliminated in the previous two stages of treatment; various unit treatment methods from chemical and biological treatment can be employed. In addition to the above three levels of treatment, there is also concentration treatment aimed at recovering pollutants from wastewater for resource utilization and reusing the purified water.