The purpose of wastewater pollutants in wastewater is a way to separate or to stabilize its decomposition into harmless substances, which purify the sewage. General to meet to prevent the spread of poison and bacteria; to avoid ill-feeling different smell and visible matter, in order to meet the requirements of different uses.
    Wastewater treatment is a complex treatment of choice must be based on water quality and quantity of wastewater discharged to the receiving waters or water use to be considered. Also to be considered wastewater treatment sludge generated in the process, residue treatment and utilization, and possible secondary pollution, and recycling of flocculant.

    Physical law: the choice of wastewater treatment depends on the nature of wastewater pollutants, composition, status, and on the water quality requirements. General wastewater treatment method can be divided into physical, chemical and biological three categories.
    The role of the use of physical handling, separation and recycling waste water pollutants. Removed by precipitation in water such as the relative density of suspended particles larger than 1, while recycling the particulate matter; flotation (or flotation) to remove the relative density of the emulsion droplets or close to one of the suspended solids; filtration can remove the water Suspended particle; evaporation method is not used to concentrate volatile water soluble substances.
    Chemical method: The role of chemical reactions or physical and chemical waste recycling soluble or colloidal substance, for example, and in France and used in acid or alkaline waste water; extraction of soluble waste using two-phase solubility in different "distribution", recovery of phenol class, heavy metals, etc.; oxidation-reduction method is used to remove waste water reduction or oxidation of contaminants, such as killing the pathogens in natural waters.
     Biological: The biological role of microbial organic matter in wastewater treatment. For example, biological filtration and activated sludge used to process sewage or organic waste water, so that degradation of organic matter converted into salts and purify.
      
     Adapt the scope of the above methods have their need to learn from each other, complement each other, often difficult in a way we can achieve good control effect. Is one kind of water use which approach, the first is based on wastewater quality and quantity, water requirements for water during discharge, the economic value of waste recovery, treatment of the characteristics of, and through research, to conduct scientific experiments, and in accordance with wastewater indicators, regional situation and the technical feasibility and determine.