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Basic methods for wastewater treatment

2021-10-21

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The purpose of wastewater treatment is to separate pollutants from wastewater in a certain way, or decompose them into harmless stable substances, in order to purify the wastewater. Generally, it is necessary to prevent the transmission of toxins and bacteria; Avoid visible objects with unpleasant odors and unpleasant sensations to meet the requirements of different uses.
The basic method of waste treatment is to use physical, chemical, or biological methods, or a combination of several methods, to remove harmful substances from wastewater. The degree of treatment is determined based on the water quality and the destination of the treated effluent. Wastewater treatment can generally be divided into primary, secondary, and tertiary treatment.
Basic methods for wastewater treatment: (1) The primary treatment adopts physical treatment methods, that is, using structures such as grids, screens, sedimentation tanks, sedimentation tanks, and oil separation tanks to remove solid suspended solids and floating oil in the wastewater, and preliminarily adjust the pH value to reduce the degree of wastewater decay. After primary treatment, wastewater generally does not meet the discharge standards (BOD removal rate is only 25-40%). Therefore, it is usually the pre-treatment stage to reduce the load of subsequent processing steps and improve the treatment effect.
Basic methods of wastewater treatment: (2) Secondary treatment is to use biological treatment methods and some chemical methods to remove degradable organics and some colloidal pollutants from wastewater. After Secondary treatment, the removal rate of BOD in wastewater can reach 80-90%, that is, the total amount of BOD can be less than 30mg/L. The water after Secondary treatment can generally meet the agricultural irrigation standards and wastewater discharge standards, so Secondary treatment is the main body of wastewater treatment. However, after Secondary treatment, there are still some suspended solids, biodegradable dissolved organic matter, dissolved inorganic compound, nitrogen and phosphorus and other algal value-added nutrients in the water, as well as viruses and bacteria. Therefore, it cannot meet the high emission standards, such as being discharged into rivers with low flow rate and poor dilution ability after treatment, which may cause pollution, and cannot be directly used as a source of supply for tap water, industrial water, and groundwater.
Basic methods of wastewater treatment: (3) tertiary treatment is to further remove pollutants that cannot be removed by Secondary treatment, such as phosphorus, nitrogen, organic pollutants, inorganic pollutants, pathogens, etc. that are difficult to degrade biologically. On the basis of Secondary treatment, the tertiary treatment of wastewater is a "advanced treatment" method that further uses chemical methods (chemical oxidation, chemical precipitation, etc.) and physical chemical methods (adsorption, ion exchange, membrane separation technology, etc.) to remove certain pollutants. Obviously, the tertiary treatment of wastewater is costly, but it can fully utilize water resources.
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