Wastewater treatment is the process of separating pollutants from clean water in wastewater and discharging them separately to achieve purification.

At present, there are mainly physical, chemical, and biological methods for wastewater treatment in the market, and some projects combine these methods according to water quality.

Wastewater treatment can generally be divided into primary, secondary, and tertiary treatments.

First level processing

Using physical treatment methods, such as grids, screens, sedimentation tanks, oil separators, and other structures, to remove solid suspended solids and floating oil from wastewater, preliminarily adjust the pH value, and 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 processing efficiency.

Secondary processing

Using biological treatment methods and certain chemical methods to remove degradable organic matter and some colloidal pollutants from wastewater. After secondary treatment, the removal rate of BOD in wastewater can reach 80-90%, which means that the combined amount of BOD can be less than 30mg/L. After secondary treatment, water can generally meet agricultural irrigation standards and wastewater discharge standards, so secondary treatment is the main body of wastewater treatment. However, after secondary treatment, there is still a certain amount of suspended solids, dissolved organic matter that cannot be decomposed by organisms, dissolved inorganic matter, and algae value-added nutrients such as nitrogen and phosphorus 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.

Third level processing

Further remove pollutants that cannot be removed by secondary treatment, such as phosphorus, nitrogen, organic pollutants that are difficult to biodegrade, inorganic pollutants, pathogens, etc. The tertiary treatment of wastewater is a "deep treatment" method that uses chemical methods (chemical oxidation, chemical precipitation, etc.) and physicochemical methods (adsorption, ion exchange, membrane separation technology, etc.) on the basis of secondary treatment to remove certain specific pollutants. Obviously, the tertiary treatment of wastewater is costly, but it can fully utilize water resources.

The process of wastewater treatment is quite complex, and we must decide what process to use based on the nature and quantity of the wastewater. At the same time, we also need to consider the sludge and residue generated during the wastewater treatment process. These pollutants can either be recycled or discharged separately, but they cannot cause secondary pollution.

Physical method

The selection of wastewater treatment methods depends on the properties, composition, status, and water quality requirements of the pollutants in the wastewater. The treatment methods for general wastewater can be roughly divided into three categories: physical methods, chemical methods, and biological methods.

Utilize physical processes to treat, separate, and recover pollutants from wastewater. For example, using precipitation method to remove suspended particles with a relative density greater than 1 in water while recovering these particles; The flotation method (or air flotation method) can remove emulsified oil droplets or suspended solids with a relative density close to 1; The filtration method can remove suspended particles from water; The evaporation method is used to concentrate non volatile soluble substances in wastewater.

Chemical method

Using chemical or physicochemical reactions to recover soluble waste or colloidal substances, for example, neutralization method is used to neutralize acidic or alkaline wastewater; The extraction method utilizes the "distribution" of soluble waste with different solubility in the two phases to recover phenols, heavy metals, etc; The oxidation-reduction method is used to remove reducing or oxidizing pollutants from wastewater, and to kill pathogens in natural water bodies.

Biological method

Utilize the biochemical action of microorganisms to treat organic matter in wastewater. For example, biofiltration and activated sludge processes are used to treat domestic wastewater or organic production wastewater, transforming and degrading organic matter into inorganic salts for purification.

These wastewater treatment methods each have their own advantages and disadvantages, and we must complement each other's strengths and weaknesses. The method to be used for wastewater treatment needs to be combined with the characteristics, water quality, and quantity of wastewater in order to achieve maximum benefits.

专业水处理的疑难问题，产品选型问题，可以单击下面的微信二维码电话联系贺工在线指导，长按微信二维码可自动识别添加贺工微信沟通解决您的疑难问题