Wastewater treatment


Wastewater is defined as a liquid that is discharged after human use and has changed its original properties. Normally, wastewater is classified according to its origin. It is also the basis for the selection of treatment methods or technologies. According to this classification, there are the following types of wastewater:

Board. Classification of sources of wastewater








(Identified source)

(Unknown source)


Wastewater from residential areas, commercial areas, offices, schools and other similar facilities.

Wastewater from operating factories, including domestic wastewater, but mainly production wastewater.

Any type of water that enters a sewer system through a leak, broken pipe, or through a retaining wall. Overflow is the amount of rainwater that flows into the sewer system from the rainwater drainage system, roofs, sidewalks, etc.

Surface water overflows due to local rain or melting snow.

Typical pollution indicators in wastewater

There are three basic groups of criteria (parameters) used to assess the quality of water sources: physical criteria, chemical criteria and biological criteria.

Including total solids content, temperature, turbidity, clarity, color, odor, taste, ... qualitative assessment of water pollution caused by industrial wastewater and domestic wastewater out.

Total solids content: Total solids are the most important characteristic physical components of wastewater. It includes suspended, colloidal and dissolved solids.

– Temperature (oC): The temperature of the wastewater affects the life of aquatic organisms and the solubility of oxygen in the water. It is also one of the important technological parameters in the process of wastewater treatment technology.

– Color degree (unit: Pt – Co): The color of wastewater is due to domestic, industrial, dyes or products created from the processes of decomposition of organic matter. Color is a qualitative parameter that can be used to determine the general state of wastewater.

– Turbidity: Turbidity of wastewater is caused by suspended and colloidal substances contained in wastewater. The usual unit of measurement for turbidity is NTU.

Including pH, acidity, alkalinity, hardness, dissolved oxygen content DO, biochemical oxygen demand BOD, chemical oxygen demand COD, content of nutrients (Nitrogen, Phosphorus, ...) heavy metals and toxic substances.

- pH: pH is a measure of the acidity or basicity of water and is calculated by the concentration of hydrogen ions (pH = – lg[H+]). pH is the most important parameter in biochemical processes because the rate of this process depends significantly on the change of pH.

- Dissolved oxygen: Dissolved oxygen (DO) is one of the important parameters in aerobic biological treatment. The amount of DO in the initial wastewater entering the treatment plant is usually zero or very small.

Chemical oxygen demand (COD): Chemical oxygen demand is the amount of oxygen required to oxidize all organic substances including organic substances including non-biodegradable organic substances present in wastewater and is expressed in mg/l. . This indicator indicates the degree of contamination of wastewater containing organic matter, the ability to decompose them in the water environment, etc.

Biochemical oxygen demand (BOD): Biochemical oxygen demand is a characteristic quantity of wastewater pollution level by biochemical oxidizable organic substances. BOD is defined as the amount of oxygen required by microorganisms to oxidize organic matter in the dark at standard conditions of temperature and time.

- Nitrogen content: Nitrogen is present in wastewater in the form of organic and inorganic bonds. In domestic wastewater, most of the organic bonds are in the protein-derived substances, excess food. And nitrogen in inorganic bonds includes reduced forms NH4+, SMALL3 and oxidized form: NO2 and NO3.

- Phosphorus content: Phosphorus in water and wastewater usually exists in the form of orthophosphate (PO .).43-, HPO42-, H2PO4, H3PO4) or organic polyphosphates and phosphates.

Indicators of total salt: chloride (Cl) can be used to assess the degree of contamination by industrial wastewater.

The parameters of grease, the content of heavy metal salts, radioactive substances… assess the contamination of different types of wastewater.

Wastewater contains many microorganisms, including many bacteria and disease-causing bacteria. To determine the biological dirtiness of wastewater, it is analyzed for the existence of a special bacteria: Coli bacillus, although it is not a typical pathogenic bacteria, its existence proves presence of other pathogenic bacteria. The degree of biological contamination of wastewater is determined by the following criteria:

– Coli number standard: The volume of wastewater at least (ml) contains 1 coli.

Total Coliform: the number of coliform bacteria in 100ml of water.

Implementation process

Image. Overall diagram of urban wastewater treatment steps
Hình. Sơ đồ khổi tổng quát dây chuyền công nghệ XLNT
Image. General block diagram of wastewater treatment technology line

List processing technology

Board. Stages and methods of wastewater treatment

The phase of wastewater treatment

Method of XLNT

Treatment works

Treatment efficiency

Preliminary treatment

Physical chemistry

– Floating Line

– Absorption

– Coagulation

– …

– Separation of suspended substances and decolorization


- Oxidize

– Neutralization

- Neutralization and detoxification

Centralized processing


- Garbage bar

– Sand settling tank

– Mechanical settling tank

– Separation of solid impurities, suspended sediment


– Creature lake

– Irrigated fields

– Filter field

- Oxidation channel

– Aeroten

– Biofin

– …

– Separation of suspended and dissolved organic substances, decolorization.


– Settling tank phase II

– Chlorine mixing station

– Mixing trough

– Contact tank

- Neutralization and detoxification of wastewater

Sludge treatment

– Methane tank

– Mud drying yard

– Sludge mechanical treatment station

– Stabilize and dry sludge

To strictly deal with


– Sand filter tank

– Separation of suspended substances



– Aerotank level 2

– Biological filter tank level 2

- Biology Lake

- Reduce Nitrogen, Phosphorus



– Oxidation tanks

- Mixing tank

– Reactor tank

- Eliminate Nitrogen, Phosphorus and other substances.



– Mixing trough

– Contact tank

– Chemical station

- Disinfect wastewater before going out.

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