Commonly Used Professional Terms in Wastewater Treatment

1. Domestic Sewage

This mainly refers to wastewater discharged from various kitchen water, washing water, and toilet water used in human life. It is mostly non-toxic inorganic salts. Domestic sewage contains a lot of nitrogen, phosphorus, and sulfur, as well as many pathogenic bacteria.

2. Municipal Wastewater

A general term for wastewater discharged into the urban sewage system. In river drainage systems, it also includes industrial wastewater and intercepted rainwater. Municipal wastewater mainly includes domestic sewage and industrial wastewater. It is collected by the city drainage network and transported to the sewage treatment plant for treatment.

3. Industrial Wastewater

Refers to wastewater, sewage, and waste liquid produced during industrial production, which contains industrial production materials, intermediate products, and products lost with the water flow, as well as pollutants generated during the production process.

4. COD

Chemical Oxygen Demand, the amount of oxidant consumed in the chemical oxidation process of oxidizable substances in water under specified conditions, expressed as the number of milligrams of oxygen consumed per liter of water sample, usually denoted as COD.

5. BOD

The amount of dissolved oxygen in surface water consumed by the process of microbial decomposition of organic matter is called Biochemical Oxygen Demand, usually denoted as BOD, with common units of mg/L.

6. BC Ratio

Indicates the biodegradability of pollutants in water, 0.1-0.25 difficult to biodegrade, 0.25-0.5 biodegradable, >0.5 easily biodegradable.

7. TOC

Refers to the total amount of carbon in dissolved and suspended organic matter in water, reflecting the content of oxidized organic compounds in water, the unit is ppm or ppb.

8. Ammonia Nitrogen

Refers to nitrogen in water that exists in the form of free ammonia ( NH3) and ammonium ions (NH4+).

9. Organic Nitrogen

A general term for nitrogen-containing substances combined with carbon, such as proteins, amino acids, amides, urea, etc.

10. Kjeldahl Nitrogen

TKN, refers to the nitrogen content measured by the Kjeldahl method. It includes ammonia nitrogen and organic nitrogen compounds that can be converted into ammonium salts under these conditions and measured.

11. Nitrate Nitrogen

NOxˉ, refers to the nitrogen element contained in nitrates. The sum of nitrate and nitrite.

12. Total Nitrogen

TN, is the total amount of various forms of inorganic and organic nitrogen in water.

13. Total Phosphorus

TP, the result measured after various forms of phosphorus in the water sample are converted into orthophosphate after digestion, measured in milligrams of phosphorus per liter of water sample.

14. Hypophosphite

In the form of H2PO2ˉ, phosphate cannot be removed by normal chemical phosphorus removal and needs to be converted into sulfate before it can be removed.

15. Color

Refers to the degree of yellowish to yellowish-brown color presented by the dissolved or colloidal substances contained in the water.

16. Screen

Used to remove floating matter in water.

17. Primary Sedimentation Tank

Also known as the primary sedimentation tank, a structure used in wastewater treatment to remove settleable and floating matter.

18. Equalization Tank

A structure used to regulate the inflow and outflow. It mainly plays a role in regulating water volume and quality, as well as wastewater pH value, water temperature, and pre-aeration regulation, and can also be used for accident drainage.

19. Accident Tank

Accident water collection tank, a type of structure required in wastewater treatment. When treating high-concentration wastewater discharged from some chemical and petrochemical plants, an accident tank is generally set up.

20. Grease Trap

It achieves separation by utilizing the different specific gravities of suspended matter and water in wastewater.

21. Flotation

A large number of fine bubbles are generated in the water, causing air to adhere to the suspended matter particles in the form of highly dispersed fine bubbles, resulting in a density less than water. Using the principle of buoyancy, it floats on the surface of the water, thereby achieving solid -liquid separation.

22. Bioreactor

The tank where bacteria metabolize in biochemical treatment.

23. Secondary Sedimentation Tank

Also known as the secondary sedimentation tank, the secondary sedimentation tank is an important component of the activated sludge system. Its main function is to separate sludge, clarify, concentrate, and return activated sludge.

24. Horizontal Flow Sedimentation Tank

The plan of the tank is rectangular, and the inlet and outlet are located at both ends of the tank length.

25. Vertical Flow Sedimentation Tank

Also known as a vertical sedimentation tank, this is a sedimentation tank where wastewater flows vertically within the tank. The tank's plan view is circular or square, with water entering the tank from top to bottom through an inlet pipe located in the center of the tank. Sedimentation occurs through the self-weight of the sludge.

26, Radial flow sedimentation tank

Wastewater enters the tank through an inlet pipe in the center of the tank and flows slowly towards the periphery of the tank along the radial direction. Suspended solids settle during flow and enter the sludge hopper along the bottom slope of the tank, while clarified water overflows from the periphery of the tank into the effluent channel.

27, Sludge tank

Generally used to hold return sludge and excess sludge.

28, Monitoring tank

Also known as a clear water tank, used to store treated wastewater.

29, Coagulation

The process by which colloids lose their stability. Commonly known as colloid destabilization.

30, Flocculation

The process by which destabilized colloids aggregate to form larger flocs.

31, Coagulation

The entire process of two stages: destabilization and flocculation to form large flocs. The general term for coagulation and flocculation.

32, Metabolism

The exchange of matter and energy between an organism and its external environment, as well as the self-renewal process of matter and energy within the organism, is called metabolism. Metabolism includes anabolism (assimilation) and catabolism (dissimilation).

33, Bacterial floc

Due to their genetic characteristics, some bacteria adhere to each other in a certain arrangement, surrounded by a common capsule to form a bacterial group of a certain shape, which is called bacterial floc.

34, Filamentous bacteria

A type of bacteria with a filamentous structure. The skeleton of bacterial flocs.

35, Autotrophic bacteria

Bacteria that use inorganic carbon sources as carbon sources.

36, Heterotrophic bacteria

Bacteria that use organic carbon sources as carbon sources.

37, Anaerobic environment

Theoretically, anaerobic refers to the absence of molecular oxygen and nitrate nitrogen. However, this is impossible in practice. In engineering, DO<0.2 is considered anaerobic.

38, Aerobic environment

Both dissolved oxygen and nitrate nitrogen are present. In engineering, DO>0.5 is considered aerobic.

39, Anoxic environment

Refers to the absence of molecular oxygen but the presence of nitrate nitrogen. In engineering, DO between 0.2 and 0.5 is considered anoxic.

40, Activated sludge process

A wastewater treatment method achieved through the adsorption, metabolism, and solid-liquid separation of bacterial flocs.

41, Biofilm process

A method of treating organic wastewater using microorganisms (i.e., biofilm) that adhere to the surface of certain solid materials.

42, Hydraulic retention time

Abbreviated as HRT, a term in water treatment technology, hydraulic retention time refers to the average retention time of wastewater to be treated in a reactor, which is the average reaction time of wastewater interacting with microorganisms in the biological reactor.

43, Sludge age

Refers to the average retention time of microbial cells in the aeration tank. For activated sludge processes with return flow, the sludge age is the time required for the average renewal of the entire aeration tank sludge (in days).

44, SV

30-minute settling ratio, refers to the ratio of the volume of settled sludge to the volume of the mixed liquid sample after settling for 30 minutes in a 1000ml graduated cylinder filled to the full mark with a well-mixed aeration tank activated sludge mixture. It is also known as sludge settling volume (SV30), expressed in mL/L. Since the sludge generally reaches or approaches its maximum density after 30 minutes of settling, this time is generally used as the standard time for determining this indicator.

45, MLSS

Sludge concentration, The weight of dry sludge contained in 1 liter of aeration tank sludge mixture.