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20 commonly used nouns in water treatment

Apr. 13, 2019

ZHEHAN is the largest manufacturer of metal filters for water treatment in China. In addition to the most common stainless steel sintered filters, we also have great advantages for stainless steel Johnson screen filters.


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This blog no longer introduces our stainless steel filter element products, mainly for those who have just entered the water treatment industry to popularize the professional terminology often used in sewage treatment, hoping to help you.


Explanation of 20 commonly used nouns in water treatment



BOD (short for Biochemical Oxygen Demand): Biochemical oxygen demand or biochemical oxygen demand (five-day chemical oxygen demand) is an environmental monitoring index, which is mainly used to monitor the contamination status of organic matter in water, indicating a comprehensive indicator of the content of aerobic pollutants such as organic matter in water. Biochemical oxygen demand (BOD) refers to the dissolved oxygen consumed by microorganisms in the biochemical process of decomposing some oxidizable substances in water under specified conditions.


Usually, the dissolved oxygen concentration in water samples is measured before and after culture in a completely sealed dissolved oxygen bottle, which is cultured in a dark place at 20 ~C for 5 days.


The dissolved oxygen consumption per liter of samples is calculated by the difference of dissolved oxygen concentration between before and after culture and expressed as BOD5. It's unit ppm or milligram/liter.


The higher the value, the more organic pollutants in water, the more serious the pollution. In order to make the test data comparable, a period of time is generally stipulated.


During this period, microorganisms are cultured with water samples at a certain temperature, and dissolved oxygen consumption in water is measured. Generally, five-day biochemical oxygen demand is called five-day BOD5.


The larger the value, the more organic matter in the water, the more serious the pollution.   




Chemical oxygen demand (COD or CODcr) refers to the number of oxidants consumed by reductive substances in water during oxidation decomposition under certain strict conditions under the action of strong oxidants, expressed in mg/L of oxygen.


Chemical oxygen demand reflects the degree of pollution by reducing substances in water. These substances include organic matter, nitrate, ferrous salt, sulfide and so on. However, the amount of inorganic reducing substances in general water and wastewater is relatively small, and the pollution by organic substances is very common.


Therefore, COD can be used as a comprehensive index of the relative content of organic substances. When the organic matter in water is decomposed by the environment, it will consume dissolved oxygen in the water.


If dissolved oxygen in the water is depleted, the anaerobic bacteria in the water will be put into operation, resulting in water body odor and environmental deterioration. Therefore, the higher the COD value, the more serious the water is polluted.  




Suspended solids refer to solid substances suspended in water, including insoluble inorganic substances, organic substances, and mud, sand, clay, microorganisms, etc. Suspended matter content in water is an index to measure the degree of water pollution.



Total nitrogen, abbreviated as TN, is one of the important indicators of water quality. Total nitrogen is defined as the total amount of various forms of inorganic and organic nitrogen in water.


Including inorganic nitrogen such as NO3-, NO2-and NH4+ and organic nitrogen such as protein, amino acids, and organic amines, calculated in milligrams of nitrogen per liter of water. It is often used to indicate the extent to which water is contaminated by nutrients. The total nitrogen content in water is one of the important indexes to measure water quality.


Its determination is helpful to evaluate the pollution and self-purification of the water body.


When nitrogen and phosphorus substances in surface water exceed the standard, microorganisms multiply in large quantities, plankton grows vigorously, and eutrophication occurs.


ammonia nitrogen


Ammonia nitrogen refers to nitrogen in water in the form of free ammonia (NH3) and ammonium ion (NH4+). The nitrogen content of animal organic matter is generally higher than that of plant organic matter. At the same time, the nitrogen-containing organic matter in human and animal manure is very unstable and easy to decompose into ammonia. Therefore, when the content of ammonia nitrogen in water increases, it refers to the synthetic ammonia in the form of ammonia or ammonium ion. Ammonia nitrogen is a nutrient in water, which can lead to eutrophication. It is the main oxygen-consuming pollutant in water and is toxic to fish and some aquatic organisms.    




The so-called chroma refers to the degree of yellowish-like or even yellowish-brown color of soluble or colloidal substances in water. The colors produced by substances in the solution state are called "true colors" and those produced by suspended substances are called "false colors". The specific meaning of water chroma is to express a multiple relationships between colored water and clear water. For example, the color of the sewage is 10, which means that the sewage is diluted 10 times, and its transparency can reach the transparency of clear water.  




The TDS value represents the content of dissolved impurities in water. The larger the TDS value, the higher the content of impurities in water, so this regulation is made for drinking water. However, the purified drinking water is not required to replace the purified drinking water because it is treated by such processes as coarse filtration, fine filtration and deionization purification (ion exchange, reverse osmosis, distillation, and other processing methods). Quantitative indicators are conductivity and pH, etc.


Raw water


Raw water is taken from natural water bodies or aquifers, such as rivers, lakes, ponds or underground aquifers, and is used as a source of water supply; or it refers to the water flowing into the first treatment unit of a water treatment plant. The water in the reservoir used to regulate the water pressure of the water supply network is not raw water. The quality of raw water varies from source to source. The raw water for pharmaceutical use is usually drinking water (water from natural water purifier).


Pure water 


Pure water, also known as deionized water, refers to water that meets the hygienic standard of drinking water as raw water and is sealed in a container without any additives after pretreatment (mainly using metal filters: sintered filters and Johnson screen filters), through electrodialysis, ion exchange, reverse osmosis, distillation and other appropriate processing methods. Drinkable water, also known as pure substance (in chemistry), is widely used in the experiment.


It is also called distilled water because it is made by distillation and other methods. The space water and distilled water sold on the market are pure water, but it is better to drink less pure water because there are not many minerals needed by the human body. Pure water is not easy to conduct electricity and is an insulator.


Pure water should be used when replenishing water for lead-acid batteries.    




Also known as denitrification. Under anoxic conditions, denitrifying bacteria reduce nitrate (NO3-) and release molecular nitrogen (N2) or nitrous oxide (N2O). Nitrification-denitrification treatment of wastewater is a kind of microbial denitrification treatment method using nitrifying bacteria and denitrifying bacteria. This method can be divided into two stages: nitrification and denitrification.




Aeration is a means of making air strongly contact with water. Its purpose is to dissolve oxygen in the air into water or to release unnecessary gases and volatile substances into the air. In other words, it is a means of promoting the exchange of substances between gases and liquids. It also has other important functions, such as mixing and stirring. There are two types of aeration: blast aeration and mechanical aeration. Blowing aeration is the aeration method that air bubbles are introduced into water by using aeration blower, aerator, diffusion plate or diffusion tube.




Desalting is the method or process of removing chemical salts. Simply put, it is the removal of anions and cations from water. The desalination methods include electrodialysis and reverse osmosis, and the positive osmosis which has recently been re-heated.   


Reverse osmosis (RO)


Reverse osmosis, also known as reverse osmosis, is a membrane separation operation in which solvent is separated from the solution by pressure difference as a driving force.

When the pressure exceeds its osmotic pressure, the solvent will reverse osmosis in the direction of natural osmosis.


The permeable solvent, i. e. osmotic solution, is obtained at the low-pressure side of the membrane, and the concentrated solution, i. e. concentrated solution, is obtained at the high-pressure side. If seawater is treated by reverse osmosis, fresh water is obtained at the low-pressure side of the membrane and brine is obtained at the high-pressure side.


Reverse osmosis technology is usually used in the fresh water of seawater and brackish water, water softening treatment, wastewater treatment, and purification, concentration and separation of food, pharmaceutical and chemical industries. Water purifier can be divided into reverse osmosis water purifier and ultrafiltration water purifier according to filtration technology. The difference between them is mainly reflected in the filter membrane.


It should be noted that pre-treatment is required through Johnson screen filter element.


Forward osmosis


Positive osmosis technology is the most advanced desalination and water purification technology in the world. Positive osmosis is proposed relative to reverse osmosis.


The technical principle is that two different concentrations of the solution are placed on both sides of a film, because of the characteristics of water, water molecules will naturally pass through the film, moving from the low concentration side to the high concentration side.


Compared with reverse osmosis, positive osmosis technology has unique advantages: low energy consumption, no external pressure to achieve separation process; hydrophilic material itself, can effectively prevent membrane fouling; high recovery, zero emissions, pollution-free.




Ultrafiltration, also known as ultrafiltration, is used to intercept colloidal particles in water, while water and low molecular weight solutes are allowed to pass through the membrane. Ultrafiltration originated in 1748. Schmidt used cotton film or Lu membrane to filter solution. When applied with a certain pressure, the solution (water) passed through the membrane, while proteins, colloids, and other substances were intercepted. Its filtering accuracy was much higher than that of filter paper. So he put forward the term "Ultrafiltration". In 1896, Martin made the first artificial UF membrane. In the 1960s, the concept of molecular weight level was put forward as follows: The beginning of modern ultrafiltration is a period of rapid development in the 1970s and 1980s, and it began to mature after the 1990s. The research on this technology in our country is relatively late, and it is still in the research period in the 1970s. Only in the late 1980s did we enter the stage of industrialized production and application.


Membrane technology


The membrane is a material with selective separation function. The process of separating, purifying and concentrating different components of feed liquid by selective separation of a membrane is called membrane separation.


It differs from traditional filtration in that the membrane can be separated in the molecular range, and this process is a physical process without phase change and additives. The pore size of membranes is generally micron.


According to the different pore sizes (or molecular weight rejection), the membranes can be divided into microfiltration membrane, ultrafiltration membrane, nanofiltration membrane and reverse osmosis membrane.


Membrane technology as a new separation technology has been widely used in gas separation, material separation and water treatment, in which the demand for membrane products is the largest in the field of water treatment. Taking drinking water as an example, since it was found that tap water contained trihalomethane, pesticides, detergents and secondary pollution of tap water pipes and towers, reverse osmosis membranes were used to prepare purified water. But because of the high cost of making pure water, and removing harmful substances in water, the inorganic salts which are beneficial to the human body are also removed.


Therefore, people use pure membrane devices to produce filtered water which has the advantages of mineral water and pure water, has biological activity and can be directly raw drinking. Ultrafiltration membrane technology can not only remove pathogens, viruses, heat sources, colloids and other harmful substances in water but also dialyze inorganic salts beneficial to human body. It has been widely used in milk degreasing, fruit juice concentration, rice wine purification, liquor aging, beer sterilization, monosodium glutamate purification, cane bran decolorization, amino acid concentration, soy sauce sterilization and other production, and also widely used in medical injection water, infusion. Preparation of water, bottle-washing water, and surgical cleaning water.


Because it overcomes the shortcomings of distilled water containing bacterial corpses and has biological activity, it is more conducive to the recovery of patients and is highly praised by the medical community.


Activated carbon


Activated carbon is also called activated carbon black. It is black, powdered or granular amorphous carbon. In addition to carbon, the main components of activated carbon include oxygen, hydrogen, and other elements. Activated carbon is a kind of porous carbon with low bulk density and large specific surface area because of its irregular arrangement of microcrystalline carbon, fine pore between cross-links and carbon defects during activation.


Activated carbon contains a large number of microporous, has a huge specific surface area, can effectively remove color, odor, can remove most organic pollutants and some inorganic substances in secondary effluent, including some toxic heavy metals. Activated carbon adsorption is the most important and effective treatment technology in the advanced treatment of municipal wastewater, and has been widely used.


Activated carbon adsorption combined with other treatment methods, such as ozone-activated carbon method, Coagulation-adsorption activated carbon method, Haberer process, activated carbon-diatomite method, etc. have appeared, which significantly prolongs the adsorption period of activated carbon, reduces the amount of activated carbon, and greatly improves the treatment effect and scope.


Johnson screen filter system


Johnson screen is the best choice. The utility model relates to a pretreatment facility for intercepting coarse sewage in wastewater.


A metal frame made of a set of parallel metal bars is obliquely placed on the channel through which the wastewater flows or at the entrance of the pump station catchment pool to intercept large pieces of suspended or floating solid pollutants so as not to clog the sludge discharge pipes of the pumps and sedimentation pools. The interception effect depends on the width of a crevice and the nature of water.


Johnson screen filter element pretreatment is the main equipment in the first process of sewage treatment in the sewage treatment plant. It plays a decisive role in the later process.


The selection of Johnson screen filter system is appropriate, which directly affects the operation of the whole water treatment implementation. Artificial grilles are generally used in small sewage treatment stations with a simple structure and high labor intensity. Mechanical grids are generally used in large and medium-sized sewage treatment plants.


These grids have complex structures and the high degree of automation.


Primary settling tank


The primary clarifier can remove sediment and floating matter from wastewater. After initial sedimentation, the wastewater can remove about 50% of sediment, grease and floating matter, and 20% of BOD.


According to the calculation of removal of BOD or solid matter per unit mass, primary sedimentation tank is the most economical purification step, and it is easy to use primary sedimentation tank for domestic sewage and industrial sewage with high suspended matter. The operation of the first process, such as grille well or sand sink, can directly affect the operation of the initial sink.


If the former process is not well operated, the load of the primary clarifier will be increased and the removal effect will be reduced.


Two sedimentation tank


Secondary settling tank. The secondary clarifier is an important part of the activated sludge system. Its main function is to separate sludge and clarify, concentrate and reflux activated sludge.


Its working effect can directly affect the effluent quality and reflux sludge concentration of activated sludge system. Besides sludge separation, sludge concentration is also carried out. Because of the change of water quantity and water quality, sludge should be temporarily stored.


RO concentrated water


After RO (reverse osmosis) treatment, the wastewater can be divided into clear water and concentrated water, which have low biodegradability, high COD content and high chroma. RO concentrated water is the discharge water of a reverse osmosis device, in which the impurities in raw water are concentrated, and direct discharge will have adverse effects on the environment. At present, there are many dense water treatment methods used abroad, such as surface discharge (ocean, tide), deep well injection, sprinkler irrigation, wastewater treatment equipment, and evaporation pond. Among the above methods, the wastewater treatment device is more suitable for China's actual situation.



Sewage Biochemical Treatment


Sewage biochemical treatment belongs to secondary treatment(Johnson screen is the first part), with the main purpose of removing unsinkable suspended solids and soluble biodegradable organic matter.


Its process consists of various methods, such as activated sludge method, AB method, A/O method, A2/O method, SBR method, oxidation ditch method, stabilization pond method and land treatment method. Activated sludge process has been used in most municipal wastewater treatment plants recently.


The principle of biological treatment is to complete the decomposition and synthesis of organic matter through biological action, especially the role of microorganisms. Organic pollutants are transformed into harmless gas products (CO2), liquid products (water) and solid products (microbial community or biological sludge) rich in organic matter.


The surplus biological sludge is separated from the purified sludge by solid-liquid separation in the sedimentation tank. Remove from sewage.


Activated sludge process


Activated sludge process is the main method of wastewater biological treatment with activated sludge as the main body. Activated sludge process is a sludge-like flocculant formed by continuous aeration into wastewater and reproduction of aerobic microorganisms after a certain period of time. It is inhabited by microorganisms mainly composed of microbial micelles, which have a strong ability to absorb and oxidize organic matter. Under the condition of artificial aeration, the activated sludge was formed by continuous mixed culture of sewage and various microbial groups. Biocoagulation, adsorption, and oxidation of activated sludge are used to decompose and remove organic pollutants from wastewater. Then the sludge is separated from water, and most of the sludge is returned to the aeration tank, and the surplus part is discharged from the activated sludge system.


AB method


AB process is the abbreviation of Adsorption-Biodegradation process. It is a new wastewater treatment technology developed on the basis of the conventional activated sludge process and two-stage activated sludge process.


In general, the removal rate of BOD and COD by AB method can reach 90%~95% and 80%~90% respectively. The disadvantage is the high sludge yield, the sludge produced in stage A is large, accounting for about 80% of the sludge output of the whole treatment system, and the high content of organic matter in excess sludge, which brings great pressure to the final stabilization disposal of sludge. A process is suitable for large and medium-sized municipal wastewater treatment plants with high sewage concentration and sludge digestion follow-up treatment facilities.


It has an obvious energy-saving effect. For municipal wastewater treatment plants with denitrification requirements, it is generally unsuitable to use them. 


SBR method


Sequential batch activated sludge process, which is composed of five basic processes of water inflow, aeration, sedimentation, drainage and standby in the same reactor, is called the SBR process for short.


SBR is the abbreviation of sequencing batch activated sludge process, which is an activated sludge sewage treatment technology operated by intermittent aeration. Its main characteristics are orderly and intermittent operation in operation. The core of SBR technology is SBR reaction tank, which integrates homogenization, initial sedimentation, biodegradation, secondary sedimentation, and other functions into one tank, without sludge reflux system.


It is especially suitable for occasions where intermittent discharge and flow rate change greatly. In recent years, more and more attention has been paid to the treatment of pig farm wastewater by SBR. Compared with other processes, this process is simpler, less troublesome to dispose of excess sludge, less investment, less land occupation, lower operating cost, resistance to organic load and toxic load impact, and flexible in operation. As it is static sedimentation, the effluent effect is better, anaerobic (anoxic) and aerobic processes alternate and sludge age occur. Short, high activity, good nitrogen, and phosphorus removal effect.


A/O method


A/O process, also known as anaerobic-aerobic process. A is an anaerobic section, mainly used for nitrogen and phosphorus removal; O is the aerobic section, mainly used for removal of organic matter in water.   


In addition to removing organic pollutants in wastewater, it can also remove nitrogen and phosphorus at the same time. For high concentration organic wastewater and refractory wastewater, setting hydrolysis acidification section before the aerobic section can significantly improve the biodegradability of wastewater.


A/O denitrification process is simple, without additional carbon source and post-aeration tank, with raw sewage as the carbon source, construction and operation costs are low. 


Land disposal method


Land-based sewage treatment technology is a method of purifying sewage with soil as a medium. It uses secondary effluent for irrigation of farmland, pasture or forest, or injects raw sewage back into groundwater after soil infiltration. In order to avoid the secondary pollution of groundwater, the method should strictly do a good job in the seepage prevention project of the system, and pay attention to the quality of the sewage water when the sewage is recharged, so as to avoid the pollution of heavy metals in the soil and control the residence time of the sewage.


MBR method


MBR - --- membrane bioreactor. In recent years, a new wastewater treatment process, which combines hollow fiber membrane with activated sludge process, replaces the secondary sedimentation tank treatment process, has low turbidity of effluent water, which is equivalent to the filter membrane of sewage.


MBR is a combination of new membrane technology and sewage biological treatment technology. Membrane bioreactor (MBR) has two biological reaction zones (ponds), one is the aerobic zone (nitrification tank) and the other is the anoxic zone (denitrification tank).


The membrane module is immersed in the aerobic zone, and the mixture is circulated between the two zones through a submersible propeller. The sewage enters the anoxic zone first, where the large molecular weight and long chain organic matter is decomposed into biodegradable small molecular organic matter, and then the sewage enters the aerobic zone for biodegradation of organic matter and biological nitrification, and denitrification is carried out through reflux to the anoxic zone to complete the denitrification function.


A submersible stirrer is installed in the anoxic zone to achieve the function of mixing. MBR system is composed of an anoxic tank, aerobic aeration tank, membrane separation tank, chemical cleaning, and backwashing system.


Three-stage treatment


Generally speaking, sewage treatment consists of three stages: the first stage treatment is mechanical treatment, such as grille, sedimentation or air flotation, removal of stones, sandstones and fats, grease and so on(Using johnson screens).


Secondary treatment is a biological treatment. Pollutants in sewage are degraded and converted into sludge by microorganisms. Three-stage treatment is the advanced treatment of water, but there are not many sewage treatment plants in our country put into practical application. It will treat secondary treated water with denitrification and dephosphorization, remove residual pollutants in water by activated carbon adsorption or reverse osmosis, disinfect and kill bacteria and viruses with ozone or chlorine, and then send the treated water into the middle channel as water source for washing toilets, spraying streets, watering green belts, industrial water, fire prevention, etc.


Water treatment agent


Water treatment agents refer to chemical agents used in water treatment. Usually refers to chemical agents used in sewage treatment. It is widely used in chemical, petroleum, light industry, daily chemical, textile, printing and dyeing, construction, metallurgy, machinery, medicine and health, transportation, urban and rural environmental protection and other industries, in order to save water and prevent water pollution. Pharmaceuticals needed for technologies such as cooling water and boiler water treatment, seawater desalination, membrane separation, biological treatment, flocculation, and ion exchange.


Such as corrosion inhibitor, scale inhibitor, and dispersant, bactericide and algaecide, flocculant, ion exchange resin, purifier, cleaning agent, pre-film agent, etc.


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