Water, which is known as the most abundant composition of the earth and is one of the most basic components of the human body, animals and plants. About 70% of the earth’s surface is covered by water. But water must be purified for the use of insulins. In this article, the steps of water treatment in the treatment plant are fully explained. There are about 1.4 billion cubic meters of water on the surface of the earth, which is in the seas, oceans, and icebergs. Of this amount, only 1% is available in the form of surface water and underground water. Surface water or rivers are the most important source of water to meet the needs of communities, which can be saved by building dams on rivers. made and settled the suspended materials in it. Groundwater is the second source of water used for communities, the quality of which depends on the geological characteristics of the region.

What is a treatment plant? What do they do in the treatment plant?

If we want to define the station, we must say that it is called a place where chemicals or bacteria are removed from water or sewage, and in this way the cycle of water use is recirculated. They are used again in industries, agriculture, factories, etc.

There are different types of refineries. For example, a sewage treatment plant, where all types of industrial and urban sewage are cleaned again and the treated sewage is reused, or a water treatment plant, which removes chemical, microbial and physical pollution in different dimensions and sizes. It makes the water clean for domestic consumption and drinking.

In this article, we try to answer questions such as, where is the treatment plant, what is the work of the treatment plant, what is done in the water treatment plant, and similar questions.

What kind of place is the treatment plant?

Refineries purify and clean different types of polluted water and so-called wastewater that have been used once. such as sanitary wastewater (hospital, residential, commercial, office) industrial wastewater (factories, power plants, workshops,…)

In a purification house, purification operations are performed in different ways. The methods that are used for partial cleaning in the water treatment plant are:

Chemical methods, physical methods, biological methods, sludge treatment
Each of these methods analyzes and cleans wastewater chemically, physically and biologically according to its own mechanisms.

Chemical purification:

This method is based on the use of chemicals for water or wastewater treatment, and in wastewater treatment plants, chemicals such as chlorferric or other polymeric materials are used to affect the soluble materials in the wastewater or the insoluble and colloidal materials. Also, substances such as chlorine for biological purification and killing microbes Water disinfection  is also used.
Chemical treatment is also on Industrial wastewater  It should happen both on sanitary sewage and urban Because the consumption of chemical compounds throughout the day and night has caused us to have all kinds of soluble and insoluble substances in household and hospital sewage.
The following methods are used to remove “soluble substances” inside the wastewater:

  1.  Neutralization
  2. Oxidation and reduction
  3. ion exchange

The following methods are used to remove “insoluble substances” or so-called colloidal particles or suspended particles in wastewater:

  • flocculation of insoluble compounds
  • flotation
  • Surface adsorption with the help of active carbon

Physical purification:

The set of processes that help to separate substances and pollutants only by physical and mechanical methods is called physical treatment of water and wastewater. Among the physical methods of purification are the following:

  • Passing sewage or water through special filters and not allowing coarse materials to pass through
  • Sedimentation of suspended materials and their separation
  • Movement of suspended matter on water and separating them

Biological treatment:

In the biological treatment plant, the basis of the work is based on the removal of organic substances and pollutants and microbial organisms, which itself includes different steps. The most important operation in this process is the growth of microorganisms in the wastewater environment, which includes the aerobic and anaerobic treatment stages.
Each of these stages, according to the type of bacteria that can work with oxygen or without oxygen, plays a role in the formation of organic particles and clots and pollutants and their transport and consumption by bacteria in biological purification.

As we mentioned at the beginning of the article, water refineries can be divided into different types according to their type of activity. Although the work in the refinery depends on the purpose of wastewater treatment in that unit, the treatment methods in all these units are similar to each other and based on physical, chemical and biological methods.Water purification of swimming pools, both domestic and public, is a process to keep the pool water healthy during repeated use. When the water of a swimming pool is properly and regularly purified, both the clarity of the water will be maintained and the transmission of infectious and microbial diseases between different people will be prevented.

The swimming pool treatment plant is actually a treatment unit in which the treatment system is equipped with a filter and a pool water treatment pump. The water purification pump circulates the pool water in the purification system and passes the water through the purification filter, thus purifying the water. Also, swimming pool water purification packages can eliminate water pollution by circulating the pool water in addition to the filtration of coarse and physical particles.

Getting to know how the hospital treatment plant works

Another type of water treatment plant is the hospital type. Hospitals are among the places that consume a large volume of water during the day and night, which can often be contaminated with soluble chemical and microbial substances, or even contamination with radioactive materials, disinfectants, sterilizers, heavy metals, etc. to have
In fact, a hospital treatment plant consists of several separate parts that eventually form a single system. Hospital treatment procedures include:

  1. Separation of wastes according to their type
  2. littering
  3. Transferring sewage to the main sewage treatment tanks
  4. Disinfection of treated wastewater
  5. Particulate filter

Each of these steps will have its own methods and methods.

Introduction of industrial wastewater treatment plant

Small and large factories and industries are one of the biggest centers of water consumption and production of industrial wastewaters, which if the wastewaters produced by these units are not treated and cleaned, they will enter the underground water or flowing water and cause environmental hazards.The water treatment plant in production and industrial units can have different types and different packages based on the type of wastewater generated. For example, in relation to production units such as poultry farms and livestock farms or slaughterhouses and factories producing dairy products, the most important feature in their wastewater treatment is biological treatment.

Three methods of physical, chemical, and biological treatment can be used jointly and simultaneously in industrial wastewater treatment plants.

Privacy of all types of treatment plants

Based on the rules and regulations of each type of water refinery; They must have certain privacy and limits to build and carry out their activities, which is in order to prevent possible financial and life damages.
Also, the privacy of the water treatment plant and the privacy of the wastewater treatment plant, based on the laws of the Ministry of Energy and the Water and Sewerage Company, have been determined for construction and operation, which must be followed. One of the successful examples in this case can be the Tehran refinery.

How does the treatment plant work?

It means how to operate and start working an industrial water treatment plant. Important parameters must be kept in mind for the establishment and operation of an industrial refinery. Including:

  • Environmental conditions and the desired land in terms of area, topography, urban boundaries, etc. The amount of incoming sewage
  • Quality type of wastewater or treated water
  • Amount of suspended matter in water
  • Determining the type of wastewater to be treated.
  • The amount and type of pollutants and colloidal and oily substances and heavy metals…
  • Amount of funds available
  • Number of manpower
In any industrial refinery, the wastewater treatment process can be physical, chemical or biological. In all wastewater treatment, physical steps such as garbage collection, material settling, sludge disposal are performed first. After that, it is time for biological treatment, which can be aerobic or anaerobic. After this stage, it is time for advanced purification, which includes the stages of decomposition of organic substances and pollutants, disinfection, active absorption, desalination, etc.

Preliminary water treatment

Preliminary treatment units that are required for some surface water are: :

  1. littering
  2. Preliminary settlement
  3. aeration
  4. Adsorption
  5. Primary chlorination

Some surface waters have high turbidity and microbial contamination, so preliminary sedimentation must be used. These waters have suspended and sedimentable substances with high sedimentation, which can be settled and removed by constructing preliminary sedimentation ponds without the need for chemicals. .

In most water treatment plants, chlorination is done before the treatment operation and chlorine solution is injected into the water. The preliminary chlorination operation prevents the production of taste and smell caused by the activity of bacteria and also prevents the growth of algae .

The main stages of water purification

Types of water purification processes


To remove undesirable gases
CO2 ،H2S and iron and manganese
They use aeration. There are a variety of aeration methods that can be used
mentioned below

  1. aeration
  2. aeration
  3. aeration

✅ Advantages
Aeration in water treatment

  • Increase
    Dissolved oxygen
  • Remove agents
    smell and taste
  • Delete
    CO2 ، H2S
  • Iron removal and


Very large and heavy solids
They are separated by bar garbage collection or fine nets. The first takeover
It is the preliminary treatment stage, the purpose of which is to protect the next units of the treatment plant
It is against large objects and increasing the efficiency of the subsequent processes of the treatment plant

Coagulation of suspended and colloidal substances and their settling

In water treatment plants that treat surface water, the most important problem is the presence of water turbidity, which must be removed from the water. One of the factors that cause turbidity is the presence of colloidal substances that have a size in the range of one millimeter to one micron. Colloidal particles have a very low settling speed, so an external force is needed to settle them. .

Chemical coagulation process is used to speed up the sedimentation of colloidal particles. In the chemical coagulation method, coagulants are used to remove colloidal substances . In water treatment plants, chemical coagulation is usually done by adding trivalent metal salts .

Among the water coagulants, we can mention aluminum sulfate or alum, chloroferric, ferrous sulfate, and ferric sulfate. When coagulants are added to water, destabilization of colloidal particles occurs and clots form. To remove the turbidity of the water, coagulants must be used. This process includes coagulation and coagulation .

The coagulation process of chemicals includes the following steps :

  • Fast coagulation
  • Slow coagulation or flocculation
  • settle down

Quick mixing

In the rapid mixing stage, the coagulant and wastewater are strongly mixed by the stirrer. In this way, the coagulant materials are spread evenly in the tank and react quickly .The amount and type of coagulant is determined by the jar test .

Mix gently

After the rapid mixing of wastewater containing coagulants, it enters the flocculation stage. At this stage, large and settleable particles are created by connecting particles to each other. At this stage, sufficient time should be considered for coagulation and also to prevent the precipitation of clots.Too much turbulence causes clots to break and turn them back into colloidal particles.

In the flocculation unit, unstable colloidal particles approach each other and form clots and flocs. The flocs settle in the sedimentation unit due to gravity and are separated from the water .

۴flatten out

Filtration or filtering (Filtration) It is a process that passes water through a porous medium to separate solid particles in order to separate the suspended solids as much as possible..Suspended solids include clots caused by chemical coagulation, microorganisms and sediments such as calcium carbonate.

Filtration is used exclusively for surface water, and in the case of underground water, it is used to remove clots caused by lightening water or removing iron and manganese. . The type of filter material or porous medium is usually sand, anthracite, garnet, activated carbon .

Types of filters

  • smooth sand
  • Sharp sand filter
  • Strainers under pressure
  • Diatom filters

5 – Disinfection and disinfection

Disinfection is a process that destroys and inactivates pathogenic microorganisms . A large number of pathogenic microorganisms are removed during processes such as coagulation and flocculation, sedimentation and filtration. But in order to comply with drinking water standards and prevent the regrowth of pathogenic agents, disinfection must be done .

6 – Water lightening or water hardening

Hardening or lightening Softening It is one of the special processes of water purification. Hardness means the presence of polyvalent metal cations in water, which react with anions in water in a supersaturated state and produce sediment. .One of the main factors that cause hardness in water are calcium and magnesium ions, which must be removed in the hardening process. Hardening is done by two chemical methods and ion exchange method .

7- Adding substances such as fluorine and iodine to it

In the last step, substances such as fluorine are added to the purified water .

Water Treatment

Water may be drunk before any consumption Purification is needed. The most important reason for water purification is to remove pathogens and impurities It is suspended and colloidal. Drinking water should be free of substances that somehow color, smell and taste They produce unpleasant things .

In addition, we should be able to use purified water Normally, we use it for cooking or washing clothes and the floor The water used in industries should be water that causes deposits on the walls of steam boilers And also do not corrode in them, because this happens Problems causing increased fuel consumption and imposition The cost increases .

Water from any source may have the following impurities and pollution be:

  • Soluble solutes in the form of inorganic and organic substances
  • Dissolved gases
  • microorganisms

 The most water impurities are caused by the erosion of the earth during the passage of water and It is the dissolution of gases from plant and animal organic matter. If these values If it exceeds the limit of drinking water standards, water treatment should be done to remove it pollutants to be done .

Groundwater treatment

Groundwater with turbidity, suspended matter, matter Organic, oxygen and sedimentable materials are very little and in contrast to the concentration of dioxide Carbon, iron and manganese are high hardness. Ammonia concentration in underground water It is an important factor that indicates that the groundwater is contaminated with sewage .

The simplest method of purifying underground water is disinfection and It is fluoridation. If there are many minerals and dissolved gases, it should be Aeration used to remove dissolved gases .

Ati Sazan Arsham Sanat Leader in the water and sewage industry