Wastewater Treatment Plant Design

• Advantages of EPC contracting in the construction of wastewater treatment plants
• Engineering design principles for wastewater treatment plants
• Features of industrial wastewater treatment
• Choosing equipment for mechanical wastewater treatment
• Chemical wastewater treatment technologies
• Biological wastewater treatment
• Aeration systems for wastewater treatment plants
• Choosing mixers for wastewater treatment plants
• Engineering design of wastewater pumps
• Wastewater treatment technology trends
• Electrical systems for wastewater treatment plants
• Modern technologies for wastewater disinfection
• How much does the engineering design of wastewater treatment plants cost?

The consumption of water for domestic, agricultural and industrial needs is growing against the background of a decrease in world supplies of clean water.

The constant growth in consumption and wastewater emissions requires an increase in the capacity of wastewater treatment plants (WWTP).

During the engineering design of wastewater treatment plants, it is very important to use advanced technologies for mechanical, chemical and biological wastewater treatment, which can ensure the production of safe and clean water with minimal costs.

Modern WWTPs must effectively treat the following types of effluent:

• Domestic wastewater, including human waste, food residues, detergents and household chemicals. They usually contain large amounts of organic matter and microorganisms.

• Atmospheric runoff, which includes naturally occurring water (rain, snow, melting ice) and runoff from watering and cleaning parks, streets and other public places.

• Industrial wastewater that is generated as a result of technological processes in factories. They may contain petroleum products, oils, surfactants, drugs and other products of mineral, chemical, plant and animal origin. The composition varies depending on the type of activity.

• Agricultural wastewater that comes from agricultural enterprises in rural areas. They are characterized by a high content of various organic substances and animal waste products.

According to the United Nations University Institute on Water, Environment and Health, developed countries treat 70% of the wastewater generated, while low-income countries treat only 8%.

These figures indicate an urgent need to expand the network of wastewater treatment facilities.

The largest wastewater treatment plants in the world in terms of performance in dry weather:

Facility name	Country	Dry performance (millions m³ / day)	Commissioning year
Lyubertsy water treatment facilities (Moscow)	Russia	3,00	1963
Jean-Marcotte WWTP (Montreal)	Canada	2,78	1984
Stickney Water Reclamation Plant (Chicago)	USA	2,67	1930
Detroit WWTP (Detroit)	USA	2,46	1940
Kuryanovskie water treatment facilities (Moscow)	Russia	2,20	1950
Atotonilco de Tula WWTP (Mexico City)	Mexico	2,00	2015
Bailonggang WWTP (Shanghai)	PRC	2,00	1999
Shanghai Zhuyan I WWTP (Shanghai)	PRC	1,70	2004

As we can see, many WWTPs were built in the middle of the last century and are still in operation without significant changes in the technology.

This requires large investments in modernization and implementation of innovative technologies for treatment, management and control.

The company SI with partners offers financing, design and construction of wastewater treatment plants under an EPC contract, providing investors a single point of contact at each stage of the environmental project.

Advantages of EPC contracting in the construction of wastewater treatment plants

According to official reports, many developing countries of the world, as well as countries of Eastern Europe, currently face an urgent need to build new and modernize existing WWTPs.

Utilitiy companies will have to make great efforts to bring the level of treatment of domestic and industrial wastewater to modern standards. In this sense, innovative technologies for chemical and biological treatment are becoming more and more important for our foreign customers.

Lack of internal resources, knowledge and technology forces investors around the world to look for engineering firms that provide all types of design and construction services under the EPC contract.

The concept of EPC contracting in the construction of wastewater treatment plants includes research, engineering design, procurement and delivery of equipment, construction, testing and commissioning of the facility.

Within the framework of such a project, a single professional EPC contractor seeks and provides all the human and material resources for design and construction. Contractor bears full responsibility for the successful implementation of the project with a predetermined cost.

A client who orders the engineering design and construction of a wastewater treatment plant expects to receive a finished facility with the specified technical parameters in time without any unexpected costs. This is a clear business advantage.

Moreover, the EPC contractor is usually responsible for maintaining the facility throughout its life. This is another advantage, as the contractor team knows all the technical details of the project and can solve problems that arise quickly and cost-effectively.

If you are interested in financing and construction of water treatment facilities under the EPC contract, write to the representatives of our company at any time.

Engineering design principles for wastewater treatment plants

In recent years, in Eastern Europe, the Middle East, Africa and Latin America, modern highly efficient wastewater treatment plants have been designed and built in many settlements.

This is one of the most important directions for the development of the water supply sector at the moment.

Most of the wastewater entering the WWTP is of a domestic nature. Their sources are sewage from residential and public buildings, restaurants, hospitals, etc. They contain mainly organic pollutants of plant and animal origin, acids, salts, surfactants and other chemicals. Their direct discharge into natural water bodies can lead to serious disruption of the ecological balance.

On the other hand, in some regions of the planet, most of the wastewater entering the WWTP is industrial wastewater.



Due to significant differences in the composition and concentration of pollutants, as well as in the volumes of wastewater, it is necessary to develop and implement different technological schemes for their treatment.

Choice of wastewater treatment technology

The choice of process flow is influenced by both the type of pollutants and other key indicators such as total dry matter, biochemical oxygen demand (BOD) and chemical oxygen demand (COD).

The possibilities of re-using water and stabilized sludge should also be explored.

When choosing a technological scheme for wastewater treatment plants, the degree of purification, the amount and composition of pollutants, predetermined by the customer, is taken into account. On the basis of these data, the most appropriate methods and equipment in a particular case are selected to achieve the desired treatment result.

The most rational is the approach based on the development of several options and the subsequent comparison of a set of technical and economic indicators, as well as the compliance of treated water with sanitary and environmental requirements.

Typically, the technological scheme of wastewater treatment plants includes a complex of several main units, where mechanical, chemical and biological treatment, disinfection and sludge treatment are carried out. However, depending on the amount of water, some steps can be eliminated.

With a small amount of wastewater, engineers can propose a simple mechanical treatment.

In these cases, the technological scheme of the WWTP may include the following:

• Mesh for retaining coarse impurities.
• Sand trap for heavy impurities of physical origin.
• Sedimentation tanks for water purification from organic matter.
• Equipment for chlorination (disinfection) of water.
• Sludge drying areas, etc.

However, in most cases, mechanical treatment precedes the biological stage or chemical water treatment.

Among the most important equipment for biological treatment are biofilters, bio-pools and secondary sedimentation tanks.

The choice of equipment is mainly determined by the amount of wastewater. For example, biological filters are usually used for biological treatment of wastewater with a volume of up to 50 thousand cubic meters per day. For wastewater volume of more than 50 thousand cubic meters per day, it is considered more appropriate to use biological treatment with bio-basins.

In small WWTPs where biofilters are used, wastewater after passing the biofilter usually enters the secondary sedimentation tanks. In case of severe water pollution, recycling of biologically treated water can be provided.

Before being discharged into natural water bodies, water must be disinfected.

The sludge is sent for dewatering to sludge drying sites, and the larger WWTPs also use high-tech filter presses, centrifuges or vacuum filters.

When using a bio-pool technological scheme, mechanical treatment is usually carried out using grates, sand traps, pre-aerators and primary sedimentation tanks. In bio-pools, water purified from mechanical particles is aerated, and organic matter is processed using activated sludge.

After passing the bio-basin, water enters the secondary sedimentation tank, where activated sludge is separated. In bio-basins, the amount of activated sludge is constantly increasing, which requires its removal from.

Excess sludge is sent to compactors, where its volume is reduced.

In recent years, due to the constantly increasing requirements for the quality of purified water, multi-stage treatment technologies have been increasingly used.

Location of wastewater treatment plants

When planning the location of the facilities that make up the wastewater treatment plant, two approaches are used.

These are block layout and functional layout.

Block layout is considered the most cost-effective solution, since all processes take place in a single block. Common walls of adjacent structures are widely used, and the length of channels / pipelines is significantly reduced.

The use of a block layout leads to a reduction in the area of the WWTP construction site, and also leaves the possibility of expanding the wastewater treatment plant and building a new block without affecting the operation of the existing blocks. Main disadvantages of this approach are usually related to the interdependence of individual equipment within the block.

If it is necessary to repair individual elements, the company must stop the operation of the entire system.

Another feature of the block layout is that in the case of WWTP expansion, it is necessary to expand all the block elements simultaneously.

The functional layout of the wastewater treatment plant is characterized by greater operational flexibility.

This solution is effectively used in areas with difficult terrain. Most often, such facilities are designed by individually combining different types of equipment, including primary sedimentation tanks, biochemical reactors and biofilters.

In addition to the main equipment, WWTP includes a number of auxiliary elements, including wastewater distribution devices, sludge stabilizers, equipment flushing devices, devices for measuring the volume of treated water, monitoring equipment, etc.

Construction site selection criteria

When designing wastewater treatment facilities, engineers should take into account the development of the territory and the approved urban planning standards, as well as sanitary, environmental, technical and economic requirements.

Sanitary requirements relate to the distance to residential and public buildings, as well as the arrangement of sanitary protection zones. It is important to carry out construction at some distance from the settlement. The exact boundaries of the sanitary zones are determined depending on the amount of effluent and the method of treatment.

When choosing equipment and a specific technological scheme, the amount and composition of effluents, the required degree of purification, treatment methods, the use of sludge, environmental requirements, and much more are taken into account.

When choosing a site to build a wastewater treatment plant, engineers should consider the direction of prevailing winds while trying to locate equipment downwind. Such facilities should be located downstream of settlements in order to ensure unhindered drainage of sewage and rainwater.

When developing a master plan for a wastewater treatment plant, photographs of the site are initially prepared.

The plan contains the main structures, pumping stations, communications and pipelines. The possibility of future expanding is also considered.

The main step in the engineering design of wastewater treatment plants is to determine the height of the equipment in order to ensure the smooth passage of wastewater through them.

Tall structures such as methane tanks and vertical tanks are recommended to be half buried. On the one hand, the volume of excavated soil is reduced, and on the other hand, the excavated soil is used for backfilling objects to improve thermal insulation.

The height difference required to ensure the gravitational movement of wastewater through the equipment is calculated depending on the difference between the height of the water levels in the supply header and in the receiver.

The design of a wastewater treatment plant requires significant hands-on experience from the engineering firm and the use of advanced technologies to perform calculations. This is due to a very wide range of technological schemes and equipment, as well as a variety of customer requirements.

Features of industrial wastewater treatment

Technological processes in many industries involve the discharge of large amounts of wastewater containing hazardous chemical pollutants and valuable reagents that can be recovered for reuse.

The high content of both harmful and valuable impurities requires engineering firms to take special measures to ensure highly effective treatment of industrial wastewater. In turn, the high demands on water quality require the use of the most advanced treatment methods.

In recent years, due to the ever-increasing pollution of water, there has been a need to find better ways of water purification.

To delay and even eliminate the possibility of a water crisis, the following wastewater treatment methods have been developed:

• Mechanical (primary) treatment.
• Physicochemical treatment.
• Chemical treatment.
• Biological (secondary) treatment.
• Additional treatment.
• Disinfection.
• Sludge treatment.

The main criterion for choosing a technology is the composition of the effluents and especially the type of pollutants they contain. Treatment of industrial wastewater, in contrast to the treatment of domestic wastewater, is usually aimed not only at achieving the necessary sanitary standards, but also at reducing the cost of both additional water use and raw materials used in industry.

Typically, post-process industrial wastewater treatment involves reusing water and recovering valuable products.

Regenerative and destructive methods

Industrial wastewater treatment should be carried out closer to the place of its use, which facilitates the return of the extracted substances and the use of treated water in an industrial enterprise.

In this case, the treated water may contain certain impurities that do not affect reuse. In case where water must be discharged into a natural water basin, it is necessary to purify it to a level that meets sanitary and hygienic requirements and does not create a risk of environmental pollution.

Treatment methods are usually classified as regenerative and destructive. Regenerative methods make it possible to extract valuable impurities that can be reused in the industrial process. Destructive methods involve the complete destruction of impurities in order to achieve the maximum degree of water purification.

In cases where the treated water is intended for industrial reuse, regenerative methods are preferred. These include mechanical treatment methods (filtration, sedimentation, flotation, filtration) as well as chemical methods (coagulation, electrocoagulation) and many others.

The use of destructive methods, completely destroying all impurities, is recommended in cases where it is planned to discharge water into water bodies. This is due to high quality requirements that do not allow any contamination.

Regeneration methods do not always meet these requirements.

To improve the quality of processing, many enterprises carry out more thorough complex treatment, using both methods in sequence. In this case, regeneration methods are used first, in which all valuable products are extracted. After that, destructive cleaning begins, in which the remaining contaminants are separated from the water.

The most common methods of destructive treatment are chemical methods using special reagents.

Mechanical treatment of industrial wastewater

As a rule, mechanical treatment is preliminary. It is used to remove coarse impurities contained in water and to prepare water for biological and physicochemical stages.

Removal of impurities is carried out by filtration and precipitation. Accordingly, the main equipment for this stage are sieves, sand traps, dust collectors, oil separators, etc.

In mechanical treatment, water first passes through filtration through various sieves, during which coarse impurities and partially insoluble substances are removed.

To release insoluble substances of various densities, sedimentation tanks are used in which heavy particles settle to the bottom and lighter particles float to the surface. Sedimentation is usually used in combination with additional techniques such as coagulation and filtration.

Mechanical filtration is a wastewater treatment method in which water is filtered through a bed of filter material using metering pumps. Various substances with a granular or porous structure are used as a filter material. During water purification, various undissolved impurities are retained in the pores or between the granules of the material.

This method can be used alone for wastewater treatment in industrial plants and in combination with chemical treatment. Mechanical treatment can be used as an independent method in cases where the resulting water is supposed to be reused in an industrial process.

In all other cases, mechanical treatment is only the first stage of a multi-stage process.

Chemical and physicochemical methods

Chemical treatment of industrial wastewater refers to the use of various chemical reagents.

Chemical methods include chemical oxidation and neutralization to achieve a neutral pH.

Among the equipment used, the main role is played by mixing reactors. Chemical treatment can be carried out directly at the point of discharge. Engineers distinguish two situations. The first situation is when the wastewater is alkaline and treated with acids to produce different salts. The second situation is when wastewater has a low pH.

The water is treated with alkaline solutions such as sodium and potassium hydroxide. As a result, soluble or insoluble salts are formed with the precipitation of different insoluble compounds.

Physicochemical methods are commonly used to remove fine suspended particles in water. This includes processes such as flotation, flocculation and coagulation.

Flotation is a method of removing various contaminants by saturating water with air bubbles.

It is mainly used for the treatment of highly polluted wastewater, including industrial wastewater.

In fact, the flotation process is an intense rise of small gas bubbles to the surface of a liquid together with adhering dispersed particles. These particles form a layer on the surface of the treated water.

Flocculation and coagulation are very similar methods. Here, water purification is based on the addition of a reagent (coagulant and flocculant), which interacts with impurities in the water and promotes their precipitation. Both methods involve the use of additional filtration to separate the formed precipitate.

Biological treatment of industrial wastewater

If the industrial wastewater contains biodegradable organic substances, it is recommended to additionally carry out biological treatment.

Depending on the concentration of organic matter, biological treatment can be carried out under aerobic or anaerobic conditions.

With BOD5 up to 400 mg / l, treatment is carried out under aerobic conditions, and with BOD5 over 2000 mg / l, anaerobic conditions are better suited. If there is a deficiency of nitrogen and phosphorus in the treated effluent, it is recommended to add them in order to achieve the optimal BOD5: N: P ratio.

Biological treatment equipment can be divided into two groups.

First, these are installations for treatment in conditions close to natural.

Secondly, these are installations in which technological process takes place in artificially created conditions.



The first group of equipment includes filtration fields and biological lakes. The second group includes biofilters.

For wastewater treatment plants with artificially created conditions, a more intensive course of the technological process is typical.

Choosing equipment for mechanical wastewater treatment

Upon entering WWTP, water goes through several stages of processing.

The first of these is mechanical treatment, in which coarse impurities are carefully removed from the water.

The mechanical method of water treatment includes several stages, such as filtration, sedimentation and separation of undissolved particles by hydrocyclones and centrifuges. The choice of the suitable technology and equipment plays an important role in the engineering design of wastewater treatment plants.

Wastewater filtration systems

In the filtration process, various sieve and grate systems are used, which are characterized by an insufficiently good cleaning effect.

Sieves are rarely used because they have relatively low efficiency and high energy consumption. Their advantage is a small installation area. They are commonly used in municipal wastewater treatment and in industry as part of systems to retain valuable materials for reuse in the manufacturing process.

Among the used filter designs, there are rotary, drum, disc, belt and others.

The main element of all these products is the filter mesh through which the wastewater flows.

Various manufacturers offer mesh filters with different mesh sizes. Perforated sheet plates are also available. They are most commonly made from stainless steel, brass and plastic.

The sieves are cleaned of accumulated dirt using brushes, compressed air or rinsing water. Self-cleaning strainers are also available. Basically, these are drums in which the sieve section is tilted, and the continuous flow of water helps to clean them.

The grates can be movable or fixed, with manual or mechanical cleaning. Automatic cleaning is usually applied to highly polluted wastewater. Crushers are also used that simultaneously hold and crush large particles. They are especially suitable for small WWTPs. Additional grates must be installed in front of them to prevent the accumulation of debris.

Grates are essential elements of any wastewater treatment plant.

Thanks to them, coarse mechanical particles captured by wastewater are retained. This is necessary to protect the expensive equipment installed after them from clogging and breakdowns.

Engineering design of sedimentation equipment

Sand traps are used to separate sand, glass, coal and other coarse particles. Most often, sand traps are reinforced concrete labyrinths in which a lot of solid particles are deposited.

In practice, three types of grit traps are used — vertical, horizontal and sand traps with rotary and translational motion. The choice depends on the direction of movement of the water flow in them. Vertical sand traps have the least practical application due to their lower cleaning capacity. Horizontal sand traps, in turn, are the most common due to their high efficiency.

In aerated sand traps, the rotational horizontal movement is supported by the supply of compressed air from pneumatic aerators and a stream of water entering in the horizontal direction.

The main requirement for achieving high efficiency of sand traps is maintaining the water flow rate within the specified limits. The recommended speed is about 0.30 m / s. It is achieved by regulating the flow rate of water flowing out of the tank.

For additional removal of particles deposited in sand traps, special bunkers, hydrocyclones and collectors are designed. Mixers are used to optimize the composition and flow of wastewater. The efficiency of the entire process is highly dependent on fast and complete mixing.

For the separation of fine particles, mainly of organic origin, special precipitating equipment is used. Sedimentation tanks are reinforced concrete reservoirs in which high density particles settle to the bottom of the structure, and light particles float to the surface.

Depending on their purpose and place in the process flow diagram of WWTP, sedimentation tanks are divided into two main groups, primary and secondary. Primary sedimentation tanks, as part of the mechanical treatment equipment, are installed at the beginning of the flow after the sand traps. Secondary sedimentation tanks are installed after biological treatment equipment.

Depending on the design features and the direction of water movement, the sedimentation tanks can be horizontal, vertical, radial and thin-film.

During the engineering design of a wastewater treatment plant, it is important to select the correct mechanical treatment method and equipment to achieve optimal results with minimum costs.

Chemical wastewater treatment technologies

The need for preliminary treatment of industrial wastewater is explained by their serious negative impact on the environment.

They can be toxic and have long-term environmental consequences.

In the practice of chemical treatment of industrial wastewater, processes such as neutralization and oxidation are used. This broad group includes electrochemical treatment and other technologies.

Chemical treatment is the preferred method if the separation of impurities is only possible through chemical reactions with other reagents.

The chemical treatment process relies on the removal of contaminants in one of the following ways:

• Separation of substances between solid and liquid phase.
• Transformation of impurities dissolved in water into insoluble compounds.
• Decomposition of complex substances into simple chemical products.
• Transformation of toxic substances into harmless compounds.

The engineering design of wastewater treatment plants includes the development of a technology for chemical neutralization of wastewater, as well as water purification using oxidants.

Wastewater pH neutralization

The neutralization process is recommended for the treatment of wastewater that is acidic or alkaline in nature and not contaminated with other components.

This technology makes it possible to obtain at the outlet water with a neutral pH, which is safe for the environment.

The technology can include the following approaches:

• Mutual neutralization of acidic and alkaline wastewater.

• Neutralization by adding reagents completely soluble in water or partially soluble in it, such as acid solutions, sodium carbonate, sodium hydroxide, ammonia.

• Filtration of wastewater through neutralizing materials such as limestone, dolomite, magnesium carbonate and others.

Neutralization by mixing acidic and alkaline water is considered one of the simplest and most economical methods. It is widely used in the chemical industry where enterprises discharge large volumes of chemically dissimilar effluents.

Due to the differences in the production and removal of these waters, special regulating devices and mixers are used to gradually discharge the wastewater into the sewer after complete neutralization. This method can only be used when the wastewater does not contain toxic or explosive substances.

When the wastewater is only acidic or only alkaline in nature, pH neutralization methods are used.

The choice of reagent depends on the concentration of contaminants and the nature of the products formed after neutralization.

For example, hydroxide ion-forming reagents are used to neutralize mineral and organic acids. Among the most commonly used reagents is calcium hydroxide in the form of limewater due to its low cost. Other commonly used reagents are sodium hydroxide and carbonate.

When calcium hydroxide is used to neutralize wastewater containing sulfuric acid, calcium sulfate precipitates at the bottom.

Therefore, wastewater treatment engineers must design a settling system.

Various acids and acid gases are widely used to neutralize alkaline wastewater, such as flue gases containing CO2, SO2, NO2, N2O3, etc. The use of such acid gases not only neutralizes wastewater, but also removes harmful components of the gases themselves.

The neutralization of alkaline water with flue gases is a very economical technology, since it eliminates wastewater discharge, reduces fresh water consumption, saves heat for heating fresh water and removes acid components and dust from flue gases.

Neutralization of industrial wastewater prevents the development of corrosion in pipeline systems, maintains optimal conditions for microorganisms in wastewater treatment plants. It is often used before the discharge of part of the treated water into water bodies.

It is a widely used method of controlling the concentration of hydrogen or hydroxyl ions in wastewater. The choice of a specific neutralization method in the process of WWTP engineering design depends on the type and concentration of acids in wastewater, the amount of incoming wastewater, the presence of chemicals, etc.

Wastewater treatment with oxidizers

Oxidation processes for industrial wastewater treatment are based on the destruction of pollutants to harmless products under the action of strong oxidants such as chlorine and its compounds, ozone, potassium permanganate, hydrogen peroxide, oxygen and others.

This technology is limitedly applicable to wastewater containing low concentrations of pollutants.

It is used for the purification of industrial wastewater containing toxic substances (cyanides, complex copper and zinc cyanides) and compounds that are impractical to extract from wastewater or remove by other methods (hydrogen sulfide, sulfides).

The activity of oxidants is determined by their oxidative potential. Chlorine or compounds containing active chlorine are the most powerful and demanded oxidants. They are used for wastewater treatment from hydrosulfides, phenols, cyanides and others.

In industrial wastewater treatment, the removal of molecular and ionically dissolved substances by oxidation with sodium hypochlorite is one of the most cost-effective treatment methods.

Chlorine dioxide is also widely used. Due to its high oxidation potential, chlorine dioxide destroys simple and complex cyanides in wastewater from electroplating plants, oxidizes phenol and its homologues, and prevents the formation of highly toxic chlorophenol.

Air oxygen is used to oxidize wastewater from cellulose, petrochemical and refinery industries. The process takes place in the liquid phase at high temperature and pressure. Atmospheric oxygen is also used in the treatment of ferrous wastewater. Carbon dioxide from flue gases can be used to effectively break down sulfide compounds.

Another strong oxidant used in wastewater treatment is ozone. It is capable of decomposing many organic compounds and impurities in aqueous solutions at normal temperature.

Oxidation with ozone simultaneously provides discoloration, taste and odor elimination, and disinfection.

Ozone oxidizes both inorganic and organic substances dissolved in wastewater. Ozonation is suitable for the treatment of wastewater containing phenols, oil, hydrogen sulfide, arsenic compounds, surfactants, cyanides, dyes, aromatic hydrocarbons, pesticides and others.

It should be borne in mind that the purifying effect of ozonation is based on the solubility of ozone in water. The key factor for its practical applicability is stability, which decreases with increasing salt content, acidity and temperature.

A combination of ozone and ultraviolet is used to discolor water contaminated with dyes. Modern wastewater treatment systems can use ozone generated from air or obtained from technical oxygen.

Removal of concentrated organic and inorganic substances

The engineering design of wastewater treatment plants for industrial facilities often faces the challenge of removing concentrated organic and inorganic pollutants.

Electrochemical oxidation based on electrolysis is considered the most suitable solution.

Chemical transformations during electrolysis can be different depending on the type of electrolyte and the material of the electrodes, as well as on the presence of various substances in the solution. Basically, electrolysis involves two processes - anodic oxidation and cathodic reduction.

Electrolytically insoluble materials such as carbon, graphite, magnetite, lead dioxide and other titanium-based coatings are widely used as the anode. Lead, zinc and stainless steel are commonly used as the cathode. The current density is extremely important for electrochemical oxidation.

To prevent mixing of electrolysis products, especially gases (hydrogen and oxygen, which can form explosive mixtures), a ceramic, polyethylene, asbestos or glass diaphragm is used, which effectively separates the anode and cathode spaces.

In the process of anodic oxidation, decomposition of organic substances obtained as intermediate or final oxidation products (organic acids, CO2 and H2O) occurs. In the process of electrolysis of alkaline wastewater containing cyanide, the anode undergoes oxidation of cyanide ions with the formation of cyanate ions and additional electrochemical oxidation to end products.

In order to increase the electrical conductivity of the wastewater, reduce energy consumption and improve the oxidation process, in some cases water and mineral salts are added.

For chemical wastewater treatment, water treatment equipment manufacturers now offer complete engineering solutions for separating sludge from the treatment process.

Chemical wastewater treatment systems include mixing tanks, reactors for mixing and dosing chemical solutions, agitators, metering pumps, monitoring and control systems and others. Sludge dewatering systems are often provided.

Chemical treatment is a very effective method of producing high quality water that can be reused in industry or discharged into water bodies. The design of chemical treatment systems for wastewater treatment plants should be based on the specifics of the industrial process at the customer enterprise.

Biological wastewater treatment

Biological treatment is a microbiological process that can take place in a natural or artificial environment.

It speeds up significantly in wastewater treatment plants.

The basis of this process is the gradual conversion of various biological pollutants into living matter, called activated sludge.

Effective biological wastewater treatment is achieved due to the increased concentration of microorganisms in the pool. No harmful chemicals are used in these processes.

The most widely used are aerobic treatment systems. They are commonly installed in dairies, sausage factories, wineries, large farms and other businesses.

At the stage of engineering design of wastewater treatment facilities, it is important to create the conditions necessary for the development of microorganisms. This is a combination of physical, physicochemical, chemical and other factors affecting activated sludge.

Conditions for the development of microorganisms are determined by energy sources, nutrients, oxygen content, temperature, pH, osmotic pressure, water surface tension, stirring, etc.

To live and reproduce, microorganisms need a source of cellular energy.

According to the type of energy source, the microorganisms used are divided into three broad categories:

• Autotrophic microorganisms that use external energy sources, including sunlight and externally supplied inorganic substances.
• Heterotrophic microorganisms, which use the energy obtained during the decomposition of organic compounds absorbed from food and included in them.
• Mixed organisms using both types of energy sources.

To maintain the life of microorganisms, nutrients are also needed, which contain carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur. The group of nutrients also includes potassium, sodium, calcium, magnesium, iron, cobalt, molybdenum, copper and zinc. These are the so-called "trace elements", the content of which in microorganisms is 10-100 times less than basic substances.

Some microorganisms also require certain organic substances, without which they cannot grow.

These substances are called growth factors.

This includes amines, amino acids, vitamins, higher fatty acids, and heterocyclic compounds.

Another important condition for the development of microbial communities is the availability of oxygen. Depending on whether the water contains dissolved oxygen, aerobic (in the presence of oxygen) and anaerobic (in the absence of oxygen) processes are distinguished.

In anaerobic processes, the rate of energy production is low, since the microbial cell receives energy only from elementary redox processes, in which electron acceptors or donors take part.

The processes that occur naturally in septic tanks are anaerobic and therefore not considered efficient enough to convert large amounts of accumulated organic waste. To increase the efficiency of biotransformation in such cases, it is recommended to change the process to aerobic.

Anaerobic wastewater treatment is relevant only in cases where it is part of a more complex treatment process or when a special biogas production technology is used.

In practice, this process is considered capricious and unstable. The reasons for this lie in its nature, the development of numerous microorganisms, complex relationships between organisms, and some poorly understood aspects of biochemistry and microbiology.

The most effective solutions for WWTPs are multi-stage systems that include aerobic processes.

Aeration systems for wastewater treatment plants

Aeration systems are one of the main elements of wastewater treatment plants that ensure the efficient flow of aerobic biological treatment processes.

These systems are classified as pneumatic, mechanical, hydraulic and combined. When designing WWTPs, it is necessary to choose the aeration system. It affects the way of supply and distribution of oxygen andthe overall efficiency of the technological process.

Pneumatic aeration systems use a variety of equipment to supply compressed air or oxygen to the equipment.

Among the most commonly used are air compressors, high pressure fans and others.

In practice, some of the most preferred are medium pressure aeration systems. This group includes aerators of various designs, such as perforated tubes, combs, valves, and others, among which perforated tubular aerators are the most widely used.

When choosing a pneumatic aeration system for WWTP, several aspects should be considered. Their effectiveness depends on the size of air bubbles, the depth of immersion, the intensity of aeration, the relative area of the aeration devices and their location in biological pools.

Types of mechanical aerators

Unlike pneumatic systems, which are characterized by forced air supply, the principle of operation of the so-called mechanical aerators is based on intensive mixing and dispersion of wastewater and activated sludge using moving elements.

Accordingly, the enrichment of water with oxygen occurs due to the diffusion of oxygen from the air. In practice, mechanical aerators of various designs and operating modes are used. These devices can float on the surface or submerge in water. They have a horizontal or vertical axis of rotation.

Commonly used surface systems include horizontal axis aerators, which contain blades or brushes partially submerged in water mounted on metal shafts.

Vertical-axis mechanical aerators can be surface and deeply submerged, and surface aerators are currently the most popular option. Here, the rotor is in direct contact with atmospheric air, and the aerator itself is partially submerged in the liquid.

A characteristic feature of such systems is the combination of the aeration effect of circular dispersion of water particles and the release of atmospheric air. At the same time, the liquid is supplied from the bio-pool to the rotor, contributing to better oxygenation of the pool water.

In deeply submerged aerators, the rotor is located at a considerable depth.

It is attached to a rotating shaft, which can be hollow or surrounded by a larger diameter tube.

The principle of operation of such systems is based on the suction of water and air through the holes in the shaft housing and tube, which are located on the surface of the water and above it. The resulting water-air mixture flows through the lower part of the tube to the rotor, then is sprayed, mixing with the liquid throughout the entire volume of the pool.

Good aeration of wastewater can also be achieved with hydraulic aeration systems. In practice, combined systems are widely used, in which the elements of the types discussed above are used.

It can be pneumo-mechanical, pneumohydraulic, and pneumohydromechanical devices.

Choosing mixers for wastewater treatment plants

Liquid mixing is considered one of the most common technological processes is wastewater treatment.

The main goals of mixing a liquid medium are:

• Getting a mixture with a homogeneous composition of two or more components.
• Preparation of emulsions or suspensions without separation of the heavy phase.
• Acceleration of a chemical reaction by increasing the contact surface.
• Acceleration of heat transfer in reactors, coolers and heaters.
• Prevention of the deposition of solid particles that impair heat transfer.
• Acceleration of mass transfer in diffusion processes.

The mixing method and the type of device used are chosen by engineers depending on the characteristics of the mixture components. In wastewater treatment, one of the main purposes of mixers is to facilitate homogenization, emulsification, dispersion and heat transfer.

They are also used when mixing wastewater with chemicals such as aluminum sulfate, etc.

The process of treating domestic and industrial wastewater goes through several stages, including mechanical, biological and chemical water treatment. When designing WWTPs, it should be borne in mind that the successful implementation of individual treatment scheme requires ensuring sufficient mixing and homogenization of wastewater.

For this purpose, mixers of various types are used.

New requirements for the quality of treated water and the improvement of treatment processes also contribute to an increase in their use in wastewater treatment plants.

These systems are widely used in activated sludge processes to induce water movement and prevent sediment build-up at the bottom of the pool. They are also used to obtain a homogeneous mixture of water and added chemical solutions.

Wastewater mixer types

Depending on the technological process, preference is given to mixers of different types, including propeller, turbine, belt, screw, submersible, surface and so on.

Paddle mixers are used for mixing low viscosity liquids, dissolving and suspending solids, and more. They are well suited for keeping particles with a low settling rate in motion.

Wastewater propeller mixers are preferred when vigorous mixing of low viscosity liquids is required, as well as for dissolving, rapidly mixing, forming emulsions, or homogenizing large quantities of liquid.

They are usually energy efficient and are available in a variety of options.

Turbine mixers can be classified as open or closed. They are used to form mixtures, the viscosity of which changes with stirring, as well as to obtain suspensions, rapid dissolution, gas absorption, and heat transfer intensification.

Belt and screw mixers are used for mixing highly viscous liquids and pasty materials, cleaning the walls of tanks. In turn, submersible mixers are used for homogenization and even aeration.

Featuring freedom of positioning, easy installation and quiet operation, submersible wastewater mixers provide efficient mixing in any tank shape, regardless of depth, length or width. Engineering design should take into account the volume and geometry of the tanks, the viscosity and density of the material, the desired speed. mixing and other factors.

When choosing a mixer, engineers should pay attention to the material. Typically, mixers are made of corrosion-resistant steel, titanium alloys and other high strength materials. Various coatings are also used to protect the main elements from corrosion.

Engineering design of wastewater pumps

In the design of wastewater treatment plants, one of the most important elements is considered to be pumps, which are selected depending on the specifics of a particular application.

They are used for collecting, cleaning, transporting sludge and many other purposes.

Various designs of centrifugal pumps and positive displacement pumps are widely used today.

In centrifugal pumps, liquid is displaced by centrifugal forces. Liquid is pumped into the inlet and flows to the periphery of the impellers. In the case of positive displacement pumps, the volumetric principle of operation is implemented as a result of a continuous decrease in the volume of the working chambers.

Centrifugal pumps for wastewater

Modern centrifugal pumps can be single-stage or multi-stage, submersible and surface-mounted.

They are supplied with a horizontal or vertical shaft.

Submersible centrifugal pumps, which are suitable for conveying liquids containing suspended solids, are widely used for pumping wastewater. They are widely used in sewage pumping stations, industrial filters, for the transportation of partially treated industrial wastewater, etc.

Submersible pumps are also a suitable solution for pumping sewage and rainwater from residential and public buildings, schools and industrial plants. They can also be used to pump clean water.

These pumps are widespread due to their relatively low installation and operating costs, low noise levels, long service life and high reliability.

Positive displacement pumps

Of the various designs of positive displacement pumps for wastewater treatment, mainly metering and eccentric screw pumps (progressing cavity pumps, PCPs) are used.

Metering pumps

The metering pumps are highly reliable and have a long service life.

They combine three separate functions including pumping, metering and regulation. This group comprises several varieties, including mechanically driven diaphragm metering pumps, hydraulically driven metering pumps, piston metering pumps and peristaltic pumps.

Metering pumps can be used in the process of disinfection, sludge treatment and others. They are suitable for handling aggressive and viscous fluids as well as acids, alkalis and solvents. Operation of pumps with aggressive media requires special attention to the materials from which their individual elements are made.

The materials used are selected taking into account such liquid characteristics as temperature, chemical aggressiveness, etc. Manufacturers widely use plastic and thermoplastic polymers.

Before installing the pump, engineers recommend assessing the operating conditions of the pump, whether the pump will work outdoors, indoors, the presence of dust, smoke, etc.

When operating the pump outdoors, it is recommended to protect it from direct sunlight. In terms of ambient temperature, most metering pumps operate stably at low temperatures.

Eccentric screw pumps

The design of screw pumps makes them suitable for the transport of liquids with high viscosity, as well as for liquids containing solids and gas, as well as water with significant amounts of sand.

The only moving part of the eccentric screw pumps is the screw, which rotates in the screw stator, gradually reducing the volume of the working chamber. Along the contact line between the screw and the stator, channels are formed through which the liquid flows. The constant area of these channels in each section along the entire length of the pump ensures smooth fluid flow without pulsations.

Screw pumps are considered suitable for transporting large amounts of wastewater at low pressure. At WWTPs, they are used for pumping raw sludge of various contents.

This equipment is extremely resistant to high loads and can be operated without water.

Wastewater treatment technology trends

Wastewater treatment plant operators are faced with growing challenges related to the identification of growing amounts of pollutants, rapid population growth, increased industrial activity and dwindling fresh water supplies.

Traditional technological processes are no longer sufficient to remove chemical and microbial contaminants from wastewater. The effectiveness of older technologies has steadily declined over the past two decades, requiring new approaches.

Greater understanding of the effects of water pollution and increased demand for high quality water has led to the imposition of stringent regulatory requirements, including broadening the range of regulated pollutants, lowering maximum permissible concentrations in effluents planned for discharges into water bodies. Special attention is now paid to the removal of phosphorus, nitrogen and synthetic organic compounds due to their significant impact on human health and the environment.

Technological trends in wastewater treatment are largely driven by depletion of water resources, population growth and industrial growth. The reuse of domestic and industrial waste water and the recovery of pollutants from industrial processes are becoming increasingly important.

This is especially true for desert regions, where the transportation of fresh water is costly.



Reuse of water is becoming important because of concerns about the contamination of water resources with toxins from industrial plants. Realizing this concept requires advanced cleaning technologies to remove potentially harmful components that cannot be removed by any conventional process.

Wastewater as a valuable resource

Wastewater treatment innovation is based on the idea that wastewater can be a valuable resource.

However, the ability to reuse and recover raw materials from them depends on many factors. These include operating costs, potential revenues, resource costs, engineering solutions for the implementation of a specific technological process, and other factors.

Most non-potable water for domestic and commercial purposes can be obtained from runoff and collected rainwater. However, in order for these systems to become sustainable in the future, it is necessary to develop and implement new methods of wastewater treatment and water management.

Innovations in physico-chemical wastewater treatment

A floating filter media (FFM) has been developed to improve the efficiency of removing solids from wastewater. 

Wastewater enters the precipitator by passing through a filter bed made of mesh materials with low density. The floating filter media is purged by air jets, creating a cyclical flow that helps separate the solid phase components on the filter.

Another recent development is a precipitator for liquids containing suspended solids. In this equipment, suspended particles are separated in two stages, natural flotation (if their density is lower than the density of the liquid) or by dissolved air flotation (DAF) followed by filtration with sand, anthracite or other filter product.

Some industrial processes, such as the manufacture of semiconductor components, discharge wastewater with a high concentration of dissolved solids. The electric field technology has been developed specifically to separate suspended and dissolved particles such as metal salts. This process involves filtering water through a membrane in the presence of an electric field that repels particles from the membrane surface.

In froth flotation, wastewater is treated with a gas (usually air) to carefully separate the solid or liquid (oil) it contains.

One of the new technologies is the multistage flotation column, which, in addition to cleaning, can be used for degreasing recycled paper, mineral enrichment and other applications. A series of axially separated suction tubes ensure thorough mixing in the flotation column, while a special gas distributor generates fine bubbles. Due to the configuration of the pipes, a closed flow of water is created at each stage of flotation.

This ensures an even distribution of gas bubbles throughout the column, greatly improving mixing and contact of the bubbles with contaminants.

Wet oxidation is another innovative wastewater treatment method in the presence of oxygen at high temperature and pressure. When the process takes place in the liquid phase without a catalyst, its speed is low. A few years ago, Japanese scientists created a catalyst that can help wet oxidation to remove organic and inorganic substances, regardless of their concentration. In addition, the use of a catalyst speeds up reactions and allows operators to easily adjust key process parameters.

Currently, a number of studies are being carried out to create membranes from nanomaterials that will ensure the effective separation of metal and bimetallic nanoparticles, mixed oxides, zeolites and carbon compounds from wastewater.

These works give hope for an increase in the efficiency of wastewater treatment.

Innovations in biological wastewater treatment

Modern wastewater treatment technology trends are aimed at improving biological treatment. 

Biological methods are used to purify domestic and industrial water by converting dissolved or suspended substrates into biomass, which is subsequently separated from the water.

There is recycling or reuse of residual biomass (sludge) requires pretreatment, which includes decomposition, compaction and dewatering to increase the solids concentration to 20-40%. The economic benefits of reducing the water content in the sludge can be significant.

Older drip filters use a biofilm attached to the filter media to remove and convert organic matter to carbon dioxide and water and ammonia to nitrate. The filter bed is usually made of gravel, wood or corrugated plastic, which increases the maximum active biological surface.

Modern drip biofilters mainly use plastic modules and virtually no re-processing of biomass attached to the substrate is required.

Several years ago, a wastewater treatment technology was developed in which mussel shells are used as a substrate for an aeration chamber. After removing the nacreous layer, their surface becomes rough and favorable for the development of microorganisms. Waste water is purified in a biological aeration chamber and then enters the adsorption chamber with activated carbon. Finally, the treated water passes through the denitrification chamber.

In general, current trends in wastewater treatment are aimed at improving water quality and removing an increasingly wide range of pollutants in the safest and most cost effective ways.

Electrical systems for wastewater treatment plants

The reliability of electrical equipment is critical to the efficient, continuous and trouble-free operation of wastewater treatment plants.

The engineering company is faced with the task of designing internal electrical networks in such a way as to guarantee the safety and stability of technological processes, as well as to ensure minimum energy losses.

The main requirements for the electrical system for WWTP are reliability, ease of operation throughout the entire life cycle, as well as the ability to scale for future expansion of the facility.

When designing wastewater treatment plants, it is important to take into account that electricity costs account for about 30% of the total operating costs of the facility.

Engineering design

Stability with minimal downtime is key priorities when selecting electrical equipment for the WWTP.

The cost of internal electrical networks is usually 5-10% of the total project budget.

These facilities are characterized by a long service life, as most of the existing wastewater treatment plants around the world are over 25 years old, and some have been in operation for over 50 years. In some countries, WWTPs dating back to the 19th century are still in operation. Experts strongly advise to invest in quality and reliable electrical equipment.

Last but not least, electrical performance, design, installation and commissioning procedures must comply with all applicable codes and standards in order to shorten project implementation time and minimize risks to personnel and property.

Operation, maintenance and monitoring

Wastewater treatment plants have a number of continuous processes that require a reliable power supply.

To achieve this, engineers are advised to:

• Choose an architecture that strikes the right balance between risk and return on investment.
• Select reliable equipment according to the intended use and expected loads.
• Provide regular maintenance and repair of electrical equipment.

Unified platforms for automation, monitoring and control, which include energy management systems, are increasingly being installed in modern wastewater treatment plants. Their purpose is to assist operators in making decisions and / or initiating necessary corrective or preventive actions.

Energy management solutions include tools for real-time monitoring, data collection, event tracking, fault analysis, remote troubleshooting of electrical equipment and some related units.

Scalability and upgradeability

Although modern wastewater treatment plants have a lifespan of several decades, technologies and processes, equipment, and legal frameworks for wastewater treatment are constantly changing.

In addition, the demands for energy efficiency and carbon footprint are constantly increasing. Consequently, wastewater treatment plant electrical systems must be, scalable, compatible with third-party equipment and use standard protocols.

Safety of personnel and material assets

First of all, the electrical equipment in the wastewater treatment plant must be safe. For this, all devices and cables are tested and validated.

The equipment itself must comply with modern standards for use at the WWTP, as well as have the necessary certificates. Ensuring adequate protection is important engineering design consideration.

To ensure safe operation and maintenance, it is important to install mechanical and electrical interlocks at the design stage, as well as create conditions for the implementation of automatic monitoring and control systems.

To ensure safety and functionality in wastewater treatment plants, electrical equipment must be ready for immediate integration with modern energy efficiency control systems.

Modern technologies for wastewater disinfection

Today, domestic wastewater is mainly treated mechanically and biologically.

Mechanical treatment effectively removes large solid particles.

Biological treatment aims to remove organic contaminants.

Since up to 98% of bacteria are removed from wastewater during biological treatment, it is usually disinfected after this stage. The aim is to remove all pathogens, bacteria and viruses contained in the water, preventing the risk of contamination of water bodies. The use of natural biological treatment methods, such as filtration fields, achieves very high disinfection rates in excess of 99%.

During the engineering design of wastewater treatment plants, chemical and physical methods are mainly planned for the disinfection of wastewater.

Chemical methods are based on special reagents (usually strong oxidants) that have a destructive effect on bacterial cells or viral particles. These methods include chlorination, ozonation, treatment with salts of heavy metals and others.

Physical methods of disinfection include exposure of microorganisms to UV rays, ultrasound, high temperatures, and others. Both physical and chemical disinfection methods are widely used today.

Chemical methods of disinfection

Specialists in the engineering design of WWTPs pay special attention to systems for chemical water disinfection.

These systems usually use chlorine and its compounds, as well as oxygen and ozone.

Chemical disinfection of wastewater can take place in two stages, each of which involves the use of a very strong oxidizing agent. This is done to maximize the quality of the disinfected water.

In both stages, a combination of ozone and chlorine can be added to the water. It is also possible to combine chemical and physical methods to reduce the amount of chemicals used.

Disinfection of wastewater by chlorination

In practice, chlorination is one of the most commonly used wastewater disinfection methods.

This is due to both high efficiency and low cost. Also, during chlorination, water acquires bactericidal properties, since the disinfecting agent remains in water for a long time.

Chlorination of water is usually carried out with chlorine in the gaseous state or with compounds that contain active chlorine, such as calcium hypochlorite, chlorine dioxide or sodium hypochlorite.

Hypochlorous acid is a strong oxidizing agent. It actively dissociates, and the resulting hypochlorite ion, together with hypochlorous acid, kills a wide range of pathogens.

Efficiency of disinfection with pure chlorine

The efficiency of wastewater disinfection with pure chlorine depends on its solubility in water, which changes under the influence of pressure and temperature.

Low temperature and high water pressure conditions are considered optimal for chlorine dissolution.

It should be borne in mind that the bactericidal effect increases as the number of undissociated hypochlorous acid molecules increases, and vice versa.

Usually, equipment for the chlorination of treated wastewater does not differ from systems for the treatment of drinking water. Their main elements include a chlorinator with chlorine storage, mixer and contact tanks. Chlorinators typically use high pressure or vacuum. Recently, there has been a tendency to install vacuum chlorinators where the risk of chlorine leakage is minimal.

Contact tanks resemble sedimentation tanks without mechanical sludge cleaners and a bottom slope of up to 5%. When designing wastewater treatment plants, it is allowed to exclude a contact tank for cases where the collector provides contact between water and chlorine for at least 30 minutes.

Disinfection of wastewater using sodium hypochlorite

Disinfection of wastewater using sodium hypochlorite is mainly planned in cases where the daily consumption of chlorine is very low and there are some difficulties with the storage, transportation and production of chlorine gas.

Sodium hypochlorite is a product obtained by hydrolysis of concentrated sodium chloride (NaCl) solution. The process is carried out in electrolytic cells with graphite electrodes. It is believed that the process of producing sodium hypochlorite is simpler than producing pure chlorine.

Sodium hypochlorite is an excellent alternative to chlorine, and the achieved efficiency of water disinfection is comparable to that of chlorine. Disinfection of water with sodium hypochlorite is achieved at a concentration of only 1.5-3.5 mg / l.

Chlorine lime, containing up to 36% active chlorine, can also be used for wastewater disinfection. It is mainly suitable for small wastewater treatment plants with a capacity of up to 1000 m³ per day.

Disinfection of wastewater with ozone

Ozone is one of the most powerful natural oxidants, with oxidizing properties superior to those of pure chlorine.

It has a high oxidizing potential, which allows it to react quickly in aqueous solution. Ozone reacts with many mineral and organic compounds and has a strong bactericidal effect.

Wastewater ozonizers are now included in process flow diagrams in wastewater treatment plant design due to their superior efficiency.

The method is considered one of the cleanest and safest for health and the environment. After the reaction is complete, ozone turns into harmless compounds. This virtually eliminates the possibility of ozone getting into the treated water.

Ozone is an allotropic form of oxygen.

The ozone is unstable and readily dissociates in air and water, turning into oxygen. The higher activity of ozone in comparison with oxygen is explained by the fact that the splitting of the ozone molecule is accompanied by the release of significant energy.

The use of ozone for wastewater disinfection has several effects:

• Oxidation of inorganic and organic substances.
• High bactericidal effect (up to 99.8%).
• Enrichment of wastewater with oxygen.
• Deodorization and discoloration.

The advantage of ozonation is that most companies do not have to import chemical reagents, and the salt composition of the treated water does not change.

Ozonizers for water treatment plants

Typically ozone is produced by the sparkless transmission of high voltage (15–25 kV) electric current through air or oxygen.

Today, mainly two types of ozonizers are used, tubular and lamellar.

Tubular ozonizers consist of special tubular elements. The electrodes are tubes that are placed inside each other, and the glass tube is used as a dielectric. In lamellar ozonizers, the main elements are in the form of plates.

Ozone production requires drying, dedusting and cooling the air before it is fed directly to the ozonizer. These are relatively expensive systems with high power consumption.

Drying takes place in special adsorbers filled with some kind of adsorbent, for example, silica gel. Special fabric filters are used to separate dust from the air. The air can be cooled in an adsorber or by passing it through heat exchangers.

Disinfection is carried out by supplying an air-ozone mixture to the prepared water, which is accumulated in the contact tank. It is preferable to feed the air-ozone mixture into the tank using metering pumps.

In practice, wastewater treatment plants usually combine disinfection methods with chlorine compounds and ozone to improve the quality of the treated water.

How much does the engineering design of wastewater treatment plants cost?

When customers consider building or expanding an existing wastewater treatment plant, they are primarily concerned with the cost of the project.

Today wastewater treatment is a complex multistage technological process.

It should always be an individual engineering solution, the cost of which varies widely depending on the technologies and equipment used.

The most important factor that affects the cost of the project is the wastewater flow rate. The investor should also consider the composition of the wastewater and regulatory requirements, as violation of the rules can result in fines during the operation of the WWTP. Understanding these factors will help identify business needs and clarify the project budget.

Some engineering solutions are suitable for industrial enterprises that dump metals, acids or petroleum products into water bodies.

Other options are being considered for utility companies where organic wastewater is predominant.

What to consider when setting the cost of wastewater treatment plants:

Factors affecting the cost of the project	Detailed description and comment
Pre-project studies and engineering design	Engineering design costs are usually around 10% of the total investment. Also, the customer will need to research the local market, regulatory requirements, etc. These funds can be allocated in several stages, as the project progresses.
Purchase or lease of land	The area of the WWTP construction site and the surrounding sanitary zone is usually large, which requires to obtain official permits for land use and purchase (lease) a land plot. This can significantly affect the final cost of the project.
Purchase and delivery of equipment and materials	Significant funds are allocated for the purchase of equipment and building materials, as well as the rental of construction equipment. Delivery to hard-to-reach areas requires additional costs.
Construction works	Land clearing and leveling, civil engineering and equipment installation are usually expensive.
Wastewater treatment plant automation	Modern WWTPs must meet strict requirements in terms of reliability and safety. Therefore, control and automation systems should be considered, which can increase the total cost of the project.
Additional expenses	This group includes local taxes and fees, electricity connection costs, environmental permits, and so on.

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