Every day, as a result of the work of industrial enterprises and people's livelihoods, huge volumes are formed wastewater. Modern processing technologies prevent their negative impact on the environment.

How wastewater is disposed of

Industrial enterprises and urban sewer systems collect significant amounts of liquid waste daily. High content toxic substances in wastewater poses a threat to the environment. All companies in Russia are obliged to organize processing in industrial enterprises, as well as human vital products.

Waste water disposal is the process of collecting sludge and neutralizing polluting compounds with the accompanying disinfection of liquid masses. In modern industry, various processing methods are used:

• mechanical;
• chemical;
• physical and chemical;
• biological.

Small treatment plants or large facilities may be disposed of based on one or more of these methods.

Sludge Processing

Russian enterprises have gained successful experience in creating biogas power plants. Such facilities recycle the collected sludge contained in wastewater. Natural gas suitable for further generation of electricity is produced at the station as a product of utilization.

Between 2009 and 2012, large biogas plants with a capacity of 10 MW each were built in Moscow. In 2016, a similar facility was built on the central water utility of the city of Ivanovo. Well-managed sludge processing helps to achieve a number of goals:

• reduction of waste disposal costs;
• improving the environmental situation in the region;
• reduction in the cost of transporting sludge;
• creation of reliable energy-saving systems.

Improvement of processing technologies reduces the time of fermentation of the sludge mixture and makes it possible to abandon the use of the dehydration workshop for disposal.

Installation of treatment facilities

The construction of large facilities or residential complexes is carried out by a sewage disposal system. The creation of treatment facilities makes the enterprise autonomous, reduces the cost of waste disposal and reduces the negative impact on environment.

The capacity and type of cleaning system depends on the nature of the wastewater and other collected waste. Installation is carried out in several stages:

1. The choice of place. Installation at a distance of at least a meter from the base of the building is allowed. Due to the periodic discharge during the disposal of waste water, purified water is equipped with ways for its collection or disposal.
2. Excavation. A foundation pit breaks out and equips, communications are laid for transporting sewage and processed products.
3. Installation of cleaning equipment. A sewage treatment plant is installed in the pit, corresponding in size to the equipment used. To ensure its operability, supply and discharge lines are connected, power supply is supplied, and additional equipment is installed.

During the final excavation works, the autonomous sewage system is poured and sprinkled, after which the structure can be used for its intended purpose.

The specifics of most production facilities involves the disposal of materials of varying degrees of danger. Processing by-products may contain specific substances for which conventional wastewater treatment plants are not suitable. The wastewater treatment system at such enterprises may include specific approaches:

1. Gravity screening. Heavy particles under their own weight settle to the bottom of the tank and are screened out mechanically.
2. Chemical neutralization. Wastewater is treated with neutralizing agents. The specific chemical compounds contained in them enter into a controlled reaction and become non-toxic.
3. Bioprocessing. Aerobic and microaerophilic microorganisms, for which the substances contained in the waste serve as food. As a result of their vital activity, complex chemical compounds are broken down into simpler ones and neutralized.

If an industrial enterprise discharges a large amount of waste different typesPhysicochemical methods are applied. They include disposal through electrolysis, ion exchange, flotation and other processes for the disposal of wastewater.

Sludge disposal

When drilling land, a large amount of specific waste is generated. Drill cuttings are the result of drilling in soil or solid formations. This is a mass of solid particles containing earth, clay, concrete and water. Disposal of sludge is carried out by placement in underground formations or burial in the landfill. Various processing methods allow you to adapt it for future use:

1. Thermal. By firing from the sludge, raw materials are obtained for the production of bitumen that does not contain organic substances.
2. Physical. Using centrifugal force or pressure, the granular mixture is divided into fractions.
3. Chemical. Pure rock is separated from the sludge by solvents and hardeners.
4. Biological. They are used for burial, they imply the use of microorganisms for gradual processing.
5. Physicochemical. Using special equipment and reagents, components harmful to the environment are removed from the sludge.

Drilling products pose a serious threat to the environment, so the procedure for handling them is enshrined in the provisions of N 89-FZ "On production and consumption waste" and other regulatory acts. Each enterprise operating in the mining sector is required to dispose of the sludge independently or by contacting specialized organizations.

Waste water disposal is necessary to prevent negative environmental impacts. To do this, use precipitation processing, treatment facilities and systems.

From the history The problems of wastewater disposal have occupied society for a very long time. In the ancient city of Xanten (now in Germany), built by the Romans in 100 AD, about 10,000 people lived. Already in those days there was a network of sewage pipes: from the houses they were discharged into the main sewage canals, and from there merged into the nearby Rhine River. These were two systems and both were protected from the effects of the external environment. Sewer pipes were lined with oak panels, and later the main channels began to be lined with stone and coated with clay. More distant Roman outposts used other methods of discharging wastewater from toilets. And to this day you can see one of these systems (122 AD) in a small Roman garrison in Huastide on the border between Scotland and England. Toilets were built over a stream where sewage flowed. Nowadays, direct discharge into the environment becomes impossible for both domestic and industrial wastewater. Even in the old days, when the population was not so large, the discharge of wastewater into streams, rivers and seas led to various diseases. The amount of water used for domestic purposes in our century is critically increasing, creating an equivalent increase in wastewater. In most countries, the discharge of untreated wastewater is prohibited and most of them must be treated before returning to nature.

Domestic wastewater treatment

Domestic wastewater must be cleaned of the solids and soluble substances such as phosphates and nitrates, and bacteria present in them. Most water treatment plants use the aerobic method, which accelerates natural processes and, thereby, treats wastewater. IN general view The cleaning process is a sequence of a number of operations, the variety and sequence of which depends on the size of the treatment plant, sanitary and hygiene standards, including territorial, and other legislative acts. First, the effluents go to the treatment plant either by gravity or through a pipeline equipped with pumping stations. Typically, incoming water is filtered to remove large solids. In fig. 1 is a diagram of a typical small wastewater treatment plant.

Primary subsidence

During the initial sedimentation process, wastewater accumulates in tanks over a period of time. Solids in the water fall to the bottom of the tank and are subsequently removed for further processing.

Recycling

At this stage, wastewater is pumped into aeration tanks, where it is mixed with bacteria that process organic waste in water. To maintain the viability of these bacteria, oxygen is required, which is usually supplied from cylinders and mixed with air. Another method is the injection of air into the tanks with compressors; sometimes both technologies are used simultaneously. In some cases, the so-called filtering layer of bacteria replaces the above technology: waste water flows over a layer of stones, and bacteria located in the voids between them contribute to the processing process.

Final precipitation

Then the water is pumped into huge tanks, where bacteria also act: falling from the bottom to the center of the tank through underground pipelines, the water rises up and slowly moves out into the spillway. The remainder of the bacteria and sediment are scraped off the bottom by slowly rotating scrapers attached to the bridge. Some rainfall is returned to the aeration station to provide a new source of bacteria. Leaking water can be drained into the nearest river, canal or lake; the last few percent of the treatment is completed naturally.

Sediment processing

After the final precipitation, the sediments are either stored in a designated place or destroyed by incineration. Currently, the priority is their further processing. The sediments are condensed and pumped into a fermentation tank, where they are stored at 32 ° C without oxygen. At the same time, dangerous bacteria are destroyed, which is accompanied by the release of methane gas, and the total amount of precipitation ultimately decreases. Methane is stored in a gas chamber and can be used as energy raw materials, for example, to generate heat for a fermentation tank or central heating station. After that, the precipitate is dehydrated by pressing and then destroyed. Another option to reduce the amount of precipitation (up to 1/20) before destruction is to store them in compost storage.

Industrial Wastewater Treatment

The process of treating industrial wastewater has some specificity. Currently, both traditional and newly developed technologies are widely used. Depending on the industry, this can be a whole range of different methods, allowing to obtain solid sediment of various concentrations. Air aeration is used to increase the buoyancy of pollutants, which are subsequently removed from the surface. Physical methods such as screening, membrane technology, centrifuges, and reverse osmosis are also common. More complex methods are physico-chemical cleaning.

These include, for example, an activated carbon filter, which is known for its absorption properties of many harmful substances. Ionic exchange is not effective for cleaning a large number wastewater with dissolved pollutants, for example, when removing silver from water in the photographic industry. The process of aerobiological treatment, which accelerates the natural biological activity of bacteria, is widely used - the process is similar to that described above for the treatment of domestic wastewater. Bioanerobic treatment - processing in an ascending anaerobic settling reactor, enclosed in a concrete shell, in an environment without oxygen.

At the same time, organic pollution is destroyed, releasing biogas as a useful product. As an example, consider the wastewater treatment process at the HEINEKEN factory in Hertogenbosch (Holland), where the PAQUES BV treatment system is installed - this technology for industrial cleaning Wastewater is quite widespread in world practice. The technological process conventionally consists of four stages:

• removal of large inclusions;
• hydraulic buffering;
• preoxidation;
• anaerobic cleaning.

Additionally, the so-called "emergency tank" is provided for the collection and neutralization of wastewater with a large amplitude of pH fluctuations.

First stage

Large inclusions that are not biodegradable are removed from the water with a strainer. These may include yeast particles, kieselguhr, bottlenecks, etc. The filtered mass is fed by means of an Archimedean screw into the press, where it is dehydrated with a corresponding decrease in volume. Compressed waste is collected in containers. The filter is automatically cleaned under high pressure, which prevents the formation of sediment.

Second stage

In two large round concrete buffer tanks with a volume of 2250 m 3, the following chemical reactions proceed simultaneously:

• alignment of hydraulic amplitude and amplitude of pollution;
• hydrolysis through the activity of microbes, as well as partial oxidation;
• buffering acid and alkaline amplitudes in etched wastewater;
• sedimentation and subsequent removal of sediment (in the first buffer tank).

Thanks to the mixers placed in the first buffer tank, the mixing process is homogeneous: the scraper mechanism slowly moves the settled substances to the central collection point. “On the way” settled waste is further processed. An additional emergency tank with a volume of 2250 m 3 is used to collect wastewater with high acid or alkaline amplitude. When the pH level in the buffer tank approaches acceptable, water at a low speed enters further processing, additionally passing through charcoal filters.

Third stage

The oxidizing tank makes it possible to control the level of acidity of the medium and, thereby, create optimal conditions for the pre-oxidation process. It flows in a round concrete tank covered with a plastic lid. Air from the tank is constantly removed and cleaned to prevent the spread of unpleasant odors. After the preoxidation step is completed, water is pumped into anaerobic reactors.

Fourth stage

The anaerobization process takes place in six Biopaq Internal Circulation reactors (each with a volume of 160 m 3) in two stages. At the first stage, in each of the reactors, intensive formation of biogas occurs, part of which is used in gas-powered pumps that provide internal circulation of wastewater. In the second stage, the reactors are used as a buffer for precipitation. The amount of sludge is gradually increasing and its excess is extracted from each reactor and pumped into the storage tank. Biogas is accumulated in the upper part of the reactor, which is purified and dried after buffering. After passing through all four stages of treatment, water is supplied to a local wastewater treatment plant.

Equipment corrosion

Corrosion susceptibility of equipment used in the wastewater treatment process is extremely high due to high humidity, dissolved salts, released hydrogen sulfide, ammonia, bacteria, sun exposure, organic and inorganic acids and various others chemical substances. Unfortunately, these are inevitable “satellites” of the processing processes.

Equipment operating in immersed or partially immersed condition, especially used in the first stages of cleaning: filters, screens, pre-deposition tanks, scrapers and aerators, is at maximum risk - the presence of hydrogen sulfide in the atmosphere promotes the formation of corrosive sulfiric acid. Many surfaces, such as the outside of tanks, are subject to corrosion even under normal use in normal climates. Industrial wastewater is sometimes so aggressive that it can cause very severe corrosion. In some situations, it is impossible to cope with it without a specialist.

Under the influence of aggressive factors, not only steel and metal elements decompose, but also concrete structures (the so-called concrete wear). For example, concrete tanks for primary cleaning. They are destroyed by acid. For the decomposition of organic inclusions of plant origin — waste of potatoes, flour, malt, sugar beets, etc. — the temperature in the tank should not be lower than 35-37 ° C, but the amount of sulfuric acid formed, and therefore the corrosivity, are directly dependent from temperature: at the same concentration of hydrogen sulfide at a temperature of 18 ° C, sulfuric acid is formed three times more than at a temperature of 12 ° C. Oxygen used in the process of decay promotes the formation of hydrogen sulfide (in the form of condensate) on the pipe walls above the water surface.

Then, under the influence of aerobic bacteria, it is oxidized to sulfuric acid. The decomposition processes are quite lengthy and wastewater is often found in tanks for a long time, the concentration of hydrogen sulfide in the condensate of which can form a solution of 6% sulfuric acid on the concrete surface. The longer the pipeline, the longer the waste water is in the system and the greater the amount of oxygen involved in the decomposition process.

For example, if wastewater arrives at a treatment plant from several areas, then the waters of the most distant of them may be in the system for a long time. Returning to our example with a concrete tank for primary treatment, the process of hydrogen sulfide formation will look as follows (Fig. 2).

An increase in acidity occurs in the condensate formed on the walls of the tank above the level of wastewater, and it acts on concrete above the water level. Closed tanks are even more vulnerable. The latest trend is the location of water treatment plants under the roof (to eliminate unpleasant odors and to eliminate cases of blowing off of plentiful foam strong wind from primary sedimentation tanks) became possible only thanks to modern high-quality anti-corrosion technologies.

The problem of corrosion is relevant for equipment used in almost all stages of wastewater treatment. Polyurethanes often do not meet the requirements, even in conditions of relatively low acidity. Polyvinyl chloride coatings can be loosened at the joints, which are also subject to increased stress due to narrowing or expansion due to temperature changes. Acid in these places seeps through cracks and corrodes concrete.

Corrosion control in wastewater treatment plants

Of course, the ideal solution is to use less steel, but in most cases replacing it with more corrosion-resistant materials leads to an incommensurate and often unjustified increase in capital costs. In addition, the service life of polymer structures is five times less than traditional steel structures with a good protective system, and the cost at the initial investment stage is doubled. The main advantage of steel is its relatively low cost and the possibility of recovery by subsequent remelting. If possible, the use of different metals should be avoided; if this is not possible, isolate them as much as possible from each other.

Protection by paint systems

To protect steel sludge tanks and other structures, modern paint systems are used. The choice of system for each specific case depends on the expected conditions of use. Where exposure is expected fatty acidscontained in wastewater, the ideal solution is paint systems based on epoxy, the most advanced of them have strong protection against abrasion and precipitation of animal and vegetable fats. It can withstand acidity from 2 to 10.

In less severe conditions, standard epoxy or carbon epoxy systems are suitable. They are well resistant to sulfuric acid. Nonetheless by environmental reasons in some countries there is a tendency to look for alternative coatings. Recent developments in the chemical industry and testing have shown that high-quality resin-free epoxy paints are more reliable than coal-tar tar epoxies.

IN as an alternative to the paint system, a “torquette-concrete” coating is used - the concrete is applied by spraying with a thickness of 5 cm with an epoxy finish. Opinions about the effectiveness of this technology are different, but with strong exposure to hydrogen sulfide this is not enough. After the shotcrete, you can use a PVC coating, the results of which are highly estimated by experts, but this is an expensive technology.

It is best to use the paint system when building new structures, but most often heavy and expensive repairs are carried out at operating stations. In any case, the coating is applied to a clean and dry surface, which is extremely difficult to achieve with operating equipment. For example, a fan system pump and an adjacent chamber cannot be dry for longer than 12-16 hours.

After that, the inlet valves should be open for wastewater for several hours, then the cycle may repeat. How difficult this is depends on the type of pump chamber. In some of them, the working overlap is quite easy to carry out. In chambers with pumps immersed in water, this is not possible. The only solution here would be to use standby pumps and tanks. The price of paint systems depends on the type and complexity of the technological cycle of each specific treatment plant, but is approximately 0.3-3% of the cost of the new design.

Summary

Equipment in the water treatment industry must function all year round 24 hours a day with a minimum stop time for maintenance. All structures must be completely reliable, withstand a long period of time between preventive and maintenance, which should be as quick and simple as possible. Although the vast majority of water treatment equipment operates in a corrosive environment, ordinary steel is still the most beneficial material for most equipment.

Effective corrosion protection in full and partial immersion conditions requires its protection with the help of modern paint systems. The standard and most common option is to apply an epoxy primer followed by an epoxy coating with a coal-tar tar. Landstar’s export manager, a world-renowned manufacturer of wastewater treatment equipment, assures that, if properly applied, such a system also works properly after 15-20 years of service.

Definitions

Like many industries, water treatment processes are characterized by their own technical terminology:

• active sediment - sediment containing live bacteria;
• aeration - dissolution of air in a liquid;
• aerobic - containing or using air;
• anaerobic - without air;
• archimedean pump— lifting pump top level by means of a rotating screw;
• hydrogen sulfide - liquid-soluble toxic gas with an unpleasant odor;
• equivalent of permanent population— a measure of the capacity of a water treatment plant in relation to the number of people it serves;
• kieselguhr - diatomaceous earth; filter material;
• screen - filter for extracting solids from wastewater;
• slop tank - a tank or tank in which solid suspended particles can sink to the bottom.
• bacteria that reduce the level of sulfuric acid salts - bacteria that can turn undissolved sulfur particles into hydrogen sulfide soluble in water.

The discharge into the environment of domestic and industrial effluents without pre-treatment would entail a real environmental disaster.

Since the chemical composition of waste becomes more diverse and aggressive as technology develops, wastewater treatment methods are constantly being improved.

because of a wide variety soluble and insoluble pollutants in wastewater to create a universal way to neutralize and remove it is not possible.

Therefore, at a sewage treatment plant, a whole set of techniques is used, each of which is oriented to work with a particular group of substances.

All these techniques can be divided into several categories:

1. Mechanical.
2. Chemical.
3. Biological and biochemical.
4. Physicochemical.