Technological features of wastewater treatment in oxidative reactors “AQUA-OR”

 

Technological features of wastewater treatment in “AQUA-AR” oxidation reactors produced by a group of companies
“AQUAMECHANIKA”

 

The water canal accepts excess wastewater discharges from the city enterprises, as well as storm drains and due to the increase of their volume does not cope with their treatment. Discharges of waste water in excess of the norms of the maximum permissible concentrations (MPC) by enterprises and organizations into the outdated sewage network of the city lead to the fact that biological wastewater purification plants do not cope with the cleaning of a large amount of chemical and mineral substances in wastewater.

The wastewaters of the utilities and food industry enterprises are classified as highly concentrated and have unstable indicators of quality and quantity. Such drains are complex multi disperse systems and contain pollution of various kinds: fat, milk, blood, animal tissue pieces, salts, mineral insoluble impurities, detergents, etc. These waters are characterized by high levels of BOD, COD, suspended solids, fats, etc.

In addition, the danger of water pollution is caused by the fact that in some cases the city enterprises have decentralized sewage systems, as well as imperfect production technologies and wastewater treatment systems.

The admission to the biological wastewater treatment plants of wastewaters with a high content of suspended organic matters can lead to disruption of the oxygen regime in the sewage treatment plant, and changes as well in the concentration of hydrogen ions, accompanied by significant acidification of the environment. It can also cause species changes in the microflora, increase the silt index and lead to removal of activated sludge from sewage treatment plants. Except that, the entrance of the wastewaters of this category of enterprises of the urban sewer network, where for quite a long time they will remain in anaerobic conditions, leads to their acidification as a result of fermentation and PH below 5, which leads to corrosion of collectors. The fats that wastewaters contain have a negative effect on sewer system (silting of pipelines, violation of operating mode of treatment facilities). The cleaning of such drains is connected with significant dissolved oxygen consumption and as a consequence, there is a need to submit a huge air volume for aeration. A significant content of nitrogen and phosphorus-containing organic substances leads to the fact that they cannot oxidize during the residence time of wastewater in wastewater treatment plants and poorly treated effluents enter water bodies, and this in its turn leads to eutrophication and effects on the flora and fauna of the reservoir.

The analysis of the volume of water consumption for technological needs, according to the qualitative and quantitative characteristics of enterprise wastewaters of various profiles and performance showed seasonal and daily variability of these characteristics, a high degree of contamination of the effluent with respect to easily oxidizing organic compounds and toxic substances.

The methods and technologies used today for cleaning high concentered wastewaters are imperfect, in some cases they don’t provide the necessary degree of purification and disposal of all byproducts formed in this process. The solutions used are not always economically viable, energy efficient, and often, solving one problem, they transform it into another, even more complex.

Considering that at most enterprises of the city local treatment facilities are absent or work inefficiently, the issue of organizing effective local cleaning becomes very relevant.

Modern solutions to the problem of cleaning industrial and municipal waste must meet the criteria for the required quality of wastewater treatment, as well as to ensure high intensity of the neutralization process, reliable operation with volley discharges, ease of maintenance, compactness of sewage treatment plants while saving resources and energy, minimal secondary waste.

Analysis of food industry wastewater treatment methods showed that the most promising technologies for cleaning wastewaters are physicochemical and combined methods.

From the physicochemical methods of wastewater treatment the most effective for enterprises and urban wastewater treatment plants is the use of oxidative reactors, which allow to assure a high degree of purification from undissolved impurities, suspended solids, fats and surfactants contained in high concentrations and characteristic for the enterprises in this industry.

To intensify the rate of extraction of particles due to their enlargement, it is advisable to use coagulation and controlled oxidation in oxidative reactors. The type and dose of reagents are selected based on the results of preliminary experimental work, which allows to increase the efficiency and speed of wastewater treatment to 15-20%. The advantage of this method is a high degree of purification and process continuity. In its turn, the simplicity and compactness of installations allows to reduce significantly the construction and installation work and place it on the territory of urban wastewater treatment plants.

The use of physicochemical (oxidative reactors) purification methods at urban wastewater treatment plants is currently important due to the fact that the composition of municipal and domestic wastewaters has changed and according to the international commission on environmental protection held in Kiev in 2011 consists of: 58% – organics, 42% – minerals, as well as a high content of nitrogen-containing compounds and phosphates. As for phosphorus, the content of this element in wastewater always exceeds the TLV (threshold limit value). The reason for this is the widespread presence of phosphates in the composition of detergents, which are used both in everyday life and in production. During wastewater treatment at oxidizing reactors, a controlled oxidation process takes place which allows oxidizing and neutralizing nitrogen-containing compounds and phosphates, which is confirmed by the laboratory.

Biological treatment results the destruction of proteins, fats, carbohydrates, surfactants, tartaric acid and other compounds by bacteria that are both immobilized and free-swimming under aerobic conditions; however, optimal conditions must be created for the development of microbial cultures. In that direction, the most promising are aero tanks, which work with high doses of activated sludge and pure oxygen. The special feature of aerobic cleaning methods is to ensure water biocenosis with oxygen for oxidation contained in water pollution with the production of carbon dioxide, mineral compounds and biomass.

Thanks to the latest developments and technology of supplying an oxidizing agent in aerobic reactors, oxygen-poor zones and zones are created enriched with oxygen. Thanks to this unoxidation reactions flow simultaneously necessary for selection and accumulation of microflora, forming polyphosphates, decomposition of nitrates (with return of activated sludge) and oxidation processes, allowing to reduce COD and BOD. The advantages of the aerobic method include:

– Ability to work with low concentrations of COD pollution;

– BOD in wastewater;

– Reduction of nitrogen and phosphorus compounds;

– Possibility of using several stages of cleaning to achieve the required TLV values;

– Relatively small investment costs.

Despite all the positive qualities of this method, aerobic biological treatment has a number of significant drawbacks, connected with high costs of aeration and disposal of excess sludge. In addition to the extreme economic inefficiency of this method, the variable composition of wastewater and high concentration pollution (more than 2000 mg / l COD) often leads to overloads of the aerobic biological treatment constructions, resulting the pollutions free entry into the environment.

A cost-effective and environmentally acceptable solution to the existing problem can be a combined anaerobic-aerobic technology for the treatment of concentrated wastewater.

The use of anaerobic-aerobic methods of wastewater treatment is most effective, since using only the anaerobic purification stage, it is impossible to achieve strict standards, both when discharging treated wastewater to urban wastewater treatment plants, and to the surface water body. In this case, the anaerobic method of purification is used as the first biological step, and one or two stages of aerobic purification are used as after-treatment.

The peculiarity of anaerobic purification methods is obtaining as final products during the decomposition of organic hydrocarbon compounds of methane and carbon dioxide. When using these methods, aeration of water with oxygen is not required and a small amount of excess sludge is formed.

The advantages of the combined technology compared to the traditional aerobic treatment are as follows:

– high degree of wastewater treatment with high concentrations of organic pollutants COD > 2000 mg / l;

– a small increase in excess biomass is 5-10 times less than with aerobic treatment (biomass is stable, does not rot during storage);

 – resistance to long interruptions in the flow of wastewater;

  • low operating costs.

Thus, the environmental problems of wastewater treatment of industries and urban wastewater treatment plants can be solved by applying physicochemical (oxidation reactors) and biological methods. However, a complex and energy-efficient solution of this problem requires a combination of physicochemical (oxidative reactors, treatment with reagents) and biological (microflora oxidation under anaerobic and aerobic conditions) methods. Such a combination eliminates the disadvantages of biological methods and makes it possible to solve the problem posed most effectively.

Based on the above, we propose to consider a combined wastewater treatment method developed by us.

For stable and uninterrupted operation of sewage treatment plants, it is necessary to foresee the construction of averagers. Averagers are designed to regulate the amount of wastewater entering the treatment plant. Entrance of the treatment plant of industrial and municipal wastewater with a constant flow rate and an average concentration of pollution, increases the effect of both mechanical and subsequent physical, chemical and biological wastewater treatment. As a result of the exclusion of the peak costs of wastewater entering the treatment, it is possible to increase the degree of wastewater treatment (excluding overshoot), significantly save electricity during the operation of sewage treatment plants and increase the reliability of their work. Averagers are equipped with a system of jet aerators operating from feed pumps. This makes it possible to mix waste water without additional devices, to saturate it with oxygen, which makes it possible to accelerate the oxidation process of the substances in the waste water, remove the smell (100%) and save energy. To save material resources and construction time, we suggest using existing reception tanks or using a geomembrane, which will save money and speed up the construction process.

Averagers must be provided in accordance with the Construction norms and rules and sanitary and epidemiological norms and rules.

Mechanical sewage treatment.

One of the main types of pollution of industrial and communal sewage is insoluble (light and heavy) mineral and organic impurities, the concentration of which varies in wide limits. Averaging the concentration and controlling the flow of wastewater, as well as the release of insoluble impurities from the water in the sewage treatment plant, is the task of mechanical treatment.

To remove suspended particles and floating debris, you must use rotary drums. Rotational drums detain coarse particles, plant and animal structural impurities, sand and other substances. The efficiency of mechanical sewage treatment using rotary drums is 50-65%, which eliminates the use of settling tanks, especially with the combined treatment of municipal and industrial wastewater. Rotary drums are equipped with internal nozzles for automatic washing of the grid cells, an adjustable knife to remove solid substances on the drum surface. Rotary drums are made of stainless steel, and the body is made of black metal with a special coating on it.

Rotary drums can be equipped with conveyor augers to remove solids and auger separator to remove liquid from solids into the container for recycling. Rotary drums are equipped with a control cabinet, operate in automatic mode and do not require constant presence of technical staff. Power consumption of one rotary drum is 1.5-3 kW / h (depending on performance). The warranty on the equipment is from 3 years. The effectiveness of water treatment on rotary drums and their throughput depends on the composition of the initial wastewater, the size of the filter grid cells, the rotation frequency of the rotary drum, the intensity of flushing and other operating conditions of the rotary installations.

Rotary drums are available in two versions. Installations with a 1.5-meter drum diameter are assembled at the factory in full and assembled and delivered to the customer. Installations with a drum diameter of 3 meters are delivered to the customer not assembled.

The capacity of the rotary drum must be refined according to the results of technological research at the customer’s facility.

The selection of the mesh size of the rotary drum used to clean industrial or municipal sewage is made on the basis of special studies at the customer’s facility.

For a normal process of synthesis of cellular matter, and, consequently, for an effective wastewater treatment process in the environment, there must be sufficient concentration of all the nutrients — organic carbon (BOD), nitrogen, phosphorus, etc. In addition to the basic elements of cell composition (C, N, O, H), other components are also required for its construction.

The adequacy of nutrients for bacteria in wastewater is determined by the ratio of BOD: N: P (ammonium or protein nitrogen and phosphorus in the form of soluble phosphates).

According to the recommendations of Construction norms and rules 11-32-74, when treating municipal wastewater, the ratio of BOD: N,: P must be at least 100: 5: 1.

It can be calculated that in domestic wastewaters, coming after mechanical treatment to biological, this ratio is approximately 100: 20: 2.5. As it can be seen, here the nitrogen and phosphorus content is much higher than that required by the standards, as a result of which it is advisable to use pre-treatment of wastewaters by the physicochemical method to relieve the load and stable biological purification work.

Toxic effects on biological processes can affect both organic and inorganic substances. Toxic effects can be microbiostatic if growth and development of microorganisms is delayed, and killing (microbicidal). Most substances exhibit a particular effect depending on their concentration in the mixture being cleaned. It should be noted that some elements, which are necessary organogenes of the cell, also become toxic at high concentrations. In this regard, one of the main tasks is the determination of the TLV values ​​for individual chemical substances, as well as the identification of the possible action of a mixture of substances simultaneously present in the treated wastewater.

The adaptive properties of microorganisms are still not unlimited, and therefore a number of organic substances (wastes) are not absorbed by microorganisms. In the technique of wastewater treatment, a large number of substances are classified as biologically non-oxidizable, but this does not always mean that it is impossible in principle to microbiological oxidation. Much more often, biological oxidation is, in principle, possible, but it takes place at such negligible speeds and requires such a long adaptation that oxidation is not observed practically under the conditions of operation of bioreactors (aeration tanks). This proves once again that, before biological treatment of wastewater, it is necessary to apply physicochemical purification methods (oxidation reactors). These methods are used to remove fine suspended particles (solid and liquid), soluble gases, minerals and organic substances from wastewater.

The use of physicochemical methods for wastewater treatment in comparison with biochemical has several advantages:

  1. the possibility of removing from wastewater toxic, biochemically non-oxidizable organic pollutants;
  2. achieving a deeper and more stable degree of purification;
  3. smaller structures;
  4. less sensitivity to load changes;
  5. the possibility of full automation;
  6. a deeper knowledge of the kinetics of some processes, as well as questions of modeling, mathematical description and optimization, which is important for the correct selection and calculation of equipment;
  7. the methods are not related to the control of the activity of living organisms;
  8. the possibility of recuperation of various substances.

The choice of a particular cleaning method (or several methods) is made taking into account sanitary and technological requirements for treated wastewater for their further use, as well as taking into account the amount of wastewater and the concentration of pollutants in them, the availability of the necessary material and energy resources and process efficiency.

The physicochemical methods play a significant role in the treatment of industrial and municipal wastewater. To increase the degree of purification they are used in combination with mechanical, chemical and biological methods.

For the recent years, the field of application of physicochemical cleaning methods has expanded, and their share among other cleaning methods has increased. One of the types of physicochemical cleaning is the use of oxidative reactors, which are designed to purify wastewater from oils, fats, petroleum products, resins, surfactants, hydroxides, organic substances, polymers, fibrous materials, particulate matter, reducing COD and BOD effluent, and also separation of sludge mixtures. To increase the degree of purification, oxidation reactors operate with the introduction of coagulants and flocculants (reagents).

The oxidation reactors developed by us have a high degree of wastewater treatment and low power consumption; they occupy small production areas. The use of oxidation reactors makes it possible to remove toxic, bio – chemically non – oxidizable organic pollutants from wastewater. They allow deeper achievements and stable degree of cleaning. Oxidizing reactors are simple and reliable in operation.

The use of oxidation reactors allows to purify wastewater with a concentration of suspended matter up to 4-5 g / l. Oxidizing reactors are manufactured from 5 to 200 cubic meters per hour in a block ground version. They work when changing parameters, the residence time in the pressure tank is 14 minutes, and in the oxidation chamber 20 – 30 minutes. The values ​​of the parameters depend on the concentration and properties of the contaminants. The use of oxidation reactors allows to purify wastewater with a high content of surfactants of any type and structure.

This allows you to remove the load from sewage treatment plants, reduce occupied space, reduce operating and maintenance costs. Two stages of cleaning exclude the possibility of pollution overshoot in the event of a salvo discharge or a jump in the concentration of pollutants, which ensures the stability of the cleaning performance at the outlet, after pressure filtration on filters with a floating load of self-washing and disinfection, the purified water can be reused for the technical needs of city enterprises equipment, car wash, for the needs of the boiler room, irrigation of agricultural crops and plants). The degree of sewage treatment on our equipment allows you to dump it into the fishery reservoirs of the second category.

 

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