These methods are used to purify domestic and industrial wastewater from many dissolved organic and some inorganic (hydrogen sulfide, ammonia, sulfides, nitrites, etc.) substances. The purification process is based on the ability of certain microorganisms to use specified substances for nutrition: organic substances for microorganisms are a source of carbon. Microorganisms partially destroy them, converting them into CO 2, H 2 O, nitrate and sulfate ions, and partially use them to form their own biomass. The process of biochemical treatment is inherently natural; its nature is the same for processes occurring both in natural reservoirs and in wastewater treatment plants.

Biological oxidation is carried out by a community of microorganisms (biocenosis), including many different bacteria, protozoa and more highly organized organisms (algae, fungi), interconnected into a single complex by complex relationships. This community is called activated sludge, it contains from 106 to 1014 cells per 1 g of dry biomass (about 3 g of microorganisms per 1 liter of wastewater).

Aerobic and anaerobic methods for biochemical wastewater treatment are known.

Aerobic process. To carry it out, groups of microorganisms are used, the life of which requires a constant flow of oxygen (2 mg O 2 /l), temperature 20 - 30 ° C, pH 6.5 - 7.5, ratio of nutrients BOD: N: P no more 100: 5: 1. The limitation of the method is the content of toxic substances is not higher than: tetraethyl lead 0.001 mg/l, beryllium, titanium, Cr 6+ and carbon monoxide compounds 0.01 mg/l, bismuth, vanadium, cadmium and nickel compounds 0.1 mg/l, copper sulfate 0.2 mg/l, potassium cyanide 2 mg/l.

Aerobic wastewater treatment is carried out in special structures: biological ponds, aeration tanks, oxytanks, biofilters.

Biological ponds designed for biological treatment and for post-treatment of wastewater in combination with other treatment facilities. They are made in the form of a cascade of ponds consisting of 3–5 stages. The wastewater treatment process is implemented according to the following scheme: bacteria use oxygen released by algae during photosynthesis, as well as oxygen from the air, to oxidize pollutants. Algae, in turn, consume carbon monoxide, phosphates and ammonia nitrogen released during the biochemical decomposition of organic matter. Therefore, for normal operation of ponds, it is necessary to maintain optimal pH values ​​and temperature of wastewater. The temperature must be at least 6 °C, and therefore the ponds are not used in winter.

There are ponds with natural and artificial aeration. The depth of ponds with natural surface aeration, as a rule, does not exceed 1 m. When artificially aerating ponds using mechanical aerators or blowing air through the water column, their depth increases to 3 m. The use of artificial aeration accelerates water purification processes. The disadvantages of ponds should also be pointed out: low oxidizing capacity, seasonal operation, and the need for large areas.

Facilities for artificial biological treatment Based on the location of active biomass in them, they can be divided into two groups:

– active biomass is suspended in the treated wastewater (aerotanks, oxytanks);

– active biomass is fixed on a stationary material, and waste water flows around it in a thin film layer (biofilters).

Aero tanks They are reinforced concrete tanks, rectangular in plan, divided by partitions into separate corridors.

To maintain activated sludge in suspension, intensively mix it and saturate the treated mixture with air oxygen, various aeration systems (usually mechanical or pneumatic) are installed in aeration tanks. From the aeration tanks, the mixture of treated wastewater and activated sludge enters the secondary settling tank, from where the activated sludge that has settled to the bottom is discharged into the reservoir of the pumping station using special devices (sludge pumps), and the purified wastewater is supplied either for further purification or is disinfected. In the process of biological oxidation, the biomass of activated sludge increases. To create optimal conditions for its life, excess sludge is removed from the system and sent to sludge treatment facilities, and the main part in the form of return activated sludge is returned to the aeration tank. The concentration of sludge mass in the aeration tank (sludge dose based on dry matter) is 2 – 5 g/l; air flow 5 – 15 m3 per 1 m3 of wastewater; load of organic pollutants 400 – 800 mg BOD per 1 g of ash-free activated sludge per day. Under these conditions, complete biological treatment is ensured. The residence time of wastewater, depending on its composition, ranges from 6 to 12 hours. Complexes of treatment facilities, which include aeration tanks, have a capacity of several tens to 2 - 3 million m3 of wastewater per day.

For pneumatic aeration of wastewater, pure oxygen can be supplied instead of air. For such a process they use oxytenki, somewhat different in design from aeration tanks. The oxidative capacity of oxytenks is 3 times higher than the latter.

Biofilters are used with daily consumption of domestic and industrial wastewater up to 20 - 30 thousand m 3 per day. Biofilters are tanks of a round or rectangular shape in plan, which are filled with loading material. Based on the nature of loading, biofilters are divided into two categories: with volumetric and flat loading. Volumetric material consisting of gravel, expanded clay, slag with a fraction size of 15 - 80 mm is filled with a layer 2 - 4 m high. Planar material is made in the form of hard (ring, tubular elements made of plastic, ceramics, metal) and soft (rolled fabric) blocks that are installed in the body of the biofilter in a layer 8 m thick.

Anaerobic process. Here, biological oxidation of organic substances occurs in the absence of molecular oxygen due to chemically bound oxygen in compounds such as SO 4 2─, SO 3 2─, CO 3 2─. The process occurs in two stages: in the first stage, organic acids are formed, in the second stage, the resulting acids are converted into methane and CO 2: organic compounds + O 2 + acid-forming bacteria → volatile acids + CH 4 + CO 2 + H 2 + new cells + other products → volatile acids + O 2 + methane-producing bacteria → CH 4 + CO 2 + new cells.

The main process is carried out in digesters. They process activated sludge and concentrated wastewater (usually BOD > 5000) containing organic matter that is destroyed by anaerobic bacteria during methane fermentation. This fermentation occurs under natural conditions in swamps.

The main goal of anaerobic treatment is to reduce the volume of activated sludge or the amount of organic substances in wastewater, producing methane (up to 0.35 m 3 under normal conditions per 1 kg of COD) and well-filtering and odorless sludge. Sediments after filtration can be used as fertilizer in crop production (if the content of heavy metals in them is below the maximum permissible concentration). The gas produced in digesters contains up to 75% (vol.) methane (the rest is CO 2 and air) and is used as fuel. At the same time, the anaerobic process is very sensitive to volley emissions, which leads to the failure of the microflora. Its restoration can take from 1 to 6 months. Due to the formation of methane, this process is explosive and fire hazardous.

Biological purification of contaminated waters can, in addition to biological ponds, be carried out in natural conditions, for which specially prepared plots of land (irrigation and filtration fields) are used. In these cases, the cleansing power of the soil itself is used to free wastewater from contaminants. Filtering through the soil layer, water leaves suspended, colloidal and dissolved impurities in it. Soil microorganisms oxidize organic pollutants, converting them into simple mineral compounds - carbon dioxide, water, salts.

Irrigation fields are used simultaneously for wastewater treatment and the cultivation of grain and silage crops, herbs, vegetables, as well as planting shrubs and trees. Filtration fields are used only for wastewater treatment.

Agricultural irrigation fields (AIF) are located on sloping terrain in steps so that water flows by gravity from one area to another. The construction of the ZPO makes it possible to comprehensively solve the problems of environmental protection, city improvement and the development of suburban agriculture.

After biological treatment of wastewater in artificial structures, the total content of bacteria in it decreases by 90 - 95%, and when treated in a waste water treatment plant - by 99%. To completely disinfect wastewater, it must be subjected to chemical disinfection (chlorine, ozone, hydrogen peroxide, ultraviolet, ultrasound).

When operating biological treatment facilities, it is necessary to comply with the technological regulations of their operation, to avoid overloads and especially volleys of toxic components, since such violations can have a detrimental effect on the vital activity of microorganisms. Therefore, in wastewater sent for biological treatment, the content of oil and petroleum products should be no more than 25 mg/l, surfactants - no more than 50 mg/l, dissolved salts - no more than 10 g/l. The acidity of wastewater entering biochemical treatment should not exceed 9, otherwise the mineralizing microorganisms will die.

They are widely used for the purification of domestic and industrial wastewater from many dissolved organic and some inorganic substances (H2S; sulfides; NH3; nitrites, etc.).

The purification process is based on the ability of microorganisms to use these substances for nutrition in the process of life, because organic substances are a source of carbon for them.

Advantages: simple hardware design, low operating costs.

Disadvantages: high capital costs, the need for preliminary removal of toxic substances, strict adherence to the technological cleaning regime.

Wastewater is characterized by: BOD - biochemical demand for O 2. mg O 2 / g or mg O 2 / l not including nitrification processes.

During biochemical treatment, substances contained in wastewater are not recycled, but are processed into excess sludge, which also requires neutralization. Activated sludge (brownish-yellow lumps) is a complex complex of microorganisms of various classes, the simplest microscopic worms, ciliates, algae, yeast, etc. A good source of C is unsaturated organic compounds.

Saturated organic compounds are more difficult to digest.

Dissolved organic substances and hydrocarbons easily penetrate into the cell; more difficult are substances whose molecules contain polar groups, ethanol > ethylene glycol > glycerol, sugars with several hydroxy groups. They diffuse into the cell even more slowly. Fatty acids > hydroxy acids > amino acids. Ammonium ions easily penetrate the cell!

The ability of microorganisms to adapt ensures the widespread use of biological wastewater treatment.

The worse the sludge is drained, the higher its sludge index. I gr. BODtotal/COD =0.2 – wastewater group (food industry, spsk, protein-vitamin...). Organic contaminants of this group are not toxic to microbes. II gr. BODtotal/COD =0.10-0.02 – Coking wastewater, shale, soda water. These waters, after mechanical purification, can be sent for biochemical oxidation. III gr. BODtotal/COD =0.01-0.001 – ferrous metallurgy wastewater, sulfide, chloride, surfactant, etc. Mechanical treatment and physico-chemical treatment are required. IV gr. BODtotal/COD

Turbulization (intensive mixing, activated sludge is in suspension) of wastewater increases the volume of nutrients and O2 supplied to microorganisms, which increases the rate of wastewater treatment.

The dose of active or depends on the sludge index.

The lower the sludge index, the greater the dose of active or must be supplied.

Increasing t o => increases the volume of the biochemical reaction. t o > 30 o can destroy microorganisms. Almost 20-30 o. The poison for activated sludge is heavy metal salts. Salts of these metals reduce the purification rate (Sb, Ag, Cu, Hg, Co, Ni, Pb, etc.).

For the oxidation of organic substances by microorganisms, O 2 is required; dissolved in wastewater, i.e. aeration - dissolution of O 2 in H 2 O.

For the successful occurrence of biochemical oxidation reactions, the presence of compounds of nutrients and microelements in wastewater is necessary: ​​(N, P, K).

Lack of P leads to the formation of filamentous bacteria, which causes swelling of activated sludge.

Biocleaning in natural conditions.

Irrigation fields are special prepared land plots; cleaning occurs under the influence of microflora of the sun, air and under the influence of living vegetation and plants.

Irrigation fields are best constructed on sandy or loamy soils. Groundwater is not higher than 1.25 m from the surface.

The soil of irrigation fields contains bacteria, yeast, fungi, algae, etc. Wastewater contains bacteria. If the fields do not grow crops and are intended only for biological wastewater treatment, then they are called filtration fields.

Irrigation fields after biological wastewater treatment are used for growing grain and silage crops, herbs, and vegetables.

Irrigation fields have the following advantages over aeration tanks: 1 – capital and operating costs are reduced;

2 – unproductive lands are involved in agricultural production.

3 – ensures stable and high yields.

Mechanism:

During the biological treatment process, wastewater passes through a filter layer of soil, in which suspended and colloidal particles are retained, forming a film, and penetrating O2 oxidizes organic substances, converting them into mineral compounds.

Wastewater can enter irrigation fields through polyethylene or asbestos-cement tubular humidifiers, i.e. subsoil irrigation.

Biological ponds are a cascade of ponds consisting of 3-5 stages. With natural aeration (their depth is 0.5-1m). Well warmed up by the sun. With artificial aeration (mechanical or pneumatic, compressor) (depth - 3.5 m). The pollution load increases by 3-3.5 times.
1. Cleaning in artificial structures.
2. Aero tanks are reinforced concrete aerating tanks. Aerated mixture of waste water + activated sludge.
3. Scheme of a biological treatment plant.
4. – primary settling tank;
5. – pre-aerator (for pre-aeration 15-20 minutes);

– aeration tank;

– regenerator (25%);
1. according to the hydrodynamic regime (aeration tanks - displacers (a); aeration tanks - mixers (b); intermediate type - with dispersed wastewater hydrogen);
2. by the method of regeneration of active or (with and without separate regeneration);
3. according to the load on activated sludge (highly loaded for incomplete treatment and ordinary or low-loaded);
4. by the number of steps (1, 2, multiple);
5. according to the mode of wastewater input (flowing, semi-flowing, contact, etc.);
6. by design features:

In the presence of harmful impurities and BOD > 150 mg/l - with regeneration.

Helpful information:

By providing conditions that increase the activity of the process of microbial destruction of hydrocarbons (the presence of water and active mixing, aeration and the provision of the required amount of mineral salts), biochemical treatment of wastewater containing oil and petroleum products in concentrations corresponding to solubility limits and even higher (up to 50 mg/l )d can be carried out in aeration tanks or, under favorable local conditions, in simpler structures - aerated biological ponds. [...]

Under appropriate conditions (presence of oxygen, temperature above 4° C, etc.), under the influence of aerobic microorganisms (nitrifying bacteria), oxidation of nitrogen of ammonium salts occurs, as a result of which salts of nitrous acid, or nitrites, are first formed, and with further oxidation - salts of nitric acid , or nitrates, i.e., the process of nitrification occurs. This biochemical process was discovered in the 70s of the 19th century. But only at the end of the 19th century. Russian microbiologist S. N. Vinogradsky managed to isolate a pure culture of nitrifying bacteria. One group of these bacteria oxidizes ammonia into nitrous acid (nitrite bacteria), the second - nitrous acid into nitric acid (nitrate bacteria). Nitrification is of great importance in wastewater treatment, since in this way a supply of oxygen accumulates, which can be used for the oxidation of organic nitrogen-free substances, when all free (dissolved) oxygen has already been completely consumed for this process. Bound oxygen is split off from nitrites and nitrates under the action of microorganisms (denitrifying bacteria) and is reused for the oxidation of organic matter. This process is called denitrification. It is accompanied by the release of free nitrogen into the atmosphere in the form of gas.[...]

Biochemical purification. The method is based on the ability of microbes to use various soluble organic and non-oxidized inorganic compounds (for example, Cr6+, ammonia, nitrites, hydrogen sulfide) in the process of their life activity. Therefore, the use of the biochemical method makes it possible to remove various toxic organic and inorganic compounds from wastewater. If the rate of the biochemical process is determined by the conditions of oxygen supply and the surface of microbial bodies (diffusion factors), they use aeration tanks - mixers with pneumatic or mechanical aeration. During pneumatic aeration, some organic compounds can be desorbed into the atmosphere. If the rate of the biochemical process depends only on kinetic factors and practically does not depend on the presence of oxygen and the number of microbial bodies, then biofilters, oxidation ponds and reservoirs are used. [...]

Biochemical purification of water from organic impurities is a fairly developed and reliable process. This process is based on the vital activity of microorganisms that use organic and mineral substances contained in wastewater as nutrients and energy sources. These processes are similar to the processes occurring during the self-purification of reservoirs.[...]

Purification of wastewater from hydrogen sulfide, as well as other impurities (formol up to 90 mg/l, formaldehyde up to 16 mg/l) is carried out in aeration tanks at one of the enterprises in Kazan. It should be noted that the biochemical process is inhibited at a formaldehyde concentration of 1000 mg/l. The pH value of the wastewater is maintained in the range of 6.5-7.5, COD (chemical oxygen demand) is equal to 100-170 mg/l 02. After 15 hours of aeration in the aeration tanks, the hydrogen sulfide content decreases from 20 to 2 mg/l. When the pH of the wastewater decreases below 6, the process of purification from hydrogen sulfide worsens, and at pH [...]

Biochemical processes of breakdown with subsequent mineralization of organic compounds can occur under both aerobic and anaerobic conditions. When assessing the possible influence of surfactants on wastewater treatment processes, the state of reservoirs and determining the efficiency of their removal, aerobic conditions characteristic of both reservoirs and the prevailing types of treatment facilities (aeration tanks, biofilters) are of decisive importance.[...]

Biochemical wastewater treatment can be carried out in aeration tanks, which are a reservoir or an open pool, where wastewater treatment occurs under the influence of active microorganisms or in the presence of atmospheric oxygen. To intensify the processes of biological wastewater treatment, the feasibility of supplying 90% technical oxygen instead of air to aeration tanks has been identified. In this case, the process of wastewater treatment is accelerated by 4-5 times.[...]

Biochemical treatment of industrial wastewater is possible in cases where it contains: organic substances that can be oxidized as a result of biochemical processes in quantities that allow biological treatment (according to the military industrial complex); nutrients (nitrogen, phosphorus, potassium, etc.) in quantities sufficient for the life of microorganisms during wastewater treatment; permissible concentration of harmful substances, at which the vital activity of microorganisms is not disrupted, and have an acceptable reaction of the environment.[...]

When treating wastewater, the oxidation of the organic substances and other reducing agents contained in them is important, since these substances, entering the reservoir, undergo chemical and biochemical oxidation due to oxygen dissolved in the water, which is vital for aquatic fauna and flora. Therefore, it is better to carry out the oxidation process before discharging wastewater into a reservoir.[...]

Wastewater is sent to biofilters after clarification in primary settling tanks. When filtering wastewater through a loading layer, the biological film adsorbs finely dispersed substances remaining in the liquid after the primary settling tanks, as well as colloidal and dissolved substances. The organic part of the contaminants retained by the biofilm undergoes biochemical oxidation (mineralization) with the help of aerobic bacteria. Oxygen, necessary for the life of bacteria, enters the body of the biofilter through its natural or artificial ventilation. The load on drip biofilters is determined by their oxidative power (OM). Oxidative power is the amount of oxygen obtained from 1 m3 of filter material per day to reduce the BOD of wastewater sent to biofilters. The essence of the process of biological wastewater treatment on biofilters does not differ from the purification process on irrigation fields and filtration fields. However, due to artificially created favorable conditions for the life of aerobic microorganisms, the process of biochemical oxidation in biofilters occurs much more intensely than in irrigation fields and filtration fields. Therefore, the size of structures for biological wastewater treatment in artificially created conditions is many times smaller than structures in natural conditions.[...]

The biochemical process of oxidation of organic substances in wastewater (biochemical oxidation) occurs with the assistance of microorganisms-mineralizers in two phases: in the first phase, the oxidation of organic substances containing mainly carbon and nitrogen-containing substances occurs before the onset of nitrification. Therefore, the first phase is often called carbonaceous. The second phase includes the process of nitrification, i.e. the oxidation of nitrogen from ammonium salts into nitrites and nitrates. The second phase lasts approximately 40 days, i.e., much slower than the first phase, which takes approximately 20 days, and requires significantly more oxygen. Biochemical oxygen demand (BOD) takes into account only the first phase of oxidation. In nature, however, it is difficult to separate both phases of oxidation, since they occur almost simultaneously. When calculating the self-purifying capacity of reservoirs, in order to decide on the required degree of purification of wastewater before releasing it into the reservoir, only the first phase of oxidation is taken into account, since it is practically difficult to obtain data for the second phase.[...]

The process of wastewater purification when filtering it through the soil in filtration fields and irrigation fields is a set of complex physicochemical and biochemical processes. Its essence lies in the fact that when wastewater passes through the soil, suspended and colloidal substances are retained in its upper layer, forming a film densely populated with microorganisms on the surface of soil particles. This film adsorbs organic substances on its surface and converts them into a soluble state. Using oxygen penetrating into the pores of the soil, microorganisms process soluble organic matter into mineral compounds. Thus, the presence of air in the soil, and therefore its looseness, are necessary conditions for the normal course of the cleaning process. The upper layers of soil (0.2-0.3 m) are in more favorable conditions of the oxygen regime, therefore the oxidation of organic substances, as well as the process of nitrification, occurs more intensely. The suitability of soils for filtration fields, and therefore the load on them, is determined by their granulometric composition and moisture-holding capacity. To increase the productivity of filtration fields, they are often supplied with pre-clarified (settled) wastewater.[...]

In biochemical wastewater treatment, nitrogen is a necessary nutrient. The appearance of nitrites and nitrates in purified water indicates a high degree of mineralization of organic contaminants. During deep treatment of wastewater, nitrogen turns into nitrates and molecular nitrogen, which is released into the atmosphere - the process of denitrification of wastewater occurs. [...]

Biochemical destruction of organic substances can be carried out under anaerobic and aerobic conditions. Anaerobic wastewater treatment is carried out using anaerobic microorganisms-mineralizers, i.e., those that do not require oxygen. The end products of anaerobic decomposition (fermentation) of organic substances are the gases CH4 (methane), CO2 (carbon dioxide, carbon dioxide), III (hydrogen), N2 (nitrogen), Hg5 (hydrogen sulfide). In addition, a certain amount of fatty acids, sulfides, humic substances and other difficult to decompose compounds remains in the water. The anaerobic process takes place in two characteristic temperature regions: 20-35 °C (mesophilic fermentation) and 45-55 °C (thermophilic fermentation). During the thermophilic process, the rate of mineralization (fermentation) increases and a deeper decomposition of organic substances occurs. The anaerobic method is used when there is a very high concentration of organic substances in industrial wastewater, more often for the mineralization of organic wastewater sludge. [...]

Biochemical wastewater treatment in sewerage systems. The high salt content does not allow the EL0U wastewater to be taken into the recycling water supply system as a recharge. Therefore, wastewater undergoes biochemical treatment before being discharged into a reservoir. Biochemical wastewater treatment can be carried out separately or in a mixture with domestic wastewater that has undergone mechanical and physical-chemical treatment. One-stage and two-stage biochemical purification are used (Fig. 36). The main structure where the biochemical process takes place is the aeration tank. The process of purifying EL0U wastewater in an aeration tank can take place in one or two stages. With single-stage cleaning in an aeration tank, the duration of aeration is 6-8 hours, the specific air flow is 20-25 m9/m3, the active sludge concentration in dry matter is 2-3 g/l, the amount of circulating activated sludge is 50-705? from wastewater consumption.[...]

When treating industrial wastewater, the choice of subsequent post-treatment is difficult. Biochemical treatment is effective only when wastewater is contaminated with “biologically soft” surfactants, while industry in its technological processes uses quite large quantities of biochemically poorly oxidized surfactants. In this case, one has to rely on destructive methods, in particular, ozonation, which not only complicates, but also greatly increases the cost of wastewater treatment.[...]

Biochemical treatment is one of the main methods for treating refinery wastewater, both when reusing it in recycling water supply systems and when discharging it into a reservoir. Currently, the main structure for biochemical wastewater treatment is the aeration tank. However, the long duration of wastewater treatment in aeration tanks, the significant capacity of structures, and the high consumption of air and electricity force us to look for ways to intensify this process to reduce capital and operating costs.[...]

When filtering through filters, suspended substances, consisting almost entirely of activated sludge, clog the upper layers of the load, and therefore the pressure loss in these filters increases not in a straight line (as in water filters), but along a parabolic curve. The experience of the filters at the Zelenograd station shows that when they get into the deeper layers of the loading, activated sludge organisms begin to grow, which creates additional pressure losses. This is one of the main features of the operation of granular filters in wastewater treatment. The microorganisms accumulated in the filter media also carry out the biochemical process of decomposition of the organic matter of wastewater, therefore, when filtering biologically treated wastewater, a significant part of dissolved oxygen (about 30%) is lost. [...]

In the process of treating refinery wastewater, mainly two types of waste are generated: oil sludge from mechanical and physicochemical treatment facilities and activated sludge from biochemical treatment facilities. With the existing oil sludge sewage system at the refinery, about 5000 tons are formed per year for every 1 million tons of oil processed. For calculations, the following sludge composition is accepted, %; oil products - 20, mechanical impurities - 5, water - 75.[...]

Control of biochemical denitrification processes is carried out similarly to control of biological wastewater treatment processes in aeration facilities, and special attention is paid to assessing the forms and concentrations of nitrogen compounds. [...]

The essence of the process of biological wastewater treatment in fields is that during the process of filtration through the soil, organic wastewater contaminants are retained on it, forming a biological film populated by a large number of microorganisms. The film adsorbs colloidal and dissolved substances, fine suspended matter, and with the help of aerobic bacteria in the presence of atmospheric oxygen they transform into mineral compounds. Atmospheric air penetrates well into the soil to a depth of 0.2-0.3 m, where the most intense biochemical oxidation occurs.[...]

The speed of biochemical processes of wastewater treatment largely depends on the temperature of the environment. At wastewater temperatures below 6 °C, the vital activity of microorganisms, and therefore their activity, sharply decreases; at temperatures above 37 °C, the rate of nitrification noticeably decreases due to a decrease in dissolved oxygen in the water. The optimal temperature is 20-28 °C (in the presence of thermophilic bacteria, the aerobic process can occur at 67 °C). At the same time, activated sludge contains the largest number of types of microorganisms. With an increase in the temperature of the purified water to 37 °C, it is necessary to increase the air supply for aeration by 1.2 times. [...]

Local wastewater treatment from emulsifiers that are not capable of biochemical decomposition. Nekal, widely used in industry as an emulsifier, is not destroyed in the process of biochemical wastewater treatment and, at certain concentrations, inhibits the processes of nitration and oxidation of other organic compounds. In addition, the presence of nekal in water significantly worsens its organoleptic properties. The possibility of using the ion exchange method for extracting nekal from wash water is based on the ability of strongly basic anion exchangers (for example, AB-16) to selectively exchange chlorine ion for the anion of bgor-butylnaphthalene sulfonic acid. Regeneration of the anion exchanger is carried out with aqueous-alcoholic solutions of sodium chloride. After distilling off the alcohol and part of the water from the regenerating solution and cooling it, the nekal precipitates in the form of crystals, and the mother liquor returns to the ion exchange or regeneration cycle.[...]

The subsequent process of activated sludge regeneration can occur either in the structure itself that performs the biochemical treatment (aeration tank), or in a separate structure (regenerator). In the first case, the time for regeneration is added to the adsorption time, and the structure is calculated for the flow of wastewater based on the sum of time; in the second case, the structure (aeration tank) can be designed only for the flow of wastewater for the time required for adsorption, and the regenerator is designed for the regeneration time only for the flow of activated sludge in it, the flow of which is significantly less than the flow of wastewater. Therefore, under certain conditions, the second case in construction and operational terms may be more profitable than the first. In order to be able to solve this problem, the designer of biochemical wastewater treatment facilities must determine the time required for the process of adsorption of organic substances by activated sludge, and the time required for the process of its regeneration.[...]

The possibility of biochemical oxidation of STEC and its influence on the processes of biological wastewater treatment were studied during the operation of model installations of biofilters and aero-mixing tanks.[...]

Biologically purified water contains a significant amount of ammonia nitrogen and phosphates. Nitrogen and phosphorus contribute to the increased development of aquatic vegetation, the subsequent death of which leads to secondary pollution of the reservoir. Control of biochemical denitrification processes is carried out similarly to control of biological wastewater treatment processes in aeration facilities, and special attention is paid to assessing the forms and concentrations of nitrogen compounds. [...]

A technology has been developed for the biochemical purification of wastewater from heavy metal ions: Cr, Cu2+, 2n2+, Ni2+, Fe2+, Fe3+. The essence of the method is the treatment of wastewater with an accumulative culture of sulfate-reducing bacteria, which, under anaerobic conditions in the presence of organic nutrition, reduce the sulfates contained in the water into insoluble sulfides, which are easily settled and removed in the form of sludge. The cleaning process takes place in special facilities - bioreductors. [...]

One of the most important tasks in biochemical wastewater treatment in aeration tanks is to provide oxygen to microorganisms that oxidize organic impurities in water. The process of wastewater treatment in an aeration tank consists of a number of parallel and sequential stages of transformation of substances involved in biochemical reactions. The changes that occur with oxygen can be presented as follows. When air is supplied to the water, bubbles are formed, from which oxygen passes into the sludge mixture and, mixing, is evenly distributed in it. Then dissolved oxygen is adsorbed by bacterial cells that are part of the activated sludge flaps, and is spent on the oxidation of organic substances also adsorbed by the sludge flaps. As a result of the synthesis of proteins in the cell and its division, new living organisms are formed. In addition, decomposition products of organic substances are formed - carbon dioxide, water, products of incomplete decomposition of organic impurities, which are removed from the activated sludge cotton into the water. Gaseous decomposition products are removed from the water during the process of aeration.[...]

From the above it follows that when analyzing waters containing nitrogen-containing organic substances, the COD value obtained using the method with KgBgOv will be higher (due to the formation of nitrates) than when using the conventional method with K2SG2O7. To differentiate, it is advisable to designate the first value with the symbol HPKM0 - It corresponds to the chemical absorption of oxygen that would occur during wastewater treatment in biochemical facilities if the process were brought to complete nitrification of nitrogen-containing substances.[...]

The intensity of the wastewater treatment process in a particular structure determines the oxidative power of the structure, which is understood as the number of grams of oxygen obtained from 1 m3 of the structure per day and used to reduce the biological demand for oxygen in wastewater, the oxidation of ammonium salts to nitrites and nitrates, and also increasing the content of dissolved oxygen in wastewater. The amount of oxidation power for different weapons varies widely. With increased requirements for the degree of purification, biochemically purified water is filtered using sand filters. [...]

A long-term lack of nitrogen during wastewater treatment, in addition to inhibition of the biochemical process, leads to the formation of difficult-to-settle activated sludge and its loss as a result of removal from secondary settling tanks. [...]

Recently, mainly when releasing wastewater in the immediate vicinity of reservoirs used for recreation and tourism, the so-called “third degree of treatment” is provided, following biochemical treatment. It consists of releasing nitrogen- and phosphorus-containing compounds from wastewater, which, being biogenic elements, can cause increased growth of algae in reservoirs and thereby harm them. During biochemical treatment, phosphates can be precipitated with iron or aluminum salts. Nitrate nitrogen can be removed in an intermediate anaerobic plant with the help of bacteria that consume nitrate oxygen and release nitrogen in the form of N2 or IgO. If possible, then, of course, it is preferable to remove all wastewater, bypassing reservoirs, using a bypass channel.[...]

The biochemical method has great potential for deep purification of wastewater, mainly from dissolved petroleum products. Its practical application in oil refineries and petrochemical plants gives positive results. However, it has yet to be implemented in the system of enterprises for storing and transporting petroleum products. For a deeper understanding of the essence and characteristics of biochemical processes during the treatment of oily wastewater, the book provides the minimum necessary scientific data. The practical application of the method should be based on the existing experience in the development and use of biochemical wastewater treatment facilities in general. In this regard, the book examines technological schemes, the main issues of construction and design of structures for biochemical wastewater treatment and sludge treatment on the scale of modern oil depots and other similar enterprises.[...]

A more universal method is the method of wastewater treatment with activated sludge. Activated sludge, under the influence of which the process of biochemical oxidation of organic contaminants occurs, is a cluster of bacteria that in appearance resembles flakes of iron hydroxide. The formation of activated sludge under natural conditions when supplying wastewater leads to the creation of a complex of bacteria capable of consuming various organic substances contained in industrial wastewater. This allows for more complete purification of wastewater from contamination than with the microbial method. A mixture of purified waste liquid and activated sludge enters secondary settling tanks, where they are separated. The main amount of sludge is returned to the aeration tanks for repeated operation. The increase in activated sludge, determined experimentally, is removed from the system. In the absence of experimental data, it can be tentatively assumed that for every 1 m3 of industrial wastewater -100-150 g of activated sludge is formed.[...]

The most intensive development of Ciliata was observed during the treatment of wastewater from the production of protein-vitamin concentrate, which corresponded to the highest coefficient of zoogleicity of the biofilm (see Table 2.10). Wastewater with a low biochemical indicator (0.005) negatively affects the condition of protozoa. Ciliates encyst, forming a cyst around the body - a temporary protective formation of a spherical shape. During encystment, all life processes slow down and the body goes into a state of suspended animation.[...]

Sludge treatment (Fig. 6.22) is used when, during the biochemical treatment of wastewater in primary and secondary settling tanks, large masses of sludge are formed that need to be either eliminated or disposed of. Compaction of sediments is associated with the removal of free moisture and is a necessary stage of all variants of technological schemes for processing sediments. At the same time, using gravity, flotation, centrifugal and vibration methods, on average, it is possible to remove 60% of moisture and reduce the mass of sediment by 2.5 times.[...]

Surfactants adversely affect, and sometimes make it impossible, wastewater treatment using conventional methods. Thus, wastewater containing salts of petroleum sulfonic acids, nonionic surfactants, etc. cannot be purified biochemically, this is due to the fact that surfactants are poisons for the biocenosis, practically do not undergo oxidation, reduce the ratio of biological oxygen demand (BOD) and oxidability, and slow down growth activated sludge and inhibit the nitrification process. The efficiency of this cleaning method increases 100 times or more after preliminary removal of the surfactant.[...]

To ensure sustainable and effective removal of surfactants, wastewater is subjected to preliminary mechanical treatment before aeration. Two-hour settling allows you to remove easily precipitated suspended substances, average the composition of wastewater and mainly equalize the temperature and reaction of the medium. Subsequent filtration through fast two-layer filters (anthracite sand) leads to deeper clarification of wastewater, which intensifies the process of subsequent foaming and reduces the amount of suspended solids in the foam. The latter circumstance is of no small importance when preparing foam concentrate for reuse for washing clothes. Aeration of wastewater for 45-60 minutes when supplying compressed air with an intensity of 25-30 m3[m2 - h ensures the removal of 80% of surfactants, i.e., it reduces their concentration in wastewater to 20-30 mg/l. Considering that only detergents based on “biologically soft” surfactants should be used for washing clothes, after such treatment, wastewater from modern laundries can be freely discharged into city sewers that have biochemical treatment. As shown by Tsvetkova’s research at the Academy of Public Utilities, after fractionation of surfactants into foam, clarified wastewater, even without dilution, can be further purified using the biochemical method. Purified wastewater can be used to wash the filters, while the wash water generated during the first 5 minutes, due to the possible high content of surfactants, is recommended to be directed into the wastewater flow entering for treatment. The rest of the wastewater, as well as sludge from settling tanks, can be discharged into the city sewerage system.[...]

The difference between COD and BOD characterizes the presence of impurities that are not oxidized biochemically and the amount of organic substances used to build microbial cells. For domestic wastewater, BODtotal is 85-90% of COD. Based on the BODtotal/COD ratio, one can judge the possibility of using a certain method of wastewater treatment. If the BOD/COD ratio is >0.5, then this indicates the possibility of using biochemical wastewater treatment; at the BOD/COD ratio [...]

Thiamine, in contrast to biotins, itself did not show physiological activity in biochemical purification processes. However, in combination with manganese and chromium naphthenates, thiamine increases the carbon content in activated sludge during the oxidation of alkanes and ketones. To increase the activity of thiamine in aerobic wastewater treatment processes, salts of iron, copper, manganese and zinc were used.[...]

One of the most common manometric instruments for determining gas exchange in chemical and biochemical processes is the Warburg device. It has found wide application in biology in the study of the life activity of microorganisms and tissue respiration. In the field of wastewater treatment, the Warburg device is used to study the toxicity of wastewater (AKH, MISS), as well as to study the intensification of the work of biochemical structures (Vodgeo).[...]

Most heterotrophic organisms obtain energy as a result of the biological oxidation of organic substances - respiration. Hydrogen from the oxidized substance (see § 24) is transferred to the respiratory chain. If only oxygen plays the role of the final hydrogen acceptor, the process is called aerobic respiration, and microorganisms are strict (obligate) aerobes that have a complete chain of transfer enzymes (see Fig. 14) and are able to live only with a sufficient amount of oxygen. Aerobic microorganisms include many types of bacteria, bacteria, algae, and most protozoa. Aerobic saprophytes play a major role in the processes of biochemical wastewater treatment and self-purification of the reservoir.

The main biochemical treatment facilities at domestic refineries are aeration tanks and secondary settling tanks. As a rule, refinery treatment plants use aeration tanks with dispersed wastewater inlet and aeration tanks—mixers. Conventional aeration tanks - displacers - are most often used at the second stage of purification.

Biological filters have practically not found application for the purification of oil-containing wastewater at domestic enterprises, since the experience of their operation at one of the refineries has shown that the purification effect in them is much lower than in aeration tanks. Currently, only two oil refineries use biological filters as a second stage of purification. Biological ponds at domestic factories are used only as structures for the post-treatment of biochemically treated refinery wastewater.

Aero tanks

An aeration tank is a device with constantly flowing wastewater, in the entire thickness of which aerobic microorganisms develop that consume the substrate, i.e. "pollution" of this wastewater.

Biological wastewater treatment in aeration tanks occurs as a result of the vital activity of activated sludge microorganisms. The wastewater is continuously mixed and aerated until the air is saturated with oxygen. Activated sludge is a suspension of microorganisms capable of flocculation.

The mechanism for removing organic substances from wastewater and their consumption by microorganisms can be represented in three stages:

Stage 1 - mass transfer of organic matter from the liquid to the cell surface. The rate of this process is determined by the laws of molecular and convective diffusion of substances and depends on the hydrodynamic conditions in the aeration tank. Optimal conditions for the supply of contaminants and oxygen are created through effective and constant mixing of the contents of the aeration tank. The first stage proceeds faster than the subsequent process of biochemical oxidation of contaminants.

Stage 2 - diffusion through semi-permeable membranes in the cell either the substance itself or the breakdown products of this substance. Most of the substance enters the cells with the help of a specific carrier protein, which forms a complex that diffuses through the membrane.

Stage 3 - metabolism of organic matter with the release of energy and the formation of new cellular matter. The transformation of organic compounds is enzymatic in nature.

The determining processes for the technological design of water purification are the rate of removal of contaminants and the rate of decomposition of these contaminants. Activated sludge in contact with contaminated liquid under aeration conditions goes through the following development phases:

1. Lag phase I, or the phase of adaptation of sludge to the composition of wastewater. There will be practically no increase in biomass.

2. Phase II of exponential growth, in which an excess of nutrients and a lack of metabolic products contribute to the maximum rate of cell reproduction.

3. Phase III of slow growth, in which the rate of biomass growth begins to be hampered by nutritional deficiencies and the accumulation of metabolic products.

4. Phase IV of zero growth, in which an almost stationary state in the amount of biomass is observed.

5. Endogenous respiration phase (or autoxidation phase) V, in which, due to lack of nutrition, cell death and decay begin, leading to a decrease in the total amount of biomass.

Aerotanks can be classified according to the hydrodynamic mode of their operation:

I) aeration tanks with ideal displacement;

2) ideal mixing aeration tanks;

3) aeration tanks of intermediate type

The hydrodynamic operating mode of aeration tanks has a fundamental impact on the conditions for cultivating microorganisms and, consequently, on the efficiency and economy of biological wastewater treatment.

The designs of aeration tanks can be different and depend on the aeration system, the method of distributing wastewater flows and return sludge, etc. There are also designs of aeration tanks combined with settling tanks and filters, with and without activated sludge regeneration.

There is also a classification of aeration tanks according to the amount of “load” on activated sludge: high-load (aeration tanks for incomplete treatment), conventional and low-load (aeration tanks for extended aeration).

The aeration system is of great importance in the design of aeration tanks. Aerotanks with pneumatic, pneumomechanical, mechanical and ejection aeration systems are used.

Aeration systems are designed to supply and distribute oxygen or air in the aeration tank, as well as to maintain activated sludge in suspension.

Mixing aeration tanks (full mixing aeration tanks) are characterized by a uniform supply of source water and activated sludge along the length of the structure and a uniform removal of the sludge mixture. Complete mixing of wastewater with the sludge mixture ensures equalization of sludge concentrations and the rates of the biochemical oxidation process, therefore aeration tanks-mixers are more suitable for treating concentrated industrial wastewater (total BOD up to 1000 mg/l) with sharp fluctuations in its flow rate, composition and amount of contaminants .

Fig.2.

Displacer aeration tanks. Unlike other types of aeration tanks (mixing aeration tanks and intermediate aeration tanks), displacer aeration tanks are structures in which purified wastewater gradually moves from the point of inlet to the point of its outlet. In this case, there is practically no active mixing of the incoming wastewater with the previously received one. The processes occurring in these structures are characterized by a variable reaction rate, since the concentration of organic pollutants decreases as the water moves. Displacer aeration tanks are very sensitive to changes in the concentration of organic substances in the incoming water, especially to volleys of toxic substances with wastewater, therefore such structures are recommended for the treatment of urban and industrial wastewater similar in composition to domestic wastewater.

Fig.3.

In the absence of sharp fluctuations in wastewater flow and the content of toxic substances, instead of mixing aeration tanks, it is preferable to use displacement aeration tanks, which are characterized by a smaller volume and simpler design.

A type of aeration tank-displacer is a sectioned aeration tank, in which, to prevent the return movement of water, the corridors of the structure are divided by transverse partitions into five to six sequential flow sections (cells). Sectioning turns out to be appropriate when the length of corridors in aeration tanks is less than 60-80 m.

The corridor aeration tank operates practically as a displacer when the ratio of the distance from the treated water inlet to the end of the last corridor to the width of the corridor is at least 50: 1. With a corridor width of 6 or 9 m, the minimum distance from the wastewater inlet to the end of the last corridor should be 300 and 450 m, respectively .

When using aeration tanks with shorter corridors, a process of significant axial mixing is observed, which distorts the displacement effect. To prevent longitudinal mixing and bring the process closer to the displacement mode, in this case it is necessary to provide for sectioning of aeration tanks. Sectioning can be carried out by installing lightweight vertical partitions with holes in the lower part in the corridors of aeration tanks. The speed of movement of the sludge mixture in the openings of the partitions is assumed to be no less than 0.2 m/s.

To eliminate the negative impact of volleys of concentrated wastewater, the first section of the aeration tank must have a larger volume. Structurally, such a section is designed as an aeration tank mixer, which is achieved by dispersed inlet of wastewater into it. The distance between outlets should be no less than the width of the corridor. The size of the outlet openings in the distribution trays must be designed to allow 50% of the flow of wastewater entering the section. The design of aeration tanks-displacers (including sectioned ones) must ensure operation according to the scheme with the regeneration of activated sludge. Sludge regeneration is assumed to be equal to 25-50% of the volume of structures

Known designs of sectioned aeration tanks with sequential flow of purified water have disadvantages that prevent their widespread use. The main disadvantage is the unsatisfactory conditions for adaptation of activated sludge due to different operating modes of the cells.

Aero tanks with dispersed wastewater inlet occupy an intermediate position between mixers and displacers; they are used to treat mixtures of industrial and municipal wastewater.

Rice. 4.

Aerotanks can be combined with free-standing secondary sedimentation tanks or combined into a block with a rectangular plan of both structures. The most compact combined structures are aeration tanks and settling tanks. Abroad, this type of structure, round in shape with mechanical aerators, is called an aero accelerator. Combining an aeration tank with a settling tank allows you to increase the recirculation of the sludge mixture without the use of special pumping stations, improve the oxygen regime in the settling tank and increase the dose of sludge to 3-5 g/l, accordingly increasing the oxidative power of the structure.

A type of aeration tank-settler - an aeroaccelerator, proposed by NIKTI GC, is a structure that is circular in plan. Clarified wastewater enters the lower part of the aeration zone, where air is supplied pneumatically or pneumomechanically, which ensures the process of biochemical oxidation, and also creates a circulation movement of liquid in this zone and the suction of the sludge mixture from the circulation zone of the settling tank. From the aeration zone, the sludge mixture enters the air separator through flooded adjustable overflow windows and then into the circulation zone of the settling tank. A significant part of the sludge mixture returns through the gap to the aeration zone, and the discharged purified wastewater enters the settling zone through a layer of suspended sediment.

Secondary settling tanks

Secondary settling tanks are an integral part of biological treatment facilities; they are located in the technological scheme directly after biooxidizers and serve to separate activated sludge from biologically purified water leaving aeration tanks, or to retain biological film coming with water from biofilters.

The efficiency of secondary settling tanks determines the final effect of water purification from suspended solids.

For technological schemes of biological wastewater treatment in aeration tanks, secondary settling tanks to some extent also determine the volume of aeration structures, which depends on the concentration of return sludge and the degree of its recirculation, and the ability of settling tanks to effectively separate highly concentrated sludge mixtures.

The sludge mixture coming from the aeration tanks into the secondary settling tanks is a heterogeneous (multiphase) system in which the dispersion medium is biologically treated wastewater, and the main component of the dispersed phase is activated sludge flaps, formed in the form of a complex three-level cellular structure surrounded by the exocellular substance of the biopolymer. composition.

The most important property of a sludge mixture as a disperse system is its aggregative instability, which is expressed in a change in the diameter of activated sludge flaps within the range of 20-300 microns, depending on the intensity of turbulent mixing.

With a decrease in the intensity of turbulent mixing and subsequent settling of the sludge mixture as a result of bioflocculation, activated sludge flakes aggregate into flakes 1-5 mm in size, which settle under the influence of gravity.

Precipitation of activated sludge flakes (when its concentration in the sludge mixture is more than 0.5-1 g/l) occurs with the formation of a visible phase boundary between the clarified water and sludge.

The hydrodynamic operating mode of secondary settling tanks is formed as a result of the combined influence of the following hydrodynamic conditions:

* the mode of inlet of the sludge mixture into the structure, estimated by the speed of its entry and determining the intensity of interaction of the incoming flow with the flows of settling sludge and clarified water;

* the process of collecting clarified water, determined mainly by the speed of water approaching the collection tray and its distance from the level of settled sludge;

* the mode of suction of settled sludge, determined by the speed of sludge entering the sludge suckers, the level of sludge standing and the distance of the suckers from the collection tray.

Secondary settling tanks are vertical, horizontal and radial. For treatment plants with a throughput capacity of up to 20,000 m 3 /day, vertical secondary settling tanks are used, for treatment stations of medium and high throughput (more than 15,000 m 3 / day) - horizontal and radial ones.

→ Wastewater treatment

Biochemical basis of biological wastewater treatment methods

Biological methods of wastewater treatment are based on the natural processes of the life activity of heterotrophic microorganisms. Microorganisms are known to have a number of special properties, of which three main ones should be distinguished, widely used for cleaning purposes:
1. The ability to consume a wide variety of organic (and some inorganic) compounds as food sources to obtain energy and ensure its functioning.

2. Secondly, this property is to multiply quickly. On average, the number of bacterial cells doubles every 30 minutes. According to Prof. N.P. Blinov, if microorganisms could multiply unhindered, then, given sufficient nutrition and appropriate conditions, in 5–7 days the mass of only one type of microorganisms would fill the basins of all seas and oceans. This, however, does not happen both due to limited food sources and due to the existing natural ecological balance.

3. The ability to form colonies and accumulations, which can be relatively easily separated from purified water after the completion of the processes of removing the contaminants contained in it.

In a living microbial cell, two processes continuously and simultaneously occur - the breakdown of molecules (catabolism) and their synthesis (anabolism), which make up the overall metabolic process - metabolism. In other words, the processes of destruction of organic compounds consumed by microorganisms are inextricably linked with the processes of biosynthesis of new microbial cells, various intermediate or final products, the implementation of which consumes the energy received by the microbial cell as a result of the consumption of nutrients. The source of nutrition for heterotrophic microorganisms are carbohydrates, fats, proteins, alcohols, etc., which can be broken down by them either under aerobic or anaerobic conditions. A significant portion of the products of microbial transformation can be released by the cell into the environment or accumulate in it. Some intermediate products serve as a nutritional reserve that the cell uses after the main nutrition is depleted.

The entire cycle of relationships between the cell and the environment in the process of removal from it and transformation of nutrients is determined and regulated by appropriate enzymes. Enzymes are localized in the Cytoplasm and in various substructures embedded in the cell membrane, released onto the cell surface or into the environment. The total content of enzymes in a cell reaches 40-60% of the total protein content in it, and the content of each enzyme can range from 0.1 to 5% of the protein content. Moreover, cells can contain over 1000 types of enzymes, and each biochemical reaction carried out by a cell can be catalyzed by 50-100 molecules of the corresponding enzyme. Some enzymes are complex proteins (proteids), containing in addition to the protein part (apoenzyme) a non-protein part (coenzyme). In many cases, coenzymes are vitamins, sometimes complexes containing metal ions.

Enzymes are divided into six classes according to the nature of the reactions that catalyze: oxidative and reduction processes; transfer of various chemical groups from one substrate to another; hydrolytic cleavage of chemical bonds of substrates; the cleavage or addition of a chemical group from the substrate; change within the substrate; connecting substrate molecules using high-energy compounds.

Since the microbial cell consumes only organic substances dissolved in water, the penetration of water-insoluble substances, such as starch, proteins, cellulose, etc. into the cell is possible only after their appropriate preparation, for which the cell releases the necessary enzymes into the surrounding liquid their hydrolytic cleavage into simpler subunits.

Coenzymes determine the nature of the catalyzed reaction and are divided into three groups according to the functions they perform:
1. Transporting hydrogen ions or electrons. Associated with redox enzymes - oxidoreductases.
2. Participating in the transfer of groups of atoms (ATP - adenosine triphosphate acid, carbohydrate phosphates, CoA - coenzyme A, etc.)
3. Catalyzing reactions of synthesis, decomposition and isomerization of carbon bonds.

The mechanism of removal from solution and subsequent dissimilation of the substrate is very complex and multi-stage in nature, interconnected and sequential biochemical reactions determined by the type of nutrition and respiration of bacteria. Suffice it to say that many aspects of this mechanism are still not entirely clear, despite its practical use, both in the field of biotechnology and in the field of biochemical purification of water from organic impurities in a wide range of technological design schemes.

The earliest model of the process of biochemical removal and oxidation of contaminants was based on three main principles: sorption removal and accumulation of the removed substance on the cell surface; diffusion movement through the cell membrane of either the substance itself, or the products of its hydrolysis, or a hydrophobic complex formed by a hydrophilic penetrating substance and an intermediary protein; metabolic transformation of nutrients entering the cell, ensuring diffusion penetration of the substance into the cell.

In accordance with this model, it was believed that the process of removing nutrients from water begins with their sorption and accumulation on the cell surface, which requires constant mixing of the biomass with the substrate, providing favorable conditions for the “collision” of cells with substrate molecules.

The mechanism of transfer of a substance from the surface of the cell into it - this model explained either by the attachment of the penetrating substance to a specific carrier protein, which is a component of the cell membrane, which, after introducing the substance into the cell, is released and returned to its surface to complete a new “capture” of the substance and a new transfer cycle , or by direct dissolution of this substance in the substance of the wall and cytoplasmic membrane, due to which it diffuses into the cell. The process of stable consumption of the substance began only after a certain “equilibrium period” of the substance between the solution and the cells, which was explained by the occurrence of hydrolysis and the diffusion movement of the substance through the cell membrane to the cytoplasmic membrane, where various enzymes are concentrated. With the onset of metabolic transformations, the sorption equilibrium is disrupted, and the concentration gradient ensures the continuity of further supply of the substrate into the cell.

At the third stage, all metabolic transformations of the substrate occur, partly into such end products as carbon dioxide, water, sulfates, nitrates (the process of oxidation of organic substances), partly into new microbial cells (the process of biomass synthesis), if the process of transformation of organic compounds occurs in aerobic conditions. If biochemical oxidation occurs under anaerobic conditions, then in its process various intermediate products (possibly for specific purposes), CH4, NH3, H2S, etc., and new cells can be formed.

This model, however, could not explain some of the kinetic features of the transport processes of substrate transfer and, in particular, the accumulation of substrate in the cell against a concentration gradient, which is the most common result of these processes and is called “active” transport, in contrast to diffusive transport. A feature of active transport processes is their stereospecificity, when substances similar in chemical structure compete for a common carrier, and do not simply diffuse into the cell under the influence of a concentration gradient.

In the light of modern views, the model of substrate movement through the cell membrane assumes the presence of a hydrophilic “channel” in it, through which hydrophilic substrates can penetrate into the cell. However, in contrast to the model described above, stereospecific movement occurs here, probably achieved due to the “relay race” transfer of substrate molecules from one functional group to another. In this case, the substrate, like a key, opens the channel appropriate for its penetration (model of a transmembrane channel).

The second alternative model can be seen as a combination of the first two, using their positive properties. It assumes the presence of a hydrophobic membrane transporter, which, through successive conformational changes caused by the substrate, conducts it from the outer to the inner side of the membrane (model of conformational translocation), where the hydrophobic complex disintegrates. In this interpretation of the mechanism of substrate transport across the cell membrane, the term “carrier” is still used, although it is increasingly being replaced by the term “permease,” which takes into account the genetic basis of its encoding as a membrane component of the cell for the purpose of transporting substances into the cell.

It has been established that membrane transport systems often include more than one protein mediator and there may be a division of functions between them. “Binding” proteins identify the substrate in the medium, supply and concentrate it on the outer surface of the membrane and transfer it to the “true” transporter, i.e. component that transports the substrate across the membrane. Thus, proteins involved in the “recognition”, binding and transport of a number of sugars, carboxylic acids, amino acids and inorganic ions into the cells of bacteria, fungi and animals have been isolated.

Transformation of the process of transfer of substances into the cell into a unidirectional process of “active” transport, leading to an increase in the content of nutrients in the cell against their concentration gradient in the environment, requires certain energy costs from the cell. Therefore, the processes of transfer of the substrate from the environment into the cell are associated with the processes of metabolic release of energy contained in the substrate occurring inside the cell. Energy in the process of substrate transfer is spent on chemical modification of either the substrate or the carrier itself in order to eliminate or impede both the interaction of the substrate with the carrier and the return of the substrate by diffusion through the membrane back into the solution.

Modern views on the processes of biochemical removal and oxidation of organic compounds are based on two cardinal provisions of the theory of enzymatic kinetics. The first position postulates that the enzyme and substrate interact with each other, forming an enzyme-substrate complex, which, as a result of one or several transformations, leads to the appearance of products that reduce the barrier to activation of the reaction catalyzed by the enzyme due to its fragmentation into a number of intermediate stages, each of which does not encounter energetic obstacles to its implementation. The second position states that, regardless of the nature of the compounds and the number of stages during the enzymatic reaction catalyzed by the enzyme, at the end of the process the enzyme comes out unchanged and is able to interact with the next molecule of the substrate. In other words, already at the stage of substrate withdrawal, the cell interacts with the substrate to form a relatively weak connection called an “enzyme-substrate complex.”

The above is well illustrated by the example of the extraction of glucose from a solution by various microorganisms containing the enzyme glucose oxidase in an environment with molecular oxygen. Glucose oxidase forms an enzyme-substrate complex - glucose - oxygen - glucose oxidase, after the breakdown of which intermediate products are formed - gluconolactone and hydrogen peroxide, as shown schematically in Fig. 11.1.

The gluconolactone formed as a result of the breakdown of this complex undergoes hydrolysis to form gluconic acid.

One of the most important properties of enzymes is their ability to be synthesized in the presence and under the influence of a certain substance. Another equally important property is the specificity of the enzyme’s action both in relation to the reaction it catalyzes and in relation to the substrate itself.

Sometimes an enzyme is able to act on one single substrate (absolute specificity), but much more often the enzyme acts on a group of substrates that are similar in the presence of certain atomic groups of substrates.

Rice. 11.1. Scheme of “recognition” of a substrate by an enzyme, formation of an enzyme-substrate complex and catalysis

Many enzymes are characterized by stereochemical specificity, which consists in the fact that the enzyme acts on a group of substrates (and sometimes on one) that differ from others in the special arrangement of atoms in space. The role of each enzyme in the process of biochemical oxidation of organic substances is strictly defined: it catalyzes either the oxidation (i.e., the addition of oxygen or the elimination of hydrogen) or the reduction (i.e., the addition of hydrogen or the elimination of oxygen) of well-defined chemical compounds. During dehydrogenation, a particular enzyme can remove only certain hydrogen atoms that occupy a certain spatial position in the molecule of the substrate or intermediate product. The same applies to enzymes that catalyze other metabolic processes.

The processes of biochemical oxidation in heterotrophic microorganisms are divided into three groups depending on what is the final acceptor of hydrogen atoms or electrons removed from the oxidized substrate. If the acceptor is oxygen, then this process is called cellular respiration or simply respiration; if the hydrogen acceptor is an organic substance, then the oxidation process is called fermentation; finally, if the hydrogen acceptor is an inorganic substance such as nitrates, sulfates, etc., then the process is called anaerobic respiration, or simply anaerobic.

The most complete process is aerobic oxidation, because its products are substances that are not capable of further decomposition in the microbial cell and do not contain a reserve of energy that could be released by ordinary chemical reactions. The main of these substances, as already noted, are carbon dioxide (CO2) and water (H20). Although both of these substances contain oxygen, the chemical path of their formation in the cell may be different, since carbon dioxide can be produced as a result of biochemical processes occurring in an oxygen-free environment under the influence of enzymes - decarboxylases, which remove CO2 from the carboxyl group (COOH) of the acid. Water, as a result of the vital activity of the cell, is formed exclusively by combining oxygen in the air with the hydrogen of those organic substances, from which it is split off in the process of their oxidation.

Aerobic dissimilation of the substrate - carbohydrates, proteins, fats - is a multi-stage process, including the initial breakdown of a complex carbon-containing substance into simpler subunits (for example, polysaccharides - into simple sugars; fats - into fatty acids and glycerol; proteins - into amino acids), which undergo, in turn, further consistent transformation. In this case, the accessibility of the substrate to oxidation significantly depends on the structure of the carbon skeleton of the molecules (straight, branched, cyclic) and the degree of oxidation of carbon atoms. Sugars, especially hexoses, are considered the most readily available, followed by polyhydric alcohols (glycerol, mannitol, etc.) and carboxylic acids. The general final path by which the aerobic metabolism of carbohydrates, fatty acids, and amino acids is completed is the tricarboxylic acid cycle (TCA cycle) or the Krebs cycle, into which these substances enter at one stage or another. It is noted that under conditions of aerobic metabolism, about 90% of the oxygen consumed is used in the respiratory tract for energy production by microbial cells.

Fermentation is a process of incomplete breakdown of organic substances, mainly carbohydrates, under conditions without oxygen, which results in the formation of various intermediate partially oxidized products, such as alcohol, glycerin, formic, lactic, propionic acids, butanol, acetone, methane, etc., which widely used in biotechnology to obtain target products. Up to 97% of the organic substrate can be converted into such by-products and methane.

The enzymatic anaerobic breakdown of proteins and amino acids is called putrefaction.

Due to the low energy output during the fermentative type of metabolism, the microbial cells that carry it out must consume a larger amount of substrate (at a lower depth of its breakdown) than cells that receive energy through respiration, which explains the more efficient growth of cells in aerobic conditions compared to anaerobic conditions .

The cell receives the greatest amount of energy for its functioning as a result of the oxidation by oxygen of hydrogen, which is cleaved from the oxidized substrate under the action of dehydrogenase enzymes, which, according to their chemical action, are divided into nicotinamide (NAD) and flavin (FAD). Nicotinamide dehydrogenases are the first to react with the substrate, removing two hydrogen atoms from it and adding them to the coenzyme. As a result of this reaction, the substrate is oxidized and NAD is reduced to NAD'H2. Next, FAD reacts, transferring hydrogen from the nicotinamide coenzyme to the flavin coenzyme, as a result of which NAD'H2 is again oxidized to NAD, and the flavin coenzyme is reduced to FADH2. Further, through an extremely important group of redox enzymes - cytochromes - hydrogen is transferred to molecular oxygen, which completes the oxidation process with the formation of the final product - water.

In this reaction, the largest part of the energy contained in the substrate is released. The entire process of aerobic oxidation can be represented by the diagram in Fig. 11.2.

The energy released during the microbial oxidation of a substance is accumulated by the cell with the help of high-energy compounds. The universal energy store in living cells is adenosine triphosphoric acid - ATP (although there are other macroenergies).

This phosphorylation reaction, as can be seen from (11.9), requires energy, the source of which in this case is oxidation. Therefore, ADP phosphorylation is closely associated with oxidation, and this process is called oxidative phosphorylation. In the process of oxidative phosphorylation, during the oxidation of, for example, one molecule of glucose, 38 molecules of ATP are formed, while in the stage of glycolysis, only 2. It should be noted that the stage of glycolysis proceeds exactly the same in both aerobic and anaerobic conditions, i.e. before the formation of pyruvic acid (PVA), and 2 out of 4 ATP molecules formed are spent on its occurrence.

The paths for further transformation of PVC under aerobic and anaerobic conditions diverge.

Aerobic transformation of glucose can be represented by the following scheme:
1. Glycolysis: SbH12Ob + 2FA-+2PVK + 2NADH2 + 4ATP (11.10)
2. Transformation of pyruvic acid (PVA): 2PVA-*2C02 + 2 Acetyl CoA + 2NADH2
3. Tricarboxylic acid cycle (Krebs cycle): Acetyl CoA -> 4C02 + 6NADH2 + 2FADH2 + 2ATP (11.12) ECbH12Ob -> 6C02 + 10NADH2 + 2FADH2 + 4ATP (11.13) where FAD is a flavoprotein.

Oxidation of NADH2 in the electron transport system produces ZATP at
1 mol; oxidation of 2FADH2 produces 4ATP,
then: SbN1206 + 602 -> 6C02 + 6H20 + 38ATP

Under conditions of anaerobic transformation of carbohydrates, the first step is the phosphorylation of glucose, carried out with the help of ATP under the influence of the enzyme hexokinase, i.e.
Glucose + A TF-hexokinase > glucose _ b – phosphate + ADP
After completion of the glycolysis stage and the formation of PVC, the course of further transformation of PVC depends on the type of fermentation and its causative agent. The main types of fermentation: alcoholic, lactic acid, propionic acid, butyric acid, methane.

Oxidative phosphorylation can also occur under the influence of an enzyme that synthesizes ATP at the substrate level. However, this formation of high-energy bonds is very limited, and in the presence of oxygen, cells synthesize most of the ATP they contain through the electron transport system.

The accumulation of a substance released during the process of dissimilation under aerobic or anaerobic conditions with the help of high-energy compounds (and primarily ATP) makes it possible to eliminate the discrepancy between the uniformity of the processes of release of chemical energy from the substrate and the unevenness of the processes of its consumption, inevitable in the real conditions of a cell’s existence.

In a simplified way, the entire process of decomposition of organic substances during aerobic transformations can be represented by the diagram shown in Fig. 11.3. The diagram of anaerobic transformations of PVC after the stage of glycolysis is presented in Fig. 11.4.

Research has established that often the type of metabolism depends not so much on the presence of oxygen in the environment, but on the concentration of the substrate.

This indicates that, depending on the specific operating conditions of the biomass in the environment, both aerobic and anaerobic processes of transformation of organic compounds can simultaneously occur, the intensity of which will also depend on the concentration of both the substrate and oxygen.

It should be noted here that in industrial biotechnology, pure cultures are used to obtain various products of microbial origin (feed or baker's yeast, various organic acids, alcohols, vitamins, drugs), i.e. microorganisms of one species are often selected, with strict maintenance of the species composition, appropriate nutritional conditions, temperature, active reaction of the environment, etc., excluding the appearance and development of other types of microorganisms, which could lead to a deviation in the quality of the resulting product from established standards.

When treating wastewater containing a mixture of contaminants of various chemical compositions, which are sometimes even very difficult to identify by analytical methods, the biomass that carries out the purification is also a mixture, or rather, a community of different types of microorganisms and protozoa with complex relationships between them. Both the species and quantitative composition of biomass from wastewater treatment plants will depend on the specific method of biological treatment and the conditions of its implementation.

According to the calculations of some experts, when the concentration of dissolved organic pollutants, assessed by the BPKP0Ln index, is up to 1000 mg/l, the use of aerobic cleaning methods is most beneficial. At concentrations of BPKPOLn from 1000 to 5000 mg/l, the economic indicators of aerobic and anaerobic methods will be almost the same. At concentrations above 5000 mg/l, it would be more appropriate to use anaerobic methods. However, it is necessary to take into account not only the concentration of pollutants, but also the consumption of wastewater, as well as the fact that anaerobic methods lead to the formation of end products such as methane, ammonia, hydrogen sulfide, etc. and do not allow obtaining the quality of purified water , comparable to the quality of cleaning using aerobic methods. Therefore, at high concentrations of contaminants, a combination of anaerobic methods is used at the first stage (or first stages) of purification and aerobic methods at the last stage of purification. It should be emphasized that domestic and municipal wastewater, unlike industrial wastewater, does not contain concentrations of contaminants that justify the use of anaerobic methods, and therefore these treatment methods are not discussed in this chapter.

Rice. 11.3. Simplified diagram of the three-step breakdown of nutrient molecules (B. Alberte et al. 1986)

Rice. 11.4. Conversion of pyruvic acid by anaerobic microorganisms into various products