MINISTRY OF EDUCATION AND SCIENCE OF UKRAINE NATIONAL TECHNICAL UNIVERSITY OF UKRAINE
«IGOR SIKORSKY KYIV POLYTECHNIC INSTITUTE»
Tolstopalova N.M., Kosogina I.V., Obushenko T.I., Fedenko Yu.M.
CHEMISTRY, TECHNOLOGY AND EQUIPMENT FOR
Approved by the Academic Council of The Faculty of Chemical Technology, Igor Sikorsky Kyiv Polytechnic Institute as a tutorial for students,
who study in specialty 161 «Chemical technology and engineering»,
specialization "Chemical technologies of inorganic substances and water purification"
Igor Sikorsky Kyiv Polytechnic Institute 2018
Reviewers: Sanginova O. V., Ph.D., Assoc.
editor Astrelin I. M., Doc. Sci., Prof.
Grif is provided by the Academic Council of The Faculty of Chemical Technology, Igor Sikorsky Kyiv Polytechnic Institute (protocol №6 from 30.05.2018 )
Electronic online educational edition
Tolstopalova Nataliya Mykhailivna, Ph.D., assoc.
Kosogina Iryna Volodymyrivna, Ph.D., assoc.
Obushenko Tetiana Ivanivna, senior lecturer Fedenko Yurii Mykolayovich, Ph.D., assist.
CHEMISTRY, TECHNOLOGY AND EQUIPMENT FOR WASTEWATER
«Chemistry, Technology and Equipment for Wastewater Treatment. Laboratory Workshop» [Electronic resource]: a tutorial for students of specialty 161 "Chemical technologies and engineering", specialization "Chemical technologies of inorganic substances and water purification" / N. M. Tolstopalova, I.V. Kosogina, T. I.
Obushenko, Yu. M. Fedenko; Igor Sikorsky Kyiv Polytechnic Institute. – Electronic text data (1 file: 1,11 Mbytes). – Kyiv : Igor Sikorsky Kyiv Polytechnic Institute, 2018.
– 64 p.
Annotation is roughly 650 characters
© N. M. Tolstopalova, I.VT. I. Obushenko, Yu. M. Fedenko, 2018
© Igor Sikorsky Kyiv Polytechnic Institute, 2018
page INTRODUCTION ... 4 Laboratory work № 1. Removal of dyes from waste water using photo-oxide methods ... 5
Laboratory work № 2. Removing of dyes by ozonation ... 12 Laboratory work № 3. Investigation of the influence of the main parameters on the effectiveness of coagulation and the determination of the optimal dose of coagulant based on waste from alumina production ... 20
Laboratory work №4. Purification of waste water from organic compounds ... 28
Laboratory work №5. Purification of waste water from chromium compounds ... 37
Laboratory work № 6. Flocculation purification of contaminated water ... 43 Laboratory work № 7. Acid regeneration of coagulant from sedimentation of sewage treatment ... 48
Laboratory work № 8. Investigation of the efficiency of sewage removal from synthetic surfactants on a mechanical flotation plant ... 57
REFERENCES ... 61
Water resources are one of the important components of the hydrosphere of the globe and an essential component of the economic and social development of each country. Ukraine belongs to low-income countries for water supplies that are available for use. The greatest impact on the state of natural waters is the waste water of enterprises of various industries, agriculture and communal services. It is from the efficiency and quality of waste water treatment that further affects the state of the aquatic ecosystem and the health of people.
The credit module of the discipline "Technology and equipment for wastewater treatment" is an integral part of the complex program of training specialists and masters in the direction of "Chemical technologies of inorganic substances"
specialization "Chemical technology of water conditioning, cleaning and utilization of emissions and waste of inorganic manufactures."
Discipline "Technology and equipment for waste water treatment" promotes knowledge on the physico-chemical bases of waste water treatment of various origins and the choice of the method of water treatment. The laboratory workshop allows you to get acquainted with some widely used methods and methods of waste water treatment on examples of typical water contaminants.
Laboratory work № 1. Removal of dyes from waste water using photo-oxide methods
Purpose: to study the efficiency of using different Fenton reagent catalytic systems for discoloration of waste water containing dyes.
The presence of dyes in wastewater causes serious difficulties in cleaning them.
Much of the dyes used in the industry, virtually unchanged, fall into the biochemical oxidation plants, causing the need for cleanup.
All known methods of physico-chemical treatment of waste water from dyes, surfactants (surfactants), formaldehyde can be divided into three main groups.
The first group of methods provides removal of contaminants by transfer of dyes in the precipitate or float shale by sorption on flakes of hydroxides of metals formed during reagent treatment of waste water (coagulation, reagent pressure flotation, etc.).
The methods of this group are characterized by the following disadvantages: low degree of purification, especially discoloration, the need for utilization of sediment water purification and their dehydration.
The second group includes separatory methods (sorption on activated carbon and macroporous ion exchangers, reverse osmosis, ultrafiltration, etc.). These methods provide a high degree of waste water treatment, but require prior mechanical and chemical treatment to remove insoluble impurities, complex in hardware design, have a high cost of cleaning. Their application can be cost-effective in closed water supply systems of enterprises.
The third group combines destructive methods based on deep oxidation-reduction transformations initiated by various physico-chemical processes, in particular the action of oxidants (O2, O3, Cl2, H2O2), ultraviolet and solar radiation.
The advantages of destructive methods include their high efficiency and processability, simplicity of automation and control. In most cases, during their
implementation, no precipitates are formed, additional water pollution is not added to the treated water in the form of chloride, sulfate and other ions.
By photo oxidation it is possible to achieve the destruction of the structure of organic impurities of the chromophore-auxochromic structure, followed by their deep splitting into simpler light oxidizing organic products or mineral compounds. It is therefore advisable, before the biochemical oxidation of waste water containing dyes, to conduct destruction of the organic component under the action of UV radiation.
Photochemical reaction is a chemical transformation, namely, the "bimolecular"
interaction of a quanta of light with a molecule, resulting in physical and chemical changes. Excited molecules can enter such reactions that do not run or at least difficult in the non-excited state, since the excess energy facilitates the overcoming of activation barriers, and on the other hand, in the excited state, the molecule often has a completely different distribution of electron density than in the main state, and therefore become
The first law of photochemistry was formulated by Grotthouse (1817) and Draeneer (1843): a photochemical transformation can take place under the action of only light absorbed by matter. For the course of a photochemical reaction, it is required that the light entering the reaction volume is absorbed by a reacting compound or sensitizer (a substance that, when irradiated with light, passes into an excited state and causes a chemical reaction of the main substance). The second law of photochemistry was formulated by Stark (1912) and Einstein (1912): each molecule involved in a chemical reaction that runs under the action of light absorbs one quantum of radiation that causes a reaction.
However, this law is valid only for the initial process, because secondary chain reactions can lead to the fact that the calculated degree of decomposition may be greater than unity. Therefore, the second law should read as follows: absorption of light by a molecule - the single-quantum process and the sum of quantum outputs of primary processes should be equal to one, that is, Σφi = 1.00, where φi is the quantum yield of the first primary process, which may be dissociation, isomerization, fluorescence, phosphorescence, irradiation transitions, that is, all possible ways of destroying or
deactivating the excited molecule.
Hydrogen peroxide is used for deep oxidation of products of destruction of dyes in waste water (WW). Its main technological advantages include high solubility in water, stability, the ability to process water in a wide range of temperatures, and simple hardware design. Hydrogen peroxide is an environmentally friendly oxidizer, because its decomposition products are oxygen and water. Especially effective oxidation process occurs in the presence of a catalyst. Thus, in the treatment of HF by hydrogen peroxide with a volume fraction of 15 % and a mass concentration of 0.5 mg / L in the presence of activated charcoal with a mass dose of 200 g / L, the degree of reduction of the chemical oxygen demand (COD) was 80-85 %, and the color - up to 95%. However, during purification of hydrogen by hydrogen peroxide, it is not always possible to achieve the desired degree of purification, since organic compounds such as benzene, toluene, ethanol and others are resistant to H2O2, and the rate of oxidation in the processing of diluted WW is rather low. In this regard, oxide methods based on the disproportionation of hydrogen peroxide with the formation of reactive hydroxyl radicals OH · (E0 = 2,38 V) are widely used; they are electrophilic reagents and can interact with electron donors. These oxidative methods include the photolysis of H2O2
and its catalytic decomposition under the action of Fe2+ ions (Fenton system).
As a result of the catalytic oxidation of Cu on a catalyst containing Fe2+ ions, using the oxygen of air or hydrogen peroxide (0.001M), the concentration of dye active blue and active red decreased by 100 and 10 times, respectively.
By the oxidative action of hydrogen, peroxide is approaching the products of water radiolysis. Most of the radicals react with each other and with hydrogen peroxide, initiating its schedule:
НО2· + ОН = Н2О + О2, (1.1) 2 НО2· = Н2О + 1,5 О2, (1.2) ОН· + Н2О2 = НО2· + Н2О. (1.3)
Therefore, when using hydrogen peroxide to oxidize organic substances in aqueous solutions, it is important to identify and maintain optimum conditions for the process. The joint use of hydrogen peroxide with ferric salts (II) significantly
affects the oxidation of organic matter. The mechanism of this process is a set of successive stages and includes the following reactions:
Fe2+ + H2O2 = Fe3+ + OH· + OH-, (1.4) Fe2+ + OH· = Fe3+ + OH-, (1.5) OH· + H2O2 =HO2· + H2O, (1.6) Fe3+ + H2O2 = Fe2+ + 2H+ +O2, (1.7) Fe3+ + O2- = Fe2+ + O2, (1.7’) Fe2+ + HO2· = Fe3+ +HO2-. (1.8)
The above steps are realized in a weakly acidic medium (pH> 2) under the condition of 0.5 < [H2O2] / [Fe2+] < 200.
From literary sources, it is known that the oxidation of various types of surfactants is carried out with the joint use of hydrogen peroxide and ferrous (II), (III) or aluminum salts. When the Fe2+ catalyst is precipitated into the waste water purified, the quality of water purification is significantly improved. The optimal
dose of H2O2 in the application of Fe2+ as a catalyst is (1,0 ÷ 10,0) · 10- 3 g / L.
At the dose of Fe2+ 0.100 g / L, the effect of cleaning from surfactant is 35 %, and with an additional introduction of 10-2 g / L H2O2 - 90% .
Materials and methods Apparatus
Glasses (a nominal volume of 100 ml - 6 pcs.; flasks (a nominal volume of 100 ml - 6 pcs.; measurement flasks (a nominal volume of 1000 ml); spatula;
pipettes (a nominal volume of 1, 2, 10 ml); sampler; photoelectrocolorimeter KFK - 2; cuvettes; analytical balances.
Reactants and materials
A model solution of contaminated water is prepared with a dye (40 mg / ml)
and a volume of 1 L. Aqueous peroxide (35%) and a standard solution of Fe2+
(1 g / L).
The model solution of sewage water is diluted in such a way as to obtain
solutions with concentrations of 2, 4, 5, 10 times less than the original and build a calibration graph using the photoelectrocolorimeter KFK-2, the dependence of the concentration of the dye on the optical density. The calibration graph further determines the residual concentration of the dye after the photooxidation.
The photooxidation is carried out using a modified Fenton reagent, namely:
1). Fenton reagent [Fe2+ / H2O2];
2). Fenton reagent [Fe2+ / H2O2] under the influence of UV radiation;
3). Fenton reagent [Fe2+ / H2O2] under direct sunlight
The process of photooxidation is carried out on an experimental installation (Fig. 1): In a water cooling box 6, a magnetic stirrer 1, a glass with a sample of 2, a UV lamp (250 W), a reflector of UV rays 4 and a starter 5 outside the box are placed on the mist bulb.
Figure 1. The scheme of laboratory installation
Progress Experiment 1
Samples of wastewater are collected per 100 cm3 with a dye concentration of 40 mg / L into 3 different glasses (sample number 1, number 2, number 3);
concentrated hydrogen peroxide and 1 ml of Fe2+ solution at a concentration of 10 mg / L are added (2 ml). After that, the sample number 2 is placed into laboratory installation, the magnetic stirrer is started and the UV lamp is turned on.
Photocoating is carried out for 5 minutes, then the solution is photometrised using the same wavelength and cuvette as for the calibration graph. After a break of 15 min. (cooling time of the lamp), the sample is again subjected to photooxidation for 10 minutes, photometrised and again after a break of 15 min. spend the third photooxidation within 15 minutes. and the final fourth photooxidation for 20 minutes. followed by the determination of the residual content of the dye after the calibration graph after each oxidation step. Based on the results obtained, calculate the degree of oxidation and build a schedule of dependence of the degree of oxidation from time to time; graphically calculate the rate constant of the photooxidation reaction.
The results of laboratory studies are noted in table:
Table 1.1 – Experimental results
Dye Initial concentration, mg / L
Concentration after oxidation, L after
after 10 min.
after 15 min.
after 20 min.
Sample number 1, after adding hydrogen peroxide and a solution of ferrum, the solution is stirred, placed on the laboratory table under the radiation of an energy saving lamp of different wavelengths (according to the teacher's instructions) and kept for 20 minutes. Then, the solution is filtered (if the solution becomes cloudy or precipitate formed) and photometrised using the same wavelength and ducts as for the calibration graph. After determining the content of the dye add 1 cm3 of Fe2 + solution at a concentration of 10 mg / dm 3 and stand for 20 minutes. on a laboratory table under the lamp, after which they are filtered and photometrically similar to the previously mentioned technique. The remaining dye content is determined every 20 minutes. within the next 120 minutes photooxidation.
The degree of discoloration of the model of waste water is calculated.
Determination of the efficacy of discoloration of sample No. 3 under direct sunlight is carried out in the same way as sample number 1, but under the conditions of solar radiation. The sample is placed on the window sill.
Investigation of the effect of the ferrum dose on the effluent efficacy of samples No.
1, No. 2, and No. 3 is carried out analogously to the procedure in the experiment 1,2,3, but in the model samples of wastewater, another volume of a Fe2+ solution with a concentration of 10 mg / L is introduced, which is determined after carrying out of the previous three experiments on the tasks of the teacher.
1. To give a description of the methods of purifying SV from dyes.
2. The essence of the methods related to the 1st group.
3. The essence of the methods pertaining to the second group.
4. The essence of the methods belonging to the 3rd group.
5. Characteristics of methods of photoconductive decomposition of dyes by the reagent of Fenton and its modifications.
Laboratory work № 2.Removing of dyes by ozonation
Purpose: to master the method of work with ozonizer and to identify patterns of influence of the main factors of the ozonation process on the effectiveness of bleaching waste water, containing dyes.
In recent years’ interest in ozone has grown as a substance that can remove organic pollution from the water. The oxidative effect of ozone on organic matter can be manifested in various forms: direct oxidation by loss of oxygen, as well as by introducing molecular ozone into a substance molecule (ozonation); catalytic action, increasing the oxidative role of oxygen contained in the ozonized air.
As a result of oxidation, harmful substances are also formed that need to be removed, which leads to complication of the technological process and increases the cost of water purification.
Ozone - has strong decontamination properties and is a strong oxidizer.
Ozone destroys organic compounds and microorganisms, while decomposing into oxygen.
О3 = О2 + О – 100,56 kJ;
О + О3 = 2О2 + 398,05 kJ;
2О3 = 3О2 + 297,49 kJ.
Chemically active gas of blue with a sharp smell, strong oxidizer. At high concentrations it decomposes with an explosion. It is formed from oxygen at an electric discharge (for example, during a thunderstorm). The bulk of ozone is in the upper atmosphere - the ozone layer, at an altitude of 10 to 50 km, with a maximum concentration of 20-25 km (the so-called ozone layer). It is he who protects the Earth from ultraviolet radiation of space. In the second half of the twentieth century. There is a tendency to decrease this layer and even the formation of
"ozone holes" - areas with a reduced concentration of ozone in the ozone layer.
This phenomenon is associated with anthropogenic pollution of the atmosphere, including Freon.
It is used in chemical synthesis, for sterilization of water, disinfection and deodorization of air, bleaching of fabrics, paper, mineral oils, etc. Germicide.
There is mutagen. The maximum permissible concentration in air is 1 mg / m3.
Ozone has a very high oxidation capacity (E0 = +2.07 V, alkaline medium E0 = 1.24 V) and, at normal temperatures, destroys many organic compounds.
During ozonation simultaneously there is an oxidation of impurities, discoloration, deodorization, disinfection of sewage and oxygen saturation.
The ozone molecule is triatomic and has a triangular structure (Fig. 2.1).
Figure 2.1. Structure of ozone molecule
In a clean and dry air, decomposition occurs more slowly than in wet and contaminated. Numerous studies have found that ozone has a high bactericidal effect. In addition, there is a stronger effect of ozone on spore forms, as well as a faster disinfectant effect of ozone compared to chlorine. However, the treatment of water with ozone has its own characteristics, which often do not allow to realize its benefits as a disinfectant. In this regard, in practice, sometimes with the treatment of water with ozone before supply to the network it is subjected to additional decontamination of chlorine.
The solubility of ozone in water depends on the pH and the amount of impurities in water. In the presence of acids and salts, the solubility of ozone in water increases, in the presence of alkalis - decreases. Ozone dissociate in air and in aqueous solution, turning into oxygen. In an aqueous solution, ozone dissociates
faster. The decomposition of ozone in water increases dramatically in the event of an increase in pH and temperature. The stability of ozone in neutral and acidic environments is associated with the formation of HO3+ associates, whose hydrate shell slows down the reaction:
О3 + Н2О = О2 + О + Н2О.
The decomposition of ozone in water is accelerated in the presence of activated charcoal, metals of valency variable (manganese, cobalt, ferrum) of some oxides (P2O5), barium peroxide (BaO2). Materials such as fluorine and chlorinated plastics, glass, some materials, do not pour on the stability of ozone.
The basis of the industrial production of ozone is the reaction of splitting the oxygen molecule into atoms under the action of a quiet or barrier discharge. The high reactivity of ozone is due to the large excess energy of the molecule:
О3 = 3/2 О2 + 100 kJ/mole.
Ozone reacts with saturated organic compounds to form free radicals. The limiting process stage is the effect of ozone on the bond С-Н:
RH + O3 = R. + HO. + O2 (or R + HO3+).
Radicals R., which formed in the atmosphere of oxygen, are mainly converted to peroxide of radicals of moderate activity. Therefore, the chain reaction of oxidation can occur only at a sufficiently high temperature, when the rate of growth chain reaction exceeds the reaction of its cliff. At low ozone oxidation temperature there is a chain reaction with the formation of hydroxyhydroperoxides:
R. + О2 = RО2;
RО2. + RH = RООH + R .
Aldehydes, in turn, are oxidized to peracids, which decompose in dilute aqueous solutions to organic acids and hydrogen peroxide. In parallel, the oxidation reaction of a hydroxyl radical may occur:
HO. + O3 = HO2. + O2
with the next recombination of peroxide-radicals:
2HO2. = Н2О2 + O2.
However, in fact, hydrogen peroxide does not accumulate and the consumption of ozone in neutral and acidic media corresponds to the reaction:
R-CH2OH + 2O3 = RCOOH + 2O2 + H2O.
Apparently, at the time of allocation hydrogen peroxide reacts with ozone:
H2O2 + O3 = H2O + 2O2.
In addition, it is possible that ozone is spent on the decomposition of hydroxyperoxides and peracids. The reaction rate increases under these conditions, which is probably due to the decomposition of hydrogen peroxide, hydroperoxide, peracid and ozone. Simultaneous increase in the number of generated primary radicals initiates the process of oxidation. Consequently, to accelerate the initiation process, the oxidation process with ozone should be carried out in an alkaline medium. For most organic compounds, the intermediate and final oxidation products are alcohols, aldehydes (ketones) and acids.
In practice, ozone is obtained in special devices - ozonizers, in which air is transmitted at a certain speed between two electrodes connected to a power supply (5 - 20 kV).
To obtain a quiet discharge, the electrodes of the ozonizers are separated by a dielectric with the maximum possible surface-to-surface resistance and dielectric constant. A layer of such material serves as a dielectric barrier, which prevents the spark or arc discharge and causes a uniform structure of a quiet discharge. At the same time, it serves as a reactive buffer resistance, limiting the current in the discharge circuit. As an insulator, ordinary or borosilicate glass, enamel, and plastics are used.
Due to the fact that 85 – 95 % of the energy consumed by the ozonizer is consumed by the heat, the electrode system needs to be cooled, because ozone at high temperatures decomposes rapidly. The main value determining the synthesis of ozone is the discharge power, attributed to gas consumption, i.e., the amount of energy that falls on the volume passed through the gas ozonizer.
Materials and methods Apparatus
Glasses (a nominal volume 250 ml - 2 pcs.); flasks (a nominal volume 100 ml - 6 pcs.); measurement flask (a nominal volume 1000 ml); spatula; conical flasks for titration (350 ml) - 2 pcs.; pipettes with a nominal volume 1, 2, 10 ml;
sampler; photoelectrocolorimeter KFK - 2; cuvettes.
Reactants and materials
A model solution of waste water with a dye (concentration 40 – 200 mg / L) (as a dye, any dye of organic nature, according to the teacher's instruction, is suitable) and a volume of 1 L is prepared. 1n solution of H2SO4; 1% starch solution, 0.005 N solution Na2S2O3; 10 % KI solution.
Measured flasks of 100 cm3 are placed; 2.0; 5.0 10; 20; 50,0 ml of the model solution of the drainage is brought to the mark with distilled water and build a calibration graph using the photoelectrocolorimeter KFK-2, the dependence of the concentration of the dye on the optical density. The calibration graph further determines the residual concentration of the dye after the ozonation process.
Ozonation is conducted in experimental installation (fig. 2.2).
For the process 600 ml of the model solution of sewage water is poured into absorption column 5, in which the ozone-air mixture (OAM) is fed through the porous partition 5.2. Cover 5.3. In the absence of the need to determine the residual ozone, the crane 7 is transferred to position 1. In this case, the gas after column 5 is sent to the absorber 10.
To determine the residual ozone, the crane 7 is transferred to position 2 and carried out in accordance with the procedure for determining O3 in the OAM.
Figure 2.2. Experimental installation of the ozonation process: 1. compressor; 2. a drain filter; 3. pressure gauge; 4. pressure control system; 5. Absorption column:
(5.1 sample sampling cube, 5.2 porous partition, 5.3 lid); 6.7 three-way cranes; 8.
Drexel for analysis; 9. gas watch; 10. ozone trap; 11. protective loop; 12. ozonizer:
12.1 (ON / OFF, 12.2 mode switches, 12.3 current controller, 12.4 indicator).
To establish kinetics of removing dye every 5 min. Perform determination of optical density, sample for analysis taken through the cock 5.1 for 60 minutes. or to completely bleed the solution.
Before starting, determine the wavelength for this dye and the length of the cuvette, using the stock solution for this purpose.
The degree of discoloration is determined by the formula:
where Ain – optical density of initial solution.
А – optical density of solution after ozonation.
Determination of the mass fraction of ozone in the ozone-air mixture (OAM)
Determination of ozone in OAM is carried out by the volume-metric method. For analysis, drexel 8 is filled with 2/3 5 ÷ 10 % solution of KI, and the column is distilled water. Turn on compressor 1: using system 4, there is an expense (at which the pressure on the pressure gauge 3 should not exceed 0,15 MPa). The crane 6 should be in position bypassing the column 5. Activate the ozonizer and exert the voltage within the limits of 20 ÷ 35 kV, transmitting 5 ÷ 10 L of OAM, which fixes the time for which this mixture will pass the drake 8.
The volume is set by gas clock 9
Transfer the drops solution 8 quantitatively to the titration flask, add 20 ml of 1N H2SO4 and 5 to 10 drops of 1% starch solution (the starch must be freshly prepared).
Titrate the resulting mixture, until discoloration, with 0,005N Na2S2O3
The content of O3 in OAM is determined by the formula:
X=(V(Na2S2O3) ∙K∙0.005∙24)/V, where: X –О3 content in OAM, g / L;
V(Na2S2O3) – volume of thiosulfate, spent on titration, ml, K – correction factor of concentration Na2S2O3,
0,005 – concentration Na2S2O3, 24 – ozone equivalent,
V – volume of OAM.
The next is finding of volume of OAM.
where V(Na2S2O3) – consumption of OAM, L / min, t – time for which V, L of gas passed.
And then the concentration of ozone is determined:
С(О3)= X∙W; g О3 / L.
Dye concentration, mg / L:
Voltage of an ozonizer, kV:
Cuvette, cm: Graphs of C(O3) residual -t, z-t.
The results of the studies are noted in tables 2.1., 2.2.
Table 2.1 – Experimental results Time, min А V,
Cresidual, g О3 / L
10 15 30
Table 2.2 – Results of analysis
V, L τ, min V(Na2S2O3), ml
Х, g О3 / L
W, L / min
С(О3), g О3 / min
1. How are the physico-chemical properties of the medium influenced the rate of decomposition of ozone?
2. Describe the conditions for improving the process of destruction of ozonation dyes 3. Compare the efficiency of removing dyes from sewage by ozonation and the application of other oxidative methods
4. Is the technological scheme of ozonation energy technology?
Laboratory work № 3. Investigation of the influence of the main parameters on the effectiveness of coagulation and the
determination of the optimal dose of coagulant based on waste from alumina production
Purpose: the establishment of regularities of the formation of the contact medium in the process of coagulation clearing the object of research and determining the optimal dose of coagulant based on waste alumina production
Salts of aluminum and ferrum are the most often used as coagulants for coagulation purification of natural and waste water.
The technology of water purification by coagulants consists of the following basic operations: reagent storage, pre-clarification, water purification, preparation and mixing of coagulant, discoloration and clarification.
In the case of the polydisperse composition of suspended matter, especially in the presence of coarse-dispersed coarse particles (sand, lobes of ore and non- metallic minerals), the waste water is pre-clarified in horizontal tangential and aeration sand-traps with a circular or straight-line motion of water. Smaller mineral or organic curves are also separated by settling or filtration on slow filters filled with sand and gravel, or microfilter. Prefiltering on microfilters can be done in front of slow sand filters, before water treatment with coagulants or before rapid sand filters. As sedimentation structures, sedimentation ponds, horizontal tanks and their combination, as well as various septic tanks of periodic and continuous action (vertical, horizontal, radial, tubular, lamellar, etc.) are used. Hydrocyclones of pressure and non-pressure type are used for separation of coarse substances. The purified water is suspended if the alkaline reserve is insufficient for satisfactory hydrolysis of the coagulants.
Hydrogen and sodium carbonate, calcium carbonate and lime, as well as a
small amount of ammonia and ammonia, are used to water the water and bind the hydroxide of the aggressive oxide of carbon (IV) formed during the hydrolysis of water. In the course of paring the pH values are maintained within (6,5-7,5). It also contributes to reducing the residual content of aluminum and ferrum in purified water and reducing its corrosive properties.
The clarification and discoloration of muddy waters with increased hardness by coagulants is expedient to carry out at high pH, and colored soft waters - for reduced. Especially important is the order of the introduction of reagents. In the case of introduction of shaving reagents in colored water before the addition of coagulants, the process of coagulation and cleaning quality deteriorate. In water there is an increased content of stained substances. It is better to discolour water in the case of introduction of shaving reagents after the introduction of coagulants, because some of the colored matter manages to absorb at the time of formation of hydroxides. Organic substances contained in water in the form of humates of sodium, at low pH values are hydrolyzed to form negatively charged particles. The latter energetically interact with positively charged polynuclear hydroxcomplexes (micelles). Therefore, in the case of treatment with coagulants of highly colored waters, they are subjected after coagulant administration.
One of the most important technological parameters of the process of water purification by coagulation is the dose of coagulant, its optimum value depends on the properties of the disperse system: temperature, the number of suspended and colloid dispersed substances, color, ionic composition of the dispersion medium, pH and other physico-chemical parameters. In the case of an insufficient dose of coagulant, the desired effect of cleansing is not achieved, and in the case of excess - in addition to over-consumption of a high-value reagent, in some cases the effectiveness of coagulation may deteriorate.
With a decrease in the temperature of treated water, the dose of coagulant increases significantly, especially in the case of muddy waters. With decreasing water turbidity, the temperature is lower.
With considerable content of suspended matter, they, coated with a "casing"
of colloidal particles of aluminum hydroxide, coagulate, preventing the formation of long chain bridges from spherical particles. As a result, a smaller dose of coagulant is required. For high-infused waters with an increase in their alkalinity, the dose of coagulant increases, for turbid - decreases.
To coagulate quickly and throughout the volume of purified water, it is
necessary to mix the reagents vigorously over a short period of time (1-2 minutes in the case of wet and no more than 3 minutes - dry dosage of
reagents) in hydraulic or mechanical mixers. The mixing of the coagulant with water should occur so that a large number of small aggregates originally formed on the surface, on which chemoresubbed charged polynuclear hydroxocomplexes of aluminum having high activity relative to the impurities to be purified. In a one- stage technological scheme, the coagulant is added in the immediate proximity of the filters.
It is desirable to introduce the reagent into a relatively small amount of purified water, and then quickly mix it with the rest (separate coagulation). An increase in the initial concentration of coagulant contributes to the intensification of the coagulation process due to an increase in the partial concentration of coagulant in the treated volume of water (concentrated coagulation). Sometimes we recommend the ratio of volumes of treated and untreated water to 1: 1.5. In the case of concentrated coagulation, the cost of ferrous sulfate is reduced by 20-30 %, as well as the turbidity and color of water are reduced.
Effective is the fractionated (fractional or partial) coagulation of water, in which the coagulant is added to the water to be purified in two or more portions or successively introducing different coagulants.
In this case, the polydisperse aggregates of the coagulant are formed, as well as the period of formation of positively charged polynuclear hydroxocomplexes is increased, as a result of which the coagulation is intensified.
The recommended optimal time interval between the introduction of individual parts of the coagulant is 90 - 120 seconds. In the case of discoloration of water, the first dose of coagulant should be half the total.
Periodic coagulation is based on a combination of methods of concentrated and fractionated. The feeding periods of increased doses of coagulant alternate with periods of complete cessation of coagulation. As a result of such treatment of low-purity water for a two-stage scheme, the cost of coagulant is reduced by 30 – 40 %, the degree of discoloration of water rises. Deeper removal of coloring impurities is due to lower pH values during the feeding of increased doses of coagulant.
Coagulation inactivation is also achieved by recirculation of coagulant (coagulated curvature). The essence of the method is to supply part of the spent siege to the zone of dosage of fresh portions of the coagulant. This helps accelerate the process and form denser flakes. The application of this method is effective for the intensification of coagulation of low-wasting waters, while significantly (up to 30 %) the costs of coagulant are reduced.
The process of formation of flakes successfully occurs with a slow and even mixing of the disperse system, which helps to agglomerate the small flakes into larger ones that easily deposit. It is especially necessary to mix at low temperatures of treated water (below 5 °C). During the mixing, the growth of the particles is accelerated as a result of their collision, the interconnection increases and solid flakes are formed. Mixing positively influences the formation of flakes in the event that the particles have reached a certain size as a result of the Brownian motion (spherical aggregates larger than 0.02 microns and larger).
The mixing of water should not be too intense to prevent the destruction of flakes. In order to ensure optimal mixing conditions in front of the septic tanks, flushing cameras are often equipped with vertical or horizontal movement of water through partitions or whirlpool devices.
The formed coagulant flakes, together with the adsorbed impurities, are separated from the water to be purified during clarification by means of settling, filtering, centrifuging or floating. In the practice of water preparation, the suspended matter is first separated by settling, and then the drains are filtered.
Horizontal, vertical or radial tanks are usually used.
Materials and methods Apparatus
Flasks (nominal volume 100 ml - 6 pcs., 50 ml - 6 pcs.); measurement flask (nominal volume 1000 ml); measurement flask (nominal volume 250 ml – 2 pcs.);
spatula; pipettes (nominal volume 1, 2, 10 ml); sampler; photoelectrocolorimeter KFK - 2; cuvettes; analytical balance, litmus paper.
A mixture of ammonium molybdate, sulfate acid, stybium chloride and tartaric acid. Up to 300 ml of palladium acetate is stirred with 144 ml of concentrated sulfuric acid, ppm. It is then cooled to 20 oC and, when stirred, add a solution of 10 g of sulfamic acid NH2SO8H pda. and 100 ml of distillate solution, 12.5 g of ammonium molybdate (NH4)2Mo7O34 · 4H2O in 200 ml of distillate solution, 0.235 g of sitbium chloride of SbCl2 pda.a. and 0.6 g of tartaric acid odd.a. in 100 ml of distillate. The icons are kept in a glass of orange glass.
Ascorbic acid. 10 % solution. Dissolve 10 g of ascorbic acid in pistacible water and bring the volume of solution to 100 cm3 in a measuring dish. Store the solution in the cold, stable for about 30-40 days.
Potassium phosphate mono substituted - standard solution.
Basic solution: Dissolve 0,7165 g of КН2РО4 pda, dried for 2 hours at a temperature of 105 оС, in a distillate. Add 2 ml of chloroform and bring the volume of the solution with distillate to 1 dm3 in a volumetric flask. 1 ml of this solution contains 0.389 mg of phosphate.
Working solution 1: Make 10.0 ml of the basic solution to 250 ml of distillate.
Use freshly prepared solution. 1 ml of this solution contains 0.0156 mg of phosphate.
Working solution 2: Make 50,0 ml working solution 1 to 250 ml distillate.
Use freshly prepared solution. 1 ml of this solution contains 0.00312 mg of phosphate.
Working solution 2 (50 ml) is placed (0; 1; 2.5; 5; 10; 25 ml) into a volumetric flask of. Add 2 ml of solution of the mixture, 0.5 ml of 10 % solution of ascorbic acid to each flask. The mixture is brought to the mark with a distillate and stirred. The first bulb (without the content of the working solution 2) - "idle experiment". After 20-25 minutes photometrically in a cell 10 mm in wavelength 670 nm and calibration graph "Optical density - concentration of phosphates" is built. An example of the calibration graph is shown in Figure 1.
Figure 1. Calibration graph
Determination of the efficiency of removal of phosphates by coagulation method, selection of the optimal dose of coagulant based on waste from alumina production.
Experiment 1: Coagulation at pH 9 (NaOH substrate reagent).
For study use working solution 1. In 4 cylinders of coagulation pour 100 cm3 of the test solution. Then add a dose of coagulant (a solution of sulfate or iron chloride) to the pipette so that its content in water is 25, 50, 75 and 100 mg / L.
Using a solution of sodium hydroxide, the pH of the solution is adjusted to 9-10.
After mixing the three-fold turning of the closed cylinder caps, the time of entering
the coagulant in water is noted. After 30 minutes, water from each cylinder is filtered through a "blue ribbon" filter in conical flasks. To analyze the coagulation efficiency, the filtrate is diluted similarly to the preparation of the solution for preparation of the calibration: 5 ml from each cylinder in a 100 ml flask and brought to the label with a distillate. From the obtained solutions, an aliquot of 5 ml is drawn into a 50 ml flask, 2 ml of a mixture solution, 0.5 ml of ascorbic acid is added and distilled to the label. After 20-25 minutes, photometrically, and on the basis of the obtained value, the residual concentration of phosphate in the solution is found.
WARNING! Time to settle solutions before photometry should be the same for all experiments.
Experiment 2: Coagulation with the addition of CaO as a sublutting reagent.
For study use working solution 1. In 4 cylinders of coagulation pour 100 ml of the test solution. Then add a dose of coagulant (a solution of sulfate or iron chloride) to the pipette so that its content in water is 25, 50, 75 and 100 mg / L. On technical scales weigh 0.3-0.5 g CaO. After the introduction of the coagulant and CaO, the solution is mixed with a three-fold turning of the closed cylinder caps.
Mark the time when the coagulant is injected into the water. After 30 minutes, water from each cylinder is filtered through a "blue ribbon" filter in conical flasks.
To analyze the coagulation efficiency, the filtrate is diluted similarly to the preparation of the solution for preparation of the calibration: 5 cm3 from each cylinder in a 100 ml flask and brought to the label with a distillate. From the obtained solutions, an aliquot of 5 ml is drawn into a 50 ml flask, 2 ml of a mixture solution, 0.5 ml of ascorbic acid is added and distilled to the label. After 20-25 minutes, photometrically, and on the basis of the obtained value, the residual concentration of phosphate is found on the schedule.
Removal degree, %:
= − Cv
X Cv ,
where Сv – initial concentration, g / L;
Ck – final concentration, g / L.
Make conclusions about the effectiveness of the dose of coagulant and the conditions for coagulation.
1. Provide the conditions (mode) of the formation of the contact environment in the suppressed state.
2. How does the characteristic of treated water affect the efficiency of the process?
3. Under what conditions depends on choosing the type of coagulant?
4. Type the types of luminaries and the principle of their operation.
5. Describe the loading of filters used in water treatment technology.
6. Types of filters and the principle of their operation.
Laboratory work №4. Purification of waste water from organic compounds
Purpose: to carry out the purification of waste water from phenol by the method of adsorption. Determine the degree of water purification depending on the method of organizing the sorption process: a) in the stationary (filtering) layer of the sorbent; b) in the device simulating the fluidized contact mode sorbent - purified water. Measure the adsorption isotherm from the aqueous solution on activated carbon. Calculate the adsorption equilibrium constant and reduce the amount of adsorption energy.
Sorption is one of the most effective methods for purifying industrial water containing impurities of organic origin, and allows to achieve deep water purification to the MPC norms. Adsorption is used to dispose of wastewater from phenols, herbicides, pesticides, aromatic nitro compounds, surfactants (surfactants), dyes, and others. Advantages of the method: the ability to adsorb substances from multicomponent systems, as well as high efficiency, especially when cleaning low- concentration wastewater. From a technical and economic point of view, adsorption is very effective for the removal of valuable products from wastewater for the purpose of using them in a closed loop of the main production.
Very important, especially from a practical point of view, the moment when adsorption purification of industrial waste water is the kinetics of the process, or the rate of adsorption, which determines the choice of the technological scheme, the dimensions of the apparatus, etc. The velocity of the adsorption process depends on the concentration of the adsorbent, the temperature, the nature and structure of the adsorbent, the adsorbent and the adsorbent and is determined by the external and internal diffusion of molecules from the volume of solution to the surface of the grains and in the pores of the adsorbent, the velocity of the adsorption of molecules on the surface and the speed of extruding exchange of molecules, which is adsorbed.
As sorbents, activated carbon, synthetic sorbents and some industrial wastes (ash, slag, chips) are used. Mineral sorbents - clays, silica gels, alumina gels and hydroxides of metals for adsorption of organic substances from wastewater are used little, since the energy of their interaction with water molecules is large - sometimes higher than the adsorption energy. The most versatile of adsorbents is activated carbon.
The process of adsorption wastewater treatment is carried out under different conditions: with intensive mixing of adsorbent with water, by filtering water through a layer of adsorbent or in a fluidized bed at installations of periodic or continuous action. When using filtration type units, sewage water should not contain solid suspended impurities. Installations of a fluidized bed should be used with high content of suspended impurities in sewage.
Physical adsorption is one of the types of manifestation of intermolecular interaction, in which the concentration of gas molecules, vapors, liquids or solution components near the phase separation surface is greater than the average concentration in volume.
The occurrence of physical adsorption, which mainly determines the adsorption on nonpolar surfaces such as carbon adsorbents, is a dispersion (Van der Waals) interaction. This interaction is due to the coordinated motion of electrons in molecules in the immediate vicinity.
Physical adsorption of organic substances - non-electrolytes or weak electrolytes from aqueous solutions most strongly manifests itself when used as an adsorbent of carbon materials. This is due to the fact that the energy of Van der Waals interactions of water molecules with carbon atoms is much less than the energy of interaction of these atoms with organic molecules. As a result of this there is a strong expressed selective adsorption of organic substances on activated carbon, which is used in the technology of water treatment and industrial effluents from organic compounds. A quantitative measure of the adsorption interaction of an organic substance with a carbon adsorbent is the free energy of Helmholtz -ΔFa0, which is the difference between the free energies of the adsorption interaction of
water -ΔFv0 and the organic matter -ΔFo.r.0 under standard conditions, since it is known from the course of physical chemistry that the absolute the value F cannot be determined:
–ΔFa0 = –ΔFо.р.0 – (–ΔFв0). (4.1) At present, -ΔFa0 is determined experimentally, by the value of the heat of adsorption or with the isotherm of adsorption, since -ΔFa0 is related to the equation of adsorption equation:
–ΔFa0 = R·T·lnKa; (4.2) At standart temperature 25 °С:
–ΔFa0 = 5,71· lgKa, kJ / mole. (4.3) -ΔFa0 for organic non-electrolytes and weak electrolytes from aqueous solutions ranges from 10 to 30 kJ / mole. Substances having -ΔFa0 <10 kJ / mole do not displaced water from the adsorption volume of activated carbon, ie practically not adsorbed from aqueous solutions.
In this paper, -ΔFa0 is determined by the adsorption isotherm, which can be represented by a equation of the type of the Langmuir equation suitable for most practical purposes, which is the equation of a convex parabola:
e о р w
V a V V C
V K a
5 , 55 1000
where a - specific adsorption of organic matter, mmole / g of coal;
Ve - limiting adsorption volume of coal, determined experimentally for each grade of coal, cm3 / g,
Vo.r. and Vw - millimolar volume of adsorbate and water, respectively, V = М/ρ, cm3 / mmole;
Cp - concentration of organic matter, mmole / ml;
55,5 - number of mole in 1 L of water.
As can be seen, the Ka equation includes only experimentally measurable quantities.
Materials and methods Apparatus
Measuring cylinder (nominal volume 100 ml); bulbs (nominal volume 100 ml - 5 pcs.; a nominal volume of 250 ml with stoppers - 10 pcs.); funnel - 5 pcs.; pipettes with a nominal volume of 10 and 25 ml; burette for titration; spatula; sampler; analytical weights; a device for shaking flasks; vertical cylindrical glass column.
Reactants and materials
Model of industrial waste water containing phenol; aqueous solution of phenol at a concentration of 5 mmole / L; coal of the brand KAD; bromide-bromate solution - 0.1N; sodium thiosulfate - 0.1 N solution; potassium iodide crystalline; starch – 1 % solution; solution of sulfate acid 1: 3; paper filter.
Removal of phenol from water by sorption in a fixed (filtering) layer of sorbent Through a vertical cylindrical glass column filled with activated carbon, water contaminated with phenol, at a rate of 2-4 m3 / (m2·h) is passed. According to the teacher's instructions, a certain amount of water is passed through the teacher, after which the phenol content is determined in the samples.
Removal of phenol from water by means of sorption in the apparatus simulating the fluidized contact mode sorbent - purified water.
In the flat-bottomed flasks, weigh the activated charcoal and determine the volume of the sewage, and then place the flasks in the shaking apparatus. According to the teacher's instructions set the contact time of water with sorbent from 10 minutes. up to 1 hour.
Calculation of the degree of water purification
The degree of purification of water from organic compounds (phenol) by
adsorption (X) is calculated by the formula, %:
X = (Cp0 – Cpi)/ Cp0·100,
where Cp0 - concentration of phenol in the initial effluent, g / L;
Cpi - phenol concentration of water samples after sorption, g / L.
Preparation of working solutions of phenol
The working solutions are prepared by dilution of the initial solution of phenol at a concentration of 5 mmole / L in the measuring flasks per 100 cubic centimeters (Table 4.1).
Table 4.1 - Preparation of working solutions
№ Volume of initial solution of
phenol Vph, ml Volume of water, ml Concentration of phenol С0, mmole / L
1 20 80 1
2 40 60 2
3 50 50 2,5
4 60 40 3
5 70 30 3,5
6 80 20 4
7 90 10 4,5
8 100 0 5
Measurement of isotherms of adsorption of organic matter on charcoal KAD by 0.1 g is weighed and entered into dry flat-bottomed flasks of 250 ml. Then, the prepared aqueous solutions of organic matter (phenol) of different concentrations (100 ml) are added to the flask. The flasks are tightly sealed, signed and shaken until an adsorption equilibrium is established (within 2 hours). After that, the coal is filtered and the residual (equilibrium) concentration of organic matter is determined in the filtrate. For the filtering, use a dry bulb.
Determination of the concentration of phenol in the solution after adsorption Determination of the concentration of phenol in water is carried out by the bromide-bromate method based on the bromination of phenol and the determination of excess bromine remaining after the reaction.
When brominated phenol runs the reaction:
C6H5OH + 3Br2 = C6H2Br3OH + 3HBr.
When bromination of phenol in acidic medium, a solution containing KBr and KBrO3 forms a white precipitate of tribromophenol.
To determine the bromine that has not reacted, crystalline potassium iodide is added to the solution. Bromine displaces potassium iodide from iodine, which is titrated with sodium thiosulfate in an acidic environment in the presence of starch:
Вr2 + 2 КІ = I2 + 2 КВr, І2 + 2 Nа2S2O3 = 2 NаІ + Nа2S4O6.
Method for determining phenol
Conical flasks with a capacity of 250 ml are selected for 25 ml of the studied solutions. All the flasks are pipetted with 10 ml of bromide-bromate solution and 5 ml of H2SO4 solution (1: 3), close the flasks with stoppers, shake and leave for 5 minutes.
To determine the bromine that has not reacted, add 1 g of potassium iodide to the flasks, close the cork and leave for 3 minutes. Titanium iodine titrate 0.1 N sodium thiosulfate solution in the presence of starch (5-6 drops) to bleach the solution. The starch is added to the solution before the titration is completed, when the titrated solution becomes light yellow.
Before performing the calculations, it is necessary to specify the concentration of bromide-bromate solution. To this end, add 10 cm3 of bromide- bromate solution and 5 ml of H2SO4 solution (1 : 3) into a conical flask of titration, close the flasks with cork, shake and titrate 0.1 N sodium thiosulfate solution in the presence of starch (5-6 drops) to bleach the solution. The starch is added to the solution before the titration is completed, when the titrated solution becomes light yellow.
Knowing the volume of titrant, its concentration and the volume of bromide- bromate solution determine its concentration and use the refined concentration in calculations.
Concentration of phenol is calculated by the formula:
Cp = (VBr – Vts)·Nts/(6·Vv), mmole / ml (4.5) where VBr is the volume of bromide-bromate solution taken for determination (10 ml);
Vts - volume of sodium thiosulfate solution, which was spent on titration, cm3;
Nts -concentration of sodium thiosulfate 0.1 mole / L;
Vv - volume of water sample, 25 ml;
6 is the equivalent of phenol.
Calculation of specific adsorption and filling adsorption volume of coal In particular, the adsorption of organic matter (a) is calculated by the ratio:
a = (C0 – Cр) · Vph / m, mmole / g, (4.6) where C0 and Cр - the concentration of organic matter in the solution before and after adsorption, respectively, mmole / ml;
Vph - volume of solution of phenol, adhered to coal smoke, ml;
m - weight of coal, g.
Table 4.2 – Experimental data С0,
mmole / ml Vts,
Ср, mmole / ml
m, g а, mmole / g
lgKa Ka Θ
0,001 0,002 0,003 0,004 0,005
The filling of the adsorption volume of coal with organic matter is calculated by the formula:
Θ = a·Vо.r./Vw. (4.7)
Experimental data are written in the form of table 4.2 and build on them an isotherm of adsorption, depositing on the axis of the ordinate the value of a, and on the abscissa the value of Cp.
Calculation of the adsorption equilibrium constant and magnitude –ΔFa0
To determine the adsorption equilibrium constant, the experimental data are presented in the form of graphical dependence: lgKa = f (Θ). In the logarithmic form, the adsorption isotherm represents a straight line. Extrapolating the straight line to the intersection of it with the ordinate axis, that is, in the region of standard conditions (Θ
→ 0), the ordinate gets a segment numerically equal to the value of lgKa.
The standard reduction of the differential molar free energy of adsorption of organic matter from aqueous solutions on activated charcoal is calculated from the ratio (4.3).
1. To carry out purification of sewage from phenol:
a) in a stationary (filtering) layer of sorbent;
b) in a device simulating a fluidized contact mode sorbent - cleared water.
2. Calculate the degree of water purification.
3. Measure the isotherm of adsorption of phenol from aqueous solutions on activated carbon KAD.
Output: Vo.r. = 0,089 ml / mmole; Vw = 0,25 mg / g; Uv = 0,018 ml / mmole. 4. To construct an isotherm of adsorption of phenol in the coordinates a = f (Cp).
5. Calculate the value -ΔFa0 of phenol.
1. Name the area of application of adsorption sewage treatment.
2. Characteristics and properties of adsorbents.
3. Name the main stages of the adsorption process.
4. On what factors depends sorption rate?
5. The main types of technological schemes of adsorption cleaning.
6. Principle of operation of adsorption cleaning machines.
7. What is the energy characteristic of the interaction of organic matter with a carbon adsorbent?
8. What is the specific adsorption of the substance, the adsorption volume of the adsorbent, the equilibrium concentration in the solution, the filling of the adsorption volume?
9. Give the equation of isotherms of adsorption of organic matter from aqueous solutions to a carbon adsorbent.
10. How is the standard reduction of the free energy of adsorption of organic matter from the aqueous solution from the experimental data?
11. Which of substances will be better adsorbed – alcohol (-ΔFa0 = 14 kJ / mole) or p-nitrophenol (-ΔFa0 = 22 kJ / mole)?
Laboratory work №5. Purification of waste water from chromium compounds
Purpose: to study existing methods of wastewater treatment of chromium compounds, to conduct a comparative description of reagent and physico-chemical methods of purification, to determine the degree of purification.
At the plants, waste water containing Cr (III) or Cr (VI) chromium compounds is formed. Sources of pollution are galvanic workshops of machine- building, metal-working, automobile, aviation factories, as well as paint shops of textile enterprises, leather, asbestos-cement, printing, chemical enterprises. As is
known, chromium compounds are toxic, in particular, Cr (VI) – MPC = 0.1 mg / dm3, MPC for Cr (III) – 0,5 mg / dm3. Therefore, methods for purifying
wastewater from Cr (VI) usually involve the transfer of Sr (VI) to Cr (III). There is a large variety of methods for purifying sewage from chromium compounds:
reagent (reduction), coagulation, separation, flotation, electrochemical, sorption, ion exchange, catalytic, and photochemical. At present, the most common reagent and ion-exchange methods. Methods of treatment of sewage from hexavalent chromium are based on its reduction to trivalent, followed by precipitation in the form of hydroxide in alkaline medium. As a reducing agent can be used: activated charcoal, ferrous sulfate (II), sodium hydrosulphite, sulfur oxide (IV), organic waste (eg newsprint), pyrite cobs and others. In practice, for the restoration of chromium, the most frequently used solutions are sodium hydrosulfite:
4Н2СrО4 + 6 NаНSО3 + З Н2SO4 = 2 Сr2(SO4)3 + 3 Nа2SO4 + 10 Н2О.
The reaction runs quickly at pH 3 - 4 and excess sulfate acid. To precipitate trivalent chromium, use alkaline reagents Sa (OH)2, NaOH and others (optimal pH value for precipitation 8 – 9.5):
Сr3+ + 3 ОН- = Сr(ОН)3.
Effective for the deposition of chromium is the use of a ferric sulfate reducer