RU2058266C1 - Method of mineralized phenol-bearing waste waters purification - Google Patents

Abstract

FIELD: waters purification. SUBSTANCE: waste waters are oxidized in anode chamber of diaphragm electrolyzer under vacuum and temperature of 70 - 75 C and feeding of purified water into cathode chamber. Removed from anode chamber air-gas mixture is treated in absorbers and catholite and anolyte are mixed and produced mixture is treated in absorbing filters with activated charcoal. Oxidation process is exercised under ratio of anolyte and catholyte usage of (0.85 - 0.88) : (0.12 - 0.16) and pH in anode chamber of 6.0 - 6.5. As purifying water for feeding into cathode chamber they use part of water, that is removed from adsorbing filters. Produced catholyte is partially used as absorbent during treatment of air-gas mixture and partially - for regeneration of activated charcoal in adsorbing filters. EFFECT: increased quality of purification. 5 cl dwg, 1 tbl

Description

 The invention relates to methods for purifying mineralized wastewater from organic compounds and in particular phenols and can be used in the treatment of geothermal effluents, industrial effluents, as well as associated water from oil fields. The discharged geothermal waters are characterized by a high salinity of sodium chloride and a high content of hardly oxidizable organic substances, for example phenols: oxybenzene, o-cresol, mp-cresol, xylenol, and the presence of polyhydric phenols is also possible.

A known method of wastewater treatment from organic compounds (phenols) in an electrolytic cell with insoluble titanium anodes with a surface active layer of a mixture of rutonium and titanium oxides in the presence of Cl ^- ions in a concentration of 1-9 g / l at an anode current density of i 1-2 A / dm ² [1] As a result of electrochemical treatment, phenols can undergo a complete destructive oxidation with the formation of carbon dioxide, water, nitrogen and other gaseous products. The transition to non-toxic compounds occurs as a result of destruction at the anode, as well as due to oxidation by sodium hypochlorite, resulting from electrolysis of treated water containing Cl ^- ions. During electrochemical oxidation, phenol degradation processes proceed more vigorously, since oxidizing agents under these conditions have increased activity.

Wastewater treatment by this method is associated with the need for a certain stoichiometric relationship between the concentration of oxidizing agent and oxidizable substance, as well as a significant excess of active chlorine for the complete destruction of phenols. This requires a special dechlorination process. In addition, during the interaction of certain phenol fractions with active chlorine, chlorphenol ClC ₆ H ₄ OH (MPC 0.0004 mg / L) can be formed, the maximum permissible concentration, which is an order of magnitude lower than phenol.

 To restore the absorption capacity of sorbents, destructive methods based on the complete oxidation of adsorbed substances and recuperative methods, accompanied by extraction of adsorbed products, are used. However, methods of destructive regeneration require large capital investments and energy costs, and methods of regenerative regeneration are associated with the problem of disposal of large volumes of regeneration products.

 The closest in technical essence to the claimed invention is an oxidation-sorption method for purifying water from tastes and odors of a phenolic nature [2] The method is a combination of preliminary oxidation of contaminants with chlorine and further filtering through a layer of activated carbon. With this treatment of water, there is not a simple summation of the effects of oxidation and sorption, but more complex processes. According to the theory put forward by A.M. Koganovsky, the products of the interaction of phenol with chlorine are better sorbed by active carbon than phenol itself. On the other hand, coal acting as a catalyst accelerates the formation of these products and their oxidation.

 However, the following disadvantages are inherent in this method. Numerous studies have established that the phenols present in geothermal water (oxybenzene, o-cresol) are the most resistant to chlorine from the class of phenols, and it is these phenols that can form chlorphenol. In other words, non-compliance with the technical regulations of the cleaning process (violation of the stoichiometric ratio, excess of active chlorine, filtering rate through a coal charge, etc.) can lead to the breakthrough of organochlorine compounds through the filter charge. Practice shows that adherence to the process of servicing sewage treatment facilities by personnel is typical only for 20-30% of existing treatment facilities and is difficult to implement in practice.

 The purpose of the invention is to increase the efficiency and reliability of the waste geothermal water treatment process and to reduce sorbent consumption.

 The claimed invention is aimed at solving the problem of environmental protection during the operation of geothermal circulating systems (GCC), in which in some cases there are situations in which the discharge of heat energy water containing toxic ingredients into water bodies of household and fishery water use is inevitable. Such situations can occur during the heating period with increasing discharge pressure and failure of pumping equipment and other reasons.

This goal is achieved by the fact that in the method of wastewater treatment with chlorine oxidation followed by sorption, a storage device (circulation channel, biological pond, etc.) is used as the first purification step, which can prevent volley discharge. Purification discharged geothermal water carried in the anode compartment of a diaphragm electrolysis under vacuum at a temperature of 70-75 ° ^C. The suggested method allows to prevent leakage of organochlorine compounds, phenols lower concentration in the cleaned stock is almost 100% and reduce 10-15 times consumption of activated charcoal.

Distinctive features of the method are:
treatment of geothermal water in the anode compartment of a diaphragm electrolysis under vacuum at 70-75 ^{° C;}
the ratio of the anolyte and catholyte costs (0.84-0.88) :( 0.12-0.16), in which a pH of 6-6.5 is reached in the anode chamber;
removal from the anode chamber with a vapor-air mixture of the most easily boiling, toxic, capable of forming organochlorine compounds and phenols that are difficult to oxidize with chlorine (oxybenzene, o-cresol, etc.);
supplying purified water to the cathode chamber in order to obtain an alkali solution for the absorber and AC regeneration.

According to the proposed method geothermal saline water (NaCl 20 g / l) containing phenols, are processed in the anode compartment of a diaphragm electrolytic flow type at a temperature of 70-75 ° ^C. When the water flows into the anode compartment under vacuum created by a vacuum pump, and gas bubbles released during electrolysis, boiling water occurs. The pH in the anode chamber drops to a value of 6-6.5. Thereby, optimal conditions are created for the isolation of the most toxic low-boiling phenol fractions with a vapor-air mixture: oxybenzene (PDK0.001 mg / L), o-cresol (MPC 0.004 mg / L). It is these phenols that are capable of forming chlorphenol ClC ₆ H ₄ OH (MPC 0.0004 mg / L) during chlorine oxidation. The destruction of phenol occurs directly on the anode in the anode chamber of the electrolyzer. The gas-air mixture containing H ₂ , Cl ₂ , C ₆ H ₅ OH is purified in absorbers where it is passed through a liquid layer (NaOH) with the formation of sodium hypochlorite and the oxidation of phenols in the contact tank. After the electrolytic cell, geothermal water contains Cl that is not released into the atmosphere and an insignificant part of non-volatile phenols (MPC 0.1-0.4 mg / L), which are destroyed more intensively by chlorine. The catalytic wastewater treatment takes place in adsorption filters with the loading of AC.

 The drawing shows a diagram explaining the proposed method.

 The operation scheme of the GCC system and the cleaning of the emergency discharge of mineralized geothermal water includes production 1 and injection 2 wells, a heat exchanger 15, an injection pump 3, a reservoir (circulation channel) 4, a settler 5, sand filters 6, a diaphragm electrolyzer 7, contact tanks 9, adsorption filters 10, a vacuum pump 11, an absorber 12, a container 13 for collecting an alkali solution with heating by geothermal water, a heat exchanger 14 for heating the discharged water, a mechanical aerator 16.

During normal operation of the HCC system during the heating period, geothermal water with t 95-100 ^о С from the production well 1 is supplied to the heat exchanger 15, heats the network water and is pumped by pump 3 into the injection well 2. When the injection pressure is increased, 3 part of the water to prevent damage to the pumping equipment and when the latter fail, the entire volume is collected in drive 4 (circulation channel, biopond, etc.) during the liquidation of the accident in the GVC system. The discharged geothermal waters go through the first purification stage in reservoirs 4, where the phenol concentration decreases due to its non-conservativeness according to the equation: C _t C _i · 10 ^-k i ^t (where k _{i is} the phenol non-conservative coefficient). 4 from the storage water flows into the sump 5 and 6 sand filters for the mechanical removal of suspended solids, and then to heat exchanger 14 where the geothermal water heated to a temperature of 70-75 ° ^C. Dale geothermal water is supplied to the anode compartment of a diaphragm electrolytic cell, wherein as a result of In order to create a vacuum and gas bubbles during electrolysis, water boils and the boiling fractions of phenol (oxybenzene and orthacresole), which form chlorophenol compounds ClC ₆ H ₄ OH, are removed. Waste gases containing Cl ₂ , H ₂ , C ₆ H ₅ OH and other volatile organic compounds are sent to the absorber 12, where they are absorbed by a solution of alkali NaOH. After the electrolyzer, water from the anode chamber with a pH of 6-6.5 and the cathode with a pH of 9-10 is mixed in a contact tank 9 with the formation of sodium hypochlorite. In the contact reservoir, an insignificant part of the remaining polyatomic phenols is oxidized, which do not form organochlorine compounds and are most easily oxidized by active chlorine.

After contact tank water temperature falls to 40 ^C. The catalytic aftertreatment water takes place in adsorbers 10 with loading UE. Purified water is discharged into a pond. Part of the purified water is sent to the cathode chamber of the electrolyzer 7, where alkali NaOH is formed, which is taken into the storage tank 13 and used as needed for the absorber 12 and regeneration of the adsorption filters 10. In the absorber 12 there is contact on the surface of the bubbles and jets that occur when passing gas-air mixtures through a liquid layer to form sodium hypochlorite, which oxidizes the absorbed phenols. Waste water from the absorbers can be discharged for re-treatment or disposed of.

PRI me R. Geothermal water containing Cl- in a concentration of 12 g / l and phenol in a concentration of 10-12 mg / l, was subjected to electrolysis in the anode compartment of a diaphragm electrolytic cell at a temperature of 70-75 ^C and a current density of 800 A / m ² under vacuum. The gas-air mixture from the electrolysis cell was passed through a vessel with an alkali solution (NaOH). The ratio of the treated water in the anode and cathode chamber was maintained at 0.85-0.15, while the pH value ranged from 6-6.5. The geothermal water that was processed in the anode and cathode chambers was mixed in an intermediate tank and fed to an adsorption column for additional treatment (filtering speed 10 m / h).

 The results of laboratory studies of the method for purification of mineralized geothermal waters from phenols are given in the table.

Processing geothermal water in the anode chamber of the diaphragm electrolyzer under vacuum at t 70-75 ^о С with post-treatment on filters with loading of AC allows you to:
increase the efficiency and reliability of the process and reduce the likelihood of the formation of organochlorine compounds;
to reduce the consumption of electricity and AC by 1 m ^{3 of} purified geothermal water;
create a virtually waste-free cycle of geothermal water treatment.

Claims (5)

1. METHOD FOR CLEANING MINERALIZED PHENOL-CONTAINING WASTE WATER, including its oxidation with chlorine and treatment with activated carbon followed by removal of purified water, characterized in that the oxidation is carried out in the anode chamber of the diaphragm electrolyzer in vacuum at 70 75 ^o C when fed to the cathode chamber treatment of the gas-air mixture removed from the anode chamber in absorbers and a mixture of anolyte and catholyte, the resulting mixture of which is then treated in adsorption filters with activated carbon, followed by guide its regeneration.  2. The method according to claim 1, characterized in that the oxidation in the cell is carried out at a ratio of the anolyte and catholyte costs 0.84 0.88 0.12 0.16 and the pH in the anode chamber is 6.0 6.5.  3. The method according to claim 1, characterized in that a portion of the water removed from the adsorption filters is used as purified water for supply to the cathode chamber.  4. The method according to claim 1, characterized in that the catholyte is partially used as an absorbent in the processing of a gas-air mixture.  5. The method according to claim 1, characterized in that the catholyte is partially used for regeneration of activated carbon in adsorption filters.

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