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Treatment the sewage of production of pesticides during an electrolysis Print E-mail
03.09.2008

Treatment the sewage of production of pesticides during an electrolysis

Novikov O.N., Tzarik L. Ya.

 

Irkutsk state university, chemical faculty 664003, Irkutsk, K.Marx, 1

        THE SUMMARYBy the example of one of proof organic pollutants - a pirinex efficiency of chain freely radical oxidation is shown at an electrolysis. The output on a current up to 550 % confirms the chain mechanism of oxidation. During an electrolysis concentration of pollutants and toxicity of impurity is reduced. Toxicity of impurity is reduced faster then concentration of pollutants.

Key-words: the oxidative destruction of resistant organic compounds, the chain - radical oxidation, the electrolysis

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Existing biological clearing constructions are developed in the middle of XX century. They work on principles of biochemical oxidation. They are not capable to solve a task of full removal proof organic pollutants (pesticides). The decision of a problem is consists of in application more severe conditions of a destruction. Electrochemical (anodi) oxidation provides the big degree of clearing. It is even more effective chain the electrooxidations.It is distinguished from anodi oxidation by the mechanism of process The purpose of work is consist of studying of a chain oxidizing destruction during an electrolysis of water solutions of pesticides. These solutions is the model of sewage of chemical manufacture. Among methods of chemical synthesis anodi electrooxidation, as is known, occur at the presence of catalysts. In the literature, as is known, there are no data on a chain radical destruction of proof organic pollutants during an electrolysis. As model of the organic pollutant causing a parameter of the COD of sewage, we used a pirinex. This substance represents not ionic connection, toxic and heavy for extraction from sewage. Under normal conditions pesticide is not oxidized oxygen of air. Biochemical destruction of a pirinex goes extremely slowly. At hit the pirinex represents direct danger to fishes to water objects. This pesticide is accumulated in trophic circuits. Experimental part For studying process of a destruction at an electrolysis the stand has been made. It will consist of from: an electrochemical cell in volume of 650 ml, a set of electrodes (graphite, lead), an adjustable power unit, the voltmeter, the ampermeter. Parameters of process of oxidation: the area of each of electrodes of 100 sm2, a current from 1,5 up to 3 A, a voltage 11-14 V, =8-9 (initial), force of a current is possible up to a preset value chloride of sodium, a pH - 10 to % Ca (OH)2, submission of air by the microcompressor, not less than 1 l/min. The express test has been applied for definition of the contents of organic substance before oxidation - a method of determination of the COD in sewage [6]. The analysis of samples has been carried out by means of spectrometry of a nuclear magnetic resonance on a spectrometer “ Varian VXR-500S ” which allows to determine the relative contents of carbons of groups CHar, =, -, 2-, 3-in a-b-c - position to aromatic without preliminary preparation of samples. At performance of measurements of intensity of resonant signals on nucleus 13 on a spectrometer of a nuclear magnetic resonance the following operating mode is established:* Frequency of a resonance of nucleus 13 (125,8 MHz) for VXR-500S;* Width of scanning -30000 Hz;* Duration of a pulse - 90 with;* Time of a relaxation delay - 20 with; * A ratio signal / noise (S/N) not less than 200;* Carrying frequency of a spectrometer on frequency of atoms of carbon is established on the middle of a frequency interval of scanning;* Irradiating frequency (for suppression ) a spectrometer on frequency of atoms of carbon is established on the middle of a frequency interval of scanning;* The temperature in the gauge should be a constant equal 298 + 0,10. For calibration of the NUCLEAR MAGNETIC RESONANCE - 13 of a spectrometer as modelling connection used acetate of sodium in concentration of 5000 mg/l and 1000 mg /l. On the NUCLEAR MAGNETIC RESONANCE - 13 a spectrum of test of the experience 2 received at the presence of a reference point signals acetate - an ion on frequency and on ratio of intensity conterminous with theoretically designed spectrum of acetate of sodium take place. To 100 ml of a modelling solution with concentration of 22000 mg/l of the COD have added 7 ml 10 % (OH)2, 13 ml 10 % derivatives of chlorites of calcium, 100 ml of water, 15 ml of 1 % solution of derivatives of chloride of iron. It is made from individual chemical compounds according to structure and a preparation containing pirinex Combat. At a voltage of 14 V and a current 3,5 A processing conducted 75 minutes. During reaction the light yellow sediment drops out. After a filtration a filtrate is pure, the roiliness is absent. Test on the NUCLEAR MAGNETIC RESONANCE - 13 and the COD - EXPRESS Test method has been made. Concentration of the COD of 7600 mg/l, including hypochlorites, chlorates, the perchlorate, chlorine. In a spectrum of a nuclear magnetic resonance there are no signals of organic carbon (less than 300 mg/l). For comparison of concentration in the same conditions at time of accumulation of a signal 1,5 hours have been taken off a spectrum of acetate of sodium with concentration of 3000 mg/l in the same test (Fig. 3). In a spectrum signals of a reference point are shown only, at 26 p.p.m. and 176 p.p.m. The initial solution has COD 11200 mg/l, pH=7.8, DOX 2200 mg/l, TOC 4400 mg/l, the weighed substances of 1000 mg/l. After clearing COD of 7600 mg/l, pH=9.0, DOX less than 100 mg/l, TOC less than 300 mg/l, the weighed substances no more than 40 mg/l. A degree of clearing on TOC not less than 93 %. There is a superfluous amount of active chlorine.Discussion of results In a review data on presence of elements of the radical mechanism in reaction of anodi electrooxidation are resulted. Without participation of oxygen of air in chain process the oxidizing potential is exhausted. The essence of chain oxidation is consists of in formation of free radicals under action of an electric current. Chain radical processes of oxidation proceed at the presence of oxygen. Reaction is supported due to energy of chemical reaction of oxidation. For a radical destruction during an electrolysis concentration of an oxidizer should be sufficient for effective continuation of a kinetic circuit of oxidation. In this case process is effective. On high conversion efficiency of clearing is connected to quantity of an electricity (passed through a solution) under linear law. The factor of correlation makes size +0,96:

Ef=69,2+0,0034•F* (1),

 where Ef-efficiency (%), F* - quantity of the electricity passed through electrolit (A*c/g). The equation is applied for efficiency of oxidation more than 70%. In view of 100% of an output on a current we had been designed expenses of quantity of the electricity necessary for clearing of pollutants on the mechanism of anodi oxidation. This value has made 12866,7 A*c/g. Experimentally certain expenses of quantity of an electricity only in one experiment from eight were more than theoretically designed value. Updating of conditions of carrying out of experiences has allowed us to lower these expenses up to 2336,8 A*c/g. In the best conditions required expenses of quantity of an electricity were in 5,5 times less theoretically designed. It confirms the chain, radical mechanism of oxidation during an electrolysis. Each electron elapsed through electrolit, promoted carry from two five electrons from molecules of organic substance, to oxygen of air. Without chain process it would be impossible. The greatest degree of clearing makes 99,6 %. Initial concentration of organic substance makes 12,7 g/l. After clearing water corresponds to ecological norms. We count the method effective. Introduction of the catalyst is necessary for additional generating free radicals. The role of the catalyst is consists of in formation of the ramified kinetic circuit and stimulation of reaction of radical disintegration a hydroperoxide and peroxids. In the conditions investigated by us influence of homogeneous catalysts (derivatives of iron, cobalt) is not determining. Speed of process is limited with concentration of an oxidizer. Probably, strong influence of the catalyst is shown only at much concentration. On 1 g of the catalyst it is necessary up to 56000 g of oxidized organic substance. The contents organic in a modelling solution made from 11,2 g/l up to 12,7 g/l. Specific expenses of the catalyst are economically justified and allowable. There was very essential an influence of composition salt, namely - presence sulfate - ions. Sulfates considerably accelerate process of oxidation. They raise its efficiency (on 40 %). Consumption of quantity of an electricity is twice reduced. Consumption of energy decreases up to 5,58 kWt*h/kg. The hypochlorite of calcium creates the strong - oxidizing medium and is participates in generation of free radicals. It is not enough its own oxidizing properties for oxidation of pollutants as it is capable to oxidize only easily oxidized impurity no more, than on 50 %. The increase in concentration of a hypochlorite of calcium does not result in increase in efficiency of process under the conditions investigated by us. Modelling solutions have been prepared on the basis of a pirinex, contained a significant amount of organic substances containing phosphorus. Chain radical process of oxidation possesses good reproducibility at presence difficultly oxidized organic containing phosphorus and chlorine of substances. Influence of time of processing on a ratio of the COD to the BOD has been investigated. The given parameter reflects a measure of toxicity of sewage. The ratio of the COD to the BOD considerably decreases. The destruction at an electrolysis reduces toxicity of sewage. Application of has investigated process in the industry will help to solve a problem of pollution by proof organic pollutants, recyclings of pesticides and organic compounds of chlorine. Efficiency of clearing grows with increase in quantity of the electricity missed through a solution. Such dependence shows prevailing influence of the chain mechanism at an electrolysis.

CONCLUSIONS:

1. By the example of a pirinex efficiency of chain freely radical oxidation is shown at an electrolysis.

2. The output on a current confirms the chain radical mechanism of oxidation at an electrolysis.

3. With increase of quantity of the electricity passed through a solution effect of clearing is increases.

4. Processing by an electrolysis of modelling sewage is reduces their toxicity twice.

5. Expenses of the electric power and the catalyst are insignificant also chain radical oxidation at an electrolysis it is possible to use as an economic way of sewage treatment.

 

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