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PHYSICAL-CHEMICAL BASE OF WATER ELECTROCONTIONTION TECHNOLOGY

The basic groups of the physical and chemical phenomena at electrocondition of water

1.   Electrical field and current distribution in the working chamber, which is filled with dispersion parking and purified water;

2.  Interaction between pollutants, which are contained in water, and materials of dispersion packing;

3. Interaction between electrical charges and molecules of water pollutants on                             electrodes and in next to electrode space 

     Scientific background based on the account of a complex of the electrochemical and physical processes occuring in working chambers of electroconditioners:

  • •coagulation in the electric field,
  • •convertible sorption,
  • •filtration,
  • •electrolysis,
  • •electroflotation, electrooxidation of substances
  • •reduction
  • •electrocatalytic heterogeneous and liquid phases processes
  • •restructurization of water in electric field

ELETCTROSORPTION

     The questions of electrocontrolled sorption of the substances belong to the major ones in the theory of water electric condition developed in the company “”ElectroEcoTechnologies”. The main point of the basic technology concept is that the most part of work on removal or neutralization of toxic admixtures in water is carried out with the help of electrical energy, which is served into the working chamber of electroconditioners with the help of electrodes. In this case, the active work is made on the surface of electrodes (electrolysis, anodic oxidation and cathodic restoration of substances), and in between electrode space. With the purpose of increasing the general efficiency of apparatuses, the total area of anodes and cathodes is chosen rather large, and between electrode space is chosen rather small. This space is filled with dispersion packing, which promotes coagulation and sorption of contamination on the packing surface, and as a result, the effects of water filtration are achieved in the space of a poured diaphragm.

     Thus, discussing the mechanisms of electrosorption apparatus "CASCADE" functioning, it is not out of place to consider consistently, and as a first independent approximation, three groups of the physical and physical-chemical phenomena:

А). An electrical field and current distribution in the working chamber, which is filled with dispersion parking and purified water;

Б). Interaction between pollutants, which are contained in water, and materials of dispersion packing;

В). Interaction between electrical charges and molecules of water pollutants on electrodes and in next to electrode space.

Fig. 1. Distribution of electrical field on the edges of two plate electrodes (black lines): blue lines – equipotential lines, red - stream-line, white – lines of equal field intensity (from left to right 0,9; 0,7; 0,5 and 0,3 rate from the value in the middle of the space between electrodes).

     А). In the simplest case, when the working chamber contains only two plate electrodes (parallel plates): the anode and cathode, and does not have any boundaries for electrical field, the picture of this field (distribution of power lines and equipotential lines of the field) is illustrated on Fig.1. 

     From Fig.1 it is obvious, that in this case the electrical field is not concentrated only in between electrode space (if there are not any special restrictions), but is extended up and down, and even in the «back» areas of the chamber. The same situation appears in the case of two co-axial cylindrical electrodes. In details, this task was solved in the corresponding chapters of electrostatics [29].

     Let us turn to the main quantitative laws of electrosorption at granular packing of different types, which are detailed considered in the scientific and technical literature [1-7, 11-13, 15-23, 25]. As it follows from theoretical researches, the electrosorption intensity and as a result, the water purification quality from corpuscular admixtures or from aggregated molecular-ionic admixtures (colloidal particles, macromolecules, ions, or molecules, associating with left sediments) is depended of a whole series of physical-chemical facts, such as:

1. Intensity of macroscopic electrical field in areas between electrodes and in another areas of working chamber of electrosorption apparatus ;

2. Local gradients of field intensity between granules of the packing;

3. Heterogeneous picture of hydrodynamic forces in packing volume;

4. Physical-chemical properties of materials of granular packing;

5. Speed of water flow, passing through the working chamber;

6. Effective height of packing layer;

7. Temperature, medium pH,

8. Initial concentrations of substances removed from water and ionic force (ionic concentration) of the medium;

9. Electro-biochemical properties of microbe cells contained in purified water.

10. Specific composite structure of components, polluting the given sample of water.

11. Microbe cells ability, contained in purified water, to change their surface charge, depending on concentration of microorganisms and intensity of an acting electrical field.

 

     It is obvious, that items 2 and 3 from the above list in many respects depend from size and form of packing granules, as well as they depend from item 4. Less obvious is the influence of item 9, which actually require a discovery of electro-biochemical mechanism of microbe cells adaptation to stress, as well as discovery of concentration effects of changing charges of microbe cells [8-10, 12, 28]. 

     Theoretical analyze of such multiple-factor picture, which reflects electrosorption process of water purification is extremely complicated due to its mathematical difficulties, connected with perception of results, represented in the strict analytical form. However, it is possible to get over such sort of difficulties, turning to experimental data. Thus, it is obvious, that for theoretical purposes of water purification, besides understanding theoretical bases, it is very important to accept experimental and known dependencies. That is why experimental material devoted to electrosorption is examined below (see. fig.4-10). Special attention was devoted to the methods of receiving the experimental data in connection with development of new electroengineering.  

     В). Many authors studied so-called electrode processes, electrocrystallization and electrocatalysis, occurring at direct interactions of electrodes with water solutions of different substance (see, [28, 29]). Now there is a rather complete representation of this group of phenomenon, as well as about processes of electricity carrying (conductivity) in water environment [13, 14], which complicate description and realization of any electrotechnologies. Let's emphasize, that due to processes of anode oxidation (taking away electrons of dissolved substances by anodes) such compounds as, nitrates, nitrites, cyanides, thiocyanates, mercaptans, sulphides and so on, are transformed and by that are neutralized. Due to cathode restoration (passing electrons from cathode to dissolved in water substances), ions of heavy and other metals, quite often polluting water, are deleted from water and are neutralized, passing them in the chemically inactive form.  

Influence of рН and sorbent surface.

     Besides electrical factors, which influence on keeping colloidal particles on packing granules due to polarization and effect of abrupt increasing of electrical field at sharp ends and sites with small radiuses of curvature, huge influence on sorption has surface condition, both particles of contamination and sorbent granules. Thus, hydrophobic surfaces, such as Teflon due to their specific entropic interactions avoid contacts with polar molecules and macro-particles and they prefer aliphatic compounds, such as oil. At the same time, polar molecules willingly interact with hydrophilic surfaces, but taking into account their charge. Value and sign of electrical charge strongly depend from value рН (acid-base balance) of solution. Value рН describes hydrogen ions concentration (protons, hydroxonium) in solution: small value рН corresponds to large concentrations of hydrogen ions (acid), and large value рН corresponds to small concentrations of protons (base). For neutral solutions рН=7. Many molecules, especially biomacromolecules are amphoteric ones; it means that they have properties of both acid and base. For example, the simplest from aminoacids –glycin, which is permanent component of proteins and microbe cells, ca exist in forms: +H3NCH2COOH (most acid form), +H3NCH2COO, H2NCH2COOH (neutral form) и H2NCH2COO(most base form). That is why, if one of such molecules is situated on a surface of protein molecule, protein cell or particle, this molecule will have positive charge at low value pH, negative charge at large value рН, and neutral at neutral value рН - (for glycin, for example, concentration of completely neutral form is 105 times less, than for bipolar form). Everything what is said above, allows to understand qualitatively the experimental results, which were obtained in electrocolumn due to purification process of model solutions of microbe cells (fig. 4) and protein pollution (fig. 5).

 

Fig. 4. Purification degree of water from cells of enteric bacillus at ferroceramics: Т 10 000 as function of рН. Green curves -intensity Е=3000 V/m, blue – without electrical field.
- clean ceramics
- slightly covered,
- greatly covered with polyvinylpyrrolidone.

 

Fig. 5. Purification degree of water from serum albumin at ferroceramics: Т 10 000 as function of рН. Green curves -intensity Е=3000 V/m, blue – without electrical field.
- clean ceramics
- slightly covered,
- greatly covered with polyvinylpyrrolidone.

     Great similarity is seen in keeping cells and proteins by ceramics in the electrical field. Elec-trical nature of the phenomenon is traced distinctly: keeping is less in the case of field absence and in the neighborhood of isoelectric points of protein molecules and cells. Surface modification of polyvinylpyrrolidone also decreases the effect, due to changing physical-chemical surface properties, but first of all because of shielding a field. Here it is essential to note, that technology of water purification on the base of «CASCADE» apparatus allows purposefully to change water рН (anolytes and catholytes), permitting to choose optimum modes of purification degree attain.

Fig. 6. Influence of water salinity at the efficiency of electrofiltration of microbe cells. ferrocera - mic s Т 4000, Е=2000 V/m, concentration
NaCl: - 0.01 m, - 0.05 М, - 0.1 m.

Fig. 2 . Electrical field distribution at the edges of alternating anodes and cathodes (black lines): blue lines - equipotential lines, red - stream-lines.

     Due to placing in the working chamber a multielectrode package (parallel plates or co-axial) the field becomes a regular one, without "back" areas, but with the vividly expressed peripheral dispersion of the field and, accordingly, with lowered intensity (see Fig. 2).  

     In the both cases, the field intensity at the electrode edges highly exceeds its value in the space between electrodes.  

     Analyzing the probable pictures of the electrical field distri-bution in working chambers of electrosorption apparatuses, it is possible to make a conclusion, that there is a real opportunity of using stratified, heterogeneous dispersion packing at various field intensities. That allows to simplify the apparatus design strongly and to extend their functional abilities. 

     The micro-particle electrosorption effects at dispersion packing, as theoretical analyze shows; fundamentally differ in the cases of powerfully and slightly polarizable materials. In the second case, it is more appropriate do not speak about electrically induced sorption of micro-particles on granules, but more likely to speak about effect of electrokeeping of micro-particles in certain spatial "traps" in the space between granules of the parking.  

     The difference, mentioned above, is illustrated by photomicrographs submitted on fig.3. The pictures of concentration of microbe cells of enteric bacillus (E.coli), which is a marker for definition of bacterial water pollution, next to packing granules differ significantly in the cases illustrated on fig.3. The case of powerfully polarizable particles of ferroceramic with dielectric permeability not less, than 10 000 is on the left photomicrography and the case of slightly polarizable particles of the porous glass with dielectric permeability not more, 3-5 is on the right one.



Fig. 3. Photomicrography on top (enlargement х 500, the intensity of electrical field is 3000 V/m, acts from left to right) illustrates the effect of considerable electrosorption of enteric bacillus cells on the granules of ferroceramics Т-10 000 (plant «Coulomb», Russia). Photomicrography below (the same conditions) illustrates considerably less dipolephoretic focusing of cells due to superposition of external electrical field on the granules of the porous glass, trademark "Bio-Glass-500" (firm “Pharmacia”, Sweden).

     Ions of molecules dissociated in water have great influence on the electrosorption, because they shield electrostatic long-range action. According to Debye-Hückel theory, as a first approximation, shielding degree increases with increasing of ion concentration of solu-tion, that for 1,1- electrolyte is proportional to salt concentration. It is evidently from fig. 6, where data of solution purification from cells E.coli on laboratory electrocolumn and different concentrations of NaCl are submitted. It is evident, that with increasing of the salt concentra-tion shielding increases too and the quality of clearing is worsened. Great influence on the purification degree has the value of acting electrical field, mate-rial, size of packing granules and other factors. That is why, it is impossible to formulate the simple recommendations about choosing packing materials and purification modes. Fig. 7


Fig. 7. Dependence purification degree of solution from cells according to packing material and intensity of electrical field.
Blue curves - Е=2000 V/m, brown - Е=1000 V/m, green- Е=500 V /m,
- ceramics Т 10 000, - sand.

 


Fig.8. Purification degree of suspension in dependence of the packing granules size. Ceramics Т 10 000, Е=2000 V/m,
- granule size 0,5 - 1,0 mm,
- granule size 1-2 mm.


     illustrates the general laws: sand packing are worse, than ferroceramics for keeping cells, but by increasing the electrical field (the truth is, that power inputs are increased simultaneously), it is possible to achieve quite good results. In spite of this, if cell concentration is small, what is common for real water supply sources, the usage of ferroceramics is preferable. 


Fig. 9. Dependence liquid purification degree from cells E.coli according to the time of treatment.
Packing – ceramics Т 10 000, E= 1000 V/m, Е=2000 V/m.

 


Fig. 10. Dependence liquid purification degree from cells E.coli according to the speed of pumping.
Packing – ceramics Т 10 000, E= 1000 V/m, Е=2000 V/m.

     In the case of waste water purification, which contain plenty of microbes cells the packing with low value of dielectric penetrability. Fig. 8 illustrates the influence of packing granule size on purification degree and allows to make a conclusion, that it is more advisable to use smaller packing, if cell concentration is small too. As in static experiments so and in dynamic experiments, the purification degree de-pends of the time of purification object being in contact with sorbent. These conclusions are confirmed by data given on fig. 9 and 10, which illustrate liquid purification from suspension cells in laboratory conditions, both for static conditions and for suspension pumping through column.

     Data, which were received during water purification from microbe cells, were represented above. During purification from other pollutants, which may be of mineral or organic nature, the general dependencies of purification degree from treatment conditions are retained, though, undoubtedly, they have their features. As it is impossible to display all of them, let us illustrate electrocolumn abilities of water purification from oil (fig. 11). Model oil-contained emulsions were pumping through electrocolumn with the effective height 70 cm. Purification up to values 0,3-1,1mg/l was realized according to inverse scheme, when electrical energy was fed to electrodes for packing regeneration. Final content of oil may be decreased less than 0,1 mg/l due to increasing of effective column length up to 150cm. 

Fig. 11. Water purification from oil.
1 – initial content of oil, 2 – after an electrocolumn. Gray – black oil,
yellow – diesel oil; more light – water salinity 0,6 mg/l, more dark – 1,5 g/l.

ELECTROCHRMICAL PROCESSES ON ELECTRODES OF CONDITIONERS, ACCOMPANYING PROCESSES OF ELECTROSOPTION

EXAMPLES OF ACCOMPANYING OXIDIZING PROCESSES ON ANODES OF ELEKTROCONDITIONERS

Destruction of methylate: СН3ОН + 2Н2О -6еСО32- + 8Н+
Destruction of carbamide: (NН2)2СО + Н2О - 6е →N2↑ + СО2↑ + 6Н+
Destruction of formaldehyde: НСНО + 2Н2О - 4еСО32- + 6Н+
Destruction of  phenol:
С6Н5ОН + 16ОН- -16еНО2ССН=СНСО2Н (цис) + 2СО2↑+ 5Н2О
Conversionof cyanides into cyanates: СN- + 2OH-- 2еСNО- + Н2O,
with further destruction of cyanates into gases and water:
2СNО-+ 4OН-- 6е→2СO2↑+ N2↑ + 2Н2O.

EXAMPLES OF REDUCTION PROCESSES ON CATHODES OF ELEKTROCONDITIONERS

Derivation of insoluble hydroxides of heavy metals:
Меn+ + nОН- → Ме(ОН)n
Direct catalytic reduction of metals:  Men++ еМе°,
(for instance, Нg2+ + 2е →2Нg;  Рb2+ + 2е → Рb)

DECREASING OF REDOX POTENTIAL OF WATER DUE TO ITS RESTRUCTURIZATION

Three  basic situations depending on value redox-potential  are distinguished for natural waters:

Oxidative

is characterized by values of Еh > + (100 - 150) mV, by presence of free radicals in water, аs well    number of elements in the highest form of their valence      (Fe3+, Mo6+, As5-, V5+, U6+, Sr4+, Cu2+, Pb2+). The situation is occured the most frequently  in surface water

Intermediate oxidative-reductive

is determined by value of Еh from 0 up to + 100 mV, unstable geochemical mode and  variable concentration of hydrogen sulphide and oxygen. In these conditions both weak oxidation and weak restoration of a lot of metals

Reductive

is characterized by values Еh <0. It is typical for underground waters, where there are metals of low degrees of valency (Fe2 +, Mn2 +, Mo4 +, V4 +, U4 +), and also hydrogen sulphide.

THE BASIC CONCLUSIONS FROM THE THEORETICAL ANALYSIS FOR PRACTICAL APPLICATION

  • •  ОRP of  internal medium of the human persons has negative values (app. from-100 up to-200 mV).
  • •  ОRP of potable (tap) water practically always has positive values (more often from +100 up to +400 mV.
  • •  Processing of water by electroconditioners " CASCADE" allows to reduce ОRP  to  biologically favourable values.
  • •  Use of the water after processing in electroconditioners "CASCADE " for drinking and water procedures is expedient to slow down processes of oxidizing destruction and premature senescence of an organism.

LIST OF MAIN LITERATURE

1.   Andreev, V.S. Potential, charge and passive electrical characteristics of a double layer on the boundary dielectric - solution.  – In book:  The problems of creating apparatuses for medical

laboratory researchers: Theses of reports on All-Union conference, part IУ. Leningrad, 1974,     p.5-17, [in Russian].

2.   Andreev, V.S. Automated biochemical analysis on the base of using of electrosorption systems, Medical engineering, 1984, №2, p.11-16, [in Russian].

3.   Andreev, V.S. Passive – electrode systems and their application in biotechnology. Thesis for a Doctor's degree, 1986,  [in Russian].

4.   Andreev, V.S.  Patent  of Russian Federation № 2077955 for invention «Method of liquid heterogeneous system division and device for its realization, 30.09.1994.

5.   Andreev, V.S., Patent  of Russian Federation № 2077594 for invention «Method of liquid purification and devices (versions) for its realization», 27.04.1995.

6.   Andreev, V.S.,  Patent  of Russian Federation № 2080302 for invention «Method of water purification from extrinsic inclusions», 10.02.1993.

7.  Andreev, V.S., European patent, «Method and device for separation of liquid heterogeneous systems», 28.03.1995 (request EP/PCT № 95915125.9-2313-DE95000453).

8.   Andreev, V.S., and others. Electroadaptation of microorganisms to negative impacts. Bioengineering,1986,1. p.41-47, [in Russian].

9.   Andreev, V.S., and others. Surface electrical charge of bacterial cultures in technological processes, Microbiology, 1987, №2, p.326-331, [in Russian].

10.  Andreev, V.S., Popov, V.G., Dronova, N.V. Electrobiochemical mechanism of microorganism adaptation to stress. Bioengineering, 1988, Т.4, N1. p. 32-36, [in Russian].

11.  Andreev, V.S., and others. Electpopolarization method of purification of bacterial and viral suspensions on sorbent «Cegnetel», Bioengineering, 1989, v.5, №4, p.479-484, [in Russian].

12.  Andreev, V.S., and Lukyanov, A.E. Concentration dependence of averaged space between particles in dispersed systems. Colloidal journal, 1989, v. 51, с. 748-750, [in Russian].

13.  Andreev, V.S. Conductometric methods and devices in biology and medicine. «Medicine» publish house, M, 1973, 335 p., [in Russian].

14.  Andreev, V.S., Popetchitelev, E.P. Laboratory devices for researchers in liquid environments. «Engineering industry» publish house, LD, 1981, p.312, [in Russian].

15.  Gvozdyak, P.I., Mogilevich, N.F., Nikonenko, V.U. Electrokeeping of microorganisms and biological molecules.  – Applied biochemistry and microbiology, 1977, 13, N 2, p. 295-298,  (in Russian).

16. Grebeniuk, V.D., Kurilenko, O.D., Duhin, S.S. and others. Electrofiltering of dispersions and electrical phenomenons.  - Colloidal journal, 1975, N 4, p.737-743, [in Russian].

17.  Duhin, S.S., Kurilenko, O.D., Grebenuk, V.D. Colloidal – chemical problems of dispersion electro- filtration. - Colloidal journal, 1975, N 5, p. 859-865, [in Russian].

18.  Duhin, S.S., Semenihin, N.M., Smirnov, O.V. Electrophoretic and dipolephoretic transportation of dispersed particles in heterogeneous electrical field during electrofiltration. - Electron treatment of materials, 1978, N 4, p. 7О-73, [in Russian].

19.  Duhin, S.S., Grebenuk, V.D., Strigak, N.P. and others. About correlation of electro-filtration and filtration processes.  - Colloidal journal, 1979, N 1, p. 13-18, [in Russian].

20.  Mushik, N.A., Shilov, V.N., Duhin, S.S. Criterion of fast reversible electrocoagulation. - Colloidal journal, 1979, N 4, с.7О9-715, [in Russian].

21.  Duhin, S.S., Deryagin, B.V. –Electrophoresis. M., Science, 1976. - 328 p., [in Russian].

22.  Kupchhik, M.P., Vorona, L.G., Bagal, I.G. Electrolyte part in the process of electrofiltration. - Colloidal journal, 1979, N 5, p. 1О13-1О16, [in Russian].

23.  Landau, L.D., Lifshits, E.M. Theoretical physics. V. VI. Hydrodynamics. M., " Science ", 1986, [in Russian].

24.  Leshenko, A.V., Korolenko, N.B., Bagal, I.G. and others. The influence of packing nature on electrofiltration process.  – Ukrainian chemical journal, 1978, N 1, p.34-38, [in Russian].

25.  Skorchelletty, V.V. Theoretical electrochemistry. «Chemistry» Publishing house, Leningrad, 1974, 568 p., [in Russian].

26.  Tomilov, A.P., Fioshin, M.Y., Smirnov, V.A. Electrochemical synthesis of organic substances. . «Chemistry» Publishing house, LD., 1976, [in Russian].

27.  Lukyanov A., Andreev V., Pozdyshev V. Influence of disperse phase concentration on character of Brownian motion of particles. Journal of Colloid and Interface Sciences, 1990, vol.137, №1, р. 111-119.

28.  Simoni K.  Theoretische Elektrotechnik. Ver Deutscscher Verlag der Wissenschaften. Berlin, 1964.

29.  Sommerfeld A. Elektrodynamik. Akademische Verlagsgesellschaft Geest & Portig K. -G. Leipzig, 1949.