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Electrochemical Activation (ECA) Technology
Water Purification System of the Future
Jim Daly M.D. PTA Ltd Discussion Document
Introduction
Water purity and sanitation are, to a large extent, taken for granted in North America and the developed world, although concerns about chlorination and organics in water have lead to a significant market for bottled water and secondary home water purification systems. In the less developed world, water quality is of constant concern, being a major vector for viruses, micro-organisms of public health concern and parasites which have and adverse effect on health and which tends to be a significant impediment to economic development. In the developed world, water quality concerns tend to be related to trace, but potentially toxic chemical impurities (e.g. pesticides, organic-chloride compounds, off flavours and water hardness), which are commonly addressed by activated carbon treatment, reverse osmosis and ion exchange techniques or combinations thereof. From the standpoint of microbial contamination, traditional chlorination and ozonolysis are effective large-scale water treatment processes used for production of potable water from central sources for municipalities and industries. Chlorination is under attack specifically to the formation of organo-chlorine compounds as well as the undesirable chlorinated flavour associated with chlorinated water. Ozonolysis is an effective water treatment which is gaining ground as a central water and waste treatment system and is effective in destroying both micro-organisms as well as organic compounds. Residential ozonolysis systems are available, but tend to be expensive, and the only other effective system which can be used at the residential is Ultraviolet (UV) radiation, which kill micro-organisms, but does not have an effect on chemical constituents present.
As such, there is no lack of effective water treatment systems being available, with large-scale systems usually focussing on microbial destruction, while residential systems focus on secondary treatment, usually removal of flavours, organics or reducing water hardness. The latter tend to use filtration/adsorption or ion exchange resin but are not effective in terms of sterilising water. Systems capable of carrying out all the desired water treatment operations either simultaneously or in sequence are very expensive and usually only available for large-scale water treatment operations.
In the developing world, water quality problems are exacerbated because water treatment infrastructure tends to be poorly and is generally unreliable in terms of delivering safe water to the public. As a result, there is a heavy reliance on bottled water and the attendant distribution inefficiencies associated with moving water around in five gallon or smaller containers, as well as its high cost. Many of these problems could be overcome if their were a simple and effective small scale water treatment device capable of taking water from sources (lakes, rivers, wells, cisterns) and treating it on site or in the home.
A New Development
Although the impetus for developing a simple and effective water treatment and purification systems has always been there, there are few situations where this need is imperative and absolute. One such situation where water purification becomes an absolute necessity has been in the space program. Astronauts have a limited water supply with which they can take with them, which in turn has to be continually purified and recycled for long missions. The Russian space program, which has focussed on long term orbital stays required that a continuous, efficient and reliable water recycling and purification system be developed. Their ability to keep the astronauts in space for up to one year, without fresh water replenishment, is testimony to the success of their electrochemical activation (ECA) based water purification system. This patented technology, which took some 20 years to develop, was successfully spun-off for civilian use in Russia and is now in the process of being commercialised in the rest of the world by Clean Technologies Associates Ltd. ECA has the potential to revolutionise basic water treatment technology and the technology is applicable to both industrial and residential water treatment .
Concept of Electrochemical Activation (ECA)
ECA( electro-chemical activation) of water involves the exposure of water and the natural salts therein or salts added to it, to a substantial electrical potential difference. If one places an anode(+) and a cathode(-) in pure water and applies a direct current, electrolysis of water occurs at the poles, leading to the breakdown of water into its constituent elements, producing gaseous oxygen and hydrogen. Electroplating is a similar process, where one adds chromium salts to water and applies a potential difference, the chromium plating out onto the material attached to the cathode. If sodium chloride (NaCl), or table salt, is used as a solution, the dominant electrolysis end product is hypochlorite, a chlorine based reagent which is commonly used to treat water to kill micro-organisms. The ECA process devised for the Russian space program is based on the latter reaction, however, the key innovation is the interposition of an ion-permeable membrane between the positive and negative electrodes as well as the design and materials used for the electrodes. The Russian electrochemical reactor separated by a patented zirconium oxide diaphragm (Figure 1). ( certain new designs use polymer membranes) The base solution used in this reactor is a 5% solution of NaCl, which is split into two channels, one running through the anode(+) chamber and the other through the cathode(-) chamber.
Figure 1 Schematic diagram of an electrochemical reactor, illustrating the migration and concentration of ions at the opposite poles in the reactor.
Salt, which is in solution in its ionised form (Na+ and Cl-), is exposed to a controlled electrical potential difference between the cathode and the anode. This potential difference causes the Na+ and Cl- ions to migrate toward the pole of opposite charge. The specially designed membrane, which separates the two chambers, allows the ions to pass unimpeded, but is largely impermeable to unionised water as well as organic molecules. The net result is an enrichment of chlorine ions in the anode chamber and sodium ions in the cathode chamber. Similarly, water is also ionised extensively and will also tend to migrate to the opposite pole.
H2 ® H+ + OH-
As high concentrations of Cl- and OH- without the compensation of Na+ and H+ build up on either side of the membrane, this unstable chemical state results in complex reactions which produces a metastable solution containing a wide variety of very reactive ions and free radicals. Some of the reactive ions and free radicals species formed in the anolyte chambers are given in Table 1.
|
|
Reactive Molecules |
Reactive Ions |
Reactive Free Radicals |
|
Anolyte |
O3 |
H+ |
HO· |
|
|
O2 |
H3O+ |
OH2· |
|
|
H2O2 |
OH- |
O2· |
|
|
ClO2 |
ClO- |
O· |
|
|
HClO |
|
ClO· |
|
|
Cl2 |
|
Cl· |
|
|
HCl |
|
O2· |
|
|
HClO3 |
|
ClO* |
|
Catholyte |
H2O2 |
|
O2· |
|
|
NaOH |
|
O2* |
|
|
H2 |
|
H3O2 |
Table 1 Reactive ions and free radicals formed in the anolyte and catholyte solutions by elecrochemical activation.
It is the formation of these complex chemical species which leads to describing the solutions formed as “electrochemically activated water”. Some of the more important reactive constituents formed include, hypochlorite (HClO), hydrogen peroxide (H2O2), ozone (O3), Chlorine (Cl2). and HClO3 Most of the compounds are formed in the anolyte chamber, they are acidic in nature and are very strong oxidising compounds; while the reactive species formed in the catholyte chamber tend to be basic and are strong reducing agents. As a result, the catholyte is acidic (pH~2.4-4), while the anolyte is basic (pH~10-12), relative to the neutral pH of the starting NaCl solution. Analogously, the anolyte and catholyte solutions develop opposing potentials, the anolyte having a redox potential of plus 1200mV, while the catholyte reaches a value of minus 1000mV, relative to a potential of plus 300-400mV for the starting NaCl solution. The redox potential can be considered a gross indicator of the indicator of the energy incorporated into the respective solutions, likened to the potential built up within thunder clouds relative to the ground, waiting to discharge if anything is available to react with, to neutralise the build-up charge. These concentrated and very reactive solutions can be used to treat water, the oxidative anolyte solution destroying micro-organisms and organic matter, while the catholyte is useful for precipitating metal ions. The solutions can maintain much of their activity for many months or even years, if mixed together in certain proportions, they can form a stable neutral product at pH 6.5 to 7.5 with a redox potential of 650mV . The sporacidal activity can be maintained for many weeks with the germicidal activity carrying on for months or years. This stability and activity is dependant upon the power density in use during production of the liquids.
The key difference between conventional electrolysis of NaCl solutions, which is a standard process used to produce hypochlorite for water disinfection, is that in the ECA process the ion selective membrane allows the concentration of ions which result in the formation of metastable ions and free radicals. Although similar take place in the conventional NaCl electrolyte process, most of the complex reactive species formed at the anode and cathode react with each other and neutralised immediately, hypochlorous acid being the dominant stable constituent formed. Not only are two reactive solutions formed in the ECA process, but the anolyte solution in particular has more oxidative microbial destruction power than chlorine based solutions when compared in terms of measurable Cl· present in solution. As a result, the anolyte has superior sterilising and disinfectant properties, since the reactive species present in the solution (Cl-, ozone, hydrogen peroxide, etc.) are more effective in destroying micro-organisms and organic molecules than chlorine alode. Organic molecules such as pesticides, tannins and phenols, which are of concern in terms of toxicity, colour and off-flavours are effectively oxidised. Chlorine, which is a key component of the anolyte solution, effectively chlorinates the water, however, because of the low redox potential of the added anolyte the formation of potentially toxic chlorinated hydrocarbons is minimised because the low redox potential of the solution does not favour their formation. As such, the anolyte is an effective means of eliminating organisms of public health concern (E.Coli, Cholera) from water, while simultaneously destroying organic constituents, which are commonly associated with off flavour and colour. The catholye, in turn does not have any sterilising properties, however, it is a useful in its own right, as the predominance of OH· ions and its reducing power combine effectively to precipitate metal ions out of solution. Hard water, which is typically characterised by high calcium (Ca++), magnesium (Mg++) and iron (Fe++) contents, is softened significantly by precipitating these ions out of solution as illustrated in the following reaction:
Me++ + 2OH- ® MeOH2
The electrochemical system described above, which produces electrochemically activated (ECA) water, is the basis for comprehensive and effective water treatment system which is capable of destroying micro-organisms of public health, oxidise dissolved organic compounds present in water as well as reduce water hardness. This basic system, designed as a “Suprox” unit is designed to produce bulk anolyte and catholyte solutions which can be added to or metered into bulk water for commercial applications (production of potable water for municipalities, food industry, etc.). In the Suprox unit, the electrodes and membrane are physically arranged in an annular fashion as illustrated in Figure 2, which represents a simplified cross-section of the flow-through electrolytic module (FEM). Later models in use use the same principle.
Figure 2 : Cross-sectional representation of the annular arrangement of the electrodes and membrane in the Suprox unit flow-through electrolytic module (FEM). The charge distribution is a simplified illustration of the concentration of charges, oxidising compounds being formed at the anode and reducing compounds being formed at the cathode.
The following figure, Figure 3, presents a generalised layout of a typical Suprox system illustrating its components as well and inputs and outputs. The unit uses a NaCl solution as its base reagent, which can be diluted to any desired concentration by metering in tap water. The more concentrated the salt solution being processed, the more reactive the products produced by the Suprox unit are. This solution is split into two streams, one passing through the anode chamber, the second passing through the cathode chamber. The relative amounts of anolyte and catholyte produced can be controlled via stopcocks, allowing the production of one solution to be favoured over the other, usually anolyte for when water sanitation is the objective or catholyte for controlling water hardness. [ This is a two product output design which is only one of many configurations available]
Figure 3. The general layout of the Suprox ECA system components
Typical commercial applications include the production of potable water, maintaining water quality in swimming pools and waste water treatment for the anolyte (with the control of water hardness being the main use of the catholyte in water applications where scale build up is a problem such as in boilers and steam generators). As such, ECA technology is a major advance in water treatment, combining the abilities of ozonation, chlorination and UV radiation as well as providing a means of treating organic compounds in water as well as water hardness.
Biocidal Action.
Suprox Sterilising solutions have a well proven track record in killing micro-organisms as diverse as spores like subtilis ver niger to MRSA the super bug found in hospitals. These solutions can be administered as neat or diluted blends. The exact mechanism by which the biocidal action operates is not yet fully understood. The fact is that the biocidal action can be quantified, is proven technology and looks impressive, giving Log 6 reductions in spores like subtilis ver niger in 30 secs . The breakdown of the cell wall of the micro organism is swift and violent ensuring that no immunity can be achieved . This sensitisation or weakening allows the chlorine to destroy the micro-organism. This is but one theory . The study of this remarkable biocide is being carried out by Clean Technologies as well as various Universities in Japan and the U.S.A.
The solutions produced particularly the neutral anolytes are benign in terms of fume , corrosion or effect on the skin of humans or animals. The solutions are oxidative but only mildly having quite a low chemical load. They are in this respect eco-friendly and present no problems to the environment.
Other biocides based on Chlorine are highly oxidative in their action and rely on this property to carry out the kill on bacteria and viruses. Suprox has a different way of killing. It is proven to be far more effective [ even on spores ! ] without the need for aggressive [ and some would say corrosive] oxidation reactions to achieve a kill efficiency. This is in essence what makes this remarkable biocidal solution a valuable tool in the fight against unhealthy micro-organisms.
Small Scale ECA Water Treatment using Emerald Technology
Although the Emerald approach to water purification is quite simple operationally, it requires monitoring, metering, dilution and, in general, careful control; all requirements not conductive to foolproof operation by the general public. By reconfiguring the Emerald system and adding some components, it is possible to continuously purify water by ECA as long as it has a reasonable degree of mineralisation (i.e., making use of the salts naturally present in the water source). Figure 4 presents a cross-sectional schematic diagram of the “Emerald” residential water purifier, illustrating its main components, the flow through electrolytic module (FEM), a reaction chamber and a chamber containing activated carbons and magnesium oxide catalyst.
Figure 4. The general layout of the Emerald continuous water purifying system,
designed to directly process small volumes of water (- 60 litres/hour).
The Emerald system makes use of the natural salts present in the source water (including NaCl, CaCl2, MgCl2, etc.) as its ion source, and as per the STEL system, these are attracted to their opposite poles though the membrane when power is applied. Although the salt levels are much lower (0.3-1.5g/L) than in the Suprox NaCl solution, ECA still takes place in a manner analogous to the Suprox unit. The objective here, however, is to sterilize the water passing through the system rather than making a concentrated solution for subsequent use. Again in the anolyte chamber Cl-, ozone, hydrogen peroxide and free radicals are produced as well as a reduction in pH, the strong oxidants chemically attacking any organic material in the water, including bacteria, viruses, and parasites. In order to allow these important reactions to continue and go to completion, the ECA anolyte flows through a residence chamber which has been incorporated into the Emerald system. After the residence chamber, the solution passes through a chamber containing activated carbon and a magnesium oxide catalyst, where any residual active oxidisers are broken down, a process which is accompanied by further oxidative reactions. The activated carbon serves to absorb any residual chlorine from the solution as well as neutral organic compounds.
The solution then proceeds to the catholytic chamber, where the water and its oxidized constituents are exposed to a high pH, reducing environment. Residual, active oxidising constituents are reduced and the acid pH of the anolyte is neutralized. If the source water is hard, the OH’ ions from the catholyte will react with metal common ions (Ca++, Mg++ etc.) as well as toxic heavy metals to precipitate them as hydroxides. At the conclusion of the process (i.e., one full pass through the system), the pH and redox potential of the finished water will be very similar to that of the starting water. Hence in the Emerald system, the ECA process is a closed loop, first providing an anolyte treatment followed by a catholyte treatment, which effectively destroys organic materials and bacteria present in the water. This then neutralises the solution, precipitating out metal and heavy metal ions if they are in high concentrations. The net result is purified water, free of micro-organisms, with acceptable levels of mineralisation and a pH (6.8) and redox potential (200-400 mV) within the range of “natural” water.
The Emerald purification system is designed for low volume processing of water for residential use, the typical capacity of such a system being about 60 litres/hour, which can be increased by increasing the number of FEM modules. This system if not only efficient in sanitizing and producing palatable, high quality water, but it is cost effective, simple and reliable. Operation only requires a power source (120 or 220V AC, DC battery or solar power) and a constant flow rate (~600 ml/in) of water delivery to the system when in operation. The appropriate flow rate can be delivered a static head provided by an elevated tank, the level of which is maintained by a float valve. The system has an estimated operational life of seven or more years, and is virtually maintenance free, only requiring intermittent backflushing with 4% acetic acid (vinegar) to remove alkali metal precipitates (scale) from the cathode, which can build up over time. Such systems are ideal for developing countries, where water quality is problematic, however, given the strong demand for secondary home water purification in North America and the Third World Emerald type systems could also find a ready market in the developed world.
Conclusion
Relative to most of the other water treatment technologies available at present (chlorination, ozonolysis, reverse osmosis, UV, ion exchange and absorbents/filtration), ECA technology is unique in that it addresses all of the common water treatment issues of concern simultaneously, microbial contamination, undesirable organic compounds and water hardness. The basic technology is available for both industrial (Suprox) and residential (Emerald) markets. The Suprox anolyte is suitable for the industrial production of potable water, waste water treatment, treating swimming pools and treating air conditioning system water (algae buildup, Legionnaire’s disease) to name but a few applications, while the catholyte is useful for controlling water hardness. The Suprox anolyte has also found important applications in the medical field, where it has been used directly to wash wounds, sterilize medical instruments and treat infections. It has also been used to extend the shelf life of fruits and vegetables, as well as meat products. The smaller scale Emerald systems are effective in the direct treatment of water for home use, having immense potential in the developing world, where water quality is of continual concern. Given the low cost, simplicity and convenience of the Emerald system, local water, even of poor quality, from rivers, wells and cisterns can be treated on demand to produce safe drinking water.
ECA water treatment is a major technological step forward and as it’s advantages become generally recognised, the demand for this technology will grow exponentially, not only in the underdeveloped world where it is badly needed, but also in the developed world, where water quality is perceived to be a concern.
Suprox is a Registered Trade Mark of Medipure Ltd
Jim Daly M.D. for Clean Technologies Associates Ltd Chester UK
