Electrocoagulation (EC) - Science and Applications
By Dr. Abe Beagles
May 2004
The Author is the President of Cal-Neva Water Quality Research Institute, Inc. in Newcastle, California.
Abstract
Although electrocoagulation is an evolving technology that is being effectively applied today for wastewater treatment, the paucity of scientific understanding of the complex chemical and physical processes involved is limiting future design and hindering progress in the mining and industrial sector of this country. The objective of this review and explanation is to explain the Haivala Targeted Water Fusion Technology and how it applies to already existing treatment process being used around the world and to bring the chemistry and physical processes involved into prespective.
1. Introduction
One of the major challenges facing mankind today is to provide clean water to a vast majority of the population around the world. The need for clean water is particularly critical in Third-World Countries. Rivers, canals, estuaries and other water-bodies are being constantly polluted due to indiscriminate discharge of industrial effluents as well as other anthropogenic activities and natural processes. In the latter, unknown geochemical processes have contaminated ground water with arsenic in many counties. Highly developed countries, such as the US, are also experiencing a critical need for wastewater cleaning because of an everincreasing population, urbanization and climatic changes. The reuse of wastwater has become an absolute necessity. There is, therefore, an urgent need to develop innovative, more effective and inexpensive techniques for treatment of wastewater. A wide range of wastewater treatment techniques are known which includes biological processes for nitrification, denitrification and phosphorous removal; as well as a range of physico-chemical processes that require chemical addition. The commonly used physico-chemical treatment processes are filtration, airstripping, ion-exchange, chemical precipitation, chemical oxidation, carbon adsorption, ultrafiltration, reverse osmosis, electrodialysis, volatililization and gas stripping. A host of very promising techniques based on electrochemical technology are being developed but are not yet to the commercial stage. One more process has been developed to the commercial stage and is being used in city wastewater treatment plants all over Europe and a few US cities have adopted parts of this technology. This process is known as the Harness Targeted Electric Water Fusion Technology or Electrocoagulation, we will refer to it as EC for simplicity in this review. One Man has patented this technology and to this day, the Finnish Scientist Erkki Haivala is the only man who really understands all of the processes that are occuring within the cells as they do their job. The scientific community has yet to understand this process and there has been very little consideration of the factors that influence the effective removal of ionic species, particularly metal ions, from wastewater by this technique. In the brief review, we wish to address these issues.
2. Technology
Treatment of wastewater by EC has been practiced for most of the 20th century with limited success and popularity. In the last decade, this technology has been increasingly used in South America and Europe for treatment of industiral wastewater containing metals. It has also been noted that in North America EC has been used primarily to treat wastewater from pulp and paper industries, mining and metal-processing industries. In addition, EC has been applied to treat water containing foodstuff waste, oil wastes, dyes, suspended particles, chemical and mechanical polishing waste, organic matter from landfull leachates, defluorination of water, synthetic detergent effluents, mine wastes and heavy metal containing solution.
8. Alternating Current Electrocoagulation (ACE)
The US EPA has applied ACE technology for remediation of aqueous waste streams at Superfund Sites all over the United States. The ACE separator consists of either a paralled electrode unit in which a series of vertically oriented aluminum electrodes form a series of monopolar electrolytic cells through which the effluent stream passes, or a fluidized bed unit with nonconductive cylinders equipped with nonconsumable metal electrodes between which a turbulent fluidized bed of aluminum pellets is maintained. Compressed air is introduced into the EC cell to maintain a turbulent fluidized bed and to enhance the aluminum dissolution efficiency by increasing the anodic surface area. The basic flow diagram for the ACE separator with fluidized bed of alumimum alloy pellets entrained between a series of noncomsumable metal electrodes is shown in Fig 3. As can be seen from Fig. 3, an AC electric field is applied to the aqueous strem as it flows through the unit. As a result, a low concentration of aluminum dissolves from the fluidized bed and neutralizes the charges on suspende or emulsified particles. Once the charge species are electrically neutraized, they tend to coagulate and separate from the aqueous phase. The treated water is then transferred to a product separator where the water and solid phases are removed separately for reuse, recycling, additional treatment or disposal.
Figure 3
In a recent publication, (D. Mills, Am. Water Works Association 92 (2000)), describes what he calls a new process for electrocoagulation which is another prototype cell of the Haivala process. He states, the unit is made up of a ladder series of electrolytic cells containing iron anodes and stainless-steel cathodes. The electrolytic cells are constructed in such a way that a norrow concentric gap is maintained between the central anode and the surrounding cathode. Wastewater is allowed to flow through the ladder of cell, by way of a labyrinth of holes in the cathodes. Application of a low-voltage DC source to the cells produces iron hydroxide flocculant. This is the method that Haivala uses when treating water that is laden with Arsenic or Cynaide
9. Conclusions
The fact that electrocoagulation is now being successfully applied to contanimated water around the world is testament to its potential which is yet to be fully realized here in the US. The Haivala cell has clearly preformed some of the more complex requirements needed to totallly remove a wide range of contaminents from water. Some of these are: Hydrogen evolution has been controlled by the size of the cathodic reaction area and the electrode overpotential of hydrogen evolution. At the same time an anode has been designed to carry out several fundamental processes at the highest possible efficiencies. These include a corrodable part, that supplies the polyvalent coagulant ions to the solution at the lowest overpotential, a part that is efficient as an lectro-oxidation catalyst to form charged organics by partial oxidation, and an oxygen evolution part, that generate the oxygen at the highest efficiency bit in controlled amounts. The latter has been achieved by limiting the oxygen evolution electrode area. Electro-oxidation catalysts are available for shallow oxidation. These may be achieved by composite electrodes or unique multi-electrode arrangements. In addition the presence of sacrificial surfactants at low concentration is helpful to improve the efficiency of the coagulation process and ad/absorption processes. In addition the ionic make up of the solution is adjustable for optimization of the processes involved.
不好意思,没有办法整理,只能这样发了
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neuqj
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呵呵，谢谢，我需要啊
2005-10-19 22:05:19
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littlebird_ren
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8. Alternating Current Electrocoagulation (ACE)
2005-08-28 16:03:28
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The US EPA has applied ACE technology for remediation of aqueous waste streams at Superfund Sites all over the United States. The ACE separator consists of either a paralled electrode unit in which a series of vertically oriented aluminum electrodes form a series of monopolar electrolytic cells through which the effluent stream passes, or a fluidized bed unit with nonconductive cylinders equipped with nonconsumable metal electrodes between which a turbulent fluidized bed of aluminum pellets is maintained. Compressed air is introduced into the EC cell to maintain a turbulent fluidized bed and to enhance the aluminum dissolution efficiency by increasing the anodic surface area. The basic flow diagram for the ACE separator with fluidized bed of alumimum alloy pellets entrained between a series of noncomsumable metal electrodes is shown in Fig 3. As can be seen from Fig. 3, an AC electric field is applied to the aqueous strem as it flows through the unit. As a result, a low concentration of aluminum dissolves from the fluidized bed and neutralizes the charges on suspende or emulsified particles. Once the charge species are electrically neutraized, they tend to coagulate and separate from the aqueous phase. The treated water is then transferred to a product separator where the water and solid phases are removed separately for reuse, recycling, additional treatment or disposal.
Figure 3
In a recent publication, (D. Mills, Am. Water Works Association 92 (2000)), describes what he calls a new process for electrocoagulation which is another prototype cell of the Haivala process. He states, the unit is made up of a ladder series of electrolytic cells containing iron anodes and stainless-steel cathodes. The electrolytic cells are constructed in such a way that a norrow concentric gap is maintained between the central anode and the surrounding cathode. Wastewater is allowed to flow through the ladder of cell, by way of a labyrinth of holes in the cathodes. Application of a low-voltage DC source to the cells produces iron hydroxide flocculant. This is the method that Haivala uses when treating water that is laden with Arsenic or Cynaide
9. Conclusions
The fact that electrocoagulation is now being successfully applied to contanimated water around the world is testament to its potential which is yet to be fully realized here in the US. The Haivala cell has clearly preformed some of the more complex requirements needed to totallly remove a wide range of contaminents from water. Some of these are: Hydrogen evolution has been controlled by the size of the cathodic reaction area and the electrode overpotential of hydrogen evolution. At the same time an anode has been designed to carry out several fundamental processes at the highest possible efficiencies. These include a corrodable part, that supplies the polyvalent coagulant ions to the solution at the lowest overpotential, a part that is efficient as an lectro-oxidation catalyst to form charged organics by partial oxidation, and an oxygen evolution part, that generate the oxygen at the highest efficiency bit in controlled amounts. The latter has been achieved by limiting the oxygen evolution electrode area. Electro-oxidation catalysts are available for shallow oxidation. These may be achieved by composite electrodes or unique multi-electrode arrangements. In addition the presence of sacrificial surfactants at low concentration is helpful to improve the efficiency of the coagulation process and ad/absorption processes. In addition the ionic make up of the solution is adjustable for optimization of the processes involved.
不好意思,没有办法整理,只能这样发了
文章原地址为:http://www.eco-web.com/
不知道大家有人使用吗?
回复 举报