Electrocoagulation

Electrocoagulation (EC), aka radio frequency diathermy or short wave electrolysis, is a technique used for wash water treatment, wastewater treatment, industrial processed water, and medical treatment. Electrocoagulation has become a rapidly growing area of wastewater treatment due to its ability to remove contaminants that are generally more difficult to remove by filtration or chemical treatment systems, such as emulsified oil, total petroleum hydrocarbons, refractory organics, suspended solids, and heavy metals. There are many brands of electrocoagulation devices available and they can range in complexity from a simple anode and cathode to much more complex devices with control over electrode potentials, passivation, anode consumption, cell REDOX potentials as well as the introduction of ultrasonic sound, ultraviolet light and a range of gases and reactants to achieve so-called Advanced Oxidation Processes for refractory or recalcitrant organic substances.

Medical treatment

Electrocoagulation
MeSHD004564

A fine wire probe or other delivery mechanism is used to transmit radio waves to tissues near the probe. Molecules within the tissue are caused to vibrate which lead to a rapid increase of the temperature, causing coagulation of the proteins within the tissue, effectively killing the tissue. At higher powered applications, full desiccation of tissue is possible.

Water treatment

With the latest technologies, reduction of electricity requirements, and miniaturization of the needed power supplies, EC systems have now become affordable for water treatment plants and industrial processes worldwide.[1]

Background

Electrocoagulation ("electro", meaning to apply an electrical charge to water, and "coagulation", meaning the process of changing the particle surface charge, allowing suspended matter to form an agglomeration) is an advanced and economical water treatment technology. It effectively removes suspended solids to sub-micrometre levels, breaks emulsions such as oil and grease or latex, and oxidizes and eradicates heavy metals from water without the use of filters or the addition of separation chemicals [2]

A wide range of wastewater treatment techniques are known, which includes biological processes for nitrification, denitrification and phosphorus removal, as well as a range of physico-chemical processes that require chemical addition. The commonly used physico-chemical treatment processes are filtration, air stripping, ion exchange, chemical precipitation, chemical oxidation, carbon adsorption, ultrafiltration (UF), reverse osmosis (RO), electrodialysis, volatilization, and gas stripping.

Benefits

  • Mechanical Filtration addresses only two issues in wash rack wash water: suspended solids larger than 30 µm, and free oil and grease. Emulsified oil and grease cause damage to the media filters, resulting in very high maintenance costs. Electrocoagulation addresses any size of suspended solids (including destructive >30 µm particles and heavy metals that can wear-and-tear pressure washers and pose an environmental and employee hazard).
  • Chemical treatment addresses suspended solids, oil and grease, and some heavy metals—but may require up to three polymer and multiple pH adjustments for proper treatment. This technology requires the addition of chemicals resulting in expensive, messy, and labor-intensive treatment. This process also requires addition of compressed air for floatation of coagulated contaminants. Generally filtration is also required as a post-treatment phase for polishing. Electrocoagulation requires no filters, no daily maintenance, no additives, and removes any size of suspended solids, oil, grease and heavy metals.

Technology

Treatment of wastewater and wash water by EC has been practiced for most of the 20th century with increasing popularity. In the last decade, this technology has been increasingly used in the United States, South America and Europe for treatment of industrial wastewater containing metals.[3] 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. A large one-thousand gallon per minute cooling tower application in El Paso, Texas illustrates electrocoagulations growing recognition and acceptance to the industrial community. In addition, EC has been applied to treat water containing foodstuff waste, oil wastes, dyes, output from public transit and marinas, wash water, ink, suspended particles, chemical and mechanical polishing waste, organic matter from landfill leachates, defluorination of water, synthetic detergent effluents, and solutions containing heavy metals.[4][5]

Coagulation process

Coagulation is one of the most important physio-chemical reactions used in water treatment. Ions (heavy metals) and colloids (organic and inorganic) are mostly held in solution by electrical charges. The addition of ions with opposite charges destabilizes the colloids, allowing them to coagulate. Coagulation can be achieved by a chemical coagulant or by electrical methods. Alum [Al2(SO4)3.18H2O] is such a chemical substance, which has been widely used for ages for wastewater treatment.

The mechanism of coagulation has been the subject of continual review. It is generally accepted that coagulation is brought about primarily by the reduction of the net surface charge to a point where the colloidal particles, previously stabilized by electrostatic repulsion, can approach closely enough for van der Waals forces to hold them together and allow aggregation. The reduction of the surface charge is a consequence of the decrease of the repulsive potential of the electrical double layer by the presence of an electrolyte having opposite charge. In the EC process, the coagulant is generated in situ by electrolytic oxidation of an appropriate anode material. In this process, charged ionic species—metals or otherwise—are removed from wastewater by allowing it to react with an ion having an opposite charge, or with floc of metallic hydroxides generated within the effluent.

Electrocoagulation offers an alternative to the use of metal salts or polymers and polyelectrolyte addition for breaking stable emulsions and suspensions. The technology removes metals, colloidal solids and particles, and soluble inorganic pollutants from aqueous media by introducing highly charged polymeric metal hydroxide species. These species neutralize the electrostatic charges on suspended solids and oil droplets to facilitate agglomeration or coagulation and resultant separation from the aqueous phase. The treatment prompts the precipitation of certain metals and salts.

"Chemical coagulation has been used for decades to destabilize suspensions and to effect precipitation of soluble metals species, as well as other inorganic species from aqueous streams, thereby permitting their removal through sedimentation or filtration. Alum, lime and/or polymers have been the chemical coagulants used. These processes, however, tend to generate large volumes of sludge with high bound water content that can be slow to filter and difficult to dewater. These treatment processes also tend to increase the total dissolved solids (TDS) content of the effluent, making it unacceptable for reuse within industrial applications."[6]

"Although the electrocoagulation mechanism resembles chemical coagulation in that the cationic species are responsible for the neutralization of surface charges, the characteristics of the electrocoagulated flock differ dramatically from those generated by chemical coagulation. An electrocogulated flock tends to contain less bound water, is more shear resistant and is more readily filterable" [7]

Description

In its simplest form, an electrocoagulation reactor is made up of an electrolytic cell with one anode and one cathode. When connected to an external power source, the anode material will electrochemically corrode due to oxidation, while the cathode will be subjected to passivation.

An EC system essentially consists of pairs of conductive metal plates in parallel, which act as monopolar electrodes. It furthermore requires a direct current power source, a resistance box to regulate the current density and a multimeter to read the current values. The conductive metal plates are commonly known as "sacrificial electrodes." The sacrificial anode lowers the dissolution potential of the anode and minimizes the passivation of the cathode. The sacrificial anodes and cathodes can be of the same or of different materials.

The arrangement of monopolar electrodes with cells in series is electrically similar to a single cell with many electrodes and interconnections. In series cell arrangement, a higher potential difference is required for a given current to flow because the cells connected in series have higher resistance. The same current would, however, flow through all the electrodes. On the other hand, in parallel or bipolar arrangement the electric current is divided between all the electrodes in relation to the resistance of the individual cells, and each face on the electrode has a different polarity.

During electrolysis, the positive side undergoes anodic reactions, while on the negative side, cathodic reactions are encountered. Consumable metal plates, such as iron or aluminum, are usually used as sacrificial electrodes to continuously produce ions in the water. The released ions neutralize the charges of the particles and thereby initiate coagulation. The released ions remove undesirable contaminants either by chemical reaction and precipitation, or by causing the colloidal materials to coalesce, which can then be removed by flotation. In addition, as water containing colloidal particulates, oils, or other contaminants move through the applied electric field, there may be ionization, electrolysis, hydrolysis, and free-radical formation which can alter the physical and chemical properties of water and contaminants. As a result, the reactive and excited state causes contaminants to be released from the water and destroyed or made less soluble.

It is important to note that electrocoagulation technology cannot remove infinitely soluble matter. Therefore ions with molecular weights smaller than Ca+2 or Mg+2 cannot be dissociated from the aqueous medium.

Reactions within the electrocoagulation reactor

Within the electrocoagulation reactor, several distinct electrochemical reactions are produced independently. These are:

  • Seeding, resulting from the anode reduction of metal ions that become new centers for larger, stable, insoluble complexes that precipitate as complex metal ions.
  • Emulsion Breaking, resulting from the oxygen and hydrogen ions that bond into the water receptor sites of emulsified oil molecules creating a water-insoluble complex separating water from oil, driller's mud, dyes, inks and fatty acids etc.
  • Halogen Complexing, as the metal ions bind themselves to chlorines in a chlorinated hydrocarbon molecule resulting in a large insoluble complex separating water from pesticides, herbicides, chlorinated PCBs, etc.
  • Bleaching by the oxygen ions produced in the reaction chamber oxidizes dyes, cyanides, bacteria, viruses, biohazards, etc. Electron flooding of electrodes forced ions to be formed to carry charge into the water, thereby eliminating the polar effect of the water complex, allowing colloidal materials to precipitate and the current controlled ion transport between the electrodes creates an osmotic pressure that typically ruptures bacteria, cysts, and viruses.
  • Oxidation Reduction reactions are forced to their natural end point within the reaction tank which speeds up the natural process of nature that occurs in wet chemistry, where concentration gradients and Solubility Products (KsP) are the chief determinants to enable reactions to reach stoichiometric completion.
  • Electrocoagulation Induced pH swings toward neutral.

Optimizing reactions

Careful selection of the reaction tank material is essential along with control of the current, flow rate and pH. Electrodes can be made of iron, aluminum, titanium, graphite or other materials, depending upon the wastewater to be treated and the contaminants to be removed. Temperature and pressure appear to have only a minor effect on the process.

In the EC process the water-contaminant mixture separates into a floating layer, a mineral-rich flocculated sediment, and clear water. The floating layer is generally removed by means of an overflow weir or similar removal method. The aggregated flocculent mass settles either in the reaction vessel or in subsequent settling tanks due to gravitational force.

Following removal to a sludge collection tank, it is typically dewatered to a semi-dry cake using a mechanical screw press. The clear, treated (supernatant) water is typically then pumped to a buffer tank for later disposal and/or reuse in the plant’s designated process.

Advantages

  • EC requires simple equipment and is easy to operate with sufficient operational latitude to handle most problems encountered on running.
  • Wastewater treated by EC gives palatable, clear, colorless and odorless water.
  • Sludge formed by EC tends to be readily settable and easy to de-water, compared to conventional alum or ferric hydroxide sludges, because the mainly metallic oxides/hydroxides have no residual charge.
  • Flocs formed by EC are similar to chemical floc, except that EC floc tends to be much larger, contains less bound water, is acid-resistant and more stable, and therefore, can be separated faster by filtration.[8]
  • EC can produce effluent with less TDS content as compared with chemical treatments, particularly if the metal ions can be precipitated as either hydroxides or carbonates (such as magnesium and calcium. EC generally has little if any impact on sodium and potassium ions in solution.
  • The EC process has the advantage of removing the smallest colloidal particles, because the applied electric field neutralises any residual charge, thereby facilitating the coagulation.[9]
  • The EC process generally avoids excessive use of chemicals and so there is reduced requirement to neutralize excess chemicals and less possibility of secondary pollution caused by chemical substances added at high concentration as when chemical coagulation of wastewater is used.
  • The gas bubbles produced during electrolysis can conveniently carry the pollutant components to the top of the solution where it can be more easily concentrated, collected and removed by a motorised skimmer.
  • The electrolytic processes in the EC cell are controlled electrically and with no moving parts, thus requiring less maintenance.
  • Dosing incoming waste water with sodium hypochlorite assists reduction of biochemical oxygen demand (BOD) and consequent chemical oxygen demand (COD) although this should be avoided for wastewater containing high levels of organic compounds or dissolved ammonia (NH4+) due to formation of trihalogenated methanes (THMs) or other chlorinated organics. Sodium hypochlorite can be generated electrolytically in an E cell using platinum and similar inert electrodes or by using external electrochlorinators.[10]
  • Due to the excellent EC removal of suspended solids and the simplicity of the EC operation, tests conducted for the U.S. Office of Naval Research concluded that the most promising application of EC in a membrane system was found to be as pretreatment to a multi-membrane system of UF/RO or microfiltration/reverse osmosis (MF/RO). In this function the EC provides protection of the low-pressure membrane that is more general than that provided by chemical coagulation and more effective. EC is very effective at removing a number of membrane fouling species (such as silica, alkaline earth metal hydroxides and transition group metals) as well as removing many species that chemical coagulation alone cannot remove. (see Refractory Organics)

See also

References

  1. ^ OilTrap Environmental Products, Tumwater, WA. "Wash Water Treatment System." Archived 2011-12-27 at the Wayback Machine Accessed 2012-12-05.
  2. ^ Noling, Calvin (2004-07-01). "New Electrocoagulation System Addresses Challenges of Industrial Storm, Wash Water." WaterWorld. PennWell Corporation.
  3. ^ Rodriguez J, Stopić S, Krause G, Friedrich B (2007). "Feasibility Assessment of Electrocoagulation Towards a New Sustainable Wastewater Treatment." Environmental Science and Pollution Research 14 (7), pp. 477–482.
  4. ^ Lai, C. L., Lin, S. H. 2003. "Treatment of chemical mechanical polishing wastewater by electrocoagulation: system performances and sludge settling characteristics." Chemosphere 54 (3), January 2004, pp. 235-242.
  5. ^ Al-Shannag, Mohammad; Al-Qodah, Zakaria; Bani-Melhem, Khalid; Qtaishat, Mohammed Rasool; Alkasrawi, Malek (January 2015). "Heavy metal ions removal from metal plating wastewater using electrocoagulation: Kinetic study and process performance". Chemical Engineering Journal. 260: 749–756. doi:10.1016/j.cej.2014.09.035.
  6. ^ Benefield, Larry D.; Judkins, Joseph F.; Weand, Barron L. (1982). Process Chemistry for Water and Wastewater Treatment. Englewood Cliffs, NJ: Prentice-Hall. p. 212. ISBN 978-0-13-722975-8.
  7. ^ Woytowich, David L.; Dalrymple, C.W.; Britton, M.G. (Spring 1993). "Electrocoagulation (CURE) Treatment of Ship Bilge Water for the US Coast Guard in Alaska". Marine Technology Society Journal. 27 (1): 92. ISSN 0025-3324.
  8. ^ Al-Shannag, Mohammad; Bani-Melhem, Khalid; Al-Anber, Zaid; Al-Qodah, Zakaria (January 2013). "Enhancement of COD-Nutrients Removals and Filterability of Secondary Clarifier Municipal Wastewater Influent Using Electrocoagulation Technique". Separation Science and Technology. 48 (4): 673–680. doi:10.1080/01496395.2012.707729.
  9. ^ Al-Shannag, Mohammad; Bani-Melhem, Khalid; Al-Anber, Zaid; Al-Qodah, Zakaria (2013). "Enhancement of COD-Nutrients Removals and Filterability of Secondary Clarifier Municipal Wastewater Influent Using Electrocoagulation Technique". Separation Science and Technology. 48 (4): 673–680. doi:10.1080/01496395.2012.707729.
  10. ^ United States Bureau of Reclamation. Yuma, AZ. "Research Facilities and Test Equipment - Chemistry Research Units." Updated 2012-07-27.
Acid Blue 25

Acid Blue 25 (C20H13N2NaO5S) is an acid dye that is water-soluble and anionic and used for adsorption researches. The structure is an anthraquinone.

Arsenic contamination of groundwater

Arsenic contamination of groundwater is a form of groundwater pollution which is often due to naturally occurring high concentrations of arsenic in deeper levels of groundwater. It is a high-profile problem due to the use of deep tubewells for water supply in the Ganges Delta, causing serious arsenic poisoning to large numbers of people. A 2007 study found that over 137 million people in more than 70 countries are probably affected by arsenic poisoning of drinking water. The problem became serious health concern after mass poisoning of water in Bangladesh. Arsenic contamination of ground water is found in many countries throughout the world, including the US.Approximately 20 major incidents of groundwater floarsenic contamination have been reported. Of these, four major incidents occurred in Asia, in Thailand, Taiwan, and Mainland China. Locations of potentially hazardous wells have been mapped in China.

Catheter ablation

Catheter ablation is a procedure used to remove or terminate a faulty electrical pathway from sections of the hearts of those who are prone to developing cardiac arrhythmias such as atrial fibrillation, atrial flutter, supraventricular tachycardias (SVT) and Wolff-Parkinson-White syndrome (WPW syndrome). If not controlled, such arrhythmias increase the risk of ventricular fibrillation and sudden cardiac arrest. The ablation procedure can be classified by energy source: radiofrequency ablation and cryoablation.

Cauterization

Cauterization (or cauterisation, or cautery) is a medical practice or technique of burning a part of a body to remove or close off a part of it. It destroys some tissue in an attempt to mitigate bleeding and damage, remove an undesired growth, or minimize other potential medical harm, such as infections when antibiotics are unavailable.The practice was once widespread for treatment of wounds. Its utility before the advent of antibiotics was said to be effective at more than one level:

To prevent exsanguination

To close amputationsCautery was historically believed to prevent infection, but current research shows that cautery actually increases the risk for infection by causing more tissue damage and providing a more hospitable environment for bacterial growth.Actual cautery refers to the metal device, generally heated to a dull red glow, that a physician applies to produce blisters, to stop bleeding of a blood vessel, and for other similar purposes.The main forms of cauterization used today in the first world are electrocautery and chemical cautery—both are, for example, prevalent in the removal of unsightly warts and stopping nosebleeds. Cautery can also mean the branding of a human, either recreational or forced.

Coagulation (water treatment)

In water treatment, coagulation flocculation involves the addition of polymers that clump the small, destabilized particles together into larger aggregates so that they can be more easily separated from the water. Coagulation is a chemical process that involves neutralization of charge whereas flocculation is a physical process and does not involve neutralization of charge. The coagulation-flocculation process can be used as a preliminary or intermediary step between other water or wastewater treatment processes like filtration and sedimentation. Iron and aluminium salts are the most widely used coagulants but salts of other metals such as titanium and zirconium have been found to be highly effective as well.

Dieulafoy's lesion

Dieulafoy's lesion is a medical condition characterized by a large tortuous arteriole most commonly in the stomach wall (submucosal) that erodes and bleeds. It can present in any part of the gastrointestinal tract. It can cause gastric hemorrhage but is relatively uncommon. It is thought to cause less than 5% of all gastrointestinal bleeds in adults. It was named after French surgeon Paul Georges Dieulafoy, who described this condition in his paper "Exulceratio simplex: Leçons 1-3" in 1898. It is also called "caliber-persistent artery" or "aneurysm" of gastric vessels. However, unlike most other aneurysms, these are thought to be developmental malformations rather than degenerative changes.

Electrodesiccation and curettage

Electrodesiccation and curettage (EDC, ED & C, or ED+C) is a medical procedure commonly performed by dermatologists, surgeons and general practitioners for the treatment of basal cell cancers and squamous cell cancers of the skin. It provides desiccation, coagulation/cauterization, and curettage to remove lesions from the skin.

Electrology

Electrology is the practice of electrical hair removal to permanently remove human hair from the body. Electrolysis is the actual process of removing hair using electricity.

In electrolysis, a qualified professional called an electrologist slides a hair-thin, solid metal probe into each hair follicle without puncturing the skin (when inserted properly). Electricity is delivered to the follicle through the probe, which causes localized damage to the areas that generate hairs, either through the formation of caustic sodium hydroxide (the galvanic method), overheating (thermolysis), or both (the blend method).

Electrosurgery

Electrosurgery is the application of a high-frequency (radio frequency) alternating polarity, electrical current to biological tissue as a means to cut, coagulate, desiccate, or fulgurate tissue. (These terms are used in specific ways for this methodology—see below). Its benefits include the ability to make precise cuts with limited blood loss. Electrosurgical devices are frequently used during surgical operations helping to prevent blood loss in hospital operating rooms or in outpatient procedures.In electrosurgical procedures, the tissue is heated by an electric current. Although electrical devices that create a heated probe may be used for the cauterization of tissue in some applications, electrosurgery is refers to a different method than electrocautery. Electrocautery uses heat conduction from a probe heated to a high temperature by a direct electrical current (much in the manner of a soldering iron). This may be accomplished by direct current from dry-cells in a penlight-type device.

Electrosurgery, by contrast, uses radio frequency (RF) alternating current to heat the tissue by RF induced intracellular oscillation of ionized molecules that result in an elevation of intracellular temperature. When the intracellular temperature reaches 60 degrees C, instantaneous cell death occurs. If tissue is heated to 60–99 degrees C, the simultaneous processes of tissue desiccation (dehydration) and protein coagulation occur. If the intracellular temperature rapidly reaches 100 degrees C, the intracellular contents undergo a liquid to gas conversion, massive volumetric expansion, and resulting explosive vaporization.

Appropriately applied with electrosurgical forceps, desiccation and coagulation result in the occlusion of blood vessels and halting of bleeding. While the process is technically a process of electrocoagulation, the term "electrocautery" is sometimes loosely, nontechnically and incorrectly used to describe it. The process of vaporization can be used to ablate tissue targets, or, by linear extension, used to transect or cut tissue. While the processes of vaporization/ cutting and desiccation/coagulation are best accomplished with relatively low voltage, continuous or near continuous waveforms, the process of fulguration is performed with relatively high voltage modulated waveforms. Fulguration is a superficial type of coagulation, typically created by arcing modulated high voltage current to tissue that is rapidly desiccated and coagulated. The continued application of current to this highly impedant tissue results in resistive heating and the achievement of very high temperatures—enough to cause breakdown of the organic molecules to sugars and even carbon, thus the dark textures from carbonization of tissue.

Diathermy is used by some as a synonym for electrosurgery but in other contexts diathermy means dielectric heating, produced by rotation of molecular dipoles in a high frequency electromagnetic field. This effect is most widely used in microwave ovens or some tissue ablative devices which operate at gigahertz frequencies. Lower frequencies, allowing for deeper penetration, are used in industrial processes.

RF electrosurgery is commonly used in virtually all surgical disciplines including dermatological, gynecological, cardiac, plastic, ocular, spine, ENT, maxillofacial, orthopedic, urological, neuro- and general surgical procedures as well as certain dental procedures.

RF electrosurgery is performed using a RF electrosurgical generator (also referred to as an electrosurgical unit or ESU) and a handpiece including one or two electrodes—a monopolar or bipolar instrument. All RF electrosurgery is bipolar so the difference between monopolar and bipolar instruments is that monopolar instruments comprise only one electrode while bipolar instruments include both electrodes in their design.

The monopolar instrument called an "active electrode" when energized, requires the application of another monopolar instrument called a "dispersive electrode" elsewhere on the patient's body that functions to 'defocus' or disperse the RF current thereby preventing thermal injury to the underlying tissue. This dispersive electrode is frequently and mistakenly called a "ground pad" or "neutral electrode". However virtually all currently available RF electrosurgical systems are designed to function with isolated circuits—the dispersive electrode is directly attached to the ESU, not to "ground". The same electrical current is transmitted across both the dispersive electrode and the active electrode, so it is not "neutral". The term "return electrode" is also technically incorrect since alternating electrical currents refer to alternating polarity, a circumstance that results in bidirectional flow across both electrodes in the circuit.

Bipolar instruments generally are designed with two "active" electrodes, such as a forceps for sealing blood vessels. However, the bipolar instrument can be designed such that one electrode is dispersive. The main advantage of bipolar instruments is that the only part of the patient included in the circuit is that which is between the two electrodes, a circumstance that eliminates the risk of current diversion and related adverse events. However, except for those devices designed to function in fluid, it is difficult to vaporize or cut tissue with bipolar instruments.

Eugène-Louis Doyen

Eugène-Louis Doyen (December 16, 1859 – November 21, 1916) was a French surgeon born in Reims. He was the son of Octave Doyen (1831–1895), who served as mayor of Reims.

Eugène Doyen studied medicine in Reims and Paris, and later opened a private medical institute in Paris that attracted a wealthy clientele. Doyen was a skilled and innovative physician who introduced several surgical techniques and medical instruments, some of which bear his name today. He was a pioneer in the use of electrosurgery and electrocoagulation, and also marketed a yeast extract he called "mycolysine" for treatment of infectious diseases.

He had a keen interest in photography and cinematography, and performed early experiments of color film, microcinematography and stereoscopic film. He produced numerous films of operations, including a craniectomy, an abdominal hysterectomy, and a surgery for separation of conjoined twins Radhika and Dudhika Nayak, united in the area of the xiphoid process of the sternum. Although his films were popular at medical conferences abroad, they were harshly criticized by his contemporaries in France, who felt that the integrity of their profession had been compromised.

For a period of time, Doyen was editor-in-chief of the Revue Critique de Médecine et de Chirurgie, as well as the Archives de Doyen, a medico-surgical journal of the Doyen Institute.

History of electrochemistry

Electrochemistry, a branch of chemistry, went through several changes during its evolution from early principles related to magnets in the early 16th and 17th centuries, to complex theories involving conductivity, electric charge and mathematical methods. The term electrochemistry was used to describe electrical phenomena in the late 19th and 20th centuries. In recent decades, electrochemistry has become an area of current research, including research in batteries and fuel cells, preventing corrosion of metals, the use of electrochemical cells to remove refractory organics and similar contaminants in wastewater electrocoagulation and improving techniques in refining chemicals with electrolysis and electrophoresis.

Microbial desalination cell

A microbial desalination cell (MDC) is a biological electrochemical system that implements the use of electro-active bacteria to power desalination of water in situ, resourcing the natural anode and cathode gradient of the electro-active bacteria and thus creating an internal supercapacitor. Available water supply has become a worldwide endemic as only .3% of the earth's water supply is usable for human consumption, while over 99% is sequestered by oceans, glaciers, brackish waters, and biomass. Current applications in electrocoagulation, such as microbial desalination cells, are able to desalinate and sterilize formerly unavailable water to render it suitable for safe water supply. Microbial desalination cells stem from microbial fuel cells, deviating by no longer requiring the use of a mediatior and instead relying on the charged components of the internal sludge to power the desalination process. Microbial desalination cells therefore do not require additional bacteria to mediate the catabolism of the substrate during biofilm oxidation on the anodic side of the capacitor. MDCs and other bio-electrical systems are favored over reverse osmosis, nanofiltration and other desalination systems due to lower costs, energy and environmental impacts associated with bio-electrical systems.

Sediment control

A sediment control is a practice or device designed to keep eroded soil on a construction site, so that it does not wash off and cause water pollution to a nearby stream, river, lake, or sea. Sediment controls are usually employed together with erosion controls, which are designed to prevent or minimize erosion and thus reduce the need for sediment controls. Sediment controls are generally designed to be temporary measures, however, some can be used for storm water management purposes.

Sonoelectrochemistry

Sonoelectrochemistry is the application of ultrasound in electrochemistry. Like sonochemistry, sonoelectrochemistry was discovered in the early 20th century. The effects of power ultrasound on electrochemical systems and important electrochemical parameters were originally demonstrated by Moriguchi and then by Schmid and Ehert when the researchers investigated the influence of ultrasound on concentration polarisation, metal passivation and the production of electrolytic gases in aqueous solutions. In the late 1950s, Kolb and Nyborg showed that the electrochemical solution (or electroanalyte) hydrodynamics in an electrochemical cell was greatly increased in the presence of ultrasound and described this phenomenon as acoustic streaming. In 1959, Penn et al. demonstrated that sonication had a great effect on the electrode surface activity and electroanalyte species concentration profile throughout the solution. In the early 1960s, the electrochemist Allen J. Bard showed in controlled potential coulometry experiments that ultrasound significantly enhances mass transport of electrochemical species from the bulk solution to the electroactive surface.

In the range of ultrasonic frequencies [20 kHz – 2 MHz], ultrasound has been applied to many electrochemical systems, processes and areas of electrochemistry (to name but a few: electroplating, electrodeposition, electropolymerisation, electrocoagulation, organic electrosynthesis, materials electrochemistry, environmental electrochemistry, electroanalytical chemistry, hydrogen energy and fuel cell technology) both in academia and industry, as this technology offers several benefits over traditional technologies. The advantages are as follows: significant thinning of the diffusion layer thickness (δ) at the electrode surface; increase in electrodeposit/electroplating thickness; increase in electrochemical rates, yields and efficiencies; increase in electrodeposit porosity and hardness; increase in gas removal from electrochemical solutions; increase in electrode cleanliness and hence electrode surface activation; lowerering in electrode overpotentials (due to metal depassivation and gas bubble removal generated at the electrode surface induced by cavitation and acoustic streaming); and suppression in electrode fouling (depending on the ultrasonic frequency and power).

To date, over 3,500 publications inc. patents, technical, research and review articles have been written on the subject with the vast majority being published post-1990 after a review paper from Mason et al. entitled 'Sonoelectrochemistry' highlighting the extraordinary effects of sonication on enhancing mass transport, aiding solution degassing, improving electrode surface cleaning, producing radical species (via sonolysis) and increasing electrochemical products and yields.

Syringoma

Syringomas are harmless eccrine sweat duct tumors, typically found clustered on eyelids, although they may also be found in the armpits, abdomen, chest, neck, scalp or groin area including genitals in a symmetric pattern. They are skin-colored or yellowish firm, rounded bumps, 1–3 mm in diameter, and may be confused with xanthoma, milia, hidrocystoma, trichoepithelioma, and xanthelasma. They are more common in women and are most commonly found in middle-aged Asian women. While they can present at any time in life, they typically present during adolescence. They are usually not associated with any other symptoms although can sometimes cause itchiness or irritation.

Variable electro-precipitator

A variable electro-precipitator (VEP) is a waste water remediation unit using electrocoagulation. The differences between a standard electrocoagulation (EC) unit and a variable Electro-precipitation unit are in the enhanced flow path and the unit electrode connections. The variable electro-precipitator's flow path has been designed to maximize retention time and to increase the turbulence of the water within the unit. This design aids in increasing the amount of effective treatment per gallon of water.

A major design weakness of the electrocoagulation units is the method used in connecting the electrode to the power source. These designs cause overheating, resulting in premature failure of the electrocoagulation reaction chamber. VEP reaction chambers are designed to resolve these performance issues by changing all electrode connections from the standard wet connection (inside the chamber) to an external dry connection. The VEP is cooler-operating, and has a longer chamber life than an electrocoagulation unit.

Wastewater treatment

Wastewater treatment is a process used to remove contaminants from wastewater or sewage and convert it into an effluent that can be returned to the water cycle with minimum impact on the environment, or directly reused. The latter is called water reclamation because treated wastewater can then be used for other purposes. The treatment process takes place in a wastewater treatment plant (WWTP), often referred to as a Water Resource Recovery Facility (WRRF) or a sewage treatment plant. Pollutants in municipal wastewater (households and small industries) are removed or broken down.

The treatment of wastewater is part of the overarching field of sanitation. Sanitation also includes the management of human waste and solid waste as well as stormwater (drainage) management. By-products from wastewater treatment plants, such as screenings, grit and sewage sludge may also be treated in a wastewater treatment plant.

William Webster (chemical engineer)

William Webster (1855-1910) was an English chemical engineer credited with developments in gas detection, sewage treatment and medical use of x-rays. A gifted artist and musician, Webster also helped found the Blackheath Concert Halls and the adjacent Conservatoire in Blackheath in south-east London during the 1890s.

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.