Patent Publication Number: US-2015076002-A1

Title: Apparatus and method for treating aqueous solutions and contaminants therein

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application Ser. No. 61/898,090, filed Oct. 31, 2013, entitled “Apparatus and Method for Treating Aqueous Solutions and Contaminants Therein;” and U.S. Provisional Patent Application Ser. No. 61/930,827, filed Jan. 23, 2014, entitled “Apparatus and Method for Treating Aqueous Solutions and Contaminants Therein;” and is a Continuation-in-Part of U.S. patent application Ser. No. 14/177,314, filed Feb. 11, 2014, entitled “Apparatus and Method for Treating Aqueous Solutions and Contaminants Therein,” which claims priority to U.S. Provisional Patent Application Ser. No. 61/930,337 filed Jan. 22, 2014, 61/812,990 filed Apr. 17, 2013, 61/782,969 filed Mar. 14, 2013, and 61/763,336 filed Feb. 11, 2013; and is a Continuation-in-Part of U.S. patent application Ser. No. 14/035,993, filed Sep. 25, 2013, entitled “Apparatus and Method for Treating Aqueous Solutions and Contaminants Therein,” which is a Continuation application of U.S. patent application Ser. No. 13/769,741, filed Feb. 18, 2013, now U.S. Pat. No. 8,568,573, which is a Continuation application of U.S. patent application Ser. No. 13/544,721, filed Jul. 9, 2012, now U.S. Pat. No. 8,398,828, which claims priority to U.S. Provisional Patent Application Ser. No. 61/613,357, filed Mar. 20, 2012 and U.S. Provisional Patent Application Ser. No. 61/583,974, filed Jan. 6, 2012; and is a Continuation-in-Part of U.S. patent application Ser. No. 14/150,915, filed Jan. 9, 2014, entitled “Apparatus and Method for Treating Aqueous Solutions and Contaminants Therein,” which is a Continuation application of U.S. patent application Ser. No. 13/899,993, filed May 22, 2013, now U.S. Pat. No. 8,663,471, which is a Continuation application of U.S. patent application Ser. No. 13/796,310, filed Mar. 12, 2013, now U.S. Pat. No. 8,658,035, which is a Continuation application of U.S. patent application Ser. No. 13/689,089, filed Nov. 29, 2012, now U.S. Pat. No. 8,658,046, which claims priority to U.S. Provisional Patent Application Ser. No. 61/584,012, filed Jan. 6, 2012 and U.S. Provisional Patent Application Ser. No. 61/566,490, filed Dec. 2, 2011; each of which is hereby incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Aqueous solutions often contain one or more contaminants. Such aqueous solutions include, but are not limited to, hydraulic fracturing fluid, hydraulic fracturing backflow water, high-salinity solutions, groundwater, seawater, wastewater, drinking water, aquaculture (e.g., aquarium water and aquaculture water), ballast water, and textile industry dye waste water. Further information of example aqueous solutions follows. 
     Hydraulic fracturing fluid includes any fluid or solution utilized to stimulate or produce gas or petroleum, or any such fluid or solution after it is used for that purpose. 
     Groundwater includes water that occurs below the surface of the Earth, where it occupies spaces in soils or geologic strata. Groundwater may include water that supplies aquifers, wells and springs. 
     Wastewater may be any water that has been adversely affected in quality by effects, processes, and/or materials derived from human or non-human activities. For example, wastewater may be water used for washing, flushing, or in a manufacturing process, that contains waste products. Wastewater may further be sewage that is contaminated by feces, urine, bodily fluids and/or other domestic, municipal or industrial liquid waste products that is disposed of (e.g., via a pipe, sewer, or similar structure or infrastructure or via a cesspool emptier). Wastewater may originate from blackwater, cesspit leakage, septic tanks, sewage treatment, washing water (also referred to as “graywater”), rainfall, groundwater infiltrated into sewage, surplus manufactured liquids, road drainage, industrial site drainage, and storm drains, for example. 
     Drinking water includes water intended for supply, for example, to households, commerce and/or industry. Drinking water may include water drawn directly from a tap or faucet. Drinking water may further include sources of drinking water supplies such as, for example, surface water and groundwater. 
     Aquarium water includes, for example, freshwater, seawater, and saltwater used in water-filled enclosures in which fish or other aquatic plants and animals are kept or intended to be kept. Aquarium water may originate from aquariums of any size such as small home aquariums up to large aquariums (e.g., aquariums holding thousands to hundreds of thousands of gallons of water). 
     Aquaculture water is water used in the cultivation of aquatic organisms. Aquaculture water includes, for example, freshwater, seawater, and saltwater used in the cultivation of aquatic organisms. 
     Ballast water includes water, such as freshwater and seawater, held in tanks and cargo holds of ships to increase the stability and maneuverability during transit. Ballast water may also contain exotic species, alien species, invasive species, and/or nonindiginous species of organisms and plants, as well as sediments and contaminants. 
     A contaminant may be, for example, an organism, an organic chemical, an inorganic chemical, and/or combinations thereof. More specifically, “contaminant” may refer to any compound that is not naturally found in an aqueous solution. Contaminants may also include microorganisms that may be naturally found in an aqueous solution and may be considered safe at certain levels, but may present problems (e.g., disease and/or other health problems) at different levels. In other cases (e.g., in the case of ballast water), contaminants also include microorganisms that may be naturally found in the ballast water at its point of origin, but may be considered non-native or exotic species. Moreover, governmental agencies such as the United States Environmental Protection Agency, have established standards for contaminants in water. 
     A contaminant may include a material commonly found in hydraulic fracturing fluid before or after use. For example, the contaminant may be one or more of the following or combinations thereof: diluted acid (e.g., hydrochloric acid), a friction reducer (e.g., polyacrylamide), an antimicrobial agent (e.g., glutaraldehyde, ethanol, and/or methanol), scale inhibitor (e.g., ethylene glycol, alcohol, and sodium hydroxide), sodium and calcium salts, barium, oil, strontium, iron, heavy metals, soap, bacteria, etc. A contaminant may include a polymer to thicken or increase viscosity to improve recovery of oil. A contaminant may also include guar or guar gum, which is commonly used as a thickening agent in many applications in oil recovery, the energy field, and the food industry. 
     A contaminant may be an organism or a microorganism. The microorganism may be for example, a prokaryote, a eukaryote, and/or a virus. The prokaryote may be, for example, pathogenic prokaryotes and fecal coliform bacteria. Example prokaryotes may be  Escherichia, Brucella, Legionella , sulfate reducing bacteria, acid producing bacteria, Cholera bacteria, and combinations thereof. 
     Example eukaryotes may be a protist, a fungus, or an algae. Example protists (protozoans) may be  Giardia, Cryptosporidium , and combinations thereof. A eukaryote may also be a pathogenic eukaryote. Also contemplated within the disclosure are cysts of cyst-forming eukaryotes such as, for example,  Giardia.    
     A eukaryote may also include one or more disease vectors. A “disease vector” refers any agent (person, animal or microorganism) that carries and transmits an infectious pathogen into another living organism. Examples include, but are not limited to, an insect, nematode, or other organism that transmits an infectious agent. The life cycle of some invertebrates such as, for example, insects, includes time spent in water. Female mosquitoes, for example, lay their eggs in water. Other invertebrates such as, for example, nematodes, may deposit eggs in aqueous solutions. Cysts of invertebrates may also contaminate aqueous environments. Treatment of aqueous solutions in which a vector (e.g., disease vector) may reside may thus serve as a control mechanism for both the disease vector and the infectious agent. 
     A contaminant may be a virus. Example viruses may include a waterborne virus such as, for example, enteric viruses, hepatitis A virus, hepatitis E virus, rotavirus, and MS2 coliphage, adenovirus, and norovirus. 
     A contaminant may include an organic chemical. The organic chemical may be any carbon-containing substance according to its ordinary meaning. The organic chemical may be, for example, chemical compounds, pharmaceuticals, over-the-counter drugs, dyes, agricultural pollutants, industrial pollutants, proteins, endocrine disruptors, fuel oxygenates, and/or personal care products. Examples of organic chemicals may include acetone, acid blue 9, acid yellow 23, acrylamide, alachlor, atrazine, benzene, benzo(a)pyrene, bromodichloromethane, carbofuran, carbon tetrachloride, chlorobenzene, chlorodane, chloroform, chloromethane, 2,4-dichlorophenoxyacetic acid, dalapon, 1,2-dibromo-3-chloropropane, o-dichlorobenzene, p-dichlorobenzene, 1,2-dichloroethane, 1,1-dichloroethylene, cis-1,2-dichloroethylene, trans-1,2-dichloroethylene, dichlormethane, 1,2-dichloropropane, di(2-ethylhexyl) adipate, di(2-ethylhexyl)phthalate, dinoseb, dioxin (2,3,7,8-TCDD), diquat, endothall, endrin, epichlorohydrin, ethylbenzene, ethylene dibromide, glyphosate, a haloacetic acid, heptachlor, heptachlor epoxide, hexachlorobenzene, hexachlorocyclopentadiene, lindane, methyl-tertiary-butyl ether, methyoxychlor, napthoxamyl (vydate), naphthalene, pentachlorophenol, phenol, picloram, isopropylbenzene, N-butylbenzene, N-propylbenzene, Sec-butylbenzene, polychlorinated biphenyls (PCBs), simazine, sodium phenoxyacetic acid, styrene, tetrachloroethylene, toluene, toxaphene, 2,4,5-TP (silvex), 1,2,4-trichlorobenzene, 1,1,1-trichloroethane, 1,1,2-trichloroethane, trichloroethylene, a trihalomethane, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, vinyl chloride, o-xylene, m-xylene, p-xylene, an endocrine disruptor, a G-series nerve agent, a V-series nerve agent, bisphenol-A, bovine serum albumin, carbamazepine, cortisol, estradiol-17β, gasoline, gelbstoff, triclosan, ricin, a polybrominated diphenyl ether, a polychlorinated diphenyl ether, and a polychlorinated biphenyl. Methyl tert-butyl ether (also known as, methyl tertiary-butyl ether) is a particularly applicable organic chemical contaminant. 
     A contaminant may include an inorganic chemical. More specifically, the contaminant may be a nitrogen-containing inorganic chemical such as, for example, ammonia (NH 3 ) or ammonium (NH 4 ). Contaminants may include non-nitrogen-containing inorganic chemicals such as, for example, aluminum, antimony, arsenic, asbestos, barium, beryllium, bromate, cadmium, chloramine, chlorine, chlorine dioxide, chlorite, chromium, copper, cyanide, fluoride, iron, lead, manganese, mercury, nickel, nitrate, nitrite, selenium, silver, sodium, sulfate, thallium, and/or zinc. 
     A contaminant may include a radionuclide. Radioactive contamination may be the result of a spill or accident during the production or use of radionuclides (radioisotopes). Example radionuclides include, but are not limited to, an alpha photon emitter, a beta photon emitter, radium  226 , radium  228 , and uranium. 
     Various methods exist for handling contaminants and contaminated aqueous solutions. Generally, for example, contaminants may be contained to prevent them from migrating from their source, removed, and immobilized or detoxified. 
     Another method for handling contaminants and contaminated aqueous solutions is to treat the aqueous solution at its point-of-use. Point-of-use water treatment refers to a variety of different water treatment methods (physical, chemical and biological) for improving water quality for an intended use such as, for example, drinking, bathing, washing, irrigation, etc., at the point of consumption instead of at a centralized location. Point-of-use treatment may include water treatment at a more decentralized level such as a small community or at a household. A drastic alternative is to abandon use of the contaminated aqueous solutions and use an alternative source. 
     Other methods for handling contaminants and contaminated aqueous solutions are used for removing gasoline and fuel contaminants, and particularly the gasoline additive, MTBE. These methods include, for example, phytoremediation, soil vapor extraction, multiphase extraction, air sparging, membranes (reverse osmosis), and other technologies. In addition to high cost, some of these alternative remediation technologies result in the formation of other contaminants at concentrations higher than their recommended limits. For example, most oxidation methods of MTBE result in the formation of bromate ions higher than its recommended limit of 10 μg/L in drinking water (Liang et al., “Oxidation of MTBE by ozone and peroxone processes,” J. Am. Water Works Assoc. 91:104 (1999)). 
     A number of technologies have proven useful in reducing MTBE contamination, including photocatalytic degradation with UV light and titanium dioxide (Barreto et al., “Photocatalytic degradation of methyl tert-butyl ether in TiO 2  slurries: a proposed reaction scheme,” Water Res. 29:1243-1248 (1995); Cater et al., UV/H 2 O 2  treatment of MTBE in contaminated water,” Environ. Sci Technol. 34:659 (2000)), oxidation with UV and hydrogen peroxide (Chang and Young, “Kinetics of MTBE degradation and by-product formation during UV/hydrogen peroxide water treatment,” Water Res. 34:2223 (2000); Stefan et al., Degradation pathways during the treatment of MTBE by the UV/H 2 O 2  process,” Environ. Sci. Technol. 34:650 (2000)), oxidation by ozone and peroxone (Liang et al., “Oxidation of MTBE by ozone and peroxone processes,” J. Am. Water Works Assoc. 91:104 (1999)) and in situ and ex situ bioremediation (Bradley et al., “Aerobic mineralization of MTBE and tert-Butyl alcohol by stream bed sediment microorganisms,” Environ. Sci. Technol. 33:1877-1879 (1999)). 
     Use of titanium dioxide (titania, TiO 2 ) as a photocatalyst has been shown to degrade a wide range of organic pollutants in water, including halogenated and aromatic hydrocarbons, nitrogen-containing heterocyclic compounds, hydrogen sulfide, surfactants, herbicides, and metal complexes (Matthews, “Photo-oxidation of organic material in aqueous suspensions of titanium dioxide,” Water Res. 220:569 (1986); Matthews, “Kinetic of photocatalytic oxidation of organic solutions over titanium-dioxide,” J. Catal. 113:549 (1987); 011 is et al., “Destruction of water contaminants,” Environ. Sci. Technol. 25:1522 (1991)). 
     Irradiation of a semiconductor photocatalyst, such as titanium dioxide (TiO 2 ), zinc oxide, or cadmium sulfide, with light energy equal to or greater than the band gap energy (Ebg) causes electrons to shift from the valence band to the conduction band. If the ambient and surface conditions are correct, the excited electron and hole pair can participate in oxidation-reduction reactions. The oxygen acts as an electron acceptor and forms hydrogen peroxide. The electron donors (i.e., contaminants) are oxidized either directly by valence band holes or indirectly by hydroxyl radicals (Hoffman et al., “Photocatalytic production of H 2 O 2  and organic peroxide on quantum-sized semi-conductor colloids,” Environ. Sci. Technol. 28:776 (1994)). Additionally, ethers can be degraded oxidatively using a photocatalyst such as TiO 2  (Lichtin et al., “Photopromoted titanium oxide-catalyzed oxidative decomposition of organic pollutants in water and in the vapor phase,” Water Pollut. Res. J. Can. 27:203 (1992)). A reaction scheme for photocatalytically destroying MTBE using UV and TiO 2  has been proposed, but photodegradation took place only in the presence of catalyst, oxygen, and near UV irradiation and MTBE was converted to several intermediates (tertiary-butyl formate, tertiary-butyl alcohol, acetone, and alpha-hydroperoxy MTBE) before complete mineralization (Barreto et al. “Photocatalytic degradation of methyl tert-butyl ether in TiO 2  slurries: a proposed reaction scheme,” Water Res. 29:1243-1248 (1995)). 
     A more commonly used method of treating aqueous solutions for disinfection of microorganisms is chemically treating the solution with chlorine. Disinfection with chlorine, however, has several disadvantages. For example, chlorine content must be regularly monitored, formation of undesirable carcinogenic by-products may occur, chlorine has an unpleasant odor and taste, and chlorine requires the storage of water in a holding tank for a specific time period. 
     Aqueous solutions used for hydraulically fracturing gas wells (e.g., fracturing or frac fluids) or otherwise stimulating petroleum, oil and/or gas production also require treatment. Such solutions or frac fluids typically include one or more components or contaminants including, by way of example and without limitation, water, sand, diluted acid (e.g., hydrochloric acid), one or more polymers or friction reducers (e.g., polyacrylamide), one or more antimicrobial agents (e.g., glutaraldehyde, ethanol, and/or methanol), one or more scale inhibitors (e.g., ethylene glycol, alcohol, and sodium hydroxide), and one or more thickening agents (e.g., guar). In addition, a significant percentage of such solutions and fluids return toward the Earth surface as flowback, and later as produced water, after they have been injected into a hydrofrac zone underground. As they return toward the Earth surface, the solutions and fluids also pick up other contaminants from the earth such as salt (e.g., sodium and calcium salts). Such fluids may also include barium, oil, strontium, iron, heavy metals, soap, high concentrations of bacteria including acid producing and sulfate reducing bacteria, etc. 
     Aqueous solutions used for hydraulically fracturing gas wells or otherwise stimulating oil and gas production are difficult and expensive to treat for many reasons including, without limitation, the salinity of the solutions. For that reason, such fluids are often ultimately disposed of underground, offsite, or into natural water bodies. In some cases, certain states and countries will not allow fracking due to remediation concerns. 
     Accordingly, there is a need in the art for alternative approaches for treating aqueous solutions to remove and/or reduce amounts of contaminants. Specifically, it would be advantageous to have apparatus and/or methods for treating various aqueous solutions including hydraulic fracturing fluid, hydraulic fracturing backflow water, high-salinity water, groundwater, seawater, wastewater, drinking water, aquarium water, and aquaculture water, and/or for preparation of ultrapure water for laboratory use and remediation of textile industry dye waste water, among others, that help remove or eliminate contaminants without the addition of chemical constituents, the production of potentially hazardous by-products, or the need for long-term storage. 
     SUMMARY 
     The present disclosure is generally directed to devices and methods of treating aqueous solutions to help remove or otherwise reduce levels or amounts of one or more contaminants. More specifically, the present disclosure is directed to a photoelectrocatalytic oxidation (PECO) system, device or apparatus employing or utilizing and/or maintaining a substantially constant or fixed current for one or more periods of time and reversing the bias for a second period of time. 
     The present disclosure is generally directed to devices and methods of treating aqueous solutions to help remove or otherwise reduce levels or amounts of one or more contaminants. More specifically, the present disclosure relates to a method for removing or reducing the level of contaminants in a solution, the method comprising: providing a solution into a cavity of a device, wherein the cavity of the device houses a light tube, a photoelectrode provided around the light tube, the photoelectrode comprising a primarily titanium foil support with nanotubes of titanium dioxide provided thereon, a counterelectrode provided in the space between the photoelectrode and a cavity wall of the device; irradiating the photoelectrode with ultraviolet light; and flowing a first constant current through a first terminal coupled to the photoelectrode and a second terminal coupled to the counterelectrode. 
     The present invention further relates to a method for removing or reducing the level of contaminants in a solution, the method comprising: providing a solution into a cavity of a device, wherein the cavity of the device houses a light tube, a photoelectrode provided around the light tube, the photoelectrode comprising a primarily titanium foil support with nanotubes of titanium dioxide provided thereon, a counterelectrode provided in the space between the photoelectrode and a cavity wall of the device; irradiating the photoelectrode with ultraviolet light; and applying a first pulse width modulation duty cycle to a first terminal coupled to the photoelectrode and to a second terminal coupled to the counterelectrode. 
     The present disclosure further relates to A method for removing or reducing the level of contaminants in a solution, the method comprising: providing an assembly for removing or reducing the level of contaminants in a solution, the assembly comprising a first light source having a longitudinal axis; a plurality of second light sources provided about a line concentric to the longitudinal axis of the first light source; a first photoelectrode provided between the first light source and plurality of second light sources; a second photoelectrode provided around the second light sources; at least one counterelectrode provided between the first photoelectrode and the second photoelectrode; wherein the first photoelectrode and second photoelectrode each comprise a primarily titanium foil support with titanium dioxide nanotubes provided on at least one surface the photoelectrodes; and wherein the first photoelectrode, second photoelectrode and at least one counterelectrode are each coupled to a respective terminal adapted to be electrically coupled to a power supply; irradiating the first photoelectrode with ultraviolet light; flowing a first constant current through the terminals coupled to the first photoelectrode, second photoelectrode and the counterelectrode; and providing a solution in the cavity between the cavity wall and the light tube. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be better understood, and features, aspects and advantages other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such detailed description makes reference to the following drawings, wherein: 
         FIG. 1  is an isometric view of a PECO system, according to various embodiments. 
         FIG. 2  is an isometric view of a PECO system, according to various embodiments. 
         FIG. 3  is an isometric cross-sectional view of the PECO system shown in  FIG. 2 , according to various embodiments. 
         FIG. 4  is an isometric cross-sectional view of a PECO apparatus, according to various embodiments. 
         FIG. 5  is an isometric view of a reactor assembly, according to various embodiments. 
         FIG. 6  is an isometric cross-sectional view of a PECO apparatus, according to various embodiments. 
         FIG. 7  is a cross-sectional view of a PECO apparatus, according to various embodiments. 
         FIG. 8  is a cross-sectional view of a PECO apparatus, according to various embodiments. 
         FIG. 9  is a cross-sectional view of a PECO apparatus, according to various embodiments. 
         FIG. 10  is a cross-sectional view of a PECO apparatus, according to various embodiments. 
         FIG. 11  is a cross-sectional view of a PECO apparatus, according to various embodiments. 
         FIG. 12  is a cross-sectional view of a PECO apparatus, according to various embodiments. 
         FIG. 13  is a cross-sectional view of a PECO apparatus, according to various embodiments. 
         FIG. 14  is a cross-sectional view of a PECO apparatus, according to various embodiments. 
         FIG. 15  is an SEM image of nanotubes grown or otherwise provided on a photoelectrode, according to one or more examples of embodiments. 
         FIG. 16  is an SEM image of nanotubes grown or otherwise provided on a photoelectrode, according to one or more examples of embodiments. 
         FIG. 17  is an SEM image of nanotubes grown or otherwise provided on a photoelectrode, according to one or more examples of embodiments. 
         FIG. 18  is an SEM image of nanotubes grown or otherwise provided on a photoelectrode, according to one or more examples of embodiments. 
         FIG. 19  is an SEM image of nanotubes grown or otherwise provided on a photoelectrode, according to one or more examples of embodiments. 
         FIG. 20  is an SEM image of nanotubes grown or otherwise provided on a photoelectrode, according to one or more examples of embodiments. 
         FIG. 21  is an SEM image of nanotubes grown or otherwise provided on a photoelectrode, according to one or more examples of embodiments. 
         FIG. 22  is an SEM image of nanotubes grown or otherwise provided on a photoelectrode, according to one or more examples of embodiments. 
         FIG. 23  is an isometric view of a spacer, according to various embodiments. 
         FIG. 24  is a top view of a spacer, according to various embodiments. 
         FIG. 25  is a side view of a spacer, according to various embodiments. 
         FIG. 26  is an isometric view of a light source assembly, according to various embodiments. 
         FIG. 27  is a partial isometric view of the light source assembly shown in  FIG. 18 , according to various embodiments. 
         FIG. 28  is a partial isometric view of a PECO system, according to various embodiments. 
         FIG. 29  is a partial side view of a PECO system, according to various embodiments. 
         FIG. 30  is a partial isometric view of a PECO apparatus, according to various embodiments. 
         FIG. 31  is an isometric view of a bulkhead member, spigot member, band and clamp, according to various embodiments. 
         FIG. 32  is an isometric view of a bulkhead member, spigot member, band and clamp, according to various embodiments 
         FIG. 33  is a top view of a bulkhead member and band, according to various embodiments. 
         FIG. 34  is a cross-sectional view of the bulkhead member and band illustrated in  FIG. 25 , according to various embodiments. 
         FIG. 35  is an isometric view of a spigot member and seal, according to various embodiments. 
         FIG. 36  is an isometric view of a bulkhead member, according to various embodiments. 
         FIG. 37  is a block diagram of a constant current topology or pulse width modulation control circuit, according to one or more examples of embodiments. 
         FIG. 38  is a schematic diagram of a constant current topology or pulse width modulation control circuit, according to one or more examples of embodiments. 
         FIG. 39  is a schematic diagram of a constant current power supply output circuit with multiple current sensors, according to one or more examples of embodiments. 
         FIG. 40  is a schematic diagram of a switcher board for providing a substantially constant current to, between, or across a photoelectrode and counterelectrode for a period of time, according to one or more examples of embodiments. 
         FIG. 41  is an example control screen, display and/or user interface, according to one or more examples of embodiments. 
         FIG. 42  is an illustration of a substantially constant voltage application and reversal program adapted for removing contaminant amounts or otherwise treating contaminants and removing fouling from components of a PECO assembly, and a corresponding illustration of cell current during the program, according to one or more examples of embodiments. 
         FIG. 43  is an illustration of switcher board voltage or duty cycle output provided by a substantially constant current application and reversal program adapted for removing contaminant amounts or otherwise treating contaminants and removing fouling from components of a PECO assembly, an illustration of a substantially constant current provided by the program, and a corresponding illustration of cell voltage during the program, according to one or more examples of embodiments. 
         FIG. 44  is a flow diagram of a first constant current control program, according to one or more examples of embodiments. 
         FIG. 45  is a flow diagram of a second constant current control program, according to one or more examples of embodiments. 
         FIG. 46  is a graph illustrating normalized dye concentration in solution over time at various time in various PECO devices, according to one or more examples of embodiments. 
         FIG. 47  is a graph illustrating the half-life of normalized dye in solution over time in various PECO devices, according to one or more examples of embodiments. 
     
    
    
     While the disclosure is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described below in detail. For example, any numbers, measurements, and/or dimensions illustrated in the Figures are for purposes of example only. Any number, measurement or dimension suitable for the purposes provided herein may be acceptable. It should be understood that the description of specific embodiments is not intended to limit the disclosure from covering all modifications, equivalents and alternatives falling within the spirit and scope of the disclosure. 
     DETAILED DESCRIPTION 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosure belongs. Although any methods and materials similar to or equivalent to those described herein may be used in the practice or testing of the present disclosure, example methods and materials are described below. 
     Various embodiments of system, apparatus, and device (e.g., a photoelectrocatalytic oxidation (PECO) system, apparatus, and device) are described. Referring to  FIGS. 1 and 2 , a photoelectrocatalytic oxidation (PECO) system  100  is shown. In various embodiments, PECO system  100  includes at least one input  110  and at least one output  120  and at least one PECO apparatus  130 . In various embodiments, the input and/or output are threaded to facilitate engagement or connection (e.g., fluid connection) of input and/or output with a hose or other fluid-conveying member. In various embodiments, input  110  is fluidly connected to an input manifold  140  that branches into multiple input manifold openings fluidly connected to one or more PECO apparatus  130  of PECO system  100 . In various embodiments, output  120  is fluidly connected to an output manifold  150  that branches into one or more output manifold openings fluidly connected to one or more PECO apparatus  130  of PECO system  100 . While input  110  is shown in the Figures as beginning or extending lower in elevation than or below each PECO apparatus  130  of system  100 , the input may be elevated above one or more of the PECO apparatus of the PECO system. While output  120  is illustrated in the Figures as beginning or extending higher in elevation than or above each PECO apparatus  130  of system  100 , the output may be lower in elevation than or below one or more of the PECO apparatus of the PECO system. In various embodiments, the output may also be coupled or fluidly connected to an output fitting (such as a u-shaped fitting) (not shown) to make it easier to couple (e.g., fluidly couple) a hose or further fittings to the output. The output fitting may also include a vent. 
     In various embodiments, PECO apparatus  130  is elevated at one end (e.g., at the end closest to the output) relative to the other. This may encourage collection of gases at the one end and may also help solution to completely, substantially, or optimally fill PECO apparatus  130  during use. Input  110  may be provided relatively lower in elevation or below PECO apparatus  130  and output  120  may be provided relatively higher in elevation or above PECO apparatus  130  to also help completely, substantially, or optimally fill PECO apparatus  130  during use. 
     Input manifold  140  and output manifold  150  each helps to allow multiple PECO apparatus  130  of PECO system  100  to be configured and/or utilized in parallel. It should be appreciated, however, that the PECO apparatus of the PECO system may also be utilized in series, or alone, in various applications and embodiments. For example, in various embodiments, one or more of the input manifold branches and one or more of the output manifold branches may be coupled to a valve  160  to help regulate and/or control flow through PECO apparatus  130  or PECO system  100  generally. 
     Multiple PECO systems  100  may be operatively and/or fluidly connected together (e.g., in series). For example, the output of a first PECO system may be fluidly connected to the input of a second PECO system to operatively and fluidly connect the systems in series. In various other embodiments, multiple PECO systems may be operatively or fluidly connected in parallel. 
     As shown in  FIGS. 1 and 2 , in various embodiments, each PECO system  100  includes multiple PECO apparatus  130 . While four PECO apparatus  130  are shown in  FIGS. 1 and 2 , it should be appreciated that any number of the PECO apparatus may be utilized in connection with the PECO system disclosed herein. Also, while multiple PECO apparatus  130  are shown in a stacked (e.g., vertically-stacked) arrangement, any variety of arrangements and configurations may be utilized within the scope of this disclosure. For example, multiple PECO apparatus may be provided in a row (e.g., side-to-side), in two rows of two, etc. 
     In various embodiments, PECO system  100  and/or PECO apparatus  130  includes and/or is a substantially self-contained system and/or apparatus (apart from the input or in-flow and output or out-flow apertures, gas vents, etc.). Each PECO apparatus  130  in various embodiments includes a housing, chamber, or container  170  which is adapted to at least partially receive components (e.g., one or more operative components) of PECO apparatus  130  and/or at least temporarily receive, contain and/or circulate fluid or aqueous solution. 
     In various embodiments, housing  170  includes at least one generally annular, tubular (e.g., a square or rectangular tube), cylindrical or conical housing member  180  extending between a first opposing end  190  and a second opposing end  200 . Housing member  180  of each PECO apparatus  130  may be formed of any suitable materials, or combination of materials, and be of any size or shape suitable for its intended purposes. In one or more examples of embodiments, housing member  180  is a molded, high-durability plastic or polyethylene (e.g., PVC) and/or may be formed to be resistant to one or more contaminants. Housing member  180  may also take alternative shapes, sizes, and configurations. One or more components of housing  170  and/or housing member may also be constructed of metal which may be lined (e.g., with an inert polymer compound such as Teflon or PPS material). 
     In various embodiments, housing  170  includes a first fitting  190  provided about first opposing end  210  and a second fitting  200  provided about second opposing end  220  of housing member  180 . Fittings  190 / 200  may be formed of any suitable materials, or combination of materials, and be of any size or shape suitable for their intended purposes. In one or more examples of embodiments, fittings  190 / 200  are made of a high-durability plastic or polyethylene (e.g., PVC) and/or may be formed to be resistant to one or more contaminants. In one or more other examples of embodiments, the fittings are made of metal. Alternative materials and shapes suitable for the purposes of the system and/or apparatus are also acceptable. 
     In various embodiments, fittings  190 / 200  are T-fittings defining one or more in-flow apertures and/or out-flow apertures. In various embodiments, the in-flow and out-flow apertures defined by fittings  190 / 200  are fluidly connected to input  110  and/or input manifold  130 , and/or output  120  and/or output manifold  140 . The locations of the in-flow and out-flow apertures may vary depending upon the desired results (e.g., the flow of solution through the apparatus, the timing and/or length of time thereof, other system configurations, etc.). For example, the in-flow and out-flow apertures may be provided through the housing member or ends of the PECO apparatus. In addition, the orientation of the in-flow and out-flow apertures (e.g., relative to each other) may be different than or modified from that shown in the Figures. 
     In various embodiments, one or both fittings  190 / 200  define a fitting cavity or other feature shaped to fit snugly or tightly to or otherwise receive or be received by one or both opposing ends  210 / 220 . However, one or both of the fittings may be coupled with or to the opposing ends and/or the housing member in other ways (e.g., through a threaded connection or by butting the respective fitting to or near the first and second opposing ends). In various embodiments, a seal (e.g., an O-ring) is provided between one or both of fittings  190 / 200  and opposing ends  210 / 220 . 
     Referring now to  FIGS. 3-4 , in various embodiments, one or more housing walls or sidewalls  230  of housing member  180  help define at least one housing cavity  240 . In various embodiments, housing cavity  240  is substantially or entirely annular, tubular, cylindrical, or conical in shape (e.g., cross-sectional shape). In various embodiments, apart from the in-flow apertures and out-flow apertures, any drainage apertures and gas vents, housing cavity  240  is sealed or substantially sealed (e.g., from an outside environment and/or an environment exterior to housing  170 ) to prevent various elements (e.g., air or oxygen) from entering housing cavity  240  and/or various elements (e.g., a solution) from exiting or escaping housing cavity  240 , except through the in-flow and/or out-flow or drainage apertures, or vents (e.g., one-way vents). For example, in various embodiments, the PECO system or PECO apparatus includes an area for collecting or allowing gases to gather or accumulate and/or a valve or other component for bleeding off or removing one or more gases (e.g., hydrogen (H2) or otherwise allowing them to escape from inside the PECO apparatus or system. In various embodiments, gases collect (e.g., at a high point of the system or an apparatus) and a float style valve allows the release of such gases while preventing fluid in the apparatus or system from escaping. The exit port on such a valve may be directed as necessary or desired (e.g., to the outside, for collection, etc.). In various embodiments, the PECO apparatus may include a drainage apparatus or feature (e.g., to help drain solution before servicing). 
     In various embodiments, housing cavity  240  is adapted to receive various components of PECO apparatus  130 . In various embodiments, at least one reactor assembly  250  is at least partially provided in or received by housing cavity  240 . In various embodiments, multiple (e.g., two) reactor assemblies  250  are provided in housing cavity  240 . For example, and as shown in  FIGS. 3-4 , a reactor assembly  250  may be provided in first and second opposing ends  210 / 220 . In various embodiments, each reactor assembly  250  extends from about opposing ends  210 / 220  into housing cavity  240  of PECO apparatus  130 . While each reactor assembly  250  is shown in the Figures as extending nearly halfway into a length of housing cavity  240 , it should be appreciated that the reactor assembly may extend into any length (including substantially the entire length) of the housing cavity. 
     Referring now to  FIGS. 5-7 , in various embodiments, reactor assembly  250  includes at least one counterelectrode (e.g., cathode)  260 , at least a first photoelectrode (e.g., anode)  270 , and at least a first light source (e.g., UV-light source) or first light source assembly  280 . In various embodiments, reactor assembly  250  includes a second photoelectrode  290 , and one or more second light sources or second light source assemblies  300 . In various embodiments, first photoelectrode  270  is provided around first light source assembly  280 . 
     In various embodiments, reactor assembly  250  includes first light source assembly  280  (e.g., a centralized UV light source) with one or more second light source assemblies  300  (e.g., six additional UV light sources) provided (e.g., in a spaced relationship) around first light source assembly  280 . In various embodiments, first light source assembly  280  is provided about a longitudinal axis  305  of reactor assembly  250 . In various embodiments, one or more second light source assemblies  300  are spaced around longitudinal axis  305 . In various embodiments, one or more second light source assemblies  300  are generally spaced symmetrically around longitudinal axis  305 . In various embodiments, one or more counterelectrodes  260  or cathodes are provided (e.g., in a spaced relationship) around first light source assembly  280  (e.g., in one or more of the spaces between the second light source assemblies  300 ). In various embodiments, one or more counterelectrodes or cathodes  260  (e.g., counterelectrode or cathode strips) are provided offset from their mounting hole centerlines. Among other things, this may allow additional counterelectrodes (e.g., an additional counterelectrode for each offset mounting hole) to be added to the reactor assembly as necessary or desired to help balance or otherwise better optimize reactions (e.g., with first and/or second photoelectrodes  270 / 290 . 
     In various embodiments, reactor assembly  250  includes second photoelectrode  290  provided between first photoelectrode  270  and housing wall  230 . In various embodiments, reactor assembly  250  includes a second light source assembly  300  provided between first photoelectrode  270  and second photoelectrode  290 . In various embodiments, reactor assembly  250  includes multiple second light source assemblies  300  (e.g., spaced second light source assemblies) provided between first light source assembly  280  and second photoelectrode  290  and/or housing wall  230 . In various embodiments, one or more second light source assemblies  300  are spaced in a radial array between first photoelectrode  270  and second photoelectrode  290 . 
     One or more of the counterelectrodes may be provided in a variety of positions in the reactor assembly, and/or the PECO apparatus. For example, in various embodiments, at least one counterelectrode  260  is provided between multiple first and/or second light source assemblies  280 / 300 . As another example, at least one counterelectrode  260  may be provided in a space between housing wall  230  and the one or more light source assemblies. In one or more examples of embodiments, one or more counterelectrodes  260  are provided in a spaced relationship radially around first photoelectrode  270 . In various embodiments, one or more counterelectrodes  260  are provided between first photoelectrode  270  and second photoelectrode  290 . In various embodiments, the one or more counterelectrodes  260  are arranged between the first photoelectrode  270  and second photoelectrode  290  and second light source assemblies  300  (e.g., on a line or ring concentric to the longitudinal axis of first light source assembly and/or housing member  180 ). 
     It should be appreciated that, while seven light source assemblies  280 / 300  are shown in the  FIGS. 5-7 , any number of light source assemblies may be utilized and/or included in the reactor assembly. It should also be appreciated that, while six counterelectrodes  260  are shown in the  FIGS. 5-7 , any number of the counterelectrodes may be utilized and/or included within or as part of the reactor assembly. 
     In various embodiments, reactor apparatus  250  includes first light source assembly  280  centrally located within a space from housing wall or walls  230  and one or more second light source assemblies  300  between first light source assembly  280  and housing wall or walls  230 . For example, reactor assembly  250  may include first light source assembly  280  at or near the longitudinal axis of housing cavity  240  at least partially surrounded, encircled, and/or ringed by multiple (e.g., six) second light source assemblies  300 , each of which is provided within housing cavity  240 . 
     It should be noted, however, that the light source assemblies may be provided with the housing cavity in any variety of ways and locations, and it is not necessary that the light source assemblies be provided concentrically within and/or centrally spaced from the wall or walls forming or defining the housing cavity. Rather, the light source assemblies may be provided in any variety of positions and/or configurations without departing from the spirit and scope of this disclosure. In various embodiments, the reactor assembly also includes a means for cleaning or unfouling the light sleeve or tube of the one or more light source assemblies. 
     In various embodiments, one or more first and second photoelectrodes  270 / 290  are provided within housing cavity  240 . In various embodiments, first photoelectrode  270  is provided at least substantially around first light source assembly located on or about the longitudinal or central axis of the housing cavity  240 . In various embodiments, second photoelectrode  290  may be wrapped, wound, or otherwise provided at least substantially around first photoelectrode  270  and one or more light source assemblies  280 / 300 , and/or housing wall  230 . In various embodiments, first photoelectrode  270  is provided between a centrally located first light source assembly and one or more second light source assemblies  300 . In various embodiments, second photoelectrode  290  is provided between all light source assemblies of the reactor assembly and the housing wall  230 . 
     In various embodiments, first photoelectrode  270  (e.g., anode) may be wrapped, wound, or otherwise provided around and/or between first light source assembly  280  concentric within and/or spaced apart from the housing wall  230  and one or more second photoelectrodes  290 . In various embodiments, second photoelectrode  290  may be wrapped, wound, or otherwise provided around and/or between first photoelectrode  270  and housing wall  230 . In examples of embodiments, one or more second light source assemblies  300  are provided between first photoelectrode  270  and second photoelectrode  290 . 
     In one or more examples of embodiments, first photoelectrode  270  and second photoelectrode  290  (e.g., a foil photoelectrode) are wrapped, wound, or otherwise provided within housing cavity  240  such that a majority or substantial portion of UV light or radiation (e.g., from the first and second light source assemblies) with housing cavity  240  is directed at or otherwise exposed to first and second photoelectrodes  270 / 290 . 
     It should be appreciated that any number of photoelectrodes and light source assembly configurations may be utilized within a scope of this disclosure. In various embodiments, the photoelectrodes are provided (e.g., around the light source assemblies) to optimize the distance, separation or spacing between the photoelectrodes and the light source assemblies. In various embodiments, one or more photoelectrodes may be wrapped, wound, or otherwise provided around the surface of a light tube or sleeve of each light source assembly, multiple light tubes or sleeves, or one light tube or sleeve. The photoelectrodes may be provided closely or tightly around or against each light source assembly. In various embodiments, a photoelectrode may be coupled (e.g., removably coupled) to a light source assembly. 
     In various embodiments, and as shown in  FIGS. 5-7 , reactor assembly  250  also includes one or more spacer members  310 . One or more spacer members  310  may be utilized, for example, to keep reactor assembly components such as the first and/or second photoelectrodes  270 / 290 , counterelectrodes  260 , and first and/or second light source assemblies  280 / 300  in a desired spatial relationship relative to each other, other components, and/or housing wall  230 . In various embodiments, portions of spacer member  310  are adapted to receive first and second light source assemblies  280 / 300 . In various embodiments, spacer member  310  is adapted to help maintain separation or spacing between at least a portion of first and second photoelectrodes  270 / 290  and one or more counterelectrodes  260  (e.g., to prevent shorting or arcing near an edge or end of reactor assembly  250 . 
     Referring now to  FIGS. 8-9 , in various embodiments, reactor assembly  250  includes one or more second light source assemblies  300  (e.g., six second light source assemblies) arranged around first light source assembly  280  on a line or ring  315  concentric to a longitudinal axis of reactor apparatus  250  and/or first light source assembly  280 . In various embodiments, reactor assembly  250  or PECO apparatus  130  may include more or less than six of the second light source assemblies and/or more or less than six of the counterelectrodes. In various embodiments, reactor assembly  250  of PECO apparatus  130  includes less than six (e.g., five) second light source assemblies  300  provided between first light source assembly  280  (and/or first photoelectrode  270 ), and second photoelectrode  290  (and/or housing wall  230 ). In various embodiments, reactor assembly  250  of PECO apparatus  130  includes less than six (e.g., five) counterelectrodes spatially arranged or otherwise provided between five second light source assemblies  300  and arranged or provided between first light source assembly  280  (and/or first photoelectrode  270 ), and second photoelectrode (and/or wall  230 ). In various embodiments, PECO apparatus  130  includes one or more counterelectrodes  260  spatially arranged between multiple second light source assemblies  300  and provided between first light source assembly  280  (and/or first photoelectrode  270 ), and second photoelectrode (and/or wall  230 ). Referring now to  FIG. 10 , in various embodiments, PECO apparatus  130  includes multiple second light source assemblies  300  provided between first light source assembly  280  (and/or first photoelectrode  270 ), and at least one counterelectrode  260  (and/or wall  230 ). 
     Referring now to  FIGS. 11-14 , reactor assembly  250  or PECO apparatus  130  may include one or more second photoelectrodes  290  provided around one or more second light source assemblies  300  and one or more counterelectrodes  260  provided around second photoelectrodes  290 . For example, PECO apparatus  130  in various embodiments includes multiple second light source assemblies  300  provided around first light source assembly  280  (and/or the longitudinal axis of housing member  180  of PECO apparatus  130 ), one or more second photoelectrodes  290  provided around one or more second light source assemblies  300  and at least one counterelectrode  260  provided around second photoelectrodes  290  and/or between second photoelectrodes  290  and wall  230 . In various embodiments, the reactor assembly may not include the first light source assembly. 
     While the figures show a variety of light source assembly configurations including a seven light source assembly configuration, a six light source assembly configuration, and a sixteen light tube or sleeve configuration, it should be appreciated that any number of light tubes or sleeves in any variety of configurations may be utilized or otherwise provided. 
     Referring again to  FIG. 5 , in various embodiments, reactor assembly  250  includes a bulkhead member  320 . In various embodiments, bulkhead member  320  defines a first light source aperture  330  and one or more second light source aperture  340  between the first light source aperture and a perimeter  350  of bulkhead member  320 . For example, as shown in  FIG. 5 , bulkhead member  320  may define a central first light source aperture  330  and multiple similarly-sized second light source apertures  340  whose centers are arranged around first light source aperture  330  on a line concentric to a center of central light source aperture  330  and/or a center of bulkhead member  320 . First and second light source aperture  330 / 340  is, in various embodiments, adapted to retain and/or releasably retain a first and/or second light source assembly  280 / 300 . In various embodiments, first and second light source apertures  330 / 340  are adapted to receive a light source assembly such as an assembly shown in  FIGS. 18-19 . In various embodiments, such assemblies include one or more light tubes or sleeves. In various embodiments, the bulkhead member may also define a recess into which a printed circuit board may be mounted for controlling the operation of the device or apparatus. 
     In various embodiments, one or more counterelectrode and/or photoelectrode apertures are defined by bulkhead member  320 . In various embodiments, the one or more counterelectrode and photoelectrode apertures defined by bulkhead member  320  are provided between and/or near two or more light source apertures  330 / 340  to allow a bias or potential to be applied to photoelectrodes  270 / 290  and counterelectrodes  260  of reactor assembly  250 . It should be appreciated that, while seven light source apertures  330 / 340  are shown, any number of the light source apertures may be defined by the bulkhead member. It should also be appreciated that, while six counterelectrode apertures and two photoelectrode apertures are defined by bulkhead member  320  are shown in the Figures, any number of the photoelectrode apertures and the counterelectrode apertures may be defined by the bulkhead member. 
     In various embodiments, terminals, terminal configurations and/or leads are electrically coupled to the photoelectrodes. The leads are adapted to receive an applied voltage bias, potential and/or current provided by a power source connected or otherwise coupled (e.g., electrically connected coupled) to the leads. The leads are formed of a conductive material, such as a conductive metal. One or more of the leads may define or be provided with an aperture for ease of connection or coupling of the lead to a wire, electrical cable or the like. 
     While not shown, the photoelectrode(s) and counterelectrode(s) may be separated by a separator. Each separator may be used or otherwise provided to prevent shorting. In one or more examples of embodiments, each photoelectrode (e.g., anode) and counterelectrode (e.g., cathode) are separated by plastic or plastic mesh separator, although alternative separators (e.g., other dielectric material(s) or other separators accomplishing or tending to accomplish the same or similar purposes) may be acceptable for use with the device and system described herein. 
     In various embodiments, first and second photoelectrodes  270 / 290  include a conductive support member. In one or more examples of embodiments, the conductive support member is constructed from metal (e.g., titanium or Ti). 
     The first and/or second photoelectrodes and/or conductive support members may be modified (e.g., to improve performance). In various embodiments, the photoelectrodes and/or conductive support members (e.g., Ti foil) are modified to increase the surface area of the photoelectrodes exposed to light such as UV light. For example, the photoelectrodes and/or conductive support members may be corrugated. As another example, the photoelectrodes and/or conductive support members may be wavy. The photoelectrodes and/or conductive support members may include various other features or microfeatures to help optimize the surface exposed to UV light and/or help cause turbulence in fluid or solution about the photoelectrode. 
     In various embodiments, photoelectrode and/or conductive support member modifications include corrugating or otherwise modifying the photoelectrodes, conductive support member or foil to produce a wave-like pattern (e.g., regular wave-like pattern) on the foil surface. In various embodiments, the height of a corrugation “wave” is from about 1-5 mm. For example, in various embodiments, corrugating the foil twice at right angles to each other produces a cross-hatched pattern on the foil surface. 
     In various embodiments, the photoelectrode and/or conductive support member modifications include holes or perforations made, defined by or provided in photoelectrodes, conductive support member, or foil. In various embodiments, the holes or perforations are made or provided at regular intervals (e.g., 0.5 to 3 cm spacing between the holes). 
     Modifications of the photoelectrodes and/or conductive support members may also include various microfeatures and/or microstructures. Accordingly to various embodiments, the modifications of the photoelectrodes, conductive support members or foils may also include various microfeatures and/or microstructures that increase the relative surface area of the photoelectrodes and/or increase or promote turbulence about the photoelectrodes. For example, according to various embodiments, such microfeatures and/or microstructures include those that are disclosed in U.S. Patent Publication Nos. 20100319183 and 20110089604, each of which is incorporated herein by reference in its entirety, or such microfeatures and/or microstructures that are provided commercially from Hoowaki, LLC (Pendleton, S.C.). In various embodiments, the microfeatures may include microholes. 
     As a result of the holes, the positioning, the corrugation, and other modifications, etc., the photoelectrodes may help create turbulence in fluid flowing in and/or through the PECO apparatus. Additionally, one or more holes may allow oxidants generated or produced on or near a surface of the photoelectrodes to more rapidly and effectively make their way into or otherwise reach or react with the fluid (e.g., aqueous solution) and/or contaminants therein. 
     In one or more examples of embodiments, the photoelectrodes are in the form of a mesh (e.g., a woven mesh, such as a 40×40 twill weave mesh or 60×60 Dutch weave mesh, or a non-woven mesh). 
     In various embodiments, modifications of the photoelectrodes and/or conductive support members include the formation of a catalyst such as nanotubes (e.g., TiO 2  nanotubes) on the photoelectrodes, conductive support members and/or foils such as, for example, those that are disclosed in U.S. Patent Publication No. 20100269894, which is incorporated herein by reference in its entirety. 
     In various embodiments, one or more of the photoelectrodes  270 / 290  includes a catalyst either grown in place and/or potentially deposited upon the conductive support member thereof. The catalyst or nanotubes may be formed on one or multiple sides of faces of the conductive support member. For example, the catalyst or nanotubes may be formed on all sides of the conductive support member oriented to be exposed to UV light. 
     Referencing  FIGS. 15-22 , in various embodiments, a catalyst  345  comprises an array of tubes or nanotubes (e.g., tightly-packed tubes (e.g., hexagonally close packed tubes)). In various embodiments, the tubes have an inner diameter of approximately 20-500 nm, or more preferably an inner diameter of approximately 40-200 nm) and an outer diameter of approximately two to three times the inner diameter. In various embodiments, the tubes have a large aspect ratio, with lengths between 200 nm and 5 μm, or more preferably between 500 nm to 4 μm. As shown in the figures, the tubes include substantially parallel walls across their entire length, but the shape of the tubes and/or walls may be varied (e.g., cone or inverted cone, having ridges around the radius, etc.). In various embodiments, the tubes are adhered (e.g., tightly adhered) to the conductive support member. 
     In various embodiments, the nanotubes are largely amorphous when they are formed or grown. In various embodiments, the catalyst is in or is converted to crystal form (e.g, through annealing). For example, photoelectrodes  270 / 290  including catalyst may be thermally annealed at 200-600 deg C. In various embodiments, anatase structure is preferred to rutile, although blends of the two may also be utilized. 
     The tubes may further be modified through doping, either during growth, before annealing, or after annealing, through chemical or physical means. The dopant can be particles on the surface, introduced into the crystal structure at the surface, or dispersed throughout the crystallite. 
     In various embodiments, counterelectrode (e.g., cathode)  260  is in the form of a rod such as a rod with an L-shaped cross-section. However, the counterelectrode may be in the form of a wire, foil, plate, cylinder, or in another suitable shape or form. In various embodiments, the counterelectrode may be corrugated and/or have other features to help cause or promote turbulence in fluid or solution in the cavity. 
     In one or more examples of embodiments, the counterelectrode or cathode is constructed from or includes Al, Pt, Ti, Ni, Au, stainless steel, carbon and/or another conductive metal. 
     Referring now to  FIGS. 15-17 , in one or more examples of embodiments, spacer member  310  is a molded, durable plastic, or polyethylene, and/or may be formed to be resistant to one or more contaminants. Spacer member  310  may be made from plastics. In various embodiments, spacer member  310  is made (e.g., molded) from a thermoplastic such a chlorinated polyvinyl chloride (CPVC). In various embodiments, spacer member  310  is made (e.g., molded) from Fortron polyphenylene sulfate (PPS). The spacer member or portions thereof may be made of titanium (e.g., titanium sheet metal). The spacer member made of conductive material such as titanium, however, may also include non-conductive mounting points for photoelectrodes and/or counterelectrodes in electrical contact therewith to prevent electrical shorting. 
     In various embodiments, spacer member  310  includes one or more dividers  350  extending between a peripheral concentric portion  325  and an axial concentric portion  335 . Divider  350  is adapted to help direct, redirect, mix, stir or otherwise influence solution as it passes through the spacer. Such mixing or flow may be advantageous in many ways. For example, such mixing or flow may help to mix oxidants generated by the device into the solution. As another example, such mixing or flow may increase the residence time of the solution in the cavity of the device for even a solution of moderate velocity. It should also be noted that any number of spacers  310  may be utilized anywhere within the cavity. In various embodiments, spacer  310  allows for flanges to be provided along the length of each counterelectrode or cathode on either or both edges of the counterelectrode or cathode to help create a counterelectrode surface that is substantially parallel or otherwise aligned with a surface of the first and/or second photoelectrode or anode. In various embodiments, the spacer has an optimal or minimal cross-sectional area to optimize or minimize any restrictions on flow through the device or apparatus. 
     Referring now to  FIGS. 18-19 , first and second light source assemblies  280 / 300  include a light source  360  (e.g., a UV light) and a light tube or sleeve  370 . The light tube or sleeve may be formed of any material suitable for the purposes provided. For example, the light tube or sleeve may be UV-transparent material, such as, but not limited to, plastic or glass, or combinations of materials including such UV-transparent and/or UV-translucent material. In one or more examples of embodiments, light tube or sleeve  340  is made of quartz. Alternatively, the light source assemblies may not include a light tube or sleeve. 
     In various embodiments, light tube or sleeve  370  includes at least one wall or sidewall  380  that helps define a tube cavity  390  that at least partially houses and/or is at least partially adapted to receive one or more light sources  360  (e.g., an ultraviolet (UV) light source, light, or lamp). For example, a UV-light bulb or bulbs may be provided or inserted into the tube cavity. In various embodiments, light source  360  is provided and/or extends a distance into tube cavity  390 , such that the light (e.g., UV) provided thereby may be exposed to one or more of the first and second photoelectrodes (and/or one or more photoelectrodes may be exposed to UV), illuminating or radiating to some or all of a surface thereof according to the various embodiments described herein. In various embodiments, each light tube or sleeve  370  is coupled to an adapter or end cap  400 . 
     In various embodiments, end cap or adapter  400  is provided around and coupled (e.g., glued) to an end of light tube or sleeve  370 . In various embodiments, adapter or end cap  400  defines an aperture through which sensors and wiring  410  (e.g., wiring for powering a UV light source) and other connections may be provided. In various embodiments, at least a portion of adapter  400  is threaded. Any threads along with various seals (e.g., O-rings) help prevent fluid from leaking while also allowing each light source assembly to be removable from the reactor assembly (e.g., for repair, replacement, etc.). 
     In various embodiments, the end cap or adapter further includes a gland cap. In various embodiments, wires are potted or otherwise sealed to the gland cap or adapter. In various embodiments, the gland cap provides a fluid seal in the event of a break or leak of the light tube or sleeve. In various embodiments, the gland cap is screwed into threads provided in an aperture defined by the end cap or adapter. In various embodiments, an O-ring is provided between the end cap and the gland cap to provide a seal to prevent fluid from leaking outside of the cavity. In various embodiments, an additional seal such as a epoxy bead may be provided between the end cap and the light tube or sleeve. 
     The light source may be provided or inserted into a socket provided in the adapter and may be secured in position. Each light source is further coupled or connected (e.g., electrically connected via wiring  410  or a socket), or adapted to be coupled or connected, to a source of power. In various embodiments, the light source or UV bulb is coupled or connected (e.g., electrically) via one or more cables or wires to one or more ballasts and/or power sources. In various embodiments, light source  360  extends into at least a majority of each light tube or sleeve  370 . However, in various embodiments, the light source may extend only partially or not at all into the light tube or sleeve. 
     In various embodiments, light source  360  is a high irradiance UV light bulb. In one or more further examples of embodiments, light source  360  is a germicidal UV bulb with a light emission in the range of 400 nanometers or less, and more preferably ranging from 250 nanometers to 400 nanometers. 
     In various embodiments, the ultraviolet light of light source  360  has a wavelength in the range of from about 185 to 380 nm. In one or more examples of embodiments, light source  360  is a low pressure mercury vapor lamp adapted to emit UV germicidal irradiation at 254 nm wavelength. In one or more alternative examples of embodiments, a UV bulb with a wavelength of 185 nm may be effectively used as the light source. Various UV light sources, such as those with germicidal UVC wavelengths (peak at 254 nm) and black-light UVA wavelengths (UVA range of 300-400 nm), may also be utilized. In one or more examples of embodiments, an optimal light wavelength (e.g., for promoting oxidation) is 305 nm. However, various near-UV wavelengths are also effective. Both types of lamps may emit radiation at wavelengths that activate photoelectrocatalysis. The germicidal UV and black light lamps are widely available and may be used in commercial applications of the instant PECO device. 
     In one or more additional examples of embodiments, light source  360  is adapted to emit an irradiation intensity in the range of 1-500 mW/cm 2 . The irradiation intensity may vary considerably depending on the type of light source used. Higher intensities may improve the performance of the device (e.g., PECO device). However, the intensity may be so high that the system is UV-saturated or swamped and little or no further benefit is obtained. That optimum irradiation value or intensity may depend, at least in part, upon the distance between the lamp and one or more photoelectrodes. 
     The intensity (i.e., irradiance) of UV light at the photoelectrode may be measured using a photometer available from International Light Technologies Inc. (Peabody, Mass.), e.g., Model IL 1400A, equipped with a suitable probe. An example irradiation is greater than 3 mW/cm 2 . 
     UV lamps typically have a “burn-in” period. UV lamps may also have a limited life (e.g., in the range of approximately 6,000 to 10,000 hours). UV lamps also typically lose irradiance (e.g., 10 to 40% of their initial lamp irradiance) over the lifetime of the lamp. Thus, it may be important to consider the effectiveness of new and old UV lamps in designing and maintaining oxidation values. 
     The light source may be disposed exterior to the light tube or sleeve, and the tube or sleeve may include a transparent or translucent member adapted to permit ultraviolet light emitted from the light source to irradiate the photoelectrode. The device may also utilize sunlight instead of, or in addition to, the light source. 
     Referring now to  FIGS. 20-21 , in various embodiments, the light source assemblies are provided (e.g., threaded) through the light source apertures of bulkhead member  320  such that the light tubes or sleeves are provided within (e.g., within the cavity) and spaced from the wall(s) of the housing. In various embodiments, each light tube or sleeve is adapted to disburse, distribute or otherwise transport or provide light over some, most, or all of the length of the light tube or sleeve, and/or some, most, or all of a length of the cavity. In various embodiments, at least one light tube or sleeve is substantially central to and/or substantially concentric within and spaced from the wall(s) (e.g., cylindrical walls) of the housing. In other embodiments, such as where the walls or cavity of the housing are not cylindrical, at least one light tube or sleeve is substantially centrally-located and spaced from one or more of the walls. 
     In various embodiments, fitting  190  includes a fitting flange  420  to which bulkhead member  320  is coupled or releasably coupled. Fitting flange  420  may be integral to the fitting or part of a component coupled to fitting  190 . In various embodiments, fitting flange  420  and bulkhead member  320  each defines one or more flange apertures  430  into which bolts or other fasteners (not shown) may be provided to help releasably couple and create a seal between bulkhead member  320  and fitting flange  420 . 
     In various embodiments, multiple counterelectrodes may be electrically-coupled together (e.g., with first bus bars  440  or other conductive material (such as stainless steel)). In addition, multiple photoelectrodes may be electrically-coupled together with one or more second bus bars  450  or other conductive material. It should be appreciated that the bus bars may also be provided internally to a reactor apparatus (e.g., to help protect them from damage, to reduce potential leaking, etc.). If provided internally, the bus bars may be made of titanium. 
     In various embodiments, and referring now to  FIGS. 22-28 , a second embodiment of a fitting  500  and bulkhead member  510  is shown. In various embodiments, bulkhead member  510  is coupled to a spigot member  520  coupled to fitting  500 . As shown in  FIGS. 8-10 , spigot member  520  includes a spigot flange  530  and bulkhead member  510  includes a bulkhead flange  540 , which flanges  530 / 540  may be releasably compressed together utilizing a clamp  550  (e.g., V-band clamp). While not commonly used with PVC flanges, the V-band clamp may be utilized as desired (e.g., where frequent access is required, or where space is limited) in connection with certain flange configurations disclosed herein such as those shown in the Figures. In various embodiments, a relatively wide or extra wide, deep V-band flange profile is utilized to allow for extra flange depth and shear section and provide added seal strength. As shown, in various embodiments, clamp  550  is a V-band clamp style (e.g., over center handle style clamp) to provide quick or easy access. In various embodiments, clamp  550  also includes multiple segments (e.g., three segments) to allow for greater flexibility for installation and removal. In various embodiments, clamp  550  is provided with a T-bolt quick release latch. It should be appreciated, however, that any number of clamp and latch styles, segment configurations, and profiles may be utilized. The clamp may be provided with a lubricant such as a dry film lubricant to help evenly distribute the clamp pressure around the flanges and reduce any need to provide a lubricant on the flanges themselves. In various embodiments, clamp  550  also includes a secondary latch  555  to prevent the inadvertent or unintended release of clamp  550 . 
     As shown in  FIGS. 27-28 , in various embodiments, spigot member  520  includes a spigot flange  530  (e.g., Van Stone spigot flange), and bulkhead member  510  includes a bulkhead flange  540  (e.g., mating flange). It should also be appreciated, however, that any variety of flange styles may be utilized. In various embodiments, a seal  560  (e.g., O-ring seal) is provided between spigot member  520  and bulkhead member  510  (e.g., when assembled or compressed together). In various embodiments, the spigot member or bulkhead member may also define a feature (e.g., a dovetail feature such as an undercut dovetail) to help retain seal  560  (e.g., an O-ring) relative to spigot member  520  and/or bulkhead member  510 . 
     In various embodiments, spigot member  520  and bulkhead member  510  also includes a tongue and groove feature. For example, in various embodiments, bulkhead member  510  may include a tongue or ring  570  that, when bulkhead member  510  is properly aligned with spigot member  520 , will fit into a groove or channel  580  defined by spigot member  520  to help align (e.g., coaxially align) spigot member  520  and bulkhead member  510  relative to each other. Such ring  570  or inner ring may also help protect a sealing face  590  of bulkhead member  510  during shipping and handling. In various embodiments, the seal  560  is provided on spigot member  520  or flange  530  to allow easy visual access for inspection and cleaning of seal  560  to help ensure particular contaminants which may compromise the integrity of seal  560  are removed during servicing. A seal (e.g., O-ring) may be provided on the bulkhead flange as an alternate or additional configuration. 
     The configuration of the clamp, spigot member  520 , and mating bulkhead member  510  may also improve ease of removal of system components, such as a reactor assembly coupled to or otherwise associated with or including bulkhead member  510 . For example, spigot  520  and/or spigot flange  530  may be shaped and sized to allow the clamp to be rested on or around spigot member  520  (e.g., next to spigot flange  530 ) during removal and installation of bulkhead member  510 . In addition, in various embodiments, a profile of bulkhead flange  540  provides an area or feature  600  that may be utilized to better grip bulkhead member  510  when removing it from the apparatus or otherwise relative to spigot member  520 . 
     In various embodiments, one or more power supplies and/or ballasts are included or provided for powering each light source and/or for providing an electrical potential or bias to one or more of the counterelectrodes (e.g., cathodes) and photoelectrodes (e.g., anodes). In various embodiments, one or more power supplies and/or ballasts are electrically coupled to the light sources and/or the photoelectrodes and provided externally to the container, housing or apparatus. At least one pump may optionally be provided internally or externally to the housing to help facilitate transfer or movement of fluid or solution through each apparatus or a system of apparatus. The pump may also be used, for example, for circulation or recirculation. 
     Referring again to  FIG. 1 , an electrical or control panel  450  according to one or more examples of embodiments is shown. In various embodiments, electrical or control panel  450  includes one or more of the following: power supplies, controls and/or lamps for one or more PECO apparatus and a master control and lamp. In various embodiments, the control panel may also include a event indicator lamp and reset control. In various embodiments, the control panel may be utilized to implement and/or operate one or more of the apparatus, devices, systems, and/or methods described herein. 
     In various embodiments, control panel  450  may also include one or more user interfaces  460 . For example, in various embodiments, user interface  460  is used to configure, set-up, monitor and/or maintain one or more of the apparatus or systems described herein. The user interface may include a button or other control for implement a sampling of solution. For example, it may be desirable to sample solution before and after it is treated using an apparatus, device, system or method described herein. For example, in various embodiments, the apparatus or system includes two valves, one provided about at or about an input line for the apparatus or system, and the other provided about an output line for the apparatus or system. Such valves may be opened to help collect solution samples. These samples may tested on-site and/or off-site (e.g., sent to a laboratory for testing). The testing may involve chemical analysis and/or biologic analysis (e.g., to determine bacteria counts and/or “xxx log kill” measurements). 
     Because such testing may be affected by polarity applied or provided to electrodes at the time of sampling and because testing results may be more accurate if sampling is conducted at a time when polarity is consistent between samples, the user interface in various embodiments may include a button or control (e.g., “START SMPL PROCESS” button) for placing the system or apparatus in a particular state of polarity (e.g., a positive or normal polarity or bias) for a predetermined or desired time period (e.g., two minutes) to allow sampling to occur during that time period. 
     In various embodiments, power supplies, ballasts, circuit boards and/or controls may be housed or otherwise provided in the electrical or control panel. The PECO system may also include temperature sensors provided at various positions (e.g., in each group of devices). In various embodiments, the electrical panels may include fans and/or heat sinks if desired. In various embodiments, the electrical panels may be provided in an environment away from hazardous or flammable reactions. 
     One or more power supplies may also be provided for supplying power to one or more UV lamps. One or more power supplies, or an alternative power supply may also be provided for providing an applied voltage and/or current between the one or more photoelectrodes and counterelectrodes. In one or more examples of embodiments, providing and/or increasing the applied voltage and/or current increases photocurrent and/or chlorine production. In various embodiments, the applied voltage and/or current between the photoelectrode and the counterelectrode is provided to help ensure that electrons freed by photochemical reaction move or are moved away from the photoelectrode. The power supply may be an AC and/or DC power supply and may include a plurality of outputs. 
     One or more power supplies, in one or more examples of embodiments, may be connected to a power switch for activating or deactivating the supply of power. In one or more further examples of embodiments, a power supply, UV lamps, and or electrodes, may be connected to or in communication with programmable logic controller or other control or computer for selectively distributing power and/or current to the UV lamps and/or to the electrodes, including photoelectrodes and counterelectrodes described herein. 
     In various embodiments, one or more power supplies are external to the system. However, one or more power supplies may be internal to the system (e.g., in an electrical panel or box coupled to the device(s)). 
     The power supply or an additional power supply may be connected to the terminals of the electrodes described hereinabove via, for example cable connection to the terminals, for providing a current, potential, voltage or bias to the electrodes as described in the described methods. 
     The PECO apparatus, system or device may also include a circuit, switch, controller, switcher board, programmable logic controller (PLC), computer-based controller, or other suitable controller device for varying the voltage applied to, between, or across the photoelectrode and counterelectrode, or each plate pair, of a PECO system, apparatus, or device. The PECO system may also include a circuit, switch, controller, switcher board, programmable logic controller (PLC), computer-based controller, or other suitable controller device for reversing the potential, bias, polarity, and/or current applied to, between, or across the photoelectrode and counterelectrode, or each plate pair, in the PECO system, apparatus, or device. A simplified block diagram and a schematic diagram of a constant current topology or pulse width modulation control circuit  700  of an exemplary switcher board or device for providing a variable voltage or bias to maintain a substantially constant current across or between the photoelectrode and counterelectrode are shown in  FIGS. 37 and 38 . 
     In various embodiments, a power supply provides voltage ranging from −15 V to 15 V to the pulse width modulation control circuit  700  of an exemplary switcher board or device for providing a variable voltage or bias to maintain a substantially constant current across or between one or more of the photoelectrodes and counterelectrodes. In various embodiments, pulse width modulation control circuit  700  includes an astable timer  710  and a monostable timer  720 . In various embodiments, the astable frequency is approximately 60 KHz, the astable space period is approximately 16 μs, and the astable mark period is approximately 0.7 μs. In various embodiments, the monostable period is approximately one-half of the astable period (e.g., 8 μs). In various embodiments, the reference voltage is approximately 2 mV and the output current is approximately 2 mA. It should be appreciated, however, that these specifications are examples only and may be varied as necessary or desired. In various embodiments, the pulse width modulation control circuit  700  of an exemplary switcher board or device also includes a difference amplifier  730  and/or a switching metal-oxide-semiconductor field-effect transistor (or MOSFET)  740 .  FIG. 39  illustrates a view of a portion of pulse width modulation control circuit, output circuit and current measurement or sensing components that may be utilized in connection with the disclosed PECO system, device, or apparatus.  FIG. 40  illustrates an example schematic diagram of a switcher board  750  that may be utilized in connection with the PECO system, apparatus, or device disclosed herein. 
     Referring now to  FIG. 41 , another example of a user interface  460  of a control panel is illustrated. As shown, user interface  460  may include a target current value indicator  760  which is represented as a broken line in the figure and may be shown in multiple locations. The target current value indicator may be superimposed or otherwise provided about or in relation to actual current measurements for one or more reactors in the system. As shown, user interface  460  may include duty cycle outputs needed or being used to reach and/or maintain the actual currents measured for the one or more reactors in the system. While the duty cycle outputs are shown in the figure as being in a range from 0 to 255, the outputs could be expressed (e.g., in the interface) as other ranges (e.g., 0 to 100). The system may, in various embodiments, automatically adjust the duty cycle in a closed loop manner as required to achieve or otherwise maintain the target current value. 
     The duty cycle outputs may be utilized as an indicator of reactor efficiency and health. For example, measuring actual current values at or about the target current value using lower relative duty cycle values (e.g., 1-4.5 V) may indicate that a reactor is working well. Actual current values at, about, or below the target current value using higher relative duty cycle values (e.g., 5-7.5 V) may indicate that maintenance may be required. By monitoring duty cycle outputs needed or being used to reach and/or maintain the actual currents measured for the one or more reactors in the system, the system can detect and/or indicate when performance in less than optimal, and also alert an operator to any maintenance actions (e.g., light tube cleaning, PECO cartridge replacement, change in solution chemistry, improve turbidity, increased UV transmission, etc.) 
     In operation of the foregoing example embodiment, contaminated fluid, such as contaminated water, may be pumped or otherwise provided or directed into the housing or container. The water may be circulated and/or recirculated within the housing or container. Multiple units, or reactors, may be connected and operated in series, which may result in increased space and time for contaminated fluid in the reactor(s) or device(s). Upon completion of processing, in various embodiments, the water exits the housing and container ready for use, or circulated or recirculated through the device, other device, or system of devices, for further treatment or purification. 
     In various embodiments, in operation, the TiO 2  catalyst or photocatalyst is illuminated with light having sufficient near UV energy to generate reactive electrons and holes promoting oxidation of compounds on the anode surface. 
     Any temperature of aqueous solution or liquid water is suitable for use with the exemplary embodiments of the device such as the instant PECO devices. In various embodiments, the solution or water is sufficiently low in turbidity to permit sufficient UV light to illuminate the photoelectrode. 
     Referring now to  FIGS. 42-45 , in various embodiments, photocatalytic efficiency is improved by applying a potential (i.e., bias) or current across each photoelectrode and counterelectrode or plate pair. Applying or providing a potential or current may decrease the recombination rate of photogenerated electrons and holes. In various embodiments, an effective potential difference or voltage range applied may be in the range of −15 V to +15 V. In various embodiments, an effective potential difference or voltage range applied may be in the range of −7.5 to 7.5 V across a photoelectrode and counterelectrode. In various embodiments, an effective potential difference or voltage range applied may be in the range of 1 V to 7.5 V across the photoelectrode and counterelectrode. 
     For various applications, including for example, fracking fluid or high-salinity applications, it may also be desirable to reverse (e.g., periodically or intermittently) the potential, bias, polarity and/or current applied to or between the photoelectrode and the counterelectrode, or plate pair, (e.g., to clean the photoelectrode and/or counterelectrode, “regen” or regenerate the photoelectrode, counterelectrode, and/or device, or to otherwise improve the performance of the photoelectrode, counterelectrode, and/or device). By reversing the potential, bias, polarity and/or current, the photoelectrode may be changed (e.g., from an anode into a cathode) and the counterelectrode may be changed (e.g., from a cathode into an anode). 
     For example, in various embodiments, initially positive voltage is electrically coupled or connected to a first or positive charge electrode and negative voltage is electrically coupled or connected to a second or negative charge electrode. For example, and referring more specifically to  FIG. 42 , phases of constant voltage may be applied.  FIG. 42  illustrates example methods that may be utilized to provide a constant or substantially constant voltage during a first period of time and to apply a reverse or opposite bias or potential difference during a second period of time. This works well in various applications. In certain applications, however, methods utilizing a constant or substantially constant current during a first period of time and to apply a reverse or opposite bias or potential difference during a second period of time may be advantageous. For example, a relatively constant voltage (e.g, 7.5 V) may be for a first period of time in a “FWD” cycle and, after the first period of time, the positive voltage is switched or electrically connected to the negative charge electrode and the negative voltage is switched or electrically connected to the positive charge electrode to apply a reverse voltage or effective voltage or bias (e.g., −7.5V) in a “REGEN cycle.” After a second period of time in the REGEN cycle, the positive voltage is switched or electrically connected back to the positive charge electrode and the negative voltage is switched or electrically connected back to the negative charge electrode to reapply a relatively constant voltage or effective voltage (e.g., 7.5V) and start another FWD cycle. 
     The length of the first period of time and the second period of time may be the same. In various embodiments, however, the length of the first period of time and the second period of time are different. In various embodiments, and as shown in  FIG. 42 , the first period of time is longer than the second period of time. 
     The length of the first and second periods of time depends on a variety of factors including solution salinity, voltage, etc. For example, fracking fluid or high salinity fluid applications may require relatively more frequent reversal of potential, bias, polarity and/or current compared to fresh water applications. In various embodiments, the lengths of the first period of time relative to the second period of time may be in a ratio of from 3:1 to 50:1, and in one or more further embodiments from 3:1 to 25:1, and in one or more further embodiments from 3:1 to 7:1. For example, in various embodiments, the first period of time and second period of time is about 5 minutes to about 1 minute. Fresh water applications may require relatively less frequent reversal of potential, bias, polarity and/or current, and the lengths of the first period of time relative to the second period of time may be in a ratio of from 100:1 to 10:1. For example, in various embodiments, the first period of time relative to the second period of time is about 60 minutes to a range of about 1 minute to about 5 minutes. 
     In various embodiments, during the second period of time, the counterelectrode or sacrificial electrode of titanium is dissolved at least in part by anodic dissolution. It is believed that a range of coagulant species of hydroxides are formed (e.g., by electrolytic oxidation of the sacrificial counterelectrode), which hydroxides help destabilize and coagulate the suspended particles or precipitate and/or adsorb dissolved contaminants. 
     In various embodiments, the main reaction occurring at the counterelectrodes or sacrificial electrodes during the second period of time (e.g., during polarity reversal) is dissolution: 
       TI (s) →Ti 4+ +4 e   − 
 
     In addition, water is electrolyzed at the counterelectrode (or sacrificial electrode) and photoelectrode: 
       2H 2 O+2 e   − →H 2(g) +2OH −   (cathodic reaction)
 
       2H 2 O→4H + +O 2(g) +4 e   −   (anodic reaction)
 
     In various embodiments, electrochemical reduction of metal cations (Me n+ ) occurs at the photoelectrode surface: 
       Me n+   +ne   −   →n Me 0    
     Higher oxidized metal compounds (e.g., Cr(VI)) may also be reduced (e.g., to Cr(III)) about the photoelectrode: 
       Cr 2 O 7   2− +6 e   − +7H 2 O→2Cr 3+ +14OH − 
 
     In various embodiments, hydroxide ions formed at the photoelectrode increase the pH of the solution which induces precipitation of metal ions as corresponding hydroxides and co-precipitation with metal (e.g., Ti) hydroxides: 
       Me n+   +n OH→Me(OH) n(s)  
 
     In addition, anodic metal ions and hydroxide ions generated react in the solution to form various hydroxides and built up polymers: 
       Ti 4+ +4OH − →Ti(OH) 4(s)  
 
         n Ti(OH) 4(s)   − →Ti n (OH) 4n(s)  
 
     However, depending on the pH of the solution other ionic species may also be present. The suspended titanium hydroxides can help remove pollutants from the solution by sorption, co-precipitation or electrostatic attraction, and coagulation.
 
For a particular electrical current flow in an electrolytic cell, the mass of metal (e.g., Ti) theoretically dissolved from the counterelectrode or sacrificial electrode is quantified by Faraday&#39;s law
 
     
       
         
           
             m 
             = 
             
               ItM 
               zF 
             
           
         
       
     
     where m is the amount of counterelectrode or sacrificial electrode material dissolved (g), I the current (A), t the electrolysis time (s), M the specific molecular weight (g mol −1 ), z the number of electrons involved in the reaction and F is the Faraday&#39;s constant (96485.34 As mol −1 ). The mass of evolved hydrogen and formed hydroxyl ions may also be calculated. 
     In various embodiments, it may be advantageous (e.g., to help limit any anodic dissolution, or pitting or other degradation of the photoelectrode) to apply certain voltages (e.g., relatively higher voltages) during the first period of time and different voltages (e.g., relatively lower voltages) during the second period of time. In various embodiments (e.g., in a fracking fluid application using a counterelectrode including aluminum), the voltage applied during the first period of time may be about 6V to 9V (e.g., about 7.5V) and the voltage applied during the second period of time may be about 0.6V-12V. In various embodiments, during application of relatively higher voltage during the first period of time, contaminants are degraded (or the removal of contaminants is promoted) by photoelectrocatalytic oxidation, and during application of a relatively lower voltage during the second period of time, contaminants are degraded (or the removal of contaminants is promoted) by and electrochemical process such electroprecipitation or electrocoagulation. 
     In various embodiments, during the second period of time, an aluminum counterelectrode or sacrificial electrode is dissolved at least in part by anodic dissolution. It is believed that a range of coagulant species of hydroxides are formed (e.g., by electrolytic oxidation of the sacrificial counterelectrode), which hydroxides help destabilize and coagulate the suspended particles or precipitate and/or adsorb dissolved contaminants. 
     In various embodiments, the main reaction occurring at the counterelectrodes or sacrificial electrodes during the second period of time (e.g., during polarity reversal) is dissolution: 
       Al (s) →Al 3+ +3 e   − 
 
     Additionally, water is electrolyzed at the counterelectrode (or sacrificial electrode) and photoelectrode: 
       2H 2 O+2 e   − →H 2(g) +2OH −   (cathodic reaction)
 
       2H 2 O→4H + +O 2 +4 e   −   (anodic reaction)
 
     In various embodiments, electrochemical reduction of metal cations (Me n+ ) occurs at the photoelectrode surface: 
       Me n+   +ne   −   →n Me 0    
     Higher oxidized metal compounds (e.g., Cr(VI)) may also be reduced (e.g., to Cr(III)) about the photoelectrode: 
       Cr 2 O 7   2− +6 e   − +7H 2 O→2Cr 3+ +14OH − 
 
     In various embodiments, hydroxide ions formed at the photoelectrode increase the pH of the solution which induces precipitation of metal ions as corresponding hydroxides and co-precipitation with metal (e.g., Al) hydroxides: 
       Me n+   +n OH − →Me(OH) n(s)  
 
     In addition, anodic metal ions and hydroxide ions generated react in the solution to form various hydroxides and built up polymers: 
       Al 3+ +3OH − →Al(OH) 3(s)  
 
         n Al(OH) 3(s)   − →Al n (OH) 3n(s)  
 
     However, depending on the pH of the solution other ionic species, such as dissolved Al(OH) 2+ , Al 2 (OH) 2   4+  and Al (OH) 4   −  hydroxo complexes may also be present. The suspended aluminum hydroxides can help remove pollutants from the solution by sorption, co-precipitation or electrostatic attraction, and coagulation.
 
For a particular electrical current flow in an electrolytic cell, the mass of metal (e.g., Al) theoretically dissolved from the counterelectrode or sacrificial electrode is quantified by Faraday&#39;s law
 
     
       
         
           
             m 
             = 
             
               ItM 
               zF 
             
           
         
       
     
     where m is the amount of counterelectrode or sacrificial electrode material dissolved (g), I the current (A), t the electrolysis time (s), M the specific molecular weight (g mol −1 ), z the number of electrons involved in the reaction and F is the Faraday&#39;s constant (96485.34 As mol −1 ). The mass of evolved hydrogen and formed hydroxyl ions may also be calculated. 
     In various embodiments, it may be desirable to apply a variable voltage and/or constant current to a photoelectrode and counterelectrode or plate pair, of a PECO system, apparatus, or device. For example, and as illustrated in  FIG. 42 , application of constant voltage (even in combination with a “REGEN” cycle) flows less current over time during operating life of a reactor. In contrast, and referring now to  FIGS. 43-45 , pulse width modulation may be utilized to vary the voltage applied to a photoelectrode and counterelectrode from 7.5 V to 0 V and back to 7.5 V (e.g., in a FWD cycle) to help maintain a substantially constant current at, between or across, the photoelectrode and counterelectrode during the cycle. 
       FIG. 43  illustrates example methods that may be utilized to maintain a constant or substantially constant current during a first period of time and to provide or apply a reverse or opposite bias or potential difference during a second period of time. As shown in  FIG. 44 , one example of a constant current control method or program  800  maintains constant or substantially constant current during the first period of time, but applies or provides constant or substantially constant voltage during the second period of time. As shown in  FIG. 45 , however, in another example of a constant current control method or program  900 , a constant or substantially constant current may be maintained during the first period of time and a reversed constant or substantially constant current may be maintained during the second period of time. 
     In various embodiments, during a first period of time (e.g., of a FWD cycle), in various embodiments, pulse width modulation is utilized to maintain a constant or substantially constant current to, across, or between the photoelectrode and counterelectrode, or plate pair. In various embodiments, during a second period of time (e.g., of a REGEN cycle), constant voltage is applied to the electrodes as illustrated in  FIG. 44  or constant current is applied to the electrodes as illustrated in  FIG. 45 . 
     Referring more specifically to  FIG. 44 , an example substantially constant current control first cycle  802  followed by a substantially fixed voltage second cycle  804  is shown. In various embodiments, in Step S 805 , constant current control first cycle  802  begins. In various embodiments, the process then moves to Step S 810  where a predetermined pulse width modulation duty cycle and/or voltage is applied to create a constant or substantially constant current (e.g., to or through one or more photoelectrodes and counterelectrodes). In various embodiments, the process moves to Step S 815  during which the current flowing through the photoelectrode and counterelectrode is sampled. In various embodiments, the process moves to Step S 820 , where the current may be averaged. In various embodiments, the process moves to Step S 825  during which a predetermined or programmed period of time is allowed to lapse. After Step S 825 , the process may return to Step S 815 , where the current is sampled again, and may be re-averaged in Step S 820 . Concurrently, in various embodiments, the process moves to Step S 830  where it is determined whether constant current control first cycle  802  may be suspended or stopped. This determination may be made based on time or some other variable. If it is determined in Step S 830  that constant current control first cycle  802  is not complete, the process moves to Step S 835  where, in various embodiments, a determination is made as to whether the current measurements are substantially in line with a predetermined target current level. If the measured current or measured current average is less than the predetermined target current, the process moves to Step S 840  where the predetermined pulse width modulation duty cycle and/or applied voltage may be increased and, in various embodiments, the process returns to Step S 815 . If the measured current or measured current average is greater than a predetermined target current level, the process moves to Step S 845  where the predetermined pulse width modulation duty cycle and/or applied voltage may be decreased and, in various embodiments, the process returns to Step S 815 . If the measured current or measured current average is equal to the predetermined target current level, the predetermined pulse width modulation duty cycle or applied voltage may be maintained and, in various embodiments, the process returns to Step S 815 . 
     If, at Step S 830  of constant current control first cycle  802 , the determination is made that constant current control first cycle  802  is complete or may otherwise be suspended or stopped, the process moves to Step S 850 , where substantially fixed voltage second cycle  804  begins. In various embodiments, at Step S 830 , constant current control first cycle  802  is shut down and reset, as, once or after the process moves to Step S 850  and substantially fixed voltage second cycle  804  begins. The process then moves to Step S 855 . In Step S 855  of substantially fixed voltage second cycle  804 , a predetermined duty cycle or voltage is applied. In various embodiments, the predetermined duty cycle and/or voltage is applied to reverse the current relative to the current flow of constant current control first cycle  802 . After the fixed voltage is applied, the process moves to Step S 860  to determine whether fixed voltage second cycle  804  is complete. This determination may be based upon time or some other variable. If it is determined that fixed voltage second cycle  804  is not complete, the process returns to Step S 855 . If fixed voltage second cycle  804  is complete, the process returns to Step S 805  of constant current control first cycle  802 . In various embodiments, at Step S 860 , substantially fixed voltage second cycle  804  is shut down and reset, as, once or after the process moves to Step S 805  and substantially constant current control first cycle  802  begins. 
     Referring now to  FIG. 45 , an example substantially constant current control first cycle  902  followed by a substantially constant current control second cycle  904  is shown. In various embodiments, in Step S 905 , constant current control second cycle  902  begins. In various embodiments, the process then moves to Step S 910  where a predetermined pulse width modulation duty cycle and/or voltage is applied to create a constant or substantially constant current (e.g., to or through one or more photoelectrodes and counterelectrodes). In various embodiments, the process moves to Step S 915  during which the current flowing through the photoelectrode and counterelectrode is sampled. In various embodiments, the process moves to Step S 920 , where the current may be averaged. In various embodiments, the process moves to Step S 925  during which a predetermined or programmed period of time is allowed to lapse. After Step S 925 , the process may return to Step S 915 , where the current is sampled again, and may be re-averaged in Step S 920 . Concurrently, in various embodiments, the process moves to Step S 930  where it is determined whether constant current control first cycle  902  may be suspended or stopped. This determination may be made based on time or some other variable. If it is determined in Step S 930  that constant current control first cycle  902  is not complete, the process moves to Step S 935  where, in various embodiments, a determination is made as to whether the current measurements are substantially in line with a predetermined target current level. If the measured current or measured current average is less than the predetermined target current, the process moves to Step S 940  where the pulse width modulation duty cycle and/or applied voltage may be increased and, in various embodiments, the process returns to Step S 915 . If the measured current or measured current average is greater than a predetermined target current level, the process moves to Step S 945  where the pulse width modulation duty cycle and/or applied voltage may be decreased and, in various embodiments, the process returns to Step S 915 . If the measured current or measured current average is equal to the predetermined target current level, the predetermined pulse width modulation duty cycle or applied voltage may be maintained and, in various embodiments, the process returns to Step S 915 . 
     If, at Step S 930  of constant current control first cycle  902 , the determination is made that constant current control first cycle  902  is complete or may otherwise be suspended or stopped, the process moves to Step S 950 , where substantially constant current control second cycle  904  begins. In various embodiments, at Step S 930 , constant current control first cycle  902  is shut down and reset, as, once or after the process moves to Step S 950  and substantially constant current control second cycle  904  begins. The process then moves to Step S 955 , where a predetermined pulse width modulation duty cycle and/or voltage is applied to create a constant or substantially constant current (e.g., to or through one or more photoelectrodes and counterelectrodes). In various embodiments, the predetermined pulse width modulation duty cycle and/or voltage is applied to reverse the current relative to the current flow of constant current control first cycle  902 . In various embodiments, the process moves to Step S 960  during which the current flowing through the photoelectrode and counterelectrode is sampled. In various embodiments, the process moves to Step S 965 , where the current may be averaged. In various embodiments, the process moves to Step S 970  during which a predetermined or programmed period of time is allowed to lapse. After Step S 970 , the process may return to Step S 960 , where the current is sampled again, and may be re-averaged in Step S 965 . Concurrently, in various embodiments, the process moves to Step S 975  where it is determined whether substantially constant current control second cycle  904  may be suspended or stopped. This determination may be made based on time or some other variable. If it is determined in Step S 975  that substantially constant current control second cycle  904  is not complete, the process moves to Step S 980  where, in various embodiments, a determination is made as to whether the current measurements are substantially in line with a predetermined target current level. If the measured current or measured current average is less than the predetermined target current, the process moves to Step S 985  where the pulse width modulation duty cycle and/or applied voltage may be increased and, in various embodiments, the process returns to Step S 915 . If the measured current or measured current average is greater than a predetermined target current level, the process moves to Step S 990  where the pulse width modulation duty cycle and/or applied voltage may be decreased and, in various embodiments, the process returns to Step S 915 . If the measured current or measured current average is equal to the predetermined target current level, the predetermined pulse width modulation duty cycle or applied voltage may be maintained and, in various embodiments, the process returns to Step S 915 . In various embodiments, at Step S 975 , substantially constant current control second cycle  904  is shut down and reset, as, once or after the process moves to Step S 905  and substantially constant current control first cycle  902  begins. 
     By combining pulse width modulation with monitoring (e.g., real time monitoring) of the current across or at the photoelectrode and counterelectrode, the effective or operating currents may be regulated and/or substantially maintained at a specified run level. The voltage, current, and pulse width modulation may be varied depending upon the desired run level, which may be determined based on a variety of factors, including the degree of biological (e.g., bacteria, viruses, protozoans, fungi, etc.) kill necessary or desired, clarity at the solution, salinity of the solution, flow rate, operating life goals or expectations, sleeve fouling, and/or a reduction or anticipated reduction in photoactivity of the photoelectrode (or anode) over time, etc. In various embodiments, current is regulated in a closed loop manner so as to run at a preset or predetermined “run level.” In various embodiments, the duty cycle is automatically changed and the effective plate voltage is increased or maintained as needed or desired to reach or maintain a predetermined or desired current. In various embodiments, passivation currents are reduced as lower operating currents are achieved. In various embodiments, run level may be based on a variety of factors (e.g., degree of kill needed or desired, salinity and flow rate of solution, operating lift goals, etc.) and reactor life may be extended. 
     Initially, lower voltage or bias may be applied or provided to the PECO device, apparatus, or system to flow a constant current between a photoelectrode and a counterelectrode. For example, newer electrodes, cleaner UV tubes or sleeves, cleaner or less turbid solution, new UV lamps, etc. allow the PECO system, device, or apparatus to maintain a predetermined run level of current at the photoelectrode and counterelectrode using pulse width modulation and a lower voltage or effective voltage. As one or more components (e.g., the electrodes, sleeves, etc.) foul, a switcher board may sense a need to adjust voltage (e.g., 1.5 to 2.5 volts), and automatically adjust the duty cycle and/or voltage over time to maintain a substantially constant current, or other target operating or effective current or range of currents. 
     Maintaining a constant or substantially constant current at the photoelectrode and counterelectrode may optimize the operating life of the PECO system, apparatus, or device. As the pulse width modulation duty cycle nears or reaches 100% without being able to maintain a predetermined or desired run level of current at the photoelectrode and counterelectrode, maintenance may be required. For example, such conditions may indicate that new photoelectrodes or counterelectrodes are needed, sleeves need to be replaced or repaired, or lamps need to be replaced, etc. 
     The voltage required to achieve a target or otherwise predetermined or desired operating current may be utilized as a performance indicator. For example, a certain voltage requirement may indicate that service of the photoelectrode, quartz sleeve, or other component of the PECO apparatus or system should or must be conducted. As one example, when the voltage required to achieve a target or effective current at the photoelectrode or anode nears or exceeds 7.0 V, this may be an indication that one or more of components of a PECO apparatus or system should be serviced and/or maintained soon. 
     As another example, and referring again to  FIG. 43 , when the current at the photoelectrode (e.g., anode) nears or falls below approximately 75% of a target, a predetermined, or otherwise desirable operating or effective current, this may indicate that maintenance of one or more components of the PECO apparatus or system is required immediately. 
     It should be appreciated that, while 7.0 V and 75% of the target operating current is shown and discussed above, the voltage and/or current point indicating or otherwise requiring maintenance may be adjusted as desired or determined by the user. 
     Various indicators may be provided to help indicate or signal when maintenance may be required soon or immediately. For example, indicators such as “change soon” or “change now,” or another visual or audible indicator may be provided (e.g., on the user interface). Other indicators such as “clean glass,” “check cartridge,” or “change cartridge,” or other alternative visual or audible indicator may further be utilized. In various embodiments, the PECO apparatus or system performance monitoring is implemented utilizing various constant current circuitry and code. 
     In addition, maintaining a constant or substantially constant current at the photoelectrode and/or counterelectrode and/or monitoring the current at the photoelectrode and counterelectrode may also be utilized to detect and/or indicate a short circuit and/or protect a PECO system, apparatus, or device from such a short circuit. The current may be monitored and the PECO apparatus, system, or device shut down when the current exceeds a certain level. For example, and referring to  FIG. 45 , a substantially constant current control second cycle or “REGEN” cycle may be shut down when measured current exceeds a predetermined level or amount for a predetermined length of time (e.g., 12 amps for more than two seconds). 
     A short may also be indicated if, during a “FWD” cycle, the current exceeds a certain level for a certain period of time. For example, a short may be indicated during a “FWD” cycle if the current is greater than 5.5 amps for at least 200 milliseconds. In various embodiments, to better determine the existence of a short or some other condition, in various embodiments, the duty cycle may be stepped down (e.g., 20%, or  51  steps of 255, of full scale), and the current sampled again after a period of time (e.g., 100 milliseconds). In various embodiments, the duty cycle may be stepped down again if the level of current over a period of time still indicates a short. This step-down process may be repeated to a predetermined percentage of full scale. For example, the step-down process may be repeated until the duty cycle is 14% of full scale. 
     The present disclosure, in one or more examples of embodiments, is directed to methods of treating an aqueous solution having one or more contaminants therein to help remove or reduce the amounts of contaminants. In various embodiments, the method includes providing an aqueous solution comprising at least one contaminant selected from the group consisting of an organism, an organic chemical, an inorganic chemical, and combinations thereof and exposing the aqueous solution to photoelectrocatalytic oxidization. 
     In one example of an application of the device described herein, the device uses photoelectrocatalysis as a treatment method for fracking fluid. While typically described herein as reducing or removing contaminants from fracking fluid, it should be understood by one skilled in the art that photoelectrocatalysis of other contaminants can be performed similarly using the device (e.g., photoelectrocatalytic oxidation or PECO device). 
     Generally, the method for reducing amount of contaminants in solution or fluid described includes introducing the solution into a housing or container or cell including: a UV light; a photoelectrode, wherein the photoelectrode comprises an anatase polymorph of titanium, a rutile polymorph of titanium, or a nanoporous film of titanium dioxide; and a cathode. The photoelectrode is irradiated with UV light, and a first potential is applied to the photoelectrode and counterelectrode for a first period of time. In various embodiments, a second potential is applied to the photoelectrode and counterelectrode for a second period of time. As a result, the contaminant amount in solution is reduced. 
     In various embodiments, one or more contaminants are oxidized by a free radical produced by a photoelectrode, and wherein one or more contaminants are altered electrochemically (e.g., by electroprecipitation or electrocoagulation). In various embodiments, one or more contaminants are oxidized by a chlorine atom produced by a photoelectrode. In various embodiments, one or more contaminants are altered electrochemically (e.g., by electroprecipitation or electrocoagulation). 
     In one or more embodiments, the apparatus and methods utilize photoelectrocatalytic oxidation, whereby a photocatalytic anode is combined with a counterelectrode to form an electrolytic cell. In various embodiments, when the instant anode is illuminated by UV light, its surface becomes highly oxidative. By controlling variables including, without limitation, chloride concentration, light intensity, pH and applied potential, the irradiated and biased TiO 2  composite photoelectrode may selectively oxidize contaminants that come into contact with the surface, forming less harmful gas or other compounds. In various embodiments, application of a potential and current to the photoelectrode provides further control over the oxidation products. Periodic or intermittent reversal of the potential or current may help further remove or reduce the amount of contaminants. 
     The foregoing apparatus and method provides various advantages. For example, photoelectrodes which include nanotubes tend to remove or reduce the amounts of contaminants in solution effectively. Further, by maintaining a fixed or constant or substantially fixed or constant current application, where the voltage or bias is varied (e.g., automatically varied) over time, initial operating voltages may be automatically reduced and the effective life of the PECO system, device, or apparatus and/or its components extended. In addition, maintaining a constant or substantially constant current also improves the uniformity and predictability of PECO apparatus, device, or system performance. 
     A temperature probe(s) or sensor(s) may also be provided in one or more examples of embodiments. For example, the temperature probe(s) may be positioned in the housing or the adapter of the UV light assembly. The temperature probe may monitor the temperature in the device or in the fluid within the respective device and communicate that temperature reading. Further the temperature probe may be in communication with a shut-off switch or valve which is adapted to shut the system down upon reaching a predetermined temperature. 
     A fluid level sensor(s) may also be provided which may communicate a fluid level reading. The fluid level sensor(s) may be positioned in the device. Further the fluid level sensor may be in communication with a shut-off switch or valve which is adapted to shut off the device or increase the intake of fluid into the device upon reaching a predetermined fluid value. 
     In one or more examples of embodiments, the device includes a carbon filter adapted to filter chlorine from the water. In various embodiments, the device includes a computer adapted to send one or more controlled signals to the existing power supplies to pulse the voltage and current. 
     The invention is further illustrated in the following Examples which are presented for purposes of illustration and not of limitation. 
     Example 1 
     A first PECO device (the NT device) was assembled including a photoelectrode made a foil with TiO 2  nanotubes grown thereon as described above. A solution including dye was provided into the first PECO device and a constant current of approximately 2.5 A was maintained across the photoelectrode and counterelectrode of the first PECO device. 
     The dye removal properties of the first PECO device were tested against the dye removal properties of a second PECO device (the Std Device) assembled using substantially similar components but photoelectrodes made of a foil with a nanoporous TiO 2  film provided thereon and manufactured as described above. A graph comparing the dye removal properties of the two PECO devices is shown in  FIG. 20 . 
     Example 2 
     First and second PECO devices were assembled including a photoelectrode made from a foil with TiO 2  nanotubes grown thereon as described above. A solution including dye was provided into the first PECO device and a constant current of approximately 2.5 A was maintained across the photoelectrode and counterelectrode of the first PECO device. A solution including dye was provided into the second PECO device and a constant voltage of approximately 7.5 V was provided across the photoelectrode and counterelectrode of the second PECO device. 
     A third and fourth PECO device were assembled including a photoelectrode made of a foil with a nanoporous TiO 2  film provided thereon as described above. A solution including dye was provided into the third PECO device and a constant current of approximately 2.5 A was maintained across the photoelectrode and counterelectrode of the third PECO device. A solution including dye was provided into the fourth PECO device and a constant voltage of approximately 7.5 V was provided across the photoelectrode and counterelectrode of the fourth PECO device. 
     The dye removal properties of the first, second, third and fourth PECO devices were tested against each other. A graph comparing the dye removal properties of the four PECO devices is shown in  FIG. 21 . 
     As utilized herein, the terms “approximately,” “about,” “substantially”, and similar terms are intended to have a broad meaning in harmony with the common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. It should be understood by those of skill in the art who review this disclosure that these terms are intended to allow a description of certain features described and claimed without restricting the scope of these features to the precise numerical ranges provided. Accordingly, these terms should be interpreted as indicating that insubstantial or inconsequential modifications or alterations of the subject matter described and claimed are considered to be within the scope of the invention as recited in the appended claims. 
     It should be noted that references to relative positions (e.g., “top” and “bottom”) in this description are merely used to identify various elements as are oriented in the Figures. It should be recognized that the orientation of particular components may vary greatly depending on the application in which they are used. 
     For the purpose of this disclosure, the term “coupled” means the joining of two members directly or indirectly to one another. Such joining may be stationary in nature or moveable in nature. Such joining may be achieved with the two members or the two members and any additional intermediate members being integrally formed as a single unitary body with one another or with the two members or the two members and any additional intermediate members being attached to one another. Such joining may be permanent in nature or may be removable or releasable in nature. 
     It is also important to note that the construction and arrangement of the system, methods, and devices as shown in the various examples of embodiments is illustrative only. Although only a few embodiments have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited. For example, elements shown as integrally formed may be constructed of multiple parts or elements show as multiple parts may be integrally formed, the operation of the interfaces may be reversed or otherwise varied, the length or width of the structures and/or members or connector or other elements of the system may be varied, the nature or number of adjustment positions provided between the elements may be varied (e.g., by variations in the number of engagement slots or size of the engagement slots or type of engagement). The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangement of the various examples of embodiments without departing from the spirit or scope of the present inventions. 
     While this invention has been described in conjunction with the examples of embodiments outlined above, various alternatives, modifications, variations, improvements and/or substantial equivalents, whether known or that are or may be presently foreseen, may become apparent to those having at least ordinary skill in the art. Accordingly, the examples of embodiments of the invention, as set forth above, are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit or scope of the invention. Therefore, the invention is intended to embrace all known or earlier developed alternatives, modifications, variations, improvements and/or substantial equivalents.