Nearly one hundred years ago, A. E. Dietrich (U.S. Pat. No.823,671) discovered that fluids passed through an electrical field would change in character. If the surfaces imparting the charge to the fluid were of specific materials, contaminants in the water would react, coagulate, and separate. The principle was applied to a system for treating bilge water from ships but was abandoned for lack of interest. The technology lay dormant for the better part of the century since commodity chemicals for chemical treatment of wastewater were readily available and inexpensive. Interest in elimination of salts caused by chemical treatment discharged into watercourses and changes in environmental rules for effluent concentration limits caused a resurgence of interest in the technology. Adding to that interest was the rise in chemical costs and the problems associated with disposal of sludge from chemical water treatment processes.
The basic principle of electrocoagulation has changed little since Dietrich. A number of companies have explored various configurations of surface, materials, and electrical current in an effort to optimize the technology. Many have failed, while some met with success. Configurations of the surfaces have included submerged rods, tubes within tubes, flat plates, and fluidized beds of small particles. Electrical supplies have included high and low voltage AC and DC currents, high frequencies, square waves, and other, exotic waveforms. The most commercially successful to date has been the Kaselco system, which uses simple, flat plates and low voltage DC current.
The patented Kaselco process (U.S. Pat. No. 5928493, 6,294,061, and others) is produced under the auspices of Kaspar Electroplating Corporation, one of three privately held Kaspar companies in Shiner, Texas. The Kaspar companies have existed since 1892 and are best known for producing 85% of the newspaper vending machines used in North America. With over 850 employees and twelve acres of manufacturing facility under roof, Kaselco probably has the greatest support base of any company that ever attempted to field working electrocoagulation systems. Introduced to the process first as a user, they quickly learned that the process could be vastly improved with good engineering. Research began in 1995 and their first system was operating the same year. Since then, over thirty systems have been fielded in a variety of applications, usually in removing metals from water. Research into the electrochemistry of the process continues in joint efforts between KASELCO, Lamar University, Texas A&M University, and others.
The process continues to prove its advantages despite the limited number of systems in use. It is capable of removing heavy and other metals, breaking oil emulsions, reducing suspended and dissolved solids, reducing BOD and COD, and many other applications. The technique typically reaches treatment levels below the capability of standard chemical precipitation processes, usually without the use of chemical reagents.
Electrocoagulation is a process that uses electricity and sacrificial plates to combine with contaminants in a waste stream, producing insoluble oxides and hydroxides that are easily removed. It replaces slow and complex chemical treatment. The need for acid, caustic, ferric chloride, sulfites or many other reagents is either reduced or totally eliminated. The process can also break oil emulsions and will oxidize low levels of organic chemicals and surfactants.
In practice the combination of fluid, contaminants, electricity, and the sacrificial plates creates an ion soup within the reactor. The reactive hydrogen, oxygen, hydroxyl groups, and electrons generated act upon the other ions and elements, allowing them to combine into their most stable forms. Hexavalent chromium is reduced to its trivalent state by the direct action of excess electrons and by the presence of iron. The trivalent chromium and other metals typically form a metal iron oxide complex that precipitates and is environmentally stable. Metallic sludges from the process survive the USEPA’s Toxicity Characteristic Leachate Procedure (TCLP) testing. Since the TCLP test is used to classify wastes, the sludge is not considered hazardous waste (unless it is a specifically “listed” waste).
Standard technologies for flotation or settling are used for separation of solids after the electrocoagulation reaction. Both floating and settling techniques may be employed concurrently with mixed wastes having lighter fractions. The normal process is to agitate the treated liquid until all electrolysis gasses are given up and the solids settle. Separation of settled solids is usually more efficient and effective than skimming or other surface removal.
Several common materials such as steel, aluminum, and titanium are available for the reactor plates. Each material has specific uses, although each can also treat a broad range within that application. Kaselco tests all the potentially applicable plate materials as part of its laboratory procedure. While earlier practitioners often found it necessary to use aluminum within the reactor, Kaselco avoids this wherever possible. To date, it has not been necessary to use anything but common (recycled) steel plates in a commercial system.
The unique design of the Kaselco reactor allows the selection of an internal configuration to match the conductivity of the waste being treated. Reactor design and plate selection are based on laboratory testing and extensive experience with electrocoagulation and are controlled predominantly by the conductivity of the solution. The minimum conductivity for most treatment is on the order of 450 microsiemens. No maximum conductivity has been found.
Treatment levels attained by the Kaselco process are typically below the capabilities of conventional chemical precipitation (see table, attached). This makes electrocoagulation the method of choice for direct dischargers or others faced with ultra-low limits. The table does not demonstrate the lowest levels possible, but shows the levels achieved by efficient, operating systems tuned for optimum plate life. Lower levels are achievable if necessary, even levels below detectable limits with difficult wastes.
Other advantages of the process are its ability to treat water with no or fewer reagents added to the waste stream and its ability to remove some dissolved solids. The combination of these two aspects results in discharge of a more environmentally acceptable water with fewer dissolved solids (the salts that are formed in conventional chemical processes). This discharge is not only better for the environment but is also more suitable for re-use. The system will remove some chlorides and sulfates, depending on their associated cations. Sulfate removals of up to 84% have been achieved. Also, the final anion concentration is lower regardless of the removal rate since fewer or no reagents are added to the wastewater for treatment. This reduces the load on and increases the recovery rates of any subsequent treatment used for water recycling, such as membrane technologies or ion exchange.
Treatment costs can be drastically reduced using electrocoagulation, particularly on dilute streams. The process typically reduces treatment costs for industrial streams to $0.84 to 4.00 per thousand gallons of wastewater, including as little as $0.24 for electricity. Concentrated solutions with metals above 150 ppm may entail a higher cost. Very concentrated streams are more appropriate for chemical treatment. Steams with flows greater than 75 gallons per minute will show increased savings, as they allow use of a high capacity (Hi-Flo)reactor. Reactors are available in 2.5, 10, 25, and 75-1,500 gallon per minute sizes.
The life of the sacrificial plates is a function of the amperage and the acidity of the water. Since the electrocoagulation process raises the pH of the water electrically it usually obviates addition of caustic or lime. Plate replacement is simple and quick. Plates may be obtained from Kaselco or prepared by the user using Kaselco drawings. No welding is required.
The electrocoagulation process uses conventional solids separation techniques to remove the sludge after reaction. Thus chemical precipitation systems can be converted simply by substituting a KASELCO reactor for the reaction vessel. Investment in new solids separation equipment is normally not required since the sludge is typically lower in volume and separates more easily. The granular structure of the coagulated solids makes them easily filtered.
Kaselco systems are designed for serviceability, with the operator and maintenance technician in mind. Easily obtained brands and models of motors, sensors, gearboxes, etc. are used throughout the systems. All plumbing components have nearby cleanouts or removable sections. Only true-union ball valves are used in waste service. A blockage in the system requires no cutting, threading, or gluing. Touch-screen PLC controls are standard for automated systems. Chemical-resistant epoxy and coal tar epoxy are used to provide an attractive, durable finish.
Successful application of each system is assured by a complete, free laboratory analysis and bench-scale pilot reaction of a representative sample. Pilot-scale testing on-site can be arranged and, once testing is complete, each system can be covered by a performance guarantee.
Additional information is available from Kaselco at 1-888-KASELCO (888-527-3526). Or stop by and see us in Shiner, Texas.
