Electrocoagulation

electrocoagulation research

Electrocoagulation (EC), the passing of electrical current through water, has proven very effective in the removal of contaminants from water. Electrocoagulation systems have been in existence for many years (Dieterich, patented 1906), using a variety of anode and cathode geometries, including plates, balls, fluidized bed spheres, wire mesh, rods, and tubes. F&T Water Solutions technology has taken a quantum leap in refining the EC process to increase removal rates and to lower capital and operating costs.

“The electrocoagulation process…is based on valid scientific principles involving responses of water contaminants to strong electric fields, currents, and electrically induced oxidation and reduction reactions. Depending on the solution matrix, this process is able to take out over 99 percent of some heavy metal cations and also appears to be able to disrupt cell wall or cell membrane of microorganisms in the water. It is also able to precipitate charged colloids and remove significant amounts of other ions, colloids, and emulsions . When the system is in place, the operating costs including electric power, replacement of electrodes, pump maintenance, and labor can be less than $1 per thousand gallons for many applications. Potential applications to agriculture and quality of rural life include removal of pathogens and heavy metals from drinking water and decontamination of food processing wash waters.”

Coagulation is one of the most important physiochemical operations used in water treatment. This is a process used to cause the destabilization and aggregation of smaller particles into larger particles. Water contaminants such as ions (heavy metals) and colloids (organics and inorganics) are primarily held in solution by electrical charges. Schulze, in 1882, showed that colloidal systems could be destabilized by the addition of ions having a charge opposite to that of the colloid (Benefield et al., 1982). The destabilized colloids can be aggregated and subsequently removed by sedimentation and/or filtration.

Coagulation can be achieved by chemical or electrical means. Chemical coagulation is becoming less acceptable today because of the higher costs associated with chemical treatments (e. g. the large volumes of sludge generated, and the hazardous waste categorization of metal hydroxides, to say nothing of the costs of the chemicals required to effect coagulation).

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

Electrocoagulation can often neutralize ion and particle charges, thereby allowing contaminants to precipitate, reducing the concentration below that possible with chemical precipitation, and can reduce or replace the use of expensive chemical agents (metal salts, polymer).

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

Electrocoagulation has reduced contaminated water volume by 98% and lowered the treatment cost by 90% for bilge water containing heavy metals and oil emulsions (Gilmore 1993).

Electrocoagulation performance for water treatment may vary because of the individual chemistry of process waters, a few examples of water treated by electrocoagulation include:

  • The reduction of bacteria from 110,000,000 (standard plate count) in sewage waste water to 2,700 bacteria per milliliter;
  • The contaminants in oily waste waters from steam cleaning operations, refineries, rendering plants, and food processors are generally reduced by 95 to 99%;
  • Dissolved silica, clays, carbon black, and other suspended materials in water are generally reduced by 98%;
  • Heavy metals in water such as arsenic, cadmium, chromium, lead, nickel, and zinc are generally reduced by 95 to 99%.

    Note: Heavy metals processed with sufficient activation energy precipitate into acid resistant oxide sludges like NiFe2O4 that pass the Toxic Classification Leaching Procedure (TCLP) which allows the sludge to be reclassified as non hazardous (Renk, 1989; Franco, 1974; Watanabe and Nojiri, 1975; Duffey, 1983).
  • F&T’s Variable Electro Precipitator™ (VEP™) delivers electrocoagulation through reaction chambers and produces several distinct electrochemical results independently. These observed reactions may be explained as:

  • Seeding resulting from the anode reduction of metal ions that become new centers for larger, stable, insoluble complexes, that precipitate as complex metal oxides;
  • Emulsion breaking resulting from the oxygen and hydrogen ions that bond into the water receptor sites of oil molecules creating a water insoluble complex separating water from oil, driller’s mud, dyes, inks, etc.;
  • Halogen complexing as the metal ions bind themselves to chlorines in a chlorinated hydrocarbon molecule resulting in a large insoluble complex separating water from pesticides, herbicides, chlorinated PCB's, etc.;
  • Bleaching by the oxygen ions produced in the reaction chamber oxidizes dyes, cyanides, bacteria, viruses, biohazards, etc.;
  • Electron flooding of the water eliminates the polar effect of the water complex, allowing colloidal materials to precipitate, and the increase of electrons creates an osmotic pressure that ruptures bacteria, cysts, and viruses;
  • Oxidation - Reduction reactions are forced to their natural end point within the EC chamber which speeds up the natural process of nature that occurs in wet chemistry;
  • EC induced pH swings toward neutral.
  • F&T’s Variable Electro Precipitator™ (VEP™) uses separate reaction chambers in series to produce distinct electrochemical results in each chamber. The Variable Electro Precipitator™ process is optimized by controlling reaction chamber anode and cathode materials (iron, aluminum, titanium, graphite, etc.), amperage, voltage, water flow rate, and the pH of the water. The technology handles mixed waste streams (oil, metals, bacteria), very effectively. Variables such as temperature and pressure typically have little effect on the process. Typically separate performance testing is conducted on each wastestream prior to deployment.

    The electrocoagulation fundamentals:

  • harvest protein, fat, and fiber from food processor waste streams.
  • recycle water, allowing closed loop systems.
  • remove metals, and oil from wastewater.
  • recondition antifreeze by removing oil, dirt, and metals.
  • recondition brine chiller water by removing bacteria, fat, etc.
  • pretreatment before membrane technologies like reverse osmosis.
  • precondition boiler makeup water by removing silica, hardness, TSS, etc.
  • recondition boiler blow down by removing dissolved solids eliminating the need for boiler chemical treatment.
  • remove BOD, TSS, TDS, FOG, etc., from wastewater before disposal to POTW, thus reducing or eliminating discharge surcharges.
  • dewater sewage sludge and stabilize heavy metals in sewage, lowering freight and allowing sludge to be land applied
  • condition and polish drinking water
  • remove chlorine and bacteria before water discharge or reuse
  • Cost: The operating costs of electrocoagulation vary greatly as a function of the chemical makeup of the specific water to be treated. For example, municipal sewage water was treated for $0.00024/ gallon, and steam cleaner water containing crude oil, dirt and a high concentration of heavy metals was treated for $0.05/gallon.