Electrocoagulation Overview
Electrocoagulation (EC), the passing of electric current through water, has proven very effective in the removal of contaminants from water. Electrocoagulation systems have been in existence for many years (Dietrich, patented, 1906) using a variety of anode and cathode geometries, including plates, balls, fluidized bed spheres, wire mesh, rods and tubes.
Scott Wade Powell of Powell Water Systems, Inc. has taken a quantum leap in refining 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 electrically induced oxidation and reduction reactions. This process is able to take out over 99 percent of some heavy metal cations and also appears to be able to electrocute 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 some 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 metal) 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 colloidal (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 replace and/or reduce the use of expensive chemical agents (metal salts, polymers).
Specific Examples
Contaminant Removal
Before and After
