The Principle of Electroflotation and Electrocoagulation

The Principle of Electroflotation and Electrocoagulation

Electroflotation involves the electrolytic production of gases (O2, H2) that can be used to attach pollutants, such as fats and oils, to the gas bubbles and carry them up to the top of the solution where they can be more easily collected and removed. Electrocoagulation refers to the electrochemical production of destabilization agents that bring about charge neutralization for pollutant removal. Electroflocculation is the electrochemical production of agents that promote particle bridging or coalescence.

In the electrocoagulation process, contaminated water is forced to flow between sacrificial electrodes while alternating or direct current electricity is applied to the system. In most cases the sacrificial electrodes are made of iron or aluminum, therefore, hydrogen gas is produced on the cathodes, and Fen+ or Al3+ ions result from the oxidation of the anode. These ions can react with the OH- ions produced at the cathode and yield insoluble hydroxides that will precipitate, absorbing pollutants out of the solution, and also will contribute to coagulation flocculation processes.

These electrocoagulation-electroflotation processes have proven to be as good as the combined chemical precipitation-air flotation processes, both can remove simultaneously and successfully oil and heavy metals from wastewaters. Opportunities for the electroflotation-electrocoagulation-electro flocculation processes include cleanup of oil-water emulsions, dye removal, phosphorus removal, and the treatment of waters containing food and protein wastes, synthetic detergents, and fluorides.

Electrocoagulation offers several advantages, such as removal of the smallest charged colloids, it reduces the number of required chemicals and avoids the need for mechanical agitation, the durability of the electrodes translates to low downtimes for maintenance or replacement, effective organic matter removal, coagulant dosing as well as required overpotentials can be easily calculated and controlled, the observed pH increase aids in the removal of heavy metal ions by their precipitation as hydroxides or by adsorption into other flocs or precipitates, operating costs are much lower when compared with most of the conventional technologies.

The major challenges for these processes are: slightly increased concentration of aluminum or iron ions in the effluent; insoluble hydroxides may agglomerate between the electrodes, hampering their further production; anode passivation and sludge deposition on the electrodes.