From the The Third Annual Australian Environmental Engineering Research Event. 23-26 November Castlemaine, Victoria 1999
ELECTROCOAGULATION AS A WASTEWATER TREATMENT
Peter Holt, Geoffrey Barton and Cynthia Mitchell Department of Chemical Engineering, The University of Sydney, New South Wales, 2006.
Coagulation and flocculation are traditional methods for the treatment of polluted water. Electrocoagulation presents a robust novel and innovative alternative in which a sacrificial metal anode doses water electrochemically. This has the major advantage of providing active cations required for coagulation, without increasing the salinity of the water.
Electrocoagulation is a complex process with a multitude of mechanisms operating synergistically to remove pollutants from the water. A wide variety of opinions exist in the literature for key mechanisms and reactor configurations. A lack of a systematic approach has resulted in a myriad of designs for electrocoagulation reactors without due consideration of the complexity of the system. A systematic, holistic approach is required to understand electrocoagulation and its controlling parameters. This will enable a priori prediction of the treatment of various pollutant types.
Electrocoagulation, electroflotation, wastewater treatment, sacrificial electrodes.
The natural resources of Australia are limited, and as such the use and reuse of water is becoming an increasing concern. Cost-effective methods are required to treat a wide range of wastewater pollutants in a diverse range of situations.
Coagulation and flocculation are traditional methods for the treatment of polluted water. In these processes, coagulating agents (e.g. alum or ferric chloride) and other additives (e.g. polyelectrolytes) are dosed to produce larger aggregates, which can be separated physically. This is a multi-stage process that requires considerable land area and a continual supply of chemicals. A more cost-effective method to clean a wide range of polluted water, on-site, and with minimal additives, is required for sustainable water management. Electrocoagulation treatment of water may fit this description.
Electrocoagulation involves dissolution of metal from the anode with simultaneous formation of hydroxyl ions and hydrogen gas occurring at the cathode. Electrocoagulation has been proposed since before the turn of the century with Vik et al. (1984) describing a treatment plant in London built in 1889 (for the treatment of sewage by mixing with seawater and electrolyzing). In 1909, in the United States, J.T. Harries (Vik et al., 1984) received a patent for wastewater treatment by electrolysis with sacrificial aluminium and iron anodes. Matteson et al. (1995) describe a device of the 1940’s, the “Electronic Coagulator” which electrochemically dissolved aluminium (from the anode) into solution, reacting this with the hydroxyl ion (from the cathode) to form aluminium hydroxide. The hydroxide flocculates and coagulates the suspended solids purifying the water. A similar process was used in Britain in 1956 (Matteson et al., 1995) for which iron electrodes were used to treat river water.
Presently electrocoagulation is marketed by a small number of companies around the world. A variety of designs have been employed with no dominant design. Often the electrocoagulation units are used simply as a replacement for chemical dosing systems and do not take advantage of the electrolytic gases produced in the electrocoagulation process.
It is clear that electrocoagulation has the capability to remove a large range of pollutants under a variety of conditions ranging from: suspended solids (Matteson et al. 1995); heavy metals (Osipenko The Third Annual Australian Environmental Engineering Research Event. 23-26 November Castlemaine, Victoria 1999 and Pogorelyi, 1977); petroleum products (Amosov et al 1976); colour from dye-containing solution (Do and Chen, 1994); aquatic humus (Vik et al. 1984); and defluoridation of water (Mameri et al. 1998).