Multiple contaminants are a problem for process engineers in a range of industries, including:
Textiles;
Pulp and paper;
Mining;
Manufacturing;
Metal finishing;
Food processing; and
Tanning. The problem is compounded in water treatment systems when these contaminants (heavy metals, fats, grease or oil) become responsible for damaging membranes or resins, putting them out of service. Electrocoagulation is an emerging technology that serves as a viable alternative for overcoming these types of bottlenecks.
The resurgence of electrocoagulation
Electrocoagulation is an electrochemical process that uses direct current to remove contaminants from wastewater. Although the process was patented and used to treat bilge water from ships as early as 1906, it was not developed further for other industrial purposes.
Factors such as a low level of environmental awareness and a lack of sufficient financial incentives were probably responsible for abandoning this technology. However, stringent regulations and a focus on cost-effective alternatives have been responsible for the resurgence of electrocoagulation.
What are its benefits?
Electrocoagulation drastically reduces the use of chemical reagents. Thus, apart from reducing operational costs, the process also does away with the extra safeguards required for storing and handling these reagents. With a very high degree of contaminant removal, there is greater potential for water reuse after electrocoagulation. Moreover, the process generates less sludge compared to other technologies.
Also, the residual concentrations in the effluents are lower, making them suitable for direct discharges.
The technology accepts a wider range of wastewater with varied pH levels, is less complicated, and is capable of self-monitoring. Thus extensive manual interface is eliminated.
During the 1990s, there was renewed interest in commercializing the electrocoagulation process. End-users were responsible for the development of most of the current processes associated with electrocoagulation.
Texas-based Kasper Electroplating had problems with the water treatment equipment it was using, and came up with its own version of electrocoagulation using a new reactor design.
The company patented it as the KASELCO process, which was successfully used to treat wastewater from the company‘s nickel-, chromium-, and zinc-plating shops.
Saddled with the problem of oily wastewater from its operations at the Vancouver Ship Yard, the Washington Marine Group (WMG) developed electrocoagulation technology.
The process has now been patented by McKay Creek Technologies (the technology arm of WMG), and is capable of turning dirty, oily, turbid, polluted, wastewater into clear water, meeting the quality standards of numerous states. This technology has also been tested for a variety of other industrial applications.
The U.S. Navy has successfully tested the electrocoagulation process for treating wastewater from aircraft engine gas-path cleaning (containing cadmium and other heavy metal pollutants), and also for aircraft wash water. The treated water can be recycled or discharged into a municipal sewer.
Further areas of application
Of particular interest is the application of the electrocoagulation process in the mining industry. The process has dealt with dewatering coal fines and wastewater from wash plants, reducing the need for chemical flocculation techniques. It has also been successfully tested on acid mine-drainage waters, resulting in increased pH values and removal of solids.
In Sydney, Australia, an electrocoagulation system has been tested for the treatment of fresh water that was unfit for drinking purposes due to the presence of clay and other contaminants such as bacteria and algae.
The experiments resulted in contaminant removal rates of greater than 98 percent, indicating that with further refinement of the process, the treated water would comply with the drinking water guidelines of Australia and many other countries.
Electrocoagulation also yielded some positive results with respect to treating wastewater in the effluent aeration unit of a municipal sewage treatment plant. Higher turbidity and bacterial count reductions were achieved and only minor antiseptic treatment was required to bring the bacteria content down to zero.
Apart from eliminating the need for chlorination, the process also achieved a reduction in suspended solids without the need for alum or any other coagulating agents.
Challenges
One of the main challenges is that electrocoagulation technology uses a great deal of electricity while treating wastewater. As it directly affects operating costs, more research into ways of reducing power consumption would aid rapid acceptance of this technology. At times, electrocoagulation increases the temperature of the water stream, rendering the direct discharge of the water difficult. This also affects certain other downstream activities.
In some rare instances, it has been found that small quantities of substances that the process is supposed to eliminate find their way back into the treated water stream, thus challenging the efficiency of electrocoagulation systems.
The process also faces stiff competition from established counterparts, such as membrane technologies and reverse osmosis systems. The ability of this technology to integrate effectively with other existing water treatment systems in use at plants would determine its maturity.
However, the ultimate success of electrocoagulation will depend on its inherent ability to satisfy certain commercial criteria, such as a fast return on investment and the ability to keep operation and maintenance costs low.
