For industrial wastewater treatment, organic compounds remain a troubling obstacle.
When electronics or pharmaceutical operations contaminate the water they use with complex solvents and other organic substances, or agriculture operations leech pesticides and herbicides into their effluent, the resulting wastewater is high in non-biodegradable contaminants that must be removed before it can return to the environment.
Traditional methods for removing these organics include adsorption and the use of membrane bioreactors. But no industrial operation would decline a technology that is more energy- and cost-efficient.
Researchers from the National University of Singapore (NUS) believe they have come up with that solution for organic compounds in industrial wastewater. Their new method utilizes electricity as a reagent for contaminant removal, removing up to 99 percent of organic compounds with low electrical power and no secondary waste.
“The need [that inspired this research] is treatment of industrial and biorefractory wastewater and sludge, for which there is no gold standard at the moment,” said Olivier Lefebvre, an assistant professor from the NUS Department of Civil and Environmental Engineering and research leader for this project. “Some industries are just stuck and forced to pay fines or even close down.”
While industrial operations typically rely on biological processes — which tend to be the most affordable — to deal with wastewater contaminants, many industries contaminate their wastewater with constituents that are not biologically degradable. These operations then turn to the use of chemicals, which can be expensive to procure and dispose of after treatment is complete. NUS sees this new system, which can be integrated as a pretreatment step and uses so little energy that it can be powered by renewable sources, as a solution to that conundrum.
“Because biological processes are cheap, when [contaminants are] not biologically degradable it becomes an issue because you have to resort to chemicals instead,” Lefebvre said. “With our technology, the only input is electricity, which can be generated from new energy sources such as solar panels.”
The NUS system turns organic compounds in wastewater into water and carbon dioxide. Wastewater goes into the system’s chamber and an electrical current generates hydrogen peroxide and hydroxyl radical, an extremely powerful oxidizing agent, through electrodes in the chamber. These break down the wastewater’s organic compounds until they have been completely degraded and the oxidizing agents have been used up, meaning that operations do not have excess chemicals or sludge to dispose of.
“[Efficiency is achieved] through adequate mass transfer of the electrodes,” Lefebvre said. “All reagents are produced in situ and consumed as soon as they have been generated. Thus, the conditions are always optimal as opposed to pouring some amount of chemicals in a tank.”
NUS is counting on the system as a solution in the increasingly popular market for wastewater recycling and reuse solutions. Industries all over the world are looking to make better use of their effluent, as environmental pressure and mounting costs from treatment and disposal grow. NUS put the global wastewater reuse market at $12.2 billion in 2016 and estimates that it will reach over $22 billion by 2021.
In addition to agricultural, pharmaceutical, and electronics producers, the system could be put to use in other industries that require ultrapure water as well as municipal settings that are dealing with micropollutants.
Along with his team, Lefebvre has applied for two patents on the technology used in the system and is testing it on different types of industrial wastewater. They are also looking to improve the electrodes that it uses and to partner with an organization that can help them bring the technology to market.
“[We are] seeking funding to scale up our current system by a factor of 10, then moving on to a pilot plant application and commercialization,” said Lefebvre.
If and when this technology is scaled up and made commercially available, industries around the world will be eager to test it out.
Image credit: “Plasma Coil,” Thomas Larsen, 2008, used under an Attribution 2.0 Generic license: https://creativecommons.org/licenses/by/2.0/