The company says the technology efficiently removes persistent organic substances in wastewater by using hydroxyl (OH) radicals generated through an electric discharge created at a gas/liquid interface. Mitsubishi Electric, aiming to contribute to sustainable water recycling, will apply the technology in an industrial wastewater reuse system that it hopes to commercialize by the fiscal year ending in March 2019.
The system’s reactor uses several inclined plate electrodes in humid oxygen over which the wastewater flows. A pulsed corona discharge generated at the interface of the humid oxygen gas and wastewater produces OH radicals, a strong oxidant with an oxidation potential of 2.85 eV, compared to 2.07 eV for ozone. Due to the OH radical’s high reactivity, persistent substances such as surfactants or dioxane decompose into carbon dioxide, water molecules and other inorganic compounds.
The effective generation of OH radicals makes the treatment twice as efficient as conventional advanced oxidation processes, such as the combined use of ozone and ultraviolet irradiation (O3/UV), the company says. Oxygen gas consumption is reduced significantly by up to 90 percent due to gas recycling. The modularized structure of the discharge units makes the equipment more simple and cost effective than the O3/UV method.
Population growth and improving living standards are expected to increase the global need for wastewater reuse. In the western US, Singapore and other water-deficient regions, the installation of water reuse systems is already under way. Since water, like electricity, is an essential part of every society, there is a compelling need for low-cost water reuse systems.
Persistent organic substances dissolved in industrial wastewater discharged from various types of production facilities must be treated before reuse, but conventional water treatment methods, such as chlorination or ozonation, are usually ineffective. Special processes have been developed to remove these substances, such as adsorption with active carbon or decomposition using the O3/UV advanced oxidation process, but they are costly.
Mitsubishi Electric is now working to apply its technology in practical industrial wastewater and sewage reuse systems that are expected to help realize societies capable of sustainable water recycling.
This technology is currently under joint development with Yasushi Minamitani, an associate professor at Graduate School of Science and Engineering, Yamagata University.
New technologies using passive aeration and process control dramatically improve wastewater treatment, according to a Lux Research study published earlier this month.
Traditional options for secondary wastewater treatment burn up huge amounts of energy — 68 GWh annually in the US alone — and still leave behind excessive amounts of sludge. With increasing pressure from growing populations and more frequent severe storm events, there is a dire need to improve this secondary wastewater treatment.