2023 Edition

Water will be the most valuable commodity in the future, and the development of simple, cost-effective, and scalable technologies to enable water reuse is a top priority of current scientific research.

In this field hydrodynamic cavitation (HC) help to overcome the mass transfer limits of most advanced oxidation processes (AOP) that are not able to completely degrade complex compounds, while also reducing oxidant consumption and process costs, and increasing energy efficiency. HC is considered a promising technology and has been widely applied in many fields, such as food processing, the removal of pharmaceuticals and biological organisms (bacteria, cyan bacteria and viruses). Cavitation is defined as the nucleation, growth and implosion of cavitation bubbles in a very short times, as caused either by the passage of ultrasound, or by alterations in flow and pressure. The result is high temperatures, high pressures and high jet flows. Under cavitation conditions, water molecules can decompose into different oxidants, including ⋅OH, ⋅OOH, H₂O₂, etc., which can react with pollutants in wastewater, while the implosion forces that are generated when cavitation bubbles collapse can destroy the molecular bonds of organic pollutants and make them thermally decompose. Cavitation phenomena are generated by pressure and flow variations in the liquids that are induced by geometric constrictions, such as orifice plates, venturi and nozzles, which are equivalents to a throttle valve. According to Bernoulli’s equation, when a fluid flows through a reduction in the cross-section of the channel, the kinetic energy increases and the pressure decreases. If the pressure drops to the saturated vapor pressure at the operating temperature, bubbles begin to form and grow, and the size of cavitation bubbles can vary from a few nanometers to a few millimeters depending on flow conditions. Once the pressure rises above the vapor pressure, the bubbles collapse and the micro-jets generate turbulence downstream of the constriction.

Non-thermal plasma (NTP) technology is one such emerging advanced oxidation method. We have recently used NTP in combination with HC to treat various pollutants, receiving widespread attention thanks to the advantages that it offers, which include high efficiency, simplicity and an environmentally-friendly approach.

The development of effective and safe non-thermal plasma technologies for use in pollutant-treatment applications is still a challenge, and this is especially true for the development of efficient application-based instruments. This technology has considerable potential for the rapid and sustainable degradation of recalcitrant pollutants in wastewater without the need for external catalysts and oxidants.