Design of systems for plasma activated water (PAW) for agri-food applications

Abstract This review explores the engineering and design aspects of plasma activated water (PAW) systems, focusing on their application in food safety and agriculture. This review aims to bridge the gap between research and practical application, paving the way for the development of robust and efficient PAW systems for enhancing food safety and agricultural productivity. By examining a variety of activation methods, including direct gas ionization, underwater discharges, and dynamic interactions of ionized gases with liquids, this work discusses the mechanical designs that facilitate these processes, highlighting their scalability and efficiency. The discussion is grounded in a comprehensive relevant scientific and patent literature, offering a critical overview of the systems’ design parameters that influence the generation of reactive oxygen and nitrogen species (RONS). The designs reported in literature have employed three major approaches, viz. direct underwater discharges, gas ionization followed by introduction of plasma into the liquid, creation of gas liquid mixtures and subsequent ionization. The laboratory systems have relied on natural convective diffusion of the RONS into water, while most of the patents advocate use of forced convective diffusion of RONS to increase transfer rates. Despite widespread laboratory-scale research in PAW, the transition to industrial-scale systems remains underexplored.