Post-Harvest Fresh Produce Wash Water Disinfection by Submerged Cold Plasma Non-Chemical Continuous Treatment System

Cold plasma is proven to be effective at rapidly inactivating pathogens in water [1, 2]. Our group, at the C&J Nyheim Plasma Institute (NPI), Drexel University, utilized prior NSF and DOE basic science funding to develop breakthrough approach of cooling thermal arc and trapping it in tornado-like reverse vortex air flow. This allowed to significantly increase the volume of plasma without increasing the power requirement and cooling plasma to below 2,000 K. Based on this new science, our team has developed a number of plasma-based water treatment technologies to meet the needs of different sources of water contamination and purification requirements [1, 3]. The goal of this proposed project is to design a plasma-based wash water management system for minimally-processed fresh produce to eliminate cross-contamination. Specific to reuse of produce wash water system is the interference from organic load. Plasma offers oxidative and non-oxidative pathways to achieve pathogen inactivation and, as organic load increases, inactivation mechanisms switch from the dominant oxidative pathways to the non-oxidative ones. The target of our technology is the minimally-processed fresh produce industry. Specifically, we are looking to replace or reduce the use of aggressive chemicals in water washing and chilling tubs because of the associated short-comings. Chlorine (NaClO), the most commonly used chemical disinfectant needs to be replenished periodically because it’s concentration declines in the presence of organic matter [4]. Additionally, there are quality (color bleaching and off-odors) and safety concerns [5]. Chlorine dioxide (ClO2) has high oxidative capacity and lower organic matter reactivity and has no carcinogenic byproducts, but it is very unstable and highly explosive as a concentrated gas. It also decomposes readily in the presence of sunlight. Chlorine and ClO2 are also inconsistent in controlling pathogen cross-contamination [6]. Even with emerging growth technologies such as vertical farming, hydroponics, aquaponics, etc. threat of cross-contamination persists and thus the need for produce washing remains [7-9]. As efficacy of chlorine and other aggressive chemicals is affected with increased organic load, new technologies for produce washing are being explored, for example UV in combination with H2O2, combined with surfactants [10] or the use of “natural” antimicrobials such as curcumin or gallic acid/propyl gallate (in combination with other methods) [11, 12]. Cold plasma is unique in being a non-chemical and continuous treatment system that does not need constant monitoring and replenishing of chemical concentration. The challenge, of course, is to provide sufficient mixing of the water treated by plasma and of bulk water in the produce washing system.