Microbubble-Enhanced Cold Plasma Activation (MB-CPA) for Promoting Vegetable Growth in Hydroponics

Abstract

Increasing global population, climate change, environmental pollution, and rapid urbanization have dramatically increased the global food demand. Innovative technologies minimizing the use of scarce freshwater resources while still boosting crop production are highly desirable. This study introduces microbubble-enhanced cold plasma activation (MB-CPA) technology to generate plasma-activated water (PAW) and investigates its effects on plant seedling growth in hydroponic systems. Coupling of the Venturi tube helped to efficiently transfer the reactive nitrogen and oxygen species (RONS) generated by air cold plasma discharge via microbubble formation. Notably, a high and stable concentration of nitrate (NO₃^–; 28 mg/L) and nitrite (NO₂^–; 5 mg/L) was estimated in PAW. Lab-scale investigations showed that garlic seedlings treated for 15 min MB-CPA have 1.5 times longer shoots and heavier weights than those irrigated with tap water and chemically prepared N-containing (NO₃^– and NO₂^–) water. Interestingly, the treated garlic showed an almost 1.3-fold increase in sulfur content (10⁴ mg/kg) compared to control, indicating an increase of beneficial natural sulfur compounds. Similar growth enhancements were observed in peanuts, garlic, and soybean sprouts, with PAW-treated plants showing 1.66, 1.5, and 1.8 times longer sprouts, respectively, compared to untreated groups. Application of MB-CPA to a large-scale commercial hydroponic system (108 units of garlic) demonstrated the accelerated rate of germination, improved shoot growth, and a higher root-to-shoot ratio. Furthermore, 32-day study comprising three growth cycles utilizing recycled PAW water resulted in a 1.53-fold increase in fresh weight and a 1.46-fold increase in dry weight of garlic during the final growth cycle. These findings demonstrate that MB-CPA is a promising, sustainable, and environmentally friendly fertilizing technology and can be an alternative for the improvement of agricultural production.