Introduction: Preliminary studies have shown that ultraviolet treatment is able to reduce microbial contamination in the nutrient water of hydroponic systems. However, it is not known how these ultraviolet treatments may impact nutrient water chemistry or crop growth and yield. Purpose: The objective of this study is to examine the impact of an ultraviolet light treatment on romaine lettuce growth parameters and nutrient levels in the treated hydroponic water. Methods: Commercially-available DWC (Deep Water Culture) hydroponic systems were used to grow romaine lettuce (Latticua lettuceia var. Sparx) in a two-part nutrient solution (Hydro-Gro Leafy and calcium nitrate). The electrical conductivity (EC) was maintained between 1.6 and 1.8 mS/cm during the study. The nutrient solution was treated with a UV-C device (MiniPure MIN-1; 500ml capacity) emitting peak irradiance at 254nm at flow rates of 0, 3 and 6 L/min. Water samples were collected before and after each treatment and the experiment will be repeated twice for a total of three times. Twice weekly during the six-week growth period, parameters including plant height, SPAD value, and chlorophyll fluorescence were measured. At the end of the production, fresh weight and dry weight of each plant sample were measured. Results: Low and high UV doses resulted in 1.17 and 1.36 log reductions of Escherichia coli in hydroponic nutrient water. Preliminary findings for the effect of UV light on the concentration of nutrients (NPK) yielded no significant difference in the nutrient level. The study is underway for assessing the effect on the lettuce growth parameters and therefore we are not reporting any results on the crop growth parameters. Significance: UV light technology at optimized dosage levels has the potential to improve the safety of hydroponic systems with minimal effect on the plant growth and nutrient water.
