Non-thermal plasma treatment as a sustainable approach for wastewater reuse in hydroponic cultivation of Lactuca Sativa

The challenge in developing modern agricultural practices is to reduce irrigation water use, identify alternative water sources, improve plant growth, increase crop yields, and, finally, reduce the use of synthetic fertilizers and pesticides. Plasma treatment and wastewater decontamination may enable the safe reuse of nutrient-rich water in agriculture. In this study, municipal drinking water and wastewater after treatment with plasma were used for the irrigation of Lactuca sativa plants grown in hydroponic systems. Variations in micro- and macro elements content in plants were determined. Laser-induced breakdown spectroscopy (LIBS) was used to determine the elemental distribution in the plant's parts. Plasma treatment was performed using a novel plasma system, the Beta device-a microwave Argon plasma torch operating at 2.45 GHz, developed by the Clean & Circle Centre of Competence at the University of Sofia. Plasma treatment achieved more than a tenfold reduction in the total bacterial count in wastewater. Wastewater application in hydroponic farming resulted in a statistically significant increase in fresh mass of L. sativa by 27%. Plasma-treated wastewater was found to enhance chlorophyll concentrations in plants by 25% compared to the hydroponic fertilizer. The application of wastewater and plasma-treated wastewater provided essential nutrients for plant development, including K, Mg, Ca, and Na.