Innovative technologies (nanobubbles and electronic water treatment) to manage highly saline irrigation water in hydroponic systems

Abstract

Irrigation water salinity presents a major and increasing problem worldwide. Methods to treat it and achieve higher efficiency will provide valuable tools to farmers to achieve more sustainable and profitable crop production systems. Most systems currently used for saline water treatment represent high energy consumption and large costs. Any new systems that can reduce the irrigation water salinity effects, will contribute significantly to the more sustainable crop production and indirectly mitigate the climate effects, by reducing the crop stresses by abiotic factors. The objective of this study was to evaluate high salinity levels of irrigation water, for growth and productivity of leafy vegetables. Two innovative and inexpensive technologies were used. One is the application of a nanobubbles system (NB: http://hal.teiemt.gr/index.php/agronb) and the other is an electronic water treatment system, based on low frequency radiation waves (MAXGROW: https://MAXGROW.tech/). The NB system produces very small size water cavities. The MAXGROW cutting edge electronics ensemble generates up to two million pulses per second in a constantly altering transmission bandwidth, enabling the system to dissolve all the ions of the metallic salts. The research was conducted in the Greenhouse Laboratory of Perrotis College/American Farm School Thessaloniki, Greece under a floating disks hydroponic system, in which three leafy vegetables species (endive, and two lettuce varieties- COS and Batavia) were grown in 4 different sections/tanks each one filled with different salinity irrigation water: a. Control (E.C.i ~1 dS/m), b. saline water (E.C.i = 10 dS/m) enriched with NB, c. saline water (E.C.i = 10 dS/m) + MAXGROW and d. saline water (E.C.i = 10 dS/m) + MAXGROW + NB). Various vegetable agronomic parameters (total fresh weight, height, root weight, SPAD units, etc.) and water parameters (Dissolved Oxygen, pH, EC, nutrients, temperature, size and concentration of NB, etc.) were periodically recorded. The results indicated that a combination of the two devices was the best treatment used, as compared to using one device separately and provided higher final fresh yield than the regular water treatment. A very important result that was also shown, refers to MAXGROW’s system ability reduce the size of water cavities by itself, thus producing additional NBs and in combination with the NB system increased the concentration of NBs. Therefore, the two devices can provide a very sustainable and affordable tool to mitigate high salinity problems in crop production systems.