Microbubble-enhanced cold plasma activation of food-industry wastewater for valorization and hydroponic crop production

Cold plasma is an emerging electrified, reagent-free technology with strong potential for green chemical engineering. However, its integration into automated flow systems converting industrial wastewater into nutrient-rich fertigation media remains limited. Here, we demonstrate an automated microbubble-enhanced cold plasma activation (MB-CPA) process as a Power-to-X strategy for simultaneous wastewater treatment and plant-growth promotion in commercial hydroponics. A programmed plasma activation (automated MBCPA) module integrating a cavitation tube (1 and 2 h day-1 at 28 W) significantly enhanced germination, shoot length, biomass, and chlorophyll of garlic seedlings compared with microbubble-only and untreated controls, owing to fertilizing plasma-generated reactive oxygen and nitrogen species (RONS). The optimized MB-CPA was applied to food-processing (malting) wastewater supplying the hydroponic loop. The plasma treated wastewater yielded >10% higher germination, >1.6-fold plant length, >1.9-fold biomass, and > 10-fold chlorophyll content than the control and low-plasma treatments. MB-CPA reduced chemical oxygen demand by ∼90% and turbidity by ∼98%, while increasing total nitrogen to 53.1 mg/L and establishing a favourable C:N ratio (2.3-18) that supported vigorous growth, consistent with plasma-assisted nitrogen fixation and enhanced bioavailability of NO 3 − and NO 2 − . Plasma-exposed plants showed systematic reactive oxygen species generation in roots, a 1.2-fold up-regulation of proline and higher uptake of nitrogen (NO 3 − , NH 4 + ) and macro/micronutrients, indicating a regulated stress response and elevated metabolic activity rather than oxidative damage. Our results demonstrate that automated MB-CPA is a dual-function green chemical engineering process upgrading industrial wastewater into a fit-for-purpose fertigation medium for boosting hydroponic crop performance that can partially displace agrochemical inputs. • Automation was achieved using programming the cold plasma activation duration • Plasma-loaded microbubbles reduced organic load (90%) and turbidity (98%) in wastewater • Programmed plasma showed dual-action of wastewater treatment and nitrogen-fixation • Hydroponic coupled with programmed plasma improved nutrient uptake and plant growth • Automated hydroponic provides opportunity for wastewater reuse and sustainable food production