Under-cover soilless cultivation is an important technique of crop production. Due to the lack of contact with soil and precipitation, the root system of crops grown must be provided with water and all necessary nutrients in the form of a solution (nutrient medium). This nutrient medium needs to be fed in excess to ensure proper plant development and the expected qualitative and quantitative parameters of the crop yield, which means that in the case of, e.g., tomato cultivation, 20–80% of the supplied medium must be removed from the root system and managed. Uncontrolled discharge of this drainage water poses a significant threat to the environment, causing contamination of surface waters and groundwaters. The article presents the latest solutions for drainage water management as well as technologies and systems that allow saving water and fertilizers, and thus recovering elements. It also characterizes methods deployed for the treatment of overflow that enable its recirculation, its re-use for fertilization of other less demanding crops (including soil crops), and its final management in the form of a discharge to the natural environment. Due to depleting resources of adequate-quality water, increase in the prices of mineral fertilizers, and depletion of natural phosphorus deposits, the future trends in water and nutrients management in this cropping system aim at closing circuits of drainage water and recovering elements before their discharge into the natural environment. These measures are expected not only to protect the natural environment but also to reduce the costs of crop production.

The study was conducted in a one-stage rotating electrobiological disk contactor (REBDC) and a rotating electrochemical disk contactor (RECDC). Synthetic wastewater with characteristics similar to the wastewater from soil-less cultivation of tomatoes was used in the experiment. Current efficiency (CE) values, that express the denitrification performance of bio- and electrochemical reactors, were higher in the electrobiological contactor than in the electrochemical one. Combining biological processes with electrochemical processes in the electrobiological contactor resulted in almost 20% higher current efficiency in the contactor operated at a density of 0.63 A/m² and hydraulic retention time (HRT) = 4 h. The study showed that, in both the electrochemical and the electrobiological contactor, current density increase and hydraulic retention time extension increased electric power consumption (E) during phosphorus compounds removal and simultaneously lowered current efficiency.

An attempt was undertaken to determine indicators of energy consumption in bio-electro reactors (BERs) i.e., an aerobic rotating electrobiological disc contactor (REBDC) and an anaerobic sequencing batch biofilm reactor (SBBR), during contaminant removal from soilless tomato cultivation wastewater having a specific composition, i.e., high nitrate and phosphorus concentrations and low COD. Because of this specificity, the energy consumption during the treatment process was characterized by a cumulative indicator for simultaneous removal of phosphorus and nitrates—EEI_NUTRIENTSrem (electric energy consumption per unit of removed nutrient load, expressed as kWh/kg_NUTRIENTSrem). Four values of direct current density were tested: 0.63, 1.25, 2.5, and 5.0 A/m². The indicator values were compared at a hydraulic retention time (HRT) of 24 h. The study demonstrated that the values of electric energy consumption per unit of removed nutrient load determined in the anaerobic SBBR ranged from 30 to 464 kWh/kg _NUTRIENTSrem and were lower than the values obtained in the aerobic REBCD, i.e., 80–1380 kWh/kg _NUTRIENTSrem.

This study examined the effect of bio-electrochemical treatment processes on nitrogen and phosphorus removal, but it also evaluated the impact of the treatment processes on the concentration of other nutrients present in hydroponic effluent. A bio-electrochemical reactor (BER) was used in the experiment to treat effluent from the hydroponic cultivation of tomatoes. It was stated that the nitrogen removal efficiency decreased with increasing current density. The study showed that an electric current density of 0.63 A/m² ensured the lowest effluent nitrate concentration. The nitrogen removal efficiency ranged from 41.6%-R1 (density of 0.63 A/m²) to 8.9%-R4 (density of 5 A/m²). Electric current density higher than 1.25 A/m² resulted in lower total nitrogen removal efficiency. The total phosphorus removal efficiency increased with increasing electric current density. The phosphorus removal efficiency was the lowest—95.1%—in the R1 reactor, whereas it was the highest in R4—99.1%. The concentration of the other elements in the effluent was determined. The content of molybdenum, boron, sulphates, and potassium did not meet the acceptable norms for discharging hydroponic effluent into the environment. The study showed that bio-electrochemical processes taking place in BER caused secondary contamination of hydroponic wastewater with molybdenum ions.