# Water and Wastewater Management in Agriculture
## 2 An Overview of Published Articles  
[PERSON] et al. (contribution 1) discuss the environmental impact of using soilless and hydroponic methods for plant cultivation, which are predominantly based onopen fertilisation, where the nutrient solution passes through the growing system once before being removed. Wastewater from soilless cultivation, especially in rural areas, is discharged into the environment, including groundwater and natural water bodies, without adequate control measures. Given the increasing prevalence of this practise and the expected growth of soilless cultivation, e.g., in urban vertical farms, there is an urgent need for uncomplicated, energy-efficient, and highly effective technological solutions for wastewater treatment. Wastewater from soilless tomato cultivation, which is characterised by low chemical oxygen demand (COD), high phosphorus concentrations, and oxidised nitrogen forms, can be efficiently treated with rotating electrochemical disc reactors (RECDC) and bioelectrochemical reactors, such as rotating electrobiological disc reactors (REBDCs). The aim of this study was to determine the optimal technological parameters for both reactor types, focusing on the electrical current density (J) and hydraulic retention time (HRT) in accordance with the effluent quality requirements. The investigation included four single-stage RECDCs and four single-stage REBDCs tested at different HRTs (4, 8, 12, and 24 h) and electrical current densities (0.63, 1.25, 2.50, 5.00, and 10.00 A/m\({}^{2}\)). The results showed that wastewater from soilless tomato cultivation could be effectively treated using electrochemical and electrobiological disc reactors and then safely discharged into the sewer system. In particular, the RECDC achieved maximum denitrification (53.4%) and dephosphatisation (99.8%) at J = 10.0 A/m\({}^{2}\) and HRT = 24 h, while the REBDC consistently achieved a phosphorus removal efficiency of over 90%. The application of J = 2.5 A/m\({}^{2}\) and HRT = 24 h in the REBDC resulted in phosphorus concentrations below 3.0 mg P/L and compliant ammonium nitrogen and nitrite levels suitable for discharge to water bodies and soils according to regulatory standards for treated industrial wastewater. The study by [PERSON] et al. (contribution 2) focuses on organic solid waste, which is not only generated in agriculture. The aim of this study was to evaluate the efficiency of hydrodynamic cavitation (HC) as a pre-treatment method for certain organic wastes. HC experiments were conducted with municipal wastewater (MW), mature landfill leachate (MLL), and mixtures of lignocellulosic waste (LB) suspended in these waste streams. Uniform operating parameters were used for all HC tests, including an inlet pressure of 7 bar and 30 recirculations through the cavitation zone. A steel orifice plate with a 3/10 mm conical concentric hole was used as the HC inductor. The solubilisation and degradation of complex organic matter were observed in almost all materials tested, leading to an improvement in the biodegradability index (BI) and soluble chemical oxygen demand (SCOD) in the cavitated mixtures. In particular, the sole series of MW showed a lower BI, while more favourable results were observed for LB and MW in the multi-component mixtures, as evidenced by a higher BI, alkalinity, and SCOD content. These results suggest that HC could serve as a pretreatment method for certain organic wastes to facilitate subsequent biomethane production. However, the successful application of HC depends on the selection of appropriate operating conditions tailored to the specific waste type. This approach could prove to be beneficial for agricultural biogas plants.