## 4 Conclusions  
The results presented in this manuscript demonstrate that soilless tomato cultivation wastewater can be treated in both electrochemical and electrobiological disk contacts, and then discharged into a sewage system. The effectiveness of removal of nitrogen and phosphorus compounds in a RECDC depended on the electric current density and hydraulic retention time. Phosphorus removal performance exceeded 80% regardless of current density and HRT. The highest effectivenesses of denitrification (53.4%) and dephosphorylation (99.8%) were achieved at \(J=10.0\) A/m\({}^{2}\) and HRT = 24 h.  
The study results showed over 90% dephosphatation effectiveness in the REBDC at all electric current densities and HRTs tested. At HRT = 24 h and all current densities, the concentrations of pollutants in the effluent met the requirements set for industrial wastewater discharged into naturals waters and the ground (3.0 mg P/L). The discharge of treated soilless tomato cultivation wastewater from a REBDC into natural waters or the ground would be feasible only upon the application of technological treatments ensuring nitrate nitrogen concentration reduction below 30 mg N/L. While basing the operation of the technological system on a REBDC, caution should be exercised regarding the limitations established during the study and related to the quality of the effluent, namely to the permissible concentrations of nitrites (below 1.0 mg N/L) and ammonia nitrogen (below 10.0 mg N/L), and the effluent temperature (below 35 \({}^{\circ}\)C). For this reason, the best technological solution will be \(J=2.5\) A/m\({}^{2}\) and HRT = 24 h. These parameters resulted in achieving a high effectiveness of nitrogen compound removal; low concentrations of phosphorus compounds, ammonia nitrogen, and nitrate in the effluent; and additionally, did not lead to an effluent temperature increase above permissible values. In the manuscript, we formulate technological assumptions for the treatment of wastewater from soilless tomato cultivation. In the case of discharging the effluent into a sewage system, the technological system should consist of a retention tank equipped with an agitator, a pumping system, a one-stage electrobiological disk contactor, and a secondary sedimentation tank. The system can be supported with devices for the collection, thickening, and dewatering of sludge. If the effluent is to be discharged into natural waters or the ground, a solution should be designed in the technological system of the treatment plant to reduce the concentration of nitrate nitrogen to a level below 30 mg N/L, which is possible by introducing an external carbon source (e.g., VFAs and methanol) in the REBDC. The facility should include acid storage tanks, solution tanks, and a feeding system. An alternative solution could be the production of volatile fatty acids from the biomass of tomato stems and leaves. The system should be extended with devices for sludge stabilization. Conceptualization, W.J. and J.R.; Methodology, J.R.; Software, A.M.; Validation, K.B., J.R., and A.M.; Formal Analysis, J.R.; Investigation, J.R.; Resources, K.B. and W.J. ; Data Curation, J.R. and W.J. ; Writing--Original Draft Preparation, A.M. and W.J. ; Writing--Review and Editing, J.R. and A.J.-T.; Visualization, J.R. and U.W. ; Supervision, W.J. ; Project Administration, U.W. All authors have read and agreed to the published version of the manuscript. **Funding:** The study was financed in the framework of project no. 29.610.023-300 at the University of Warmia and Mazury in Olsztyn, Poland. The project was financially co-supported by the Minister of Science and Higher Education in the range of the program entitled \"Regional Initiative of Excellence\" for the years 2019-2022, project no. 010/RID/2018/19 (amount of funding 12.000.000 PLN). **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** Data sharing not applicable. **Conflicts of Interest:** The authors declare no conflict of interest.