In this case, an abundant carbon source or appropriate C:N ratio has been proven to be a key factor for achieving efficient removal of nitrate [10]. Biological, physical, \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{3}{*}{**Parameter**} & **Maximum Permissible Values of Pollutants,** & **Permissible Values of Pollution** \\  & **Generated during the Production and** & **Indicators in Industrial Wastewater** \\  & **Processing of Fruit and Vegetables,** & **Introduced into Sewage Systems** \\  & **Discharged into the Water or Ground** & \\ \hline COD [mg O\({}_{2}\)/L] & 125 & * \\ Total nitrogen [mg N/L] & 30 & - \\ Ammonia nitrogen [mg N/L] & 10 & 100 (\({}^{1}\)) 200 (\({}^{2}\)) \\ Nitrite [mg N/L] & 1 & 10 \\ Nitrate [mg N/L] & 30 & - \\ Total phosphorus [mg P/L] & 3 & * \\ Temperature [\({}^{\circ}\)C] & 35 & 35 \\ pH & 6.5–9.0 & 6.5–9.5 \\ Iron [mg/L] & 10 & 10 \\ Aluminium [mg/L] & 3 & 10 \\ \hline \hline \end{tabular}  
* The values of the indicators should be determined on the basis of the permissible load of the treatment plant with the load of these pollutants. (\({}^{1}\)), Applies to wastewater discharged to treatment plants for agglomerations with a population equivalent \(<\) 5000; (\({}^{2}\)), applies to wastewater discharged to treatment plants for agglomerations with a population equivalent \(\geq\) 5000.  
\end{table} 
Table 1: The EU regulations for wastewater discharged into natural waters and the ground and Polish regulations regarding industrial wastewater discharged into municipal sewage systems. and chemical methods have been applied for removing biogenic compounds from this type of wastewater [5]. Previous research and papers by the authors of this article have shown that wastewater with a low COD, for example, from soilless cultivation systems, with typically high concentrations of oxidized forms of nitrogen and phosphorus, may be effectively treated in electrochemical reactors, such as a rotating electrochemical disk contactor (RECDC), and in a bioelectrochemical reactor (BER), such as a rotating electrobiological disk contactor (REBDC) [11; 12; 13]. The passage of electric current through a REBDC with an aluminum anode [14] results in water electrolysis and the generation of gaseous hydrogen which is a source of energy for autotrophic bacteria that conduct hydrogenotrophic denitrification. These processes are accompanied by heterotrophic denitrification with organic matter present in wastewater. Carbon dioxide formed in this reaction serves as an additional source of inorganic carbon for autotrophic bacteria [15]. The aluminum anode also enables electrochemical reduction of nitrate, whereas phosphorus compounds are removed in the process of electrocoagulation. Nitrogen and phosphorus are also removed during the growth of biofilm biomass. In a REBDC, some processes may be limited due to the small amount of carbon compounds in wastewater from soilless plant cultivation. The introduction of an external source of carbon may increase the contribution of the heterotrophic denitrification process in the removal of nitrate nitrogen. More intensive biomass growth also influences an increase in N and P removal. A REBDC with heterotrophic-autotrophic denitrification (HAD) may create conditions for synergistic interactions between autotrophic and heterotrophic bacteria [16]. In turn, in a rotating electrochemical disk contactor, the removal of nitrogen and phosphorus compounds is a result of electrochemical reduction of nitrate and electrocoagulation of phosphorus compounds. In a RECDC, the disks are not covered with a biofilm. During experiments, the disks are regularly cleansed to remove developing microorganisms on the biofilm. The results of previous studies have shown that electrochemical and bioelectrochemical methods ensured a high degree of neutralization of pollutants, and were also characterized by a minimum amount of sludge as well as low investment and operating costs as compared with physicochemical processes such as ultrafiltration or ion exchange [17; 18; 19].