Evaluation of Hybrid Constructed Wetland Performance and Reuse of Treated Wastewater in Agricultural Irrigation

Agriculture is being negatively affected by the decrease in precipitation that has been observed over the last few years. Even in the Czech Republic, farmers are being urged to irrigate their fields despite the fact that sources of water for irrigation are rapidly being depleted. This problem might be partially solved via the reuse of treated wastewater in certain agricultural sectors. However, the public perception of the reuse of wastewater remains negative primarily due to unknown risks to the environment and public health. To overcome this barrier, a semi-operated irrigation field was established at Kostelec nad Ohri in the Central Bohemian region of the Czech Republic and planted with common garden crops such as tomatoes (Lycopersicon esculentum), potatoes (Solanum tuberosum) and lettuces (Lactuca sativa L.) irrigated with two different water sources, i.e., treated wastewater from a local nature-based treatment system, a hybrid constructed wetland (HCW), and local fresh water from well. The HCW was put into operation in 2017 and was reconstructed in 2018 and includes both horizontal and vertical flow beds; the trial irrigation field was added in the same year. The reconstruction of the facility significantly enhanced the removal efficiency with respect to all monitored parameters, e.g., biochemical oxygen demand (BOD5), chemical oxygen demand (COD), N-NH4+, total N and the suspended solids (TSS), except for total P. The HCW also ensured the significant removal of several observed pathogenic microorganisms (E. coli, intestinal enterococci and thermotolerant coliforms). During the 2018 and 2019 growing seasons, we observed the significantly enhanced growth of the crops irrigated with wastewater from the HCW due to the fertilizing effect. The risks associated with the contamination of crops irrigated with treated water are not negligible and it is necessary to pay sufficient attention to them, especially when introducing irrigation with wastewater into practice.