Decade-long performance of constructed wetlands in the dairy industry following an aerated facultative pond

Long-term data are essential for decision-making in the operation of constructed wetlands; however, such data are scarce. In the present study, a subsurface flow CW system was monitored over a 10-year period for the treatment of wastewater from the dairy industry. Prior to the CW, an aerated facultative lagoon was operated, and its data were also included in the study. The integration of both natural treatment systems (Lagoon + CW) revealed synergy in the combined removal of pollutants and nutrients. Up until the seventh year of operation, the integration of the systems removed more than 98% of COD, BOD₅, and TSS, as well as 99.8%, 96.5%, and 71.3% of oils and greases, ammoniacal nitrogen, and total phosphorus, respectively. Surfactants, oils, and greases were entirely removed. The presence of significant clogging and surface flow from the seventh year onwards led to a reduction in treatment efficiency, indicating that this is the maximum recommended operating time for CWs following an aerated facultative lagoon in the dairy industry. After this period, all substrates should be replaced.