Diseño y modelización de humedales para el tratamiento de efluentes de depuradora. Aplicación en el entorno del Parque Natural de las Tablas de Daimiel.

The Upper Guadiana Basin has suffered numerous water-related problems for decades. On the one hand, the irrigation of large areas since mid-twentieth century led to the extraction of groundwater at a rate much higher than the renewable resource replacement. Furthermore, many of the characteristic wetlands in the area were drained and channeled, before the declaration of the Mancha Humeda Biosphere Reserve. On the other hand, population growth and agriculture and associated industry development supposed water pollution. These environmental impacts had a synergistic effect that aggravated the problem, resulting in water regimes modification, aquatic ecosystems disappearance or disturbance and even the unsustainability of the area's economic model itself, highly dependent on agriculture. One of the most striking examples of these impacts is the Tablas de Daimiel National Park. It is a large floodplain wetland (1928 ha) formed by the confluence of two rivers: Giguela (which contributes brackish water) and Guadiana (which contributes fresh water and is fed by groundwater discharges from the Ojos del Guadiana spring). Despite its ecological significance, The Tablas de Daimiel wetland was drained in the 1960s; however, a few years later, they were declared a National Park (1973), the most important nature reserve protection in Spain. At that time, the authorities began to consider several recovery strategies. Despite the many measures undertaken (damming, water transfers, groundwater pumping, etc.), none has managed to effectively correct the water shortage and pollution in the wetland. The Tablas de Daimiel receives polluted water mainly by two ways: i) diffuse pollution from the surrounding agriculture and ii) Wastewater Treatment Plants which discharge to tributary channels. In this second case, the pollution is mainly due to the plants inability to treat the flow of water entering the plant during storm situations, either to the incapacity to achieve acceptable levels of wastewater decontamination. In this context, the feasibility of constructed wetlands for the treatment of Wastewater Treatment Plants effluents in the surroundings of the Tablas de Daimiel has been studied. The constructed wetlands could complement the intensive treatment that currently receives wastewater, producing water with enough quality for the receiving environment. Two possibilities for the water use after the treatment wetlands have been analyzed: i) the artificial recharge of the underlying aquifer, to assist in the groundwater level recovery; ii) the discharge in the Tablas de Daimiel, to maintain base flooding for the survival of the aquatic ecosystem under extreme drought events. After the analysis of alternatives, it was concluded that it could be achieved greater benefits using the treated water in the Tablas de Daimiel. Thus, the quality requirements imposed by this sensitive receiving environment were analyzed and, accordingly, the treatment wetlands surface needed to achieve the treatment goals was sized. Treatment wetlands have been modeled in order to simulate their operation, trying to improve the understanding of the biochemical processes that occur within them. The feasibility study has shown the ability of treatment wetlands for wastewater polishing, reaching a high-level treatment in a complicate situation because of the semi-arid conditions. Moreover, the treatment design was based on the ecological engineering principles, without major needs of construction, operation or maintenance.