Attenuation mechanisms and key parameters to enhance treatment performance in vegetation filters: A review

In times when environmental concerns are on the rise and the search of ways to reduce waste generation and to create a circular economy is booming, Nature Based Solutions (NBSs) play a very important role. Vegetation Filters (VFs) are a type of Land Application System (LAS) in which wastewater is used to irrigate a forestry plantation to treat the water and produce biomass. VFs show multiple benefits that render this technology a suitable solution for wastewater treatment, especially for scattered populations or isolated buildings that lack of connection to sewer systems. This review aims to provide a comprehensive state of the art of VF implementation, highlighting the do's and don'ts for a successful performance focusing on those factors that are essential to water treatment. Results show that VFs have a great treatment capacity when all involving factors are considered, and their efficiency tends to increase with time, as the VF develops and "gets older". Indeed, the presence of fine-textured soils, the selection of a proper vegetation species, the use of pre-treated wastewater and a water balance-based irrigation schedule alternating wetting and -drying cycles are all factors that help to achieve the best performance. However, it is necessary to design and follow a simple but rigorous operation and maintenance schedule to avoid system failure, which could lead to NO₃-N leaching towards groundwater.

Using old cartography for the inventory of a forgotten heritage: The hydraulic heritage of the Community of Madrid

Hydraulic heritage is a legacy that has generally been forgotten in territorial management and protective actions. This heritage expresses the way in which inhabitants have used their water resources and related structures for centuries. For proper management, it is necessary to draw up an inventory. Using Geographical Information System (GIS) tools, we have created a spatial and thematic inventory of the hydraulic heritage located in the Community of Madrid. This inventory shows the good conditions, both in abundance (more than 5800 point type entities) and diversity (28 categories in the point entities type layer), of historical hydraulic elements in the region. All the information in this work has been extracted from old maps (1870-1960). A database was designed to provide spatial, thematic and temporal information on this heritage. Element distribution was concentrated mainly in the river plains and the metropolitan areas of the region, and it has been proven how hydraulic elements are endangered due to increasing urban pressure. This phenomenon and agricultural modernisation are the main factors influencing the survival of this type of assets. Thanks to this methodology, it should be possible to analyse the status of the heritage ensemble included in the inventory.

Removal of emerging organic contaminants in a poplar vegetation filter

Vegetation filters (VFs), a type of land application system, are a robust technology based on natural treatment mechanisms for the removal of wastewater contaminants. Their capacity to attenuate emerging organic contaminants (EOCs) has not yet been evaluated. The present study reports the results of a 2-year EOC monitoring carried out using a poplar VF receiving wastewater primarily treated by an Imhoff tank. The compounds selected included analgesics, a β-adrenergic blocker, stimulants, an anticonvulsant, an anti-depressant, an anti-inflammatory, an antibiotic and analgesic and stimulant metabolites. EOCs were analysed in the Imhoff tank effluent, in the infiltrated water at a depth of 90cm and in the groundwater at a depth of 10m. The results demonstrated that EOC attenuation was more significant in the first 90cm than in the rest of the soil profile. The removal efficiency for all of the selected EOCs was higher than 90% with the exception of ketoprofen, which may pose a higher threat of groundwater contamination. The observed attenuation correlated with the hydrophobicity and charge state of the EOCs. The higher persistence of the metabolites 4-AAA and 4-FAA shows that progression in the degradation pathway does not always imply a mitigation of contamination.