RESUMEN
In the context of climate changes, characterized by an increase of short but intense rainfall events and rise of the average temperature, the fast population growth and consequent urbanization require the implementation of innovative solutions to mitigate pluvial floods and, at the same time, reduce the water demand. Among the different nature-based solutions, multilayer blue-green roofs have been widely recognized for their high capacity of reducing runoff generation from rooftops, and their additional storage layer enables to collect water, which could be reused for different purposes. However, the quality of the collected water in a multilayer blue-green roof and the influence that the additional storage layer has on it have not been analysed yet. Following this knowledge gap, we investigated the potential benefits of a multilayer blue-green roof installed in Cagliari, with respect to a traditional roof. The outflow triggered by artificial irrigation and natural rainfall events was analysed, both from a quantitative and qualitative perspective. Results confirm the high contribution of multilayer blue-green roofs in mitigating runoff generation, which is however influenced by antecedent soil moisture and water level conditions. The outflow from the multilayer blue-green roof presents lower suspended solids and heavy metals concentrations than from a traditional roof. On the other hand, Carbon Oxigen Demand (COD) concentrations in the multilayer blue-green roof outflow exceed the limits defined by the Italian regulations (125 mg/l) for water discharge or reuse, partially due to the high residence time in the storage layer. Specific treatments could be planned to reuse the collected water for urban purposes.
RESUMEN
Groundwater pollution and salinization have increased steadily over the years. As the balance between water demand and availability has reached a critical level in many world regions, a sustainable approach for the management (including recovery) of saline water resources has become essential. A 3-compartment cell configuration was tested for a new application based on the simultaneous denitrification and desalination of nitrate-contaminated saline groundwater and the recovery of value-added chemicals. The cells were initially operated in potentiostatic mode to promote autotrophic denitrification at the bio-cathode, and then switched to galvanostatic mode to improve the desalination of groundwater in the central compartment. The average nitrate removal rate achieved was 39±1 mgNO3--N L-1 d-1, and no intermediates (i.e., nitrite and nitrous oxide) were observed in the effluent. Groundwater salinity was considerably reduced (average chloride removal was 63±5%). Within a circular economy approach, part of the removed chloride was recovered in the anodic compartment and converted into chlorine, which reached a concentration of 26.8±3.4 mgCl2 L-1. The accumulated chlorine represents a value-added product, which could also be dosed for disinfection in water treatment plants. With this cell configuration, WHO and European legislation threshold limits for nitrate (11.3 mgNO3--N L-1) and salinity (2.5 mS cm-1) in drinking water were met, with low specific power consumptions (0.13±0.01 kWh g-1NO3--Nremoved). These results are promising and pave the ground for successfully developing a sustainable technology to tackle an urgent environmental issue.