The treatment of wastewater from small towns supposes problems of economic efficiency, leading to very high environmental costs in areas with low population density. Constructed wetlands (CW) seems to be the more suitable solution for this kind of situation, but further investigations are needed regarding their efficiency under different climatic conditions. This work presents the results concerning urban wastewater treatment by means of two different constructed wetlands using macrophytes: horizontal subsurface flow (HSSF) and free water surface (FWS). The systems are located in a Mediterranean continental climate area and are fed by a by-pass at the entrance of a wastewater treatment plant. A four-year sampling campaign at the outlet of the CW allowed verifying their relative effectiveness in removing pollutants in the different seasons of the year. BOD₅, COD, and TSS were significantly removed (with average reductions of 55%, 60%, and 57%, respectively) by these natural phytodepuration systems, with HSSF being more efficient during plants’ dormancy than FWS, but the concentrations of nutrients indicated that cumulative effects occur in CW with the need of adequate annual maintenance. It was found that the main factors controlling the efficiency of such systems throughout the year are the period of vegetative development, the presence/absence of a solid substrate, and the pollutant load of the wastewater inlet.

Different hydroclimatology researchers apply eigenvectors-based techniques to compress large volumes of information while preserving the invariant structure of the original data. This research developed a methodology applying one of these techniques, Principal Component Analysis, on the elements of variability in hydroclimatic time series, and then to identify clusters with the "k-means" method. The result is a regionalized map by variable. Finally, these maps are intersected, obtaining areas with a homogeneous hydroclimatic structure, because the variables have similarity in their variance structure. In the case study, 8 variables were evaluated for Colombia (9268 time series), obtaining as a result 26 hydroclimatic regions. Obtaining hydroclimatically homogeneous regions The progressive increment of impervious areas in many of our cities contributes to the increase of surface runoff volumes that, moreover, reach the drainage network or, directly, the receiving water bodies without any type of filter provided by the vegetation. In this context, that in several sites could be exacerbated by the effects of climate change that are determining a drastic increase of maximum rainfall intensities, Sustainable Urban Drainage Systems (SUDS) suppose a valid alternative to address these kinds of problems, and providing, at the same time, a long series of other co-benefits at environmental and social level. The objective of this study is to propose the implementation of green roofs in a new urbanization of the city of Zaragoza and assess their hydraulic, environmental and socioeconomic benefits. The analysis of the hydraulic and environmental benefits has been performed through the USEPA-SWMM5 software that includes a specific module for SUDS simulations with special regard to green roofs, allowing to define and fully characterize their main layers and to simulate their effects at local or catchment scale. The hydrological simulations carried out for extreme rainfall events (return periods of 2, 5 and 10 years), indicate that the reduction of the hydrograph peaks can be between 31 y 38%, while the reduction in terms of runoff volumes is ranged from 17 up to 27 %. Concerning the simulation of a continuous annual rainfalls' series, the reduction in runoff volumes would vary approximately between 30% and 37% depending on the type of green roof used. Finally, regarding the water quality parameters of the sewer discharged overflows, the reduction of pollutants would be very significant, varying from 92% to 99% depending on the type of pollutant and the type of roof.

Inspection and maintenance tasks are essential to guarantee the correct operation of sewer drainage networks. In combined sewers, these tasks are generally carried out during dry periods when only wastewater flow circulates in the system. When the sewer is big enough to allow the access of people, this inspection is done in person with consequent potential exposure to several hazards such as the presence of toxic gases, the possibility to fall or the loss of stability due to the presence of a continuous wastewater flow. In this context, this paper presents a methodology to assess hazard conditions related to human stability in sewer systems during dry weather periods. Hazard assessment has been performed by applying several hazard criteria to the results of a 1D sewer model simulations regarding a real network in Spain. Results show that the influence of the selection of hazard criteria is relevant, although only a small part of the whole system can be classified as high hazard. Regardless, the proposed method is highly effective to detect these kinds of pipes and we consider them as critical point to improve health and safety procedures during maintenance and inspection tasks.