Exploring the performances of a new integrated approach of grey, green and blue infrastructures for combined sewer overflows remediation in high-density urban areas

Most sewage collection systems designed between 19th and early to mid-20th century use single-pipe systems that collect both sewage and urban runoff from streets, roofs and other impervious surfaces. This type of collection system is referred to as a combined sewer system. During storms, the flow capacity of the sewers may be exceeded and the overflow discharged into a receiving water body (RWB) through spillways without any control and remediation. Combined sewer overflows (CSOs) may, therefore, produce serious water pollution and flooding problems in downstream RWBs. Methodologies for a rational management of CSOs quantity and quality share many commonalities, and these two aspects should be considered together in order to maximize benefits and promote local distributed actions, especially in high urban density areas where the space availability for the construction of CSO storage tanks is often a limiting factor. In this paper, a novel strategy to control downstream flow propagation of a CSO as well as to improve its quality is tested on a real case study in the area of the metropolitan city of Milan. The approach is based on the combination of grey, green and blue infrastructures and exploits the integrated storage and self-depuration capacities of a first-flush tank, a constructed wetland and a natural stream to obtain admissible flow rates and adequate water quality in the RWB. The results, evaluated through a modelling framework based on simplified equations of water and pollutants dynamics, show excellent performances for the integrated system, both in terms of flow control and pollution mitigation. The pollution, using biological oxygen demand concentration as a proxy of the whole load, was decreased by more than 90% and downstream flooding situations were avoided, despite the spillway was not regulated. Concerning the economic point of view, from a rough estimate of the costs, the system allows reducing the investment of 30 to 50% in respect to the traditional CSO controls based solely on flow detention tanks. The proposed approach, as well as the modelling framework for its effective implementation, appear strongly scalable in different world contexts and aim to fill the gap between urban and rural environments in the management of stormwater and CSOs, promoting the involvement of the water managers, the irrigation-reclamation agencies and regional authorities

A tailored green-approach for managing CSOS in high density urban areas

This study was aimed at providing evidence about the possibility to adopt low-cost \u201cgreen-approaches\u201d for mitigating peak flow, volume and pollution loads of CSO in areas where high density of urbanization occur. In particular, the proposed approach exploits detention, infiltration and self-depuration capacities of natural systems already existing in peri-urban areas, in order to achieve a tailored solution that is suited to the specific context. The findings presented in this work show that combining first-flush tank (FFT) with a constructed wetland system (CW) and finally managing the flows in the receiving water body (RWB) about 90% of pollutant load abatement can be achieved. Therefore, the system can be simultaneously designed to pursue flood risk reduction (abatement of flow peak) and improvement of receiving water quality objectives. Moreover, each component of the proposed system has some peculiarities. For example, CW performs a dual function, i.e. on one hand it cuts the peak of flow thanks to its storage capacity, while on the other hand it reduces the volume thanks to its infiltration capacity. This features are most important especially in the context of \u201chydraulic-hydrologic\u201d invariance measures (that are becoming more and more present at local scale) where the reduction of peak discharge has necessarily to be accompanied by a reduction of volumes. Further improvements can be obtained through the control of flow in the RWB aimed to maintaining a correct ratio between upstream accumulation and downstream flow control according (i) the variability of flow in input to the RWB and (ii) the downstream canal hydraulic capacity. Flow control can be achieved by installing smart gates that operate automatically based on flow sensors and software-based actuators. Finally, the additional ecosystem services that can be provided by the green components of the system combined with the relatively low-cost of the interventions make the approach particularly attractive for small municipalities where large investments are seldom possible

IMPLICAZIONI GESTIONALI DELL\u2019APPLICAZIONE ESTESA DELLA TELELETTURA AI CONTATORI

L\u2019introduzione dei sistemi di telelettura dei contatori, le cui prime applicazioni erano principalmente votate a scopi di fatturazione, si sono in seguito rivelate un utile strumento per l\u2019analisi della domanda idrica a livello di dettaglio. La tecnologia consente di caratterizzare la domanda idrica svincolandosi dagli approcci top-down (bilancio idrico) o bottom-up (ricostruzione della domanda mediante tecniche stocastiche). Le letture sono infatti effettuate con scansioni temporali personalizzabili, la cui frequenza \ue8 in ogni caso largamente superiore al dato di consumo fornito (di norma semestralmente) dalla tradizionale lettura contatori. Applicazioni della telelettura sono note per la stima del livello di perdita in tempo reale (possibile in quanto i dati sono raccolti in modo sincrono), tuttavia in questo lavoro l\u2019accento verr\ue0 posto sulla caratterizzazione della domanda delle singole utenze. L\u2019obiettivo \ue8 quello di verificare se esistono delle differenze rilevanti nel consumo di acqua in relazione alle dimensioni e alle caratteristiche del nucleo familiare, nonch\ue9 alla stagionalit\ue0 Il consumo idrico preso in considerazione \ue8 quello relativo a un distretto della rete di distribuzione di Fano (PU), monitorato mediante telelettura. I dati coprono un lasso di tempo di quasi 5 anni, con diverse frequenze di campionamento, che hanno in ogni caso permesso di condurre l\u2019analisi sia sui consumi medi giornalieri sia sui consumi idrici notturni.Particolare importanza \ue8 stata attribuita alla stima del consumo notturno degli utenti (Customer Night Use); concentrandosi in particolare su utenze condominiali, i cui maggiori valori di consumo notturno risultano meno affetti dagli errori di troncamento dei contatori

Modeling for sustainability: Life cycle assessment application to evaluate environmental performance of water recycling solutions at the dwelling level

The reduction in drinking water consumption, also through the reuse and recycling of unconventional sources of water, has been identified as one of the goals of the sustainable development. This study focuses on evaluating and comparing the environmental impacts attributable to the use of source of water supply, such as rainwater harvesting and greywater recycling, alternative to the traditional one. The environmental impacts of both positive (reduction of the potable water consumption, stormwater runoff mitigation, wastewater reduction, etc.) and negative factors (system complexity, double network, tank, pump system, etc.) have been evaluated through the combined use of two models. The first is a Life Cycle Assessment (LCA) model, developed by means of Simapro software and based on Recipe 2008 method. The second is a hydrological model, realized with the EPA SWMM software. Models have been used to estimate the environmental impact of the following scenarios: (i) Business-As-Usual; (ii) rainwater harvesting system; (iii) greywater recycling system. Those scenarios have been applied to several configuration of single dwellings and apartment buildings. The Life Cycle stages evaluation showed how energy consumption for distribution system plays a critical role in the overall environmental performance of the solutions proposed, as well as use intensity of the technology. For greywater recycling system, the application of 1 m3 storage and treatment system serving thirty population equivalent results in a net positive impact, while for rainwater harvesting system, the high use intensity should be combined with an alternative reuse for recycled water, i.e. washing machine supply, to obtain an overall environmental benefit

IMPACT OF COMBINED SEWER OVERFLOWS ON WATER QUALITY OF RURAL CANALS IN AGRO-URBAN ENVIRONMENTS

In many parts of the world, rural canals in agro-urban environments represent the water bodies intended to receive stormwater runoff from urban, industrial and agrarian surfaces. The risk of acute and chronic contamination of riparian vegetation and sediments, and the deterioration of water quality, make it problematic to use these canals to convey water for irrigation purposes and, more generally, to maintain environmental and ecological equilibriums of peri-urban areas. In this work, the spatio-temporal impact of Combined Sewer Overflows (CSOs) on water quality of a rural canal located in the metropolitan city of Milan, which is one of the most anthropized areas in Europe, was investigated through periodic water samplings. The presence of both chemical and microbial contaminants was evaluated over dry and wet periods along canal stretches that cross urban, industrial and agricultural areas. The results show that CSOs contribute to an increase in the chemical and microbial loads during rainy periods. Maximum contamination values are found downstream the collection of all CSOs, nevertheless the canal proves to be effective in the dilution of pollutants along its path. The impact of CSOs appears to be influenced by seasonality. Chemical and microbial pollutant loads gradually increase from winter to spring in the urban and industrial canal stretches, whereas in agricultural strength chemical gradually decrease from winter to spring and microbial remains stable. These preliminary findings provide useful information for managing the anthropic impact on the water quality of rural canals in agro-urban settings