Barcelona Metropolis

Wastewater reflects our habits: when we wake up or go to sleep, when we go on holiday, and even the medications we consume. The peaks in water elimination reveal our activities. This is how the SCOREwater study has unveiled variations in the everyday life of three neighbourhoods with markedly different incomes, namely, El Carmel, Poblenou and Sant Gervasi.

The city’s wastewater is a direct result of its residents’ daily activities. It contains not only products disposed of through sinks or toilets – which are not always organic and sometimes harmful – but also information about the foods, medications and drugs we consume. Furthermore, wastewater clearly mirrors our habits, indicating whether we wake up earlier or later, our bedtime, and the periods of the year when we go on holiday, as the peaks in water elimination reveal our activities.

The 1,643 kilometres of sewers in the city of Barcelona have been a subject of research for quite some time, specifically in a field known as “sewer sociology”. Indeed, wastewater serves as a faster and more reliable source of observation compared to inspections or surveys. In essence, these methodologies complement each other, contributing to more effective management and public policies.

Barcelona City Council, through Barcelona Cicle de l’Aigua (BCASA), the Catalan Institute for Water Research (ICRA-CERCA), the Metrópoli Institute, the Eurecat Technology Centre of Catalonia, and the company s::can Iberia, is participating in the European project SCOREwater.[1] Within this initiative, Barcelona has opened an urban innovation laboratory that, over the course of a year, has gleaned insights from the wastewater of three neighbourhoods with varying income levels: El Carmel (low), Poblenou (medium) and Sant Gervasi (high). Presented at the Smart City Expo World Congress 2023, the project is groundbreaking because, until now, only wastewater reaching treatment plants had been analysed; never had such a localised scale been studied. Comparisons between neighbourhoods shed light on social realities and, at the same time, point to numerous application possibilities. Among other things, extracted knowledge enables better targeting of inspections for illegal discharges, early detection of health or environmental alerts and more effective implementation of environmental education or public health campaigns.

This project stands out as a good example of how to extract value from “smart city” data for various reasons. It effectively defines its objectives, incorporates diverse data sources such as online sensors, laboratory sample analysis results and surveys; it applies big data and artificial intelligence, with a strong emphasis on transparency and citizen involvement. In terms of the latter, the “Wastewater Speaks About You”[2] awareness campaign presents the findings and offers guidance on appropriate actions. In addition, a game has been developed to instil good practices,[3] successfully tested with two hundred children from schools in the participating neighbourhoods.

Different findings across neighbourhoods
Over the span of a year, continuous analysis of 11 parameters, supplemented by laboratory samples, has been conducted in all three areas. This extensive analysis has enabled the processing of data related to the consumption of medications, tobacco, alcohol, coffee and drugs per flush. It also highlights environmentally unsustainable practices, such as the disposal of wet wipes, oils, fats or excessive food residues. Risks associated with lesser-known sources, like plastics released by certain foods or cosmetics expelled through urine, have been measured. Moreover, the study explores the effects of parabens and sunblock filters, both of which ultimately find their way into the water. Finally, there has been an epidemiological monitoring of SARS-CoV-2, and the presence of antibiotic resistance genes in microorganisms has been examined.

The main question researchers posed was whether there would be significant differences in wastewater among the three neighbourhoods. The data indeed shows such variations. For instance, peaks in water release in the sewer system reveal that the residents of El Carmel wake up earlier, almost 1.5 hours before those in Poblenou, although overall, on weekends, the population reduces daily activity hours from 13 to 10. The time of a break in a Barça-Madrid football match can even be determined by the increase in wastewater flow. Holiday periods show the opposite pattern: in summer, there’s a temporary decrease in flow, evident in Sant Gervasi and El Carmel, but not as much in Poblenou, perhaps due to year-round tourist and leisure activities. On weekends, however, residents of Sant Gervasi generally leave the city. In the other two neighbourhoods, there’s no difference between weekdays and holidays. In this case, the dynamics can be clearly linked to the average income of Sant Gervasi, which is three times that of Carmel and twice that of Poblenou.