SARS-CoV-2 was detected in Barcelona sewage long before the declaration of the first COVID-19 case, indicating that the infection was present in the population before the first imported case was reported. Sentinel surveillance of SARS-CoV-2 in wastewater would enable adoption of immediate measures in the event of future COVID-19 waves. Article Summary Line: SARS-CoV-2 genomes occur in sewage long before the declaration of COVID-19 cases among the population.

Monitoring bacterial communities in a drinking water treatment plant (DWTP) may help to understand their regular operations. Bacterial community dynamics in an advanced full-scale DWTP were analyzed by 16S rRNA metabarcoding, and microbial water quality indicators were determined at nine different stages of potabilization: river water and groundwater intake, decantation, sand filtration, ozonization, carbon filtration, reverse osmosis, mixing chamber and post-chlorination drinking water. The microbial content of large water volumes (up to 1100 L) was concentrated by hollow fiber ultrafiltration. Around 10 million reads were obtained and grouped into 10,039 amplicon sequence variants. Metabarcoding analysis showed high bacterial diversity at all treatment stages and above all in groundwater intake, followed by carbon filtration and mixing chamber samples. Shifts in bacterial communities occurred downstream of ozonization, carbon filtration, and, more drastically, chlorination. Proteobacteria and Bacteroidota predominated in river water and throughout the process, but in the final drinking water, the strong selective pressure of chlorination reduced diversity and was clearly dominated by Cyanobacteria. Significant seasonal variation in species distribution was observed in decantation and carbon filtration samples. Some amplicon sequence variants related to potentially pathogenic genera were found in the DWTP. However, they were either not detected in the final water or in very low abundance (<2%), and all EU Directive quality standards were fully met. A combination of culture and high-throughput sequencing techniques may help DWTP managers to detect shifts in microbiome, allowing for a more in-depth assessment of operational performance.

The aquifer storage and recovery system of Sant Joan Despí (SJD) in the Llobregat Basin (Barcelona, Spain) has been injecting potable water since its construction in 1969. In order to increase the environmental and economic sustainability of the process, the substitution of potable water by sand-filtered surface water (SFSW) has been considered. This study aims at assessing the clogging potential of SFSW by reproducing the aquifer storage and recovery (ASR) system in a column-type pilot system. Developed clogging of a metallic screen simulating a well screen in the ASR was observed by direct visualization and by scanning electron microscopy (SEM), and was measured by the pilot column head loss and by the analysis of extracellular polymeric substances formed. The results show that although there is a detectable clogging formation, the experiment could run with no flow limitation, suggesting that SFSW could be a feasible candidate water for aquifer injection in a real well demonstration phase.