Abstract
At the beginning of 2020, about 9 million inhabitants of the Metropolitan Region of Rio de Janeiro, dependent on the Guandu Basin, experienced a water-supply crisis when their water tasted badly and gave off an odor. This work presents the results of analyses of the sanitary quality of raw water in this system at two different times during the water crisis, with respect to the presence of cyanobacteria found using metagenomic studies, and cyanotoxins, microcystin (MC) and saxitoxin (SXT) quantified by ELISA. Analyses of raw water quality parameters were carried out through the determination of total coliforms and Escherichia coli levels and some physical-chemical parameters. The raw water collected in both periods presented levels of Escherichia coli levels above the maximum allowed values (MAV) described in Resolution 357/2000 of the National Environmental Agency, as well as the levels of MC in a filter sample. The physical-chemical parameters analyzed and the SXT levels were in accordance with this resolution. The most abundant cyanobacterial genus in the critical period was Planktothricoides sp. Therefore, it is necessary to implement basic sanitation in cities upstream from the point of capture of raw water from this source, so that events similar to those that occurred in the 2020 water crisis do not recur.
Highlights
The lack of sanitation in the cities upstream of the point of captation of water from the spring used by water treatment plants (WTS) means that the cities are consuming a type of indirect reuse water (Hespanhol, 2015; Moura, 2019)
The aim of this work was to verify the sanitary quality of the raw water of the Guandu Basin, destined for treatment for human consumption in the Metropolitan Region of the state of Rio de Janeiro, and in particular the presence of cyanobacteria associated with the production of substances that cause odor and smell, and cyanotoxins, during two periods of the water crisis of 2020
The level of Escherichia coli, the main bioindicator parameter of the recent presence of sewage in raw water, was above MAC in both periods, even for Class 2 raw water, according to Resolution no.357/2005. This result indicates how much the Guandu River Basin is impacted by the lack of sanitation in the cities upstream of the water catchment point used by the Guandu WTP
Summary
The lack of sanitation in the cities upstream of the point of captation of water from the spring used by water treatment plants (WTS) means that the cities are consuming a type of indirect reuse water (Hespanhol, 2015; Moura, 2019). As described by Hespanhol (2015), this occurs when effluents are discharged into the environment (upstream), and are again used downstream, in their diluted form, in an unintentional and uncontrolled manner. In this way, in the Guandu River Basin, sewage discharged into the waters of the Ipiranga, Queimados and Poços Rivers brings a load of nutrients to the water bodies, which combines with the high luminosity and low movement of the water in lagoons near the point of capture of raw water and favors the growth of microorganisms (INEA, 2012). The risk of returning to conditions conducive to the proliferation of cyanobacteria and favoring the
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