Characterization of Periods of Crisis and Post-Crisis in the Raw Water of Guandu System through Quality Parameters

Abstract

At the beginning of the year 2020, about 9 million inhabitants of the Metropolitan Region of Rio de Janeiro dependent of the Water Guandu System, experienced a crisis in the water supply, receiving water with taste and odor issues. In this way, this work carried out the analysis of the sanitary quality of raw water that is captured from this system, at two different moments, "in crisis" and "post-crisis", in relations to the presence of cyanobacteria and cyanotoxins in raw water, through studies of metagenomics and quantification of microcystin (MC) and  saxitoxin (SXT) cyanotoxins by ELISA test, comparing extraction and processing methods. The analysis of raw water quality parameters was also carried out, through the evaluation of the levels of total coliforms and Escherichia coli and some physical-chemical parameters in order to compare with data from INEA analyzes. The raw water collected at both times had levels of Escherichia coli above the Maximum Acceptable Values (MAV) described in Resolution no. 357/2000 of CONAMA, while it presented satisfactory levels in the analyzed physical-chemical parameters as well as for cyanotoxin levels, for SXT. However, it is noteworthy that in the filter extraction methodology, the sample “after crisis” was not within the MAV for MC, so if it were done by this same method the samples of the moment ¨ in crisis¨ would have the values ​​of MC also much higher of the MAV, since in the commonly used methodology the value for MC was above the value for the moment ¨after crisis¨. Therefore, in the review of the Potability Ordinance, it is necessary to describe an extraction methodology that can express the real risk in relation to the levels of cyanotoxins present in raw water. Thus, it is important that sanitation be carried out as soon as possible in the cities upstream of the water treatment plant, so that events such as those that occurred during the “water crisis” are not experienced again. In addition, in the short term, it is necessary to perform periodic monitoring of reservoirs, integrating genomics, biogeochemistry and toxicity analyzes, in order to signal any problems in advance and guarantee the quality of supply, in addition to being able to support data on the implementation of the Contingency Plan, as a precaution so that the flowering situation does not increase.