Avaliação microbiológica do efluente de uma ETE descentralizada com vistas ao reúso

Abstract

In Brazil, the hydrical stress is a reality already, resulting of the increasing demands from the populational growing and economic activities based on water using. The deficit on the sanitation sector is high, mostly when it is about sewage collection, so that the decentralization and universalization of basic housing and sanitation services have been defended as a way of progress. The reuse of treated wastewater shows itself as a viable option for attending urban uses that don’t require potable quality, contributing to increase the water availability. The using of this water alternative source, however, must be done with due caution because of the health risks associated to its handling. Before this context, the objective of this study was to execute the Quantitative Microbiological Risk Assessment (QMRA) associated to the nonpotable reuse of the wastewater from a sewage treatment plant responsible for the wastewater treatment of a residential complex and restaurant in São Paulo-SP. The use of the QMRA technique intended to estimate the Escherichia Coli risk infection and set the maximum allowed values of this microorganism concentration on the wastewater to be reused, based on the tolerable risk established by the World Health Organization (WHO). To do so, it has been estimated the amount of pathogens ingested for exposure event and it has been calculated the infection likelihood for a single exposure and for multiple exposures throughout a year, according to the reuse modality. Then, the reverse path has been executed in order to set the maximum allowed values of E. coli, assessing the need of post treatment and the respective minimum efficiency. The results found have been compared to the reference values delimitated on the legislation and guidelines related to wastewater reuse. The experimental system studied has not shown enough efficiency to attend the majority of the reuse activities assessed, so that only the vehicle washing and floor washing activities, through the exposure route by aerosols and 0,01 mL ingested volume, have shown themselves proper to immediate reuse, with risks of 0,0005 and 0,0001, respectively. The efficiencies needed to adequate the wastewater destined to the reuse have been located in the range between 79% and 100%, with a few isolated minor values, around 11% and 34%. The international and national guidelines have shown themselves to be very restrictive, as the majority maximum allowed values calculated have not been considered proper to attend the legislations and guidelines. The addition of a specific treatment stage for the disinfection of the wastewater in the experimental system could contribute to higher efficiencies of pathogens removal, making possible more reuse prospects for the wastewater.