Avaliação Quantitativa de Risco Microbiológico (AQRM) associado à E. coli em efluente tratado em uma unidade de ensino localizada em Salvador-BA

Abstract

Brazil has a great hydric potential, but the access to water reserves is not available to the entire population. In addition to this, there is the large-scale use of water resources, making them scarce. As an alternative that saves and preserves this resource, there is the reuse of wastewater. However, some precautions must be considered, related to health safety. This study aimed to evaluate the microbiological risks associated with human health, from the reuse of effluent from a decentralized wastewater treatment plant (WWTP), from a school located in the city of Salvador (BA). The Quantitative Microbiological Risk Assessment (QMRA) tool was used to estimate the risk of infection caused by Escherichia coli and its Maximum Allowable Values (MAV's), depending on the acceptable risk established by the WHO (World Health Organization) of 10-3 per person per year (pppy). In addition, the need and efficiency of an additional treatment with chlorine in the treated effluent was evaluated. For this, the number of ingested pathogens per exposure route was estimated and the probabilities of infection were calculated over a period of one year, according to the reuse modalities interesting for the school (garden irrigation, toilet flushing and washing floor). After that, the reverse path was performed, and the E. coli MAVs were obtained. The results were compared with the parameters specified in national norms and guidelines about reuse and it was found that the experimental system did not present sufficient efficiency to meet the reuse activities evaluated, so that no activity proved to be suitable for immediate reuse, being the chlorine post-treatment required. In all cases, the minimum efficiency required for the reuse of wastewater was above 97% and reached 100% in the three studied modalities. After the post-treatment, it was verified that with 15 mg/L of chlorine, the parameters continued not showing sufficient efficiencies for immediate reuse. For 20 mg/L, some parameters were within the allowed range and for 25 mg/L and 30mg/L of chlorine, all parameters were within, being an efficient additional treatment when applied in correct dosages. The national norms/guidelines proved to be rigid in general, so that the MAVs did not fit them, being the ideal to formulate a legal instrument at the national level to standardize the reference values for the reuse of wastewater and not make the reuse of wastewater unfeasible.