Otimização do método de floculação orgânica de concentração viral para avaliação do impacto de tratamento por lodo ativado na Estação de Tratamento de Esgoto Barbosa Lage, Juiz de Fora - Minas Gerais

Abstract

Sewage treatment may be insufficient for the complete elimination of enteric viruses such as human adenoviruses (HAdV) and group A rotaviruses (RVA). Thus, the return of sewage sludge and treated effluent to the environment poses concerns potential for public health. This study was conducted to optimize an organic flocculation procedure for viral recovery from sludge and treated effluent, and carry out a surveillance of HAdV and RVA in a wastewater treatment plant (WWTP) at Juiz de Fora, MG. In optimization studies, conditions were proposed for sludge and treated effluent with changes in the stirring time, in the final concentration of skimmed-milk and/or in the centrifugation step. In surveillance study, raw sewage (P1), primary sewage (P2), sludge (P3) and treated effluent (P4) were collected bimonthly in 2014 (during the dry and the rainy season), totaling 96 samples (simple and composite). Quantitative PCR determined viral loads and PP7 bacteriophage was used as internal control. HAdV and RVA strains were selected for sequencing, and the HAdV viability was evaluated in P4 samples. Physicochemical parameters and thermotolerant coliforms (TC) counting were determined at each point. After the optimization studies, two conditions were selected: the ones that showed the highest viral recovery rates in sludge (lower stirring time and higher concentration of skimmed-milk) and treated effluent (without the first centrifugation step and with a higher concentration of skimmed-milk). These conditions proved to be a useful tool for viral search in the field samples, including for the research of giant virus. In surveillance study, HAdV was detected in 85.4% (82/96) of the concentrated, with viral loads ranging from 3.27 x 102 to 2.42 x 106 genome copies per milliliter (gc/mL), throughout the year. RVA presence was observed in 52.1% (50/96) of the samples (1.38 x 103 to 3.65 x 105 gc/mL) with detection greater in the dry season. Viral load was not influenced by the type of sample being detected both in single samples, as in composite samples. All the sequenced HAdV strains belonged to species F type 41, and RVA strains belonged to genotype I1. Sewage treatment reduced the content of organic matter and solids, as well as the TC counts and the viral loads. However, the presence of HAdV and RVA was observed after treatment, even in samples considered adequate by current laws with detection of infectious HAdV particles. Positive correlations were observed between viral load and biochemical oxygen demand, sedimented solids and total suspended solids. Two optimized protocols in this study are easily suitable for routine laboratory use and can boost viral monitoring in by-products generated in the WWTP. Viral load detected in WWTP stress the environmental dissemination of HAdV and RVA and addressed the potential of HAdV as a virological marker of contamination in aquatic environments.