Abstract
Pathogenic viruses are frequently present in marine and estuarine waters, due to poor wastewater (WW) treatments, which consequently affect water quality and human health. Chlorination, one of the most common methods used to ensure microbiological safety in tertiarily treated effluents, may lead to the formation of toxic chemical disinfection by-products on reaction with organic matter present in the effluents. Antimicrobial photodynamic therapy (aPDT) can be a promising disinfecting approach for the inactivation of pathogens, without the formation of known toxic by-products. Additionally, some studies have reported the potentiator effect on aPDT of some compounds, such as potassium iodide (KI) and hydrogen peroxide (H2O2). In the present study, the aPDT efficiency of a PS formulation constituted of five cationic porphyrins (Form) in the inactivation of E. coli T4-like bacteriophage, a model of mammalian viruses, in different aqueous matrices with different organic matter content, was evaluated. Photoinactivation studies were performed at different concentrations of Form and in the presence of the adjuvants KI and H2O2. The results showed that the efficiency of bacteriophage photoinactivation is correlated with the Form concentration, the amount of the organic matter in WW, and the adjuvant type. Form can be an effective alternative to controlling viruses in WW, particularly if combined with H2O2, allowing to significantly reduce PS concentration and treatment time. When combined with KI, the Form is less effective in inactivating T4-like bacteriophage in WW.
Highlights
The presence of pathogens in wastewater (WW) is a subject of great concern due to the impact on the quality of the receiving water where this type of effluent is discharged
Aliquots of the samples and controls were collected at defined times of light exposure and the bacteriophage concentration was quantified as described above
Assays in phosphate-buffered saline (PBS), with 0.45 μm filtered WW, were performed to test if longerlived reactive species generated when Antimicrobial photodynamic therapy (aPDT) was done in the presence of KI [e.g., free iodine/triiodide (I2 /I3 − ), iodine radicals (I2 − ), and hydrogen peroxide (H2 O2 )] were able to continue reducing the content of viruses in the sample after the light treatment
Summary
The presence of pathogens in wastewater (WW) is a subject of great concern due to the impact on the quality of the receiving water where this type of effluent is discharged. Even though WW is, in general, secondarily treated before being launched into seawater and rivers, it contains high concentrations of microorganisms, but dilution makes it acceptable in terms of microbiological quality, to levels comparable to those found in natural waters, achieving the guidelines of the World Health Organization (WHO) and the United States Environmental Protection Agency (EPA) standards for microorganisms’ presence in water [4]. Viruses have been proposed to be included alongside bacteria as indicators of the microbiological quality of different water bodies and water treatment [10,11,12]. Despite the advances in wastewater treatment plants (WWTP), a large number of human enteric viruses are discharged into the aquatic environment [9,13,14]. Genome copies of SARS-CoV-2 have been found in untreated and treated WW [15], and a recent study has shown that infectious SARS-CoV-2 can be detected for at least seven days in WW (laboratory experiments using a virus high-titre) [16]
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