Effectiveness of solar water disinfection in the era of COVID-19 (SARS-CoV-2) pandemic for contaminated water/wastewater treatment considering UV effect and temperature

Abstract

Long is the way and hard, that out of COVID-19 leads up to light. The virus is highly contagious and spread rapidly and the number of infections increases exponentially. The colossal number of infections and presence of the novel coronavirus RNA in human wastes (e.g. Excreta/urine) even after the patients recovered and the RT-PCR tests were negative, results in massive load of the viral in water environments. Numerous studies reported the presence of SARS-CoV-2 in wastewater samples. The risk of contaminating water bodies in the regions which suffer from the lack of proper sanitation system and wastewater treatment plants (mostly in developing countries) is higher. Since solar water disinfection (SODIS) is usually used by people in developing countries, there is a concern about using this method during the pandemic. Because the SARS-CoV-2 can be eliminated by high temperature (>56 °C) and UVC wavelength (100-280 nm) while SODIS systems mainly work at lower temperature (<45 °C) and use the available UVA (315-400 nm). Thus, during a situation like the ongoing pandemic using SODIS method for wastewater treatment (or providing drinking water) is not a reliable method. It should be reminded that the main aim of the present study is not just to give insights about the possibilities and risks of using SODIS during the ongoing pandemic but it has broader prospect for any future outbreak/pandemic that results in biological contamination of water bodies. Nevertheless, some experimental studies seem to be necessary by all researchers under conditions similar to developing countries.

Keywords: Contaminated water; Developing countries; Novel coronavirus; Solar disinfection (SODIS); UV disinfection; Water treatment.

Graphical abstract

Fig. 1

Photo-reactivation repair mechanism of DNA. a) In normal condition, adjacent nucleotides within a single strand of DNA (ssDNA) are linked by a type of covalent bond, named phosphodiester bond, which is formed between the 5′ phosphate group of one nucleotide and the 3′-OH group of another. b) UV radiation leads two adjacent pyrimidine bases on one strand, become covalently fused, so cyclobutane pyrimidine dimers (CPDs) and 6-4 photoproducts are formed which can inhibit normal cellular function. (CPDs are composed when two vicinal pyrimidines joint through sharing two double bonded carbons. A covalent joint between a carbon at the 6 position of one pyrimidine ring and a carbon at the 4 position of the other one forms 6–4 photoproducts). c) In order to restore the integrity of DNA, Photolyase enzyme uses near-UV light to initiate electron transfer to break covalent bonds so that UV photoproducts become repaired.

Fig. 2

Important parameters that can be affected the inactivation of viral. Crucial parameters that in most of SODIS researches were examined and discussed are solar intensity, temperature of water, fixation, and ROS.

Fig. 3

Possible routes of contamination of water bodies. Some routes such as wastewater discharge (a) and WWTPs have significant contribution on the contamination of water bodies while some routes such as secondary host (animals). Some routes such as open defecation and pit toilet mainly happened in developing countries and poor communities. The possible routes can be mentioned as: a) discharging cities wastewater, b) contaminated wastes, c) improper disposing personal protective equipment (PPE), d) wastewater treatment plants (WWTPs), e) sewer leakage, f) secondary hosts (animals), g) hospital sewage, h) combined sewer overflows (CSOs), i) open defecation and pit toilets.

Fig. 4

T₉₀ of the SARS-CoV-2 for various wastewaters and tap water samples with respect to water temperature. By increasing the water temperature the T₉₀ is decreased and vice versa. The upper and lower boundaries represent the maximum and minimum T₉₀ of the samples in different temperature considering standard deviation a) autoclaved wastewater (standard deviations for temperature 4 °C, 15 °C, 25 °C, and 37 °C are ±5.95, ±2.39, ±0.85, and ±0.5 respectively), b) tap water (standard deviations for temperature 4 °C, 15 °C, 25 °C, and 37 °C are ±8.68, ±4.54, ±0.45, and ±0.03 respectively), c) untreated wastewater (standard deviations for temperature 4 °C, 15 °C, 25 °C, and 37 °C are ±4.45, ±2.13, ±0.59, and ±0.23 respectively).