SODIS potential: A novel parameter to assess the suitability of solar water disinfection worldwide

This paper studies the worldwide applicability of solar water disinfection (SODIS) technology through a novel parameter: the SODIS potential. This parameter is defined as the inverse ratio between the required exposure time to achieve a four log disinfection of E. coli and the six hours recommended by the standard SODIS protocol. The E. coli inactivation kinetics was predicted by fitting the results under different temperature and incident radiation to a semi-empirical inactivation model, including a synergy term between bacterial stress sources (light/heat). To estimate the SODIS potential, a solar calculator was developed based on the Sun's position, atmospheric extinction, cloud-cover, and elevation. The time-varying total incident radiation available at any location worldwide was estimated for each day along the year during sunlight hours. The time-varying temperature was also estimated from minimum and maximum values, introducing its dynamic variation along with the solar exposure of the water. Both incident radiation and temperature values are input into the kinetic model to estimate the disinfection rate. Based on these values, the number of batch disinfections that can reach the goal of 99.99% bacterial elimination in 1 day and the minimum daily time required to achieve this goal is computed; the latter is finally transformed to the SODIS potential. The results of the study, illustrated as contours indicating the SODIS potential and other relevant indicators overlayed on a world map, confirm that latitude has a significant contribution to the SODIS potential, with the highest values close to the equator. However, the results also highlight the importance of temperature and cloud-cover, with critical differences between equal latitude regions.

Visible light plays a significant role during bacterial inactivation by the photo-fenton process, even at sub-critical light intensities

Stefanos Giannakis, Rosa Mosteo, David Muzard, César Pulgarin, Angelica Varon Lopez

The aim of this research is to clarify the contribution of sunlight wavelengths, irradiance and Fe2+/H2O2 during bacterial disinfection by the photo-Fenton process in clear surface waters. We considered different solar spectrum distributions (visible, UVA-Visible), sub-critical irradiances (0-400 W/m(2)), focusing on the action modes of E. coli inactivation by the constituents involved in the composite process, at low tM reactants concentration (Fe2+/H2O2) in in ultrapure (MQ) water. We report that solar disinfection improved with Fenton reagents (photo-Fenton process) is a reality from very low light irradiance values (200 W/m(2)), and made possible even without the presence of UVA radiation, even when using low quantities of the Fenton reagents (0.5 mg/L Fe2+, 5 mg/L H2O2). Under light exposure, H2O2 was found to augment the intracellular Fenton process and Fe2+ to initiate further, distinct oxidative actions. Finally, validation was performed in Lake Geneva water over a wider irradiance range, where the photo-Fenton process was found to be reagent-dependent in low irradiance, shifting to light-driven in the higher values. (C) 2020 Elsevier Ltd. All rights reserved.

PERGAMON-ELSEVIER SCIENCE LTD2020

Solar photolytic and photocatalytic disinfection of water at laboratory and field scale. Effect of the chemical composition of water and study of the post-irradiation events

César Pulgarin

Background. In recent years, there has been a growing interest in the development of new processes for water disinfection since the traditional processes, such as chlorination, can lead to the production of toxic disinfection by-products. Sunlight has been used as a method of water disinfection and heliophotocatalysis by titanium dioxide (TiO2) has been recently considered as a new approach to improve the conventional solar water disinfection. This paper discusses the effect of the chemical composition of water on the E. coli photo inactivation. Method of Approach. Ten types of water having a different chemical composition were contaminated by E. coli K12 and exposed to a simulated solar irradiation in the absence of TiO2 (photolysis) and in presence of TiO2 (photocatalysis). Bacteria were monitored by plate count. The durability of disinfection was assessed in terms of the effective disinfection time (EDT) in a subsequent dark period of 24 h (EDT24). Natural water from the Leman Lake (LLW), milli-Q water (MQW), MQW containing a mixture of NO3-, PO4-3, SO4-2, Cl− and HCO3-, phosphate buffered saline water, water from the outlet of a biological wastewater treatment plant (WW); MQW containing a mixture of KCl-NaCl and commercial bottled drinking water (CBW) where used to suspend E. coli at laboratory scale. Field scale experiments using solar irradiation in a compound parabolic concentrator (CPC) with E. coli suspended in LLW were also carried out. Results. The sensitivity of bacteria to the phototreatment depends on the nature of the water. Moreover, experiments systematically performed under the solar simulator showed that the order of E. coli inactivation rate and the EDT24 are different for each system. In photolytic systems, E. coli solar inactivation rate is accelerated by the presence in water of NO3- and HCO3- when compared to that observed in MQW. EDT24 was reached at 3 h of irradiation for only 3 (WLL, WW1, and CBW) of the ten studied waters. In the presence of TiO2, the rate of the solar disinfection generally increased. However, a negative effect of chemical substances present in water on the E. coli photocatalytic inactivation was observed in waters when compared to MQW. This effect was especially important in the presence of phosphate, and carbonate. EDT24 was less than 2 h for the majority of the water types. In the presence of TiO2, a “residual disinfection effect” was observed for samples even when bacterial culturability below the detection limit was not reached after photocatalytic treatment. Solar irradiation in a CPC photoreactor indicates that the presence of TiO2 accelerates the detrimental action of sunlight. The EDT24 was reached before 3 h, in photocatalytic experiments but not in those in the absence of TiO2. The influence of TiO2 surface characteristics and charge, as well as the postirradiation events observed in heliophototreated water, in an optimal growth medium are also discussed. Conclusions. The presence of NO3-, HCO3-, PO4-3, SO4-2, Cl−, and HCO3- greatly affects the photolytic and photocatalytic disinfection processes. The natural ions and organic matter affect the solar disinfection of water in the presence and absence of TiO2 and influences the post irradiation events after sunlight illumination. Antagonistic effect in several conditions or synergistic effects in others can be expected when inorganic and/or organic substances are present in phototreated water sources. EDT24 is useful tool for standardization of solar water disinfection. EDT24 values depend on parameters such as the chemical composition of water, light intensity, initial bacterial concentration, and TiO2 concentration.

2007

Solar photolytic and photocatalytic disinfection of water at laboratory and field scale. Effect of the chemical composition of water and study of the post-irradiation events

César Pulgarin

2007