ArticlePDF Available

Abstract and Figures

Solar water disinfection (SODIS) is a simple, inexpensive and sustainable Household Water Treatment (HWT) that is appropriate for low-income countries or emergency situations. Usually, SODIS involves solar exposure of water contained in transparent polyethylene terephthalate (PET) bottles for a minimum of 6 h. Sunlight, especially UVB radiation, has been demonstrated to photoinactivate bacteria, viruses and protozoa. In this work, an in-depth study of the optical and mechanical properties, weathering and production prices of polymeric materials has been carried out to identify potential candidate plastic materials for manufacturing SODIS device. Three materials were ruled out (polystyrene (PS), polyvinyl chloride (PVC) and polyethylene (PE)) and four materials were initially selected for study: polymethylmethacrylate (PMMA), polypropylene (PP), polycarbonate (PC) and polyethylene terephthalate (PET). These plastics transmit sufficient solar radiation to kill waterborne pathogens with production costs compensated by their durability under solar exposure. A predictive model has been developed to quantitatively estimate the radiation available for SODIS inside the device as a function of the material and thickness. This tool has two applications: to evaluate design parameters such as thickness, and to estimate experimental requirements such as solar exposure time. In this work, this model evaluated scenarios involving different plastic materials, device thicknesses, and pathogens (Escherichia coli bacterium, MS2 virus and Cryptosporidium parvum protozoon). The developed Solar UV Calculator model is freely available and can be also applied to other customized materials and conditions.
Content may be subject to copyright.
Journal Pre-proof
Material selection and prediction of solar irradiance in plastic
devices for application of solar water disinfection (SODIS) to
inactivate viruses, bacteria and protozoa
Ángela García-Gil, Cristina Pablos, Rafael A. García-Muñoz,
Kevin G. McGuigan, Javier Marugán
PII: S0048-9697(20)32643-7
DOI: https://doi.org/10.1016/j.scitotenv.2020.139126
Reference: STOTEN 139126
To appear in: Science of the Total Environment
Received date: 12 February 2020
Revised date: 10 April 2020
Accepted date: 28 April 2020
Please cite this article as: Á. García-Gil, C. Pablos, R.A. García-Muñoz, et al., Material
selection and prediction of solar irradiance in plastic devices for application of solar water
disinfection (SODIS) to inactivate viruses, bacteria and protozoa, Science of the Total
Environment (2020), https://doi.org/10.1016/j.scitotenv.2020.139126
This is a PDF file of an article that has undergone enhancements after acceptance, such
as the addition of a cover page and metadata, and formatting for readability, but it is
not yet the definitive version of record. This version will undergo additional copyediting,
typesetting and review before it is published in its final form, but we are providing this
version to give early visibility of the article. Please note that, during the production
process, errors may be discovered which could affect the content, and all legal disclaimers
that apply to the journal pertain.
© 2020 Published by Elsevier.
Journal Pre-proof
1
MATERIAL SELECTION AND PREDICTION OF SOLAR IRRADIANCE IN PLASTIC
DEVICES FOR APPLICATION OF SOLAR WATER DISINFECTION (SODIS) TO
INACTIVATE VIRUSES, BACTERIA AND PROTOZOA
Ángela García-Gil1, Cristina Pablos1, Rafael A. García-Muñoz1, Kevin G. McGuigan2, Javier
Marugán1*
1 Department of Chemical and Environmental Technology (ESCET), Universidad Rey Juan Carlos,
C/ Tulipán s/n, 28933 Móstoles, Madrid, Spain.
2 Department of Physiology & Medical Physics, Royal College of Surgeons in Ireland (RCSI), Dublin 2, Ireland.
*Corresponding author email: javier.marugan@urjc.es
Abstract
Solar Water Disinfection (SODIS) is a simple, inexpensive and sustainable Household Water
Treatment (HWT) that is appropriate for low-income countries or emergency situations. Usually,
SODIS involves solar exposure of water contained in transparent polyethylene terephthalate (PET)
bottles for a minimum of 6h. Sunlight, especially UVB radiation, has been demonstrated to
photoinactivate bacteria, viruses and protozoa. In this work, an in-depth study of the optical and
mechanical properties, weathering and production prices of polymeric materials has been carried
out to identify potential candidate plastic materials for manufacturing SODIS device. Three
materials were ruled out (polystyrene (PS), polyvinyl chloride (PVC) and polyethylene (PE)) and four
materials were initially selected for study: polymethylmethacrylate (PMMA), polypropylene (PP),
polycarbonate (PC) and polyethylene terephthalate (PET). These plastics transmit sufficient solar
radiation to kill waterborne pathogens with production costs compensated by their durability under
solar exposure.
A predictive model has been developed to quantitatively estimate the radiation available for SODIS
inside the device as a function of the material and thickness. This tool has two applications: to
Journal Pre-proof
Journal Pre-proof
2
evaluate design parameters such as thickness, and to estimate experimental requirements such as
solar exposure time. In this work, this model evaluated scenarios involving different plastic
materials, device thicknesses, and pathogens (Escherichia coli bacterium, MS2 virus and
Cryptosporidium parvum protozoon). The developed Solar UV Calculator model is freely available
and can be also applied to other customized materials and conditions.
Keywords
Mechanical properties, optical properties, UV Calculator, Photoinactivation, Household Water
Treatments, Sustainable Development Goals.
1. Introduction
In 2015, the General Assembly of United Nations announced the Sustainable Development Goals
(SDGs) to “end poverty in all its forms” (United Nations (UN) 2015). That same year, there were
almost 900 million people without access to safe drinking water (United Nations (UN) 2018) which
is one of the priority themes of the SDGs. SDG 6 “Clean water and sanitation” aims to “ensure
availability and sustainable management of water for all”. Provision of drinking water is the first
challenge that must be approached and is considered the first target of the goal titled Achieve
access to safe and affordable drinking water . Most people without access to safe drinking water
live in low-income countries with few financial resources, thus, they require low-cost, sustainable
and simple systems for Household Water Treatment (HWT). Moreover, these countries are located
in regions where solar irradiance levels are very high throughout the year. Therefore, a suitable
HWT alternative for them is the use of solar water disinfection (SODIS), commonly carried out in 1-
2L polyethylene terephthalate (PET) bottles exposed to solar radiation for a minimum of 6 h
(McGuigan et al. 2012). This process is based on the harmful effect of UV radiation and its synergy
Journal Pre-proof
Journal Pre-proof
3
with temperature on pathogens (Joyce et al. 1996; McGuigan et al. 1998; Romero et al. 2011;
Gómez-Couso et al. 2012; Castro-Alférez et al. 2017).
SODIS photoinactivation processes can follow direct and indirect mechanisms and are strongly
affected by the different UV spectral ranges and specific microbiological features of the pathogens
(bacteria, viruses or protozoa).
i) Direct photoinactivation is an endogenous process that takes place when a constituent of the
microorganism itself (e.g. nucleic acids, proteins or other macromolecules) absorbs photons,
inducing changes to their chemical structure. For example, nucleic acids absorb radiation of
wavelengths below 320 nm. As a result, many viruses can be photoinactivated with the UVB
component of the solar spectrum (Lytle and Sagripanti 2005; Mattle et al. 2015; Nelson et al. 2018).
Similarly, Cryptosporidium parvum protozoon has been also proved to be inactivated under solar
light, predominantly by the direct genome damage produced by the UVB radiation (Liu et al. 2015;
Nelson et al. 2018). Bacterial pathogens are also sensitive to direct photoinactivation by solar UVB
radiation (Jagger 1985).
ii) Indirect photoinactivation occurs when a photo-produced reactive intermediate (PPRI) (e.g.
hydrogen peroxide, hydroxyl radical, singlet oxygen, carbonate radical and superoxide) damages
microorganism components. Endogenous indirect inactivation takes place when PPRI are generated
from internal sensitizers. For viruses, insufficient generation of PPRI produced by a few internal
sensitizers makes endogenous indirect damage negligible and slower than direct damage (Love et
al. 2010). When only UVA and visible radiation is available, indirect damage produced by internal
sensitizers can slowly damage protozoon components (Liu et al. 2015; Nelson et al. 2018). Several
studies confirm the importance of indirect endogenous mechanisms for bacteria when internal
sensitizers (catalase, alkyl hydroperoxide reductase (Ahp) and peroxidase enzymes) are illuminated
with wavelengths across the solar UV (UVA and UVB radiation) and visible ranges, promoting the
formation of PPRIs such as reactive oxygen species (ROS) (Nelson et al. 2018). For example, in
Escherichia coli endogenous damage decreases as wavelength increases, with negligible effects for
Journal Pre-proof
Journal Pre-proof
4
wavelengths above 400 nm. In contrast, Enterococcus faecalis extends its susceptibility up to 500
nm (Silverman and Nelson 2016). In such cases, direct and indirect endogenous damage can
interact and, for this reason, both are often studied simultaneously.
If the sensitizer is external, then the indirect photoinactivation is exogenous. This mechanism is
only possible if the water contains these sensitizers. For example, as external PPRI are not present,
indirect exogenous photoinactivation does not happen in pure water (Nelson et al. 2018). In other
water matrices, the photoinactivation of viruses and bacteria can be enhanced under UVA and
visible radiation (Kohn and Nelson 2007; Romero et al. 2011; Mattle et al. 2015). However, it is a
complex mechanism that depends on many factors (pathogen species, physiological state, radiation
wavelength, type of sensitizers and its relationship with the pathogen) (Maraccini et al. 2016). For
protozoa, exogenous indirect damage is generally negligible due to the thick resistant oocyst-wall
(Liu et al. 2015; Nelson et al. 2018).
Summarizing, protozoa and viruses are mainly photoinactivated by direct endogenous mechanisms
caused through the action of UVB radiation while bacteria are damaged by direct and indirect
endogenous processes through the action of UVA and UVB radiation. In addition, if the water is not
pure, exogenous indirect damage can enhance solar disinfection for bacteria and viruses but not for
protozoa.
Consequently, the efficiency of SODIS processes for the different types of pathogens is strongly
affected by the transmission spectra of the materials used for the devices. Usually, SODIS treatment
is carried out using PET bottles due to their low-cost and accessibility. Concerns about chemical
contaminants from plastic migration have been addressed by previous studies (Wegelin et al. 2001;
Ubomba-Jaswa, Fernández-Ibáñez, and McGuigan 2010). Alternative materials have been
successfully evaluated, such as polypropylene copolymer (PPCO), polycarbonate (PC) and
polystyrene (PS) 1 L bottles (Fisher et al. 2012), polyethylene (PE) bags (Lawrie et al. 2015),
polymethylmethacrylate (PMMA) (Ubomba-Jaswa, Fernández-Ibáñez, Navntoft, et al. 2010;
Reyneke et al. 2020) and glass reactors (Kalt et al. 2014; Mac Mahon and Gill 2018; García-Gil et al.
Journal Pre-proof
Journal Pre-proof
5
2018) fitted with compound parabolic collectors (CPC). The design of SODIS systems requires the
selection of optimal materials for the manufacturing of the devices considering the UV transmission
spectra but also the mechanical properties, resistance to weathering and production cost.
Moreover, the predictive estimation of the SODIS efficacy requires accurate calculation of the
radiation intensity and spectrum inside the devices. For these reasons, the goals of this work are
the selection of the optimal candidate materials for SODIS device manufacturing and the estimation
of solar available radiation and its spectral distribution as a function of the material and wall
thickness. For the latter, a tool called the Solar UV Calculator has been developed and evaluated to
predict SODIS under different scenarios of plastic materials, device thicknesses and target
pathogens (E. coli bacterium, MS2 virus and C. parvum protozoon). This Solar UV Calculator, was
developed as part of the WATERSPOUTT H2020 project which aims to develop HWT technologies
based on the SODIS process for African settlements in rural areas of Malawi, Ethiopia, Uganda and
South Africa. The Solar UV Calculator is freely available to any potential user interested in the
evaluation of SODIS devices with customized materials and conditions or even for other solar
applications based on spectral transmission calculations.
2. Materials and methods
2.1. Mechanical properties
Selection of candidate plastics for the manufacturing of SODIS devices has been carried out through
an exhaustive review of literature data. Only transparent plastics and without any kind of UV-
stabilizer were considered in the study. Three sets of plastics were studied depending on their
photostability:
Poorly photostable plastics (Polystyrene (PS), polyvinyl chloride (PVC), polypropylene (PP)
and polyethylene (PE)).
Moderately photostable plastics (Polyethylene Terephthalate (PET) and polycarbonate
(PC)).
Journal Pre-proof
Journal Pre-proof
6
Highly photostable plastics (polymethylmethacrylate (PMMA)).
Mechanical properties such us tensile strength, elasticity, impact resistance and weathering
resistance (humidity, temperature and solar radiation) as well as degradation mechanisms of
photooxidation, were analysed. Finally, manufacturing costs were also considered using Ecoinvent
and Plastic Europe Databases (Frischknecht et al. 2005; PlasticEurope 2012).
2.2. Optical properties
The optical properties of candidate plastic materials were experimentally evaluated by recording
their transmission spectra with a UV-Vis-NIR spectrophotometer (Varian Cary 500, Palo Alto,
California, USA). Three independent and replicated measurements for different thicknesses of the
plastic samples were considered.
2.3. Solar UV Calculator tool
A predictive tool called the Solar UV Calculator has been developed to predict the total radiation
available and its spectral distribution inside the plastic device as a function of the thickness and
type of plastic. For this purpose, maximum solar radiation inside the device has been calculated by
applying Eq. 1 in the solar UV-Visible range from 290 nm to 800 nm:
  
(Eq. 1)
where  is the monochromatic radiation intensity (W·m-2·nm-1) inside the device, 
the monochromatic solar radiation intensity (W·m-2·nm-1) and  is the transmittance of the
plastic material at each wavelength (dimensionless). The transmittance ( is directly related to the
absorbance  of the material (dimensionless) by the well-known Eq 2:
 
(Eq. 2)
whereas the absorbance is related to optical path length  in (m) by the Beer-Lambert law (Eq. 3):
   
(Eq. 3)
where  is the monochromatic extinction coefficient (m-1) for wavelength , which depends on
the material. For each type of plastic, the absorption spectrum was measured for three different
Journal Pre-proof
Journal Pre-proof
7
thicknesses and the monochromatic extinction coefficients were obtained from the slope of the
linear regression of absorbance vs thickness plot (for each wavelength).
Based on Eq. 1, Eq. 2 and Eq.3, the radiation intensity inside the device can be expressed as:
 
(Eq. 4)
where the optical path length for the light transmission is the wall thickness of the device in
(m).
2.4. Application of the Solar UV Calculator tool to different SODIS scenarios
The Solar UV Calculator tool was tested for the design of SODIS devices. For that, the influence of
the thickness on the available radiation and its spectral distribution inside device was assessed.
Evaluations were performed with selected plastic devices with a typical thickness of 2 mm for high-
capacity devices (20 L) and 0.5 mm for low-capacity bottles (2 L). The ASTM G-173 reference AM 1.5
solar spectrum was considered for the incident solar radiation calculations. For the estimation of
the UVB, UVA and Visible radiation, the integrals in the wavelength ranges of 290 - 320 nm, 320 -
400 nm and 400 - 800 nm were calculated, respectively.
The Solar UV Calculator tool was also tested for estimating the experimental requirements to
ensure a specific pathogen inactivation. For that, a pseudo first-order kinetic model that relates the
inactivation with the radiation intensity was used (Eq. 5):

       (Eq. 5)
By integrating Eq. 5, the expression for the logarithmic inactivation of the pathogen with time is
obtained:

       (Eq. 6)
Where is the final concentration of the pathogen (microorganisms·mL-1), is the initial
concentration of the pathogen (microorganisms·mL-1), is the kinetic constant (m2·W-1·h-1), is the
incident radiation and is the reaction time (h). For decimal logarithmic reductions, the napierian
reduction has to be divided by 2.303.
Journal Pre-proof
Journal Pre-proof
8
To calculate the kinetic constant, the lethal doses (D) for a specific inactivation logarithmic
reduction of three model pathogens (E. coli bacterium, MS2 virus and C. parvum protozoon) were
found in the literature (Fisher et al. 2012; Lawrie et al. 2015; Abeledo-Lameiro et al. 2017). The
three disinfection experiments were carried out under natural sunlight, were performed at low
water temperature and in clear water to avoid inactivation speeding up due to temperature or
exogenous damage and ensure that the damage is only product of solar radiation. Moreover, no
attenuation coefficient is required in clear water as many authors describe a diffuse attenuation
coefficient related to the water composition (Kirk 1994; Craggs et al. 2003).
Finally, with Eq. 7 (combination of Eq. 4 and Eq. 6) the minimum exposure time for a specific
thickness or the maximum thickness for a specific time reaction can be calculated for a set
logarithmic reduction.

      (Eq. 7)
Using Eq. 7, the minimum exposure time was calculated for a specific thickness of 0.5 mm and the
minimum thickness was obtained when the exposure time is 6 h, the reaction time recommended
in the SODIS manual with cloudless sky (Luzi et al. 2016).
3. Results and discussion
3.1. Selection of candidate plastic materials based on mechanical properties
The determination of the tensile stiffness of a plastic prior to breaking or permanently deforming
and the energy required to fracture a plastic (toughness), ascertained by the measurement of the
tensile modulus of elasticity and impact resistance, respectively, are critical mechanical properties
for any plastics to be used as devices material. However, in addition to them, resistance to
weathering is also critical. The harmful effects of weather exposure on plastics has been attributed
to photo-degradation or photo-oxidation processes by UV light and the action of oxygen (Gillen and
Celina 2017). In general, polymer degradation is usually controlled using UV-stabilizers that block
UV-transmission through plastic or avoiding the exposure to high temperatures, water or oxygen.
Journal Pre-proof
Journal Pre-proof
9
However, in the case of SODIS processes, blocking UV is not desirable, while oxygen is dissolved in
the water and present in the surrounding air. Consequently, the plastic materials candidate for
SODIS devices should be pure plastics, without any kind of UV stabilizer. In this sense, poorly
photostable plastics are generally dismissed and moderately photostable polymers will require
regular replacement (Feldman 2002).
Polystyrene (PS), polyvinyl chloride (PVC) and polyolefins such as polypropylene (PP) and
polyethylene (PE) are poorly photostable polymers. General Purpose Polystyrene (GPPS), the only
transparent PS, exhibits high stiffness, but brittle behaviour (Nexant’s ChemSystems Solutions
2006). PS becomes brittle when chain scissions are produced by radiation action and O2 addition to
chain radicals (Wypych 2015a). PVC can be either flexible and malleable or rigid and brittle (Titow
1984). When PVC is exposed to natural weathering, mechanical properties such as tensile strength,
elasticity, and impact resistance decline, and the material becomes increasingly discoloured,
indicating lower transparency (Feldman and Barbalata 1996). In the case of polyolefins, degradation
by photooxidation proceeds by a free radical chain mechanism in four steps: initiation, propagation,
chain branching, and termination. This is initiated by the presence of hydroperoxides and their
decomposition leads to the formation of other radicals, chain scissions and crosslinking. Although
the degradation mechanism of PE and PP by photooxidation is similar, the initiation, termination,
and chain-branching reaction rates are different. Thus, PP chains contain tertiary hydrogens that
make the formation of intermediate hydroperoxides much easier and faster. In addition, the
reaction rates of the termination step for PE are 100-1000 times higher than for PP (Wypych
2015b). Overall, these polymers have a lifetime less than one year when exposed to weathering
without any stabilizer. Non-stabilized PE becomes exceedingly brittle within a few weeks (Rånby
1993; Feldman 2002). PP and HDPE are used in the production of many products (estimated at 10
and 6.3 million tonnes in 2017 by Plastics Europe Market Research Group, respectively) due to their
low production prices valued at 8.25€/kg and 7.77 €/kg (data from Database Plastic Europe
(PlasticEurope 2012)).
Journal Pre-proof
Journal Pre-proof
10
Polyethylene Terephthalate (PET) and polycarbonate (PC) are considered to be moderately
photostable polymers. These plastics have considerable lifetimes in the outdoors without
stabilizers. PC is a tough and transparent plastic material with excellent strength, stiffness, impact
resistance, and resistant to high temperature, that suffers a slow attenuation of these properties
under photodegradation by UV radiation. Humidity does not affect PC ageing, however, it produces
a synergistic effect when UV radiation initiates photooxidation. At lower humidity, the reaction
happens at a slower rate but UV penetrates deeper into the polymer, resulting in a thick layer of
degraded material. At higher humidity, a thin photooxidized layer is quickly formed which shields
the core of the polymer from further damage by UV radiation (McKeen 2019). Turton and White
(2014) confirmed experimentally that photodegradation decreases with the depth of unstabilized
PC (Turton and White 2014). PET is a strong, stiff engineering plastic with excellent machining
characteristics, and chemical resistance. PET is often used for food applications where low moisture
absorption, low thermal expansion, resistance to staining, or resistance to cleaning chemicals is
required. Most PET photodegradation occurs at the surface. Photooxidation produces
hydroperoxides that lead to chain scission causing the ageing of the material (Wypych 2015b). PET
can be transparent in the amorphous state with physical and chemical resistance and good
hardness although it degrades upon weathering exposure (McKeen 2019). Photodegradation of PET
and PC leads to more brittle materials with eroded surfaces and lower transmittance. Wall
thickness is obviously an important factor for both polymers. Some authors have studied the
suitable lifetime of polymer ageing taking into account the distribution of the reaction products
across the width of the material and the problems related with the use of Fick’s law for estimating
this goal (Audouin et al. 1994). Wall thickness has to be sufficiently high to ensure that
photodegradation reactions do not affect the core of the plastic piece but as thin as possible to
allow maximum UV transmission to the interior. The production prices for PET and PC are
estimated at 13.9 €/kg and 19.6 €/kg respectively (data from Database 2.0 Ecoinvent (Frischknecht
et al. 2005)).
Journal Pre-proof
Journal Pre-proof
11
Finally, polymethylmethacrylate (PMMA) is a highly photostable polymer typically used without any
stabilizer for extended (many years) outdoor applications (McKeen 2019). PMMA has a number of
advantages over other candidate materials including outstanding weathering, resistance to UV
radiation, transparency, hardness, rigidity and dimensionally stable. In addition, PMMA weakly
absorbs UV radiation producing some chain scission and the formation of methyl methacrylate
monomer. However, these reaction products hardly impair the stability of PMMA due to the fact
that the monomers can combine again (Rånby 1993). PMMA also has a good impact strength. Its
main disadvantage is its high price: 28.9€/kg (data from Database 2.0 Ecoinvent (Frischknecht et al.
2005)). A summary of the mechanical properties for PS, PVC, PE, PP, PC, PET and PMMA are
provided in Table 1.
Summarising, PS, PVC, PE and PP are poorly photostable and non-durable polymers that makes
photostabilization necessary for outdoors. However, PP with 1% of UV stabilizers remains stable for
long periods, consequently maintains transparency and can also be easily and cheaply replaced.
For this reason, PP has been considered as a possible plastic material for SODIS devices while PS,
PVC and PE were excluded as candidate materials for the manufacturing. The production prices for
PET and PC are higher than that of the PP, however it is compensated by durability. Finally,
considering weathering resistance and UV radiation transmission PMMA could be the optimal
material for manufacturing SODIS devices. Furthermore, although its production price exceeds that
of the rests of polymers described, again, this is compensated for by durability. Therefore, on the
basis of mechanical properties, PP, PET, PC and PMMA were the four candidate materials
considered for manufacturing SODIS devices.
3.2. Optical analysis of candidate plastic materials
SODIS relies on the damage caused by solar UV radiation to pathogens. However, pathogen
susceptibility varies with the wavelength and microbiological features. Thus, the wavelengths
transmitted inside the SODIS device is an important factor for disinfection performance.
Journal Pre-proof
Journal Pre-proof
12
Consequently, the transmission spectra of the four materials selected on the basis of their
mechanical properties were experimentally analysed and are shown in Figure 1. PP transmits
radiation from 235 nm, PMMA from 250 nm and PC from 290 nm. At first sight, PP is more
transparent than PMMA and both of them are more transparent than PC. However, the solar
radiation reaching the Earth’s surface does not include wavelengths below 290 nm, and therefore
this wavelength range can be overlooked in the analysis. For wavelengths of solar spectra,
transmittance is higher in the case of PMMA and therefore better for manufacturing SODIS devices
than PP, followed by PC. Nevertheless, all three polymers were found to be suitable plastics for
SODIS process considering optical properties, since they transmit UVB and consequently, cause the
inactivation of protozoa, viruses and bacteria. PET blocks UVB radiation transmission and, as a
result, viruses and protozoa inactivation is difficult (Busse et al. 2019).
3.3. Solar UV Calculator tool
Both mechanical and optical properties, critical for manufacturing SODIS devices, are directly
related to the wall thickness: the higher thickness, the higher resistance to deformation or
breakage and the lower transmission. Consequently, it is necessary to achieve a compromise
between both of them to estimate the optimal thickness for the walls of the device. The developed
Solar UV Calculator allows the assessment of the impact of thickness on the transmission of
radiation. The tool estimates the available radiation inside device using Eq. 4, where  is the
thickness of the device and  is the extinction coefficients as a function of wavelengths for every
specific plastic. The extinction coefficients () for the candidate plastics were obtained using Eq.
3 and are shown in Figure 2.
PET only allows the transmission of visible and UVA radiation due to the high values of extinction
coefficient for wavelengths between 290-320 nm (UVB radiation). PC, PP and PMMA all allow
transmission of UVB, UVA and visible radiation. For wavelengths lower than 290 nm, the dramatic
increase of the extinction coefficients indicates that this radiation is completely absorbed.
However, this fact is hardly significant since the solar spectrum reaching the Earth surface does not
Journal Pre-proof
Journal Pre-proof
13
include wavelengths below 290 nm. In contrast, for wavelengths higher than 290 nm, the values of
PP and PC extinction coefficients are higher than that of PMMA. Therefore, the PMMA will transmit
more solar radiation than PP and PC plastics for equal thickness.
The Solar UV Calculator has been evaluated and tested for two different purposes: i) to evaluate
design parameters such as the thickness; and, ii) to estimate experimental requirements of the
SODIS process, such as the solar exposure time.
3.3.1. Evaluation of design parameters
The thickness of the plastic material is determined primarily by mechanical resistance
considerations but also by the device size/volume. The thickness of the plastic material should
provide enough resistance to carry the water inside. However, the thickness of the plastic material
has a critical effect on the optical properties of the material and therefore on the solar radiation
available inside the device for SODIS purposes. When thickness increased, the transmittance
decreased for all polymers. However, due to the differences in the extinction coefficients, the
influence of the thickness on the available radiation inside device is very dependent on the
material. In order to show the importance of estimating the transmitted radiation before
manufacturing, predictions were performed with devices with a typical thickness of 2 mm for high-
capacity devices (20 L) and 0.5 mm for low-capacity bottles (2 L). For a thickness of 0.5 mm the
incident radiation (transmitted radiation) seems to be very similar for each polymer (Figure 3).
However, from the numerical data shown in Table 2 it follows that PET does not transmit UVB
radiation and this is a critical factor for protozoa and viruses inactivation. PMMA transmits a high
percentage of the solar radiation UVB (97%) and UVA (97.9%), while the behavior of PP and PC is
very similar transmitting around 65% of UVB radiation and 70-80% of UVA solar radiation. However,
when the thickness is increased up to 2 mm, transmitted UVB radiation decreases strongly to 17%
in the case of PP and PC. Even though only 0.26-0.29 W/m2 of the UVB is available inside the device,
it is still a useful result due to its potential to inactivate protozoa and viruses. The transmitted UVA
radiation also decreases, reaching values similar to the transmitted UVA radiation by PET with 2
Journal Pre-proof
Journal Pre-proof
14
mm of thickness. In contrast, PMMA behavior hardly changes due to its low extinction coefficient
spectra maintaining high levels of UVB and UVA incident radiation (88.5% and 92.0% of the solar
irradiance).
To sum up, PMMA, PP and PC transmit UVB radiation and a higher percent of UVA; however, the
thickness must be taken into account due to the fact that a small increase in the thickness can
cause a disproportionately large decrease of the radiation available for SODIS inside the device.
3.3.2. Estimation of experimental requirements for SODIS applications
A lethal UV dose must be attained inside the device during SODIS in order to achieve complete
disinfection. Moreover, the susceptibility of pathogens to be photoinactivated is wavelength-
dependent; therefore, the lethal UV dose required is different for each pathogen (Mattle et al.
2015; Silverman and Nelson 2016; Busse et al. 2019).
3.3.2.1. MS2 virus
As it was previously explained, in general, viruses only can be photo-damaged by UVB radiation.
Fisher et al. (2012) found that MS2 needed a lethal UVB lethal dose of 12.83 kJ/m2 (0.31W/m2
during 11.5 h) to achieve three-log inactivation under sunlight conditions using polypropylene
copolymer (PCCO) bags transparent to the complete UV region. Taking into account Eq. 6, kinetic
constant of the virus inactivation was estimated to be 5.38·10-3 cm2/mJ.
Using the results of the Solar UV Calculator, the kinetic model was employed to estimate the
required solar exposure time to ensure 3-log inactivation of the virus for a minimum thickness of
0.5 mm. In the case of PP and PC, the exposure time was very similar (3.36 and 3.40 h, respectively)
due to its similar transmission in the UVB region. For PMMA, disinfection is achieved in only 2.24 h
as a result of its low extinction coefficient and its high transmission in the UVB range. Finally, since
PET does not transmit UVB radiation, the viruses cannot be inactivated by solely photoactivated
processes in PET devices (Table 3). The maximum thickness of the devices to guarantee virus
inactivation for an exposure time of 6 h was also calculated. As expected, in the case of PP and PC
Journal Pre-proof
Journal Pre-proof
15
devices the thickness was almost the same (1.17 mm and 1.16 mm). For PMMA devices, the
thickness reached a value of 16.8 mm, a value extremely high that assures resistance and durability.
Again, the opacity of PET to UVB radiation range makes us conclude that PET cannot be considered
a good candidate for device manufacture if only photoinactivation is considered (Table 4). The
available radiation inside each device for this scenario is shown in Figure 4.
3.3.2.2. Cryptosporidium parvum protozoon
When UVB is present in the solar spectrum, protozoan photoinactivation is mainly mediated by
these wavelengths. Abeledo-Lameiro et al. (2017) found that under sunlight conditions, C. parvum
viability decreases to 35% of its original value with a UVB dose of 32.29 kJ/m2 (5 h at an average
UVB radiation of 0.78 W/m2). Fitting to a first order kinetic model (Eq. 6), the kinetic constant was
3.25·10-4 cm2/mJ. The thickness and the exposure time effect were also evaluated for C. parvum
photoinactivation. PET was not evaluated due to the opacity to the UVB radiation. Although UVA
radiation can also inactivate the protozoa slowly, a synergistic temperature contribution (above
37°C) is then required (Gómez-Couso et al. 2010), since the temperature of the experiments of
Abeledo-Lameiro et al. (2017) was always below 35°C. For a reduction in C. parvum oocyst global
viability of up to 50% with a thickness of 0.5 mm, the exposure time was determined, resulting in
5.58, 5.64 and 3.72 h for the PP, PC and PMMA, respectively (Table 3). The required solar exposure
time of PP and PC devices is very close to the standard SODIS time of 6 h. The thickness required
to achieve a 50% the oocyst viability in 6 h was determined. The maximum thicknesses of devices
were 0.58 mm for PP, 0.57 mm for PC and 8.24 mm for PMMA (Table 4). Again, as a result of the
high UVB transmission of PMMA, C. parvum is inactivated quicker when the water is exposed in
PMMA than in PP and PC devices, which have similar transmittances and, therefore, similar
thickness to achieve the same oocyst viabilities. Available radiation inside each device for this
scenario is shown in Figure 5.
3.3.2.3. Escherichia coli bacterium
Journal Pre-proof
Journal Pre-proof
16
Bacteria can be inactivated with UVB and UVA solar radiation so both radiation ranges must be
considered for determining the SODIS inactivation time Lawrie et al. (2015) found diverse UV lethal
doses for the inactivation of E. coli, Enterococcus spp. and Clostridium perfringens in plastic bags (PE
and PET) with different transmission spectra. For this reason, it is necessary to know the sensitivity
coefficient of the pathogen for each wavelength  for determining its wavelength contribution
(m2·W-1·h-1),. Silverman and Nelson (2016) developed a biological weighting function (BWF) to
estimate the sunlight inactivation rates of E. coli. Therefore, Eq. 6 is modified as follows:

     (Eq. 8)
Considering the sensitivity coefficients from Silverman and Nelson (2016) and the developed tool,
Eq. 9 (derived from Eq. 6 and Eq. 8) was applied to the two scenarios to estimate the effect of the
thickness, plastic material and exposure time in the E. coli inactivation by SODIS technology.

      (Eq. 9)
The solar exposure time required to ensure a 3-log inactivation for a thickness of 0.5 mm was very
similar for PP and PC (0.97 and 0.90 h, respectively) as a result of their similar transmission across
the whole UV region. Inactivation using PMMA was achieved in only 0.69 h due to its low extinction
coefficient and its high transmission in the UV range. Finally, PET cannot transmit UVB radiation,
and UVA slowly inactivates bacteria. In this case, 1.52 h were required to achieve a three-log
inactivation (Table 3). The maximum thickness of the devices has also been calculated for a three
log-inactivation in an exposure time of 6 h. Obviously, the widest thickness allowed is for PMMA
material (47.20 mm) due to its high UV transmission in the UVA and UVB range, followed by
thickness of PP and PC (3.10 mm and 4.22 mm) because of the combination of moderated UVA and
UVB transmission, and finally maximum thickness for PET was 2.47 mm as a result of only UVA
transmission (Table 4). Available radiation inside each device for this scenario is shown in Figure 4.
To sum up, considering the solar exposure time and plastic thickness, PMMA provides the best
results to be used as device for SODIS process. However, PC and PP also meet the requirements for
solar water disinfection due to the fact that they are able to transmit UVB radiation and therefore,
Journal Pre-proof
Journal Pre-proof
17
bacteria, viruses and protozoa can be inactivated. Finally, if considering solely endogenous and non-
thermal processes, then PET devices are suitable only for bacterial photoinactivation.
4. Conclusions
PP, PC, PMMA and PET have been shown to be suitable candidate materials for solar water
disinfection devices: PP has low durability but can be economically replaced, PET and PC have
moderate durability and production costs, and PMMA is an expensive plastic but relatively
unaffected by weathering. From the optical point of view, with the exception of PET in the UV
range, they all achieve the required UV transmission.
The Solar UV Calculator presented in this work has been proved to be a useful tool to evaluate
design parameters and estimate experimental requirements for solar water disinfection in suitable
plastic devices. Taking into account the thickness and the spectral transmission of the materials, the
tool allows the estimation of the radiation available for SODIS inside the device and especially its
spectral distribution, since the sensitivity of pathogens are strongly dependent on the wavelength
range. The Solar UV Calculator was able to evaluate design parameters such as thickness, type of
plastic, and radiation spectra. For example, for a thickness of 0.5 mm, the transmitted solar UV-A
radiation was 97.9%, 70%, 72.8% and 81.0% for PMMA, PET, PP and PC, respectively, whereas the
transmitted solar UV-B radiation was 97%, 0%, 64.9% and 64.5% for the same plastics.
Furthermore, PMMA was found to be less sensitive to changes in thickness due to its low extinction
coefficients, thus, the radiation transmitted remains high. The Solar UV Calculator was an essential
tool for the estimation of the experimental requirements such as solar exposure time or
inactivation level for three model pathogens (E. coli bacterium, MS2 virus and C. parvum
protozoon). As an example, for a thickness of 0.5 mm and a 3-log inactivation of bacteria, the
required solar exposure time was determined at 0.69h for PMMA, 1.52h for PET, 0.97h for PP and
0.90h for PC.
Journal Pre-proof
Journal Pre-proof
18
Finally, although the Solar UV Calculator has been validated for the specific materials and pathogen
scenarios used in this study, it is freely available as Supplemental Data to any potential user
interested in the evaluation of SODIS processes with other materials and conditions, or even to the
evaluation of other solar processes subjected to a strong spectral dependence on materials
transmission.
Supplemental data
The developed Solar UV Calculator is made freely available for anybody interested in performing
their calculations with user-defined materials defined by its transmission spectra.
Acknowledgements
The authors declare no conflicts of interest. The authors gratefully acknowledge the financial
support of the European Union’s Horizon 2020 research and innovation programme under
WATERSPOUTT H2020-Water-5c-2015 project (GA 688928). Ángela Garcia Gil also acknowledges
Técnicas Reunidas for the economic support to finance her scholarship in Residencia de Estudiantes
and Spanish Ministry of Education for her FPU grant (FPU17/04333).
Figure Captions
Figure 1: Transmission spectra of PMMA, PP, PC and PET.
Figure 2: Spectral distribution of the experimental extinction coefficients for the studied
polymers.
Figure 3: Spectral incident/transmitted radiation for a thickness of 0.5 mm (left) and 2 mm
(right). The arrow indicates the order of the lines from the top to the bottom.
Figure 4: Spectral incident radiation required to reach three-logarithmic units inactivation
of MS2 virus and E. coli bacterium in 6 h for the maximum thickness values. The arrow
indicates the order of the lines from the top to the bottom.
Journal Pre-proof
Journal Pre-proof
19
Figure 5: Spectral incident radiation required to reach 50% viability of C. parvum oocysts in
6 h for the maximum thickness values. The arrow indicates the order of the lines from the
top to the bottom.
References
Abeledo-Lameiro MJ, Reboredo-Fernández A, Polo-López MI, Fernández-Ibáñez P, Ares-Mazás E,
Gómez-Couso H. 2017. Photocatalytic inactivation of the waterborne protozoan parasite
Cryptosporidium parvum using TiO2/H2O2 under simulated and natural solar conditions. Catal
Today. 280:132138. doi:10.1016/j.cattod.2016.05.046.
Audouin L, Langlois V, Verdu J, de Bruijn JCM. 1994. Role of oxygen diffusion in polymer ageing:
kinetic and mechanical aspects. J Mater Sci. 29(3):569583. doi:10.1007/BF00445968.
Busse MM, Becker M, Applegate BM, Camp JW, Blatchley ER. 2019. Responses of Salmonella
typhimurium LT2, Vibrio harveyi, and Cryptosporidium parvum to UVB and UVA radiation. Chem Eng
J. 371:647656. doi:10.1016/j.cej.2019.04.105.
Castro-Alférez M, Polo-López MI, Marugán J, Fernández-Ibáñez P. 2017. Mechanistic model of
the Escherichia coli inactivation by solar disinfection based on the photo-generation of internal ROS
and the photo-inactivation of enzymes: CAT and SOD. Chem Eng J. 318:214223.
doi:10.1016/j.cej.2016.06.093.
Craggs RJ, Davies-Colley RJ, Tanner CC, Sukias JP. 2003. Advanced pond system: performance
with high rate ponds of different depths and areas. Water Sci Technol. 48(2):259267.
doi:10.2166/wst.2003.0129.
Feldman D. 2002. Polymer weathering: Photo-oxidation. J Polym Environ. 10(4):163173.
doi:10.1023/A:1021148205366.
Feldman D, Barbalata A. 1996. Synthetic polymers : technology, properties, applications.
Chapman & Hall.
Fisher MB, Iriarte M, Nelson KL. 2012. Solar water disinfection (SODIS) of Escherichia coli,
Enterococcus spp., and MS2 coliphage: Effects of additives and alternative container materials.
Water Res. 46(6):17451754. doi:10.1016/j.watres.2011.12.048.
Frischknecht R, Jungbluth N, Althaus H-J, Doka G, Dones R, Heck T, Hellweg S, Hischier R,
Nemecek T, Rebitzer G, et al. 2005. The ecoinvent database: Overview and methodological
framework. Int J Life Cycle Assess. 10:39. doi:10.1065/lca2004.10.181.1.
García-Gil Á, Casado C, Pablos C, Marugán J. 2018. Novel procedure for the numerical simulation
Journal Pre-proof
Journal Pre-proof
20
of solar water disinfection processes in flow reactors. Chem Eng J. doi:10.1016/J.CEJ.2018.10.131.
Gillen KT, Celina M. 2017. Predicting Polymer Degradation and Mechanical Property Changes for
Combined Radiation-Thermal Aging Environments. Rubber Chem Technol. 91(1):2763.
doi:10.5254/rct.18.81679.
Gómez-Couso H, Fontán-Sainz M, Ares-Mazás E. 2010. Thermal contribution to the inactivation
of Cryptosporidium in plastic bottles during solar water disinfection procedures. Am J Trop Med
Hyg. 82(1):3539. doi:10.4269/ajtmh.2010.09-0284.
Gómez-Couso H, Fontán-Sainz M, Navntoft C, Fernández-Ibáñez P, Ares-Mazás E. 2012.
Comparison of different solar reactors for household disinfection of drinking water in developing
countries: Evaluation of their efficacy in relation to the waterborne enteropathogen
Cryptosporidium parvum. Trans R Soc Trop Med Hyg. 106(11):645652.
doi:10.1016/j.trstmh.2012.07.014.
Jagger J. 1985. Solar-UV actions on living cells. Praeger.
Joyce TM, McGuigan KG, Elmore-Meegan M, Conroy RM. 1996. Inactivation of fecal bacteria in
drinking water by solar heating. Appl Environ Microbiol. 62(2):399402.
Kalt P, Birzer C, Evans H, Liew A, Padovan M, Watchman M. 2014. A solar disinfection water
treatment system for remote communities. Procedia Eng. 78:250258.
doi:10.1016/j.proeng.2014.07.064.
Kirk J. 1994. Light and photosynthesis in aquatic ecosystems. Cambridge: Cambridge University
Press.
Kohn T, Nelson KL. 2007. Sunlight-Mediated Inactivation of MS2 Coliphage via Exogenous Singlet
Oxygen Produced by Sensitizers in Natural Waters. Environ Sci Technol. 41(1):192197.
doi:10.1021/ES061716I.
Lawrie K, Mills A, Figueredo-Fernández M, Gutiérrez-Alfaro S, Manzano M, Saladin M. 2015. UV
dosimetry for solar water disinfection (SODIS) carried out in different plastic bottles and bags.
Sensors Actuators B Chem. 208:608615. doi:10.1016/J.SNB.2014.11.031.
Liu Y, Dong S, Kuhlenschmidt MS, Kuhlenschmidt TB, Drnevich J, Nguyen TH. 2015. Inactivation
mechanisms of Cryptosporidium parvum oocysts by solar ultraviolet irradiation. Environ Sci Water
Res Technol. 1(2):188198. doi:10.1039/c4ew00079j.
Love DC, Silverman A, Nelson KL. 2010. Human virus and bacteriophage inactivation in clear
water by simulated sunlight compared to bacteriophage inactivation at a Southern California beach.
Journal Pre-proof
Journal Pre-proof
21
Environ Sci Technol. 44(18):69656970. doi:10.1021/es1001924.
Luzi S, Tobler M, Suter F, Meierhofer R. 2016. SODIS manual: Guidance on solar water
disinfection. Switzerland: EAWAG.
Lytle CD, Sagripanti J-L. 2005. Predicted inactivation of viruses of relevance to biodefense by
solar radiation. J Virol. 79(22):1424452. doi:10.1128/JVI.79.22.14244-14252.2005.
Mac Mahon J, Gill LW. 2018. Sustainability of novel water treatment technologies in developing
countries: Lessons learned from research trials on a pilot continuous flow solar water disinfection
system in rural Kenya. Dev Eng. 3:4759. doi:10.1016/j.deveng.2018.01.003.
Maraccini PA, Wenk J, Boehm AB. 2016. Photoinactivation of Eight Health-Relevant Bacterial
Species: Determining the Importance of the Exogenous Indirect Mechanism. Environ Sci Technol.
50(10):50505059. doi:10.1021/acs.est.6b00074.
Mattle MJ, Vione D, Kohn T. 2015. Conceptual model and experimental framework to determine
the contributions of direct and indirect photoreactions to the solar disinfection of MS2, phiX174,
and adenovirus. Environ Sci Technol. 49(1):334342. doi:10.1021/es504764u.
McGuigan KG, Conroy RM, Mosler H-J, Preez M du, Ubomba-Jaswa E, Fernandez-Ibañez P. 2012.
Solar water disinfection (SODIS): A review from bench-top to roof-top. J Hazard Mater. 235:2946.
doi:10.1016/j.jhazmat.2012.07.053.
McGuigan KG, Joyce TM, Conroy RM, Gillespie JB, Elmore-Meegan M. 1998. Solar disinfection of
drinking water contained in transparent plastic bottles : characterizing the bacterial inactivation
process. J Appl Microbiol. 84(6):11381148. doi:10.1046/j.1365-2672.1998.00455.x.
McKeen LW. 2019. The Effect of UV Light and Weather on Plastics and Elastomers. 4th ed.
William Andrew Publishing.
Nelson KL, Boehm AB, Davies-Colley RJ, Dodd MC, Kohn T, Linden KG, Liu Y, Maraccini PA,
McNeill K, Mitch WA, et al. 2018. Sunlight-mediated inactivation of health-relevant microorganisms
in water: a review of mechanisms and modeling approaches. Environ Sci Process Impacts.
20(8):10891122. doi:10.1039/c8em00047f.
Nexant’s ChemSystems Solutions. 2006. PERP Program - Polystyrene New Report Alert.
PlasticEurope. 2012. Eco-profiles and environmental declarations - LCI methodology and PCR for
uncompounded polymer resins and reactive polymer precursor. v. 3.0.
Rånby B. 1993. Basic Reactions in the Photodegradation of Some Important Polymers. J
Macromol Sci Part A Pure Appl Chem. 30(910):583594. doi:10.1080/10601329308021247.
Journal Pre-proof
Journal Pre-proof
22
Reyneke B, Ndlovu T, Vincent MB, Martínez-García A, Polo-López MI, Fernández-Ibáñez P,
Ferrero G, Khan S, McGuigan KG, Khan W. 2020. Validation of large-volume batch solar reactors for
the treatment of rainwater in field trials in sub-Saharan Africa. Sci Total Environ. 717:137223.
doi:10.1016/j.scitotenv.2020.137223.
Romero OC, Straub AP, Kohn T, Nguyen TH. 2011. Role of Temperature and Suwannee River
Natural Organic Matter on Inactivation Kinetics of Rotavirus and Bacteriophage MS2 by Solar
Irradiation. Environ Sci Technol. 45(24):1038510393. doi:10.1021/es202067f.
Silverman AI, Nelson KL. 2016. Modeling the endogenous sunlight inactivation rates of
laboratory strain and Wastewater E. coli and enterococci using biological weighting functions.
Environ Sci Technol. 50(22):1229212301. doi:10.1021/acs.est.6b03721.
Titow W V. 1984. Introduction. In: PVC Technology. Dordrecht: Springer Netherlands. p. 135.
Turton TJ, White JR. 2014. Degradation depth profiles and fracture of UV exposed
polycarbonate. Plast Rubber Compos. 30(4):175182. doi:10.1179/146580101101541606.
Ubomba-Jaswa E, Fernández-Ibáñez P, McGuigan KG. 2010. A preliminary Ames fluctuation
assay assessment of the genotoxicity of drinking water that has been solar disinfected in
polyethylene terephthalate (PET) bottles. J Water Health. 8(4):712719. doi:10.2166/wh.2010.136.
Ubomba-Jaswa E, Fernández-Ibáñez P, Navntoft C, Polo-López MI, McGuigan KG. 2010.
Investigating the microbial inactivation efficiency of a 25 L batch solar disinfection (SODIS) reactor
enhanced with a compound parabolic collector (CPC) for household use. (April):10281037.
doi:10.1002/jctb.2398.
United Nations (UN). 2015. The 2030 AGENDA for Sustainable Development.
United Nations (UN). 2018. Sustainable Development Goal 6. Synthesis Report on Water and
Sanitation 2018.
Wegelin M, Canonica S, Alder AC, Marazuela D, Suter MJ-F, Bucheli TD, Haefliger OP, Zenobi R,
McGuigan KG, Kelly MT, et al. 2001. Does sunlight change the material and content of polyethylene
terephthalate (PET) bottles? doi:10.2166/aqua.2001.0012.
Wypych G. 2015a. UV degradation & stabilization of polymers & rubbers. In: Handbook of UV
degradation and stabilization. ChemTec Publishing. p. 177292.
Wypych G. 2015b. UV degradation & stabilization of polymers & rubbers. In: Wypych G, editor.
Handbook of UV degradation and stabilization. 2nd Editio. ChemTec Publishing. p. 177292.
Journal Pre-proof
Journal Pre-proof
23
Table 1: Summary of mechanical properties and production costs for the selected plastic as
candidate material for manufacturing SODIS devices.
Resistance
Photostability
Durability
Production cost
Low
Low
Very low
-
High
Low
Very low
-
High
Low
Very Low
Very Low
High
Low
Low
Very low
High
Moderate
Reasonable
Moderate
High
Moderate
Reasonable
Moderate
High
High
High
High
Table 2: UVB, UVA, Visible and total incident/transmitted radiation for thickness values (Th) of 0.5
mm and 2 mm.
Incident/Transmitted Radiation
Solar
PP
PC
Th=0.5 mm
Th= 2 mm
Th=0.5 mm
Th= 2 mm
(W·m-2)
(W·m-2)
%
(W·m-2)
%
(W·m-2)
%
(W·m-2)
%
UVB
(280 - 320 nm)
1.63
1.06
64.9
0.26
17.7
1.05
64.5
0.29
17.5
UVA
(320 - 400 nm)
45.6
33.2
72.8
12.9
28.3
37.05
81.0
20.1
44.0
Visible
(400 - 800 nm)
543
462
85.2
288
53.0
480
88.3
333
61.3
UV-Visible
(280-800 nm)
590
497
84.1
301
51.0
518
87.7
353
59.8
Journal Pre-proof
Journal Pre-proof
24
Incident Radiation
Solar
PMMA
PET
Th=0.5 mm
Th= 2 mm
Th=0.5 mm
Th= 2 mm
(W·m-2)
(W·m-2)
%
(W·m-2)
%
(W·m-2)
%
(W·m-2)
%
UVB
(280 - 320 nm)
1.63
1.59
97.0
1.45
88.5
0.00
0
0.00
0
UVA
(320 - 400 nm)
45.6
44.7
97.9
42.0
92.0
31.9
70.0
14.5
31.8
Visible
(400 - 800 nm)
543
534
98.3
506
93.3
484
89.1
342
62.9
UV-Visible
(280-800 nm)
590
580
98.2
550
93.2
516
87.3
356
60.3
Journal Pre-proof
Journal Pre-proof
25
Table 3: Required solar exposure time (h) with a thickness of 0.5 mm to reach three-logarithmic
units inactivation of MS2 virus and E. coli bacterium and 50% viability of C. parvum oocysts.
PP
(h)
PC
(h)
PMMA
(h)
PET
(h)
MS2
3.36
3.40
2.24
-
C. parvum
5.58
5.64
3.72
-
E. coli
0.97
0.90
0.69
1.52
Table 4: Maximum thickness (mm) to reach three-logarithmic units inactivation of MS2 virus
and E. coli bacterium and 50% viability of C. parvum oocysts in 6 h.
PP
(mm)
PC
(mm)
PMMA
(mm)
PET
(mm)
MS2
1.17
1.16
16.8
-
C. parvum
0.58
0.57
8.24
-
E. coli
3.10
4.22
47.2
2.47
Author statement
Angela García-Gil: Investigation, Writing - Original draft.
Cristina Pablos: Investigation, Methodology, Writing Review and Editing.
Rafael García-Muñoz: Methodology, Validation, Writing Review and Editing.
Kevin G McGuigan: Funding acquisition, Validation, Writing Review and Editing.
Javier Marugán: Conceptualization, Funding acquisition, Validation, Writing Review and
Editing.
Declaration of interests
Journal Pre-proof
Journal Pre-proof
26
The authors declare that they have no known competing financial interests or personal
relationships that could have appeared to influence the work reported in this paper.
The authors declare the following financial interests/personal relationships which may be
considered as potential competing interests:
Graphical abstract
Highlights:
- Revision of mechanical and optical properties, weathering and costs of plastics
- Selection of optimal materials for SODIS container manufacturing
- Development of a tool for estimating UV radiation available inside containers
- Predictive evaluation of bacteria, viruses and protozoa solar inactivation
- Freely available Solar UV Calculator for custom evaluation of solar irradiance
Journal Pre-proof
... This amount of radiation is known as the "lethal UV dose" (expressed as W · h/m 2 ), and depends on the properties of the water, the level and type of the microbiological contamination, and the characteristics of the SODIS containers (transmittance to UV light, size, and shape) [6]. There are several studies in the literature [7][8][9][10] that have established methods for estimating the lethal UV dose for different type of SODIS containers and pathogens. ...
... Traditionally, transparent polyethylene terephthalate (PET) bottles have been widely used due to their efficient transmission of UV-A radiation (about 85-90 percent) [4]. However, this type of material does not transmit UV-B radiation [11], which produces the most powerful genome damage to viruses and bacterial pathogens through direct photo-inactivation mechanisms [7,12]. In addition, there are concerns about the migration of chemical contaminants from PET bottles into water, although there is no direct scientific evidence of this [13]. ...
... In addition, there are concerns about the migration of chemical contaminants from PET bottles into water, although there is no direct scientific evidence of this [13]. Thus, more efficient and safer materials have been studied and successfully evaluated in the literature, such as polystyrene (PS) [14], polycarbonate (PC) [7], polymethylmethacrylate (PMMA) [15], and polyethylene (PE) [5]. In particular, the use of PE bags [6] has been viewed as a promising solution, as this material has good transmission of UV-B radiation. ...
Article
Full-text available
The lack of safe drinking water is one of the main health problems in many regions of the world. In order to face it, Solar water disinfection (SODIS) proposes the use of transparent plastic containers, which are filled with contaminated water, and exposed to direct sunlight until enough UV radiation is received to inactivate the pathogens. However, a reliable method for determining the end of the disinfection process is needed. Although several approaches have been proposed in the literature for this purpose, they do not strictly accomplish two critical constraints that are essential in this type of project, namely, low cost and sustainability. In this paper, we propose an electronic device to determine when the lethal UV dose has been reached in SODIS containers, which accomplishes both constraints mentioned above: on the one hand, its manufacturing cost is around EUR 12, which is much lower than the price of other electronic solutions; on the other hand, the device is sufficiently autonomous to work for months with small low-cost disposable batteries, thereby avoiding the use of rechargeable batteries, which are considered hazardous waste at the end of their useful life. In our approach, we first analyze different low cost UV sensors in order to select the most accurate one by comparing their response with a reference pattern provided by a radiometer. Then, an electronic device is designed using this sensor, which measures the accumulated UV radiation and compares this value with the lethal UV dose to determine the end of the disinfection process. Finally, the device has been manufactured and tested in real conditions to analyze its accuracy, obtaining satisfactory results.
... Assuming an average of 4.7% of UVA radiation in the total solar spectrum (Table S1), the minimum accumulated UVA dose during the year in Tigray region is 442.4 ± 2.6 Wh/m 2 . Only UVA radiation is considered since PET does not transmit UVB radiation 26 . ...
... The container dimensions were: height 526 mm, base length 240 mm, base depth 263 mm; with an average wall thickness of 0.55 mm. Preliminary studies of the optical and mechanical properties of these containers showed that the UV-A transparency of the plastic material was adequate and that the resistance of the 25 L PET TJC to falls and impact was adequate to ensure its suitability to the harsh field conditions 26,32 . 70 TJC units were used for the experiments to evaluate the microbial quality of the water, and 1650 TJC units were transported to Ethiopia for distribution to the communities for the health impact assessment in the field. ...
Article
Full-text available
The lack of safe drinking water affects communities in low-to-medium-income countries most. This barrier can be overcome by using sustainable point-of-use water treatments. Solar energy has been used to disinfect water for decades, and several efforts have been made to optimise the standard procedure of solar water disinfection (SODIS process). However, the Health Impact Assessment of implementing advanced technologies in the field is also a critical step in evaluating the success of the optimisation. This work reports a sustainable scaling-up of SODIS from standard 2 L bottles to 25 L transparent jerrycans (TJC) and a 12-month field implementation in four sites of Tigray in Ethiopia, where 80.5% of the population lives without reliable access to safe drinking water and whose initial baseline average rate of diarrhoeal disease in children under 5 years was 13.5%. The UVA dose required for 3-log reduction of E. coli was always lower than the minimum UVA daily dose received in Tigray (9411 ± 55 Wh/m²). Results confirmed a similar decrease in cases of diarrhoea in children in the implementation (25 L PET TJC) and control (2 L PET bottles) groups, supporting the feasibility of increasing the volume of the SODIS water containers to produce safer drinking water with a sustainable and user-friendly process.
... Contrary to these two studies, it was reported that placing a reactor at the focus of a concentrator collector in a parabolic basin with a reflective surface increased by 21-28% the photolysis rate of the drug (ciprofloxacin) in water by solar UV radiation [128]. Reactors made of quartz, borosilicate, polypropylene, polymethylmethacrylate, pyrex (with low iron content) and methacrylate have been shown to be more suitable for solar water disinfection processes based on UV radiation [129][130][131]. As for the shape of the concentrator, two studies showed slightly contrasting results [123,131]. ...
... Reactors made of quartz, borosilicate, polypropylene, polymethylmethacrylate, pyrex (with low iron content) and methacrylate have been shown to be more suitable for solar water disinfection processes based on UV radiation [129][130][131]. As for the shape of the concentrator, two studies showed slightly contrasting results [123,131]. In the study by McLoughlin et al. [123] it was reported that in the system based on CPC collectors a higher efficiency was obtained (with a reduction in bacterial viability of >4 log FUC/mL) than in the system based on PTC and V-groove collectors (with a reduction in viability of ~3 log FUC/mL). ...
Article
Solar drinking water treatment technologies are one of the most promising strategies to increase access to safe drinking water worldwide, as they are effective, affordable and sustainable. However, the development of affordable, high-performance solar water treatment systems applicable to large-scale public drinking water supply remains necessary. In this work, the state of the art in the development of solar water disinfection systems is systematically reviewed and a critical discussion is presented. Studies reporting high-performance solar water disinfection systems, or those capable of being upgraded for application in large-scale potable water supplies, were included. The solar disinfection systems described in the literature are of the SOPAS type (solar pasteurization), SODIS (solar disinfection by ultraviolet radiation) or mixed type (SOPAS + SODIS) and are based on concentrating or non-concentrating solar collectors. SOPAS + SODIS systems are more effective at microbial inactivation and, continuous flow or intermittent flow disinfection approaches in systems based on concentrating solar collectors or evacuated tubes are more productive. All systems reviewed can be improved, integrating or improving the concentration capacity of solar radiation, and increasing the efficiency of absorbers and/or reactors. Combining improved SOPAS and SODIS systems to develop mixed systems has been found to be one of the most important advances in the development of high performance systems. The integration of photovoltaic-powered artificial UV radiation disinfection technology as well as photothermal and photocatalytic materials into improved mixed solar disinfection systems needs to be explored. The performance of these systems needs to be evaluated in scenarios that simulate real large-scale water supply contexts.
... The optical pathways on the other hand are far more complex and intriguing. The UVC component of solar radiation is fully absorbed by atmospheric ozone (Frederick, 2015), and the trace UVB that reaches the earth's surface does not usually penetrate the glass and plastic containers that are used for SODIS; for example, depending on the bottle composition, the UVB irradiation (290-320 nm) might be filtered out, as in the case of polyethylene terephthalate (PET) or borosilicate, whereas polycarbonate moderately permits its passage (García-Gil et al., 2020b). Since SODIS is mainly applied in resource-poor regions, the materials commonly used are PET and glass, which with minor deviations allow part of UVA, visible and infrared light to penetrate the material. ...
Article
Full-text available
Solar disinfection (SODIS) was probed for its underlying mechanism. When Escherichia coli was exposed to UVA irradiation, the dominant solar fraction acting in SODIS process, cells exhibited a shoulder before death ensued. This profile resembles cell killing by hydrogen peroxide (H2O2). Indeed, the use of specialized strains revealed that UVA exposure triggers intracellular H2O2 formation. The resultant H2O2 stress was especially impactful because UVA also inactivated the processes that degrade H2O2—peroxidases through the suppression of metabolism, and catalases through direct enzyme damage. Cell killing was enhanced when water was replaced with D2O, suggesting that singlet oxygen plays a role, possibly as a precursor to H2O2 and/or as the mediator of catalase damage. UVA was especially toxic to mutants lacking miniferritin (dps) or recombinational DNA repair (recA) enzymes, indicating that reactions between ferrous iron and UVA-generated H2O2 lead to lethal DNA damage. Importantly, experiments showed that the intracellular accumulation of H2O2 alone is insufficient to kill cells; therefore, UVA must do something more to enable death. A possibility is that UVA stimulates the reduction of intracellular ferric iron to its ferrous form, either by stimulating O2− formation or by generating photoexcited electron donors. These observations and methods open the door to follow-up experiments that can probe the mechanisms of H2O2 formation, catalase inactivation, and iron reduction. Of immediate utility, the data highlight the intracellular pathways formed under UVA light during SODIS, and that the presence of micromolar iron accelerates the rate at which radiation disinfects water.
Article
Introduction: Solar disinfection (SODIS) is an effective method for microbiologic inactivation of contaminated water using ultraviolet rays at low elevations. The aim of this study was to determine the effectiveness of SODIS at higher elevations. Methods: The ability of SODIS to inactivate Escherichia coli bacteria was evaluated at an altitude of ≥1600 m using Nalgene bottles, disposable plastic water bottles, and Ziploc plastic bags. Bacterial viability was determined through measurement of colony forming units (CFUs). Decreases in CFUs were determined at each time point relative to those at the baseline, and a multivariable regression analysis was used to assess significant changes in CFUs. Results: Bacterial CFUs in exposed containers decreased by >5 log after 6 h of exposure to sunlight. In contrast, the CFUs remained nearly unchanged in unexposed containers, showing a mean decrease of 0.3 log. By 2 h, bacterial inactivation at high altitudes was 1.7-fold greater than that at lower altitudes (P<0.05). By 6 h, nearly all bacteria were inactivated at high or low altitudes. At 6 h, no statistical difference was observed in the efficiency of inactivation between elevations. Compared with Nalgene bottles, plastic bottles had a 1.4-fold greater decrease in CFUs (P<0.05). No statistical difference in bacterial inactivation was found between plastic bottles and plastic bags. Conclusions: At high altitudes, SODIS is an effective method for inactivating E coli. Further research investigating other microorganisms is warranted to determine whether SODIS is suitable for disinfecting contaminated water at high altitudes.
Article
Access to safe, sufficient water for health and sanitation is a human right, and the reliable disinfection of water plays a critical role in addressing this need. The environmental impact and sustainability of water disinfection methods will also play a role in overall public health. This study presents an investigation of the environmental life cycle impacts of four ultraviolet disinfection systems utilizing ambient solar radiation directly and indirectly for water disinfection in comparison to chlorination and water delivery for application in low-income settings. Product inspection and existing literature were used to define a life cycle functional unit of 1 m 3 of water for each system, which allowed quantification of material use, infrastructure requirements, and life cycle of the original components of each system and those needed to keep them operational for the studied lifespans (1, 5, 10, and 20 years) and scales (30, 100, 500, and 1000 L per day). For all studied cases, chlorine had the lowest impact in all impact categories, but end-user acceptance of chlorine in some settings is low, driving interest in low-impact alternatives. Disinfection based on low-pressure mercury lamps had the next lowest normalized impact in most categories and may represent a viable alternative, particularly for long-term (10+ years), high production (500+ liters per day) scenarios.
Article
In this work, a novel internally LED illuminated prototype photobioreactor (IIPBR) was designed, rationalizing the light supply with a hexagonal geometry and matching the light spectrum to the most photosynthetically active wavelengths. The IIPBR was designed and operated to produce the biomass in a continuous mode. In this system, Acutodesmus obliquus was cultivated under different light intensities (100–400 µmol m⁻² s⁻¹) and residence times (1–1.9 d). At steady state, a maximum productivity of 40.09 ± 1.99 g m⁻² d⁻¹ and a photosynthetic efficiency around 22 % were obtained. The data collected were used to carry out a first evaluation of the costs related to illumination, finding that the correct setting of the operative conditions has a great impact on costs, which span from a minimum of 1.82 up to to 20.63 € kg⁻¹ (with electricity supply rated at autumn–winter 2021). The photoconversion efficiency of the lamps and the plant location play an important role and should be taken into account to increase the economic feasibility of the system proposed, thus enlarging the possible fields final applications of the biomass obtained.
Article
Full-text available
Following the recent outbreak of the COVID-19 pandemic caused by the SARS-CoV-2 virus, monitoring sewage has become crucial, according to reports that the virus was detected in sewage. Currently, various methods are discussed for understanding the SARS-CoV-2 using wastewater surveillance. This paper first introduces the fundamental knowledge of primary, secondary, and tertiary water treatment on SARS-CoV-2. Next, a thorough overview is presented to summarize the recent developments and breakthroughs in removing SARS-CoV-2 using solar water disinfection (SODIS) and UV (UVA (315–400 nm), UVB (280-315 nm), and UVC (100–280 nm)) process. In addition, Due to the fact that the distilled water can be exposed to sunlight if there is no heating source, it can be disinfected using solar water disinfection (SODIS). SODIS, on the other hand, is a well-known method of reducing pathogens in contaminated water; moreover, UVC can inactivate SARS-CoV-2 when the wavelength is between 100 to 280 nanometers. High temperatures (more than 56°C) and UVC are essential for eliminating SARS-CoV-2; however, the SODIS systems use UVA and work at lower temperatures (less than45°C). Therefore, using SODIS methods for wastewater treatment (or providing drinking water) is not appropriate during a situation like the ongoing pandemic. Finally, a wastewater-based epidemiology (WBE) tracking tool for SARS-CoV-2 can be used to detect its presence in wastewater.
Article
As a widely used substrate for flexible electronics, indium‐tin oxide‐based polymer electrodes (polymer‐ITO electrodes) exhibit poorly visible light transmittance of less than 80%. The inferior transmittance for polymer‐ITO electrodes severely limits the performance improvement of polymer‐ITO based electronics. Here, a conceptually different approach of the double‐sided antireflection coatings (DARCs) strategy is proposed to modulate both the air–polymer substrate interface and ITO–air interface refractive index gradient, to synergistically improve the transmittance of polymer‐ITO electrodes. On the basis of SiO2 nanoparticles antireflection layer on polymer substrate, a polymer–metal oxide composite antireflection film is fabricated on the ITO side. Resultantly, the transmittance of ITO‐based flexible electrodes is successfully improved from 76.8% to 89.8%, which is the highest transmittance among the reported ITO‐based flexible electrodes. Furthermore, the photoluminescence emission intensity of luminescent materials enveloped with the DARCs electrodes increases by 74% over that with reference electrodes, demonstrating the DARCs antireflection strategy can efficiently improve the performance of flexible optoelectronic devices. With DARCs electrode, the flexible perovskite solar cells exhibit an enhanced efficiency from 18.80% to 20.85%. The double‐sided antireflection coatings (DARCs) strategy improves the average transmittance of indium‐tin oxide‐based flexible electrodes from 76.8% to 89.8%. The photoluminescence intensity of luminescent materials enveloped with DARCs flexible electrodes increases by 74% and the DARCs flexible perovskite solar cell exhibits an improved efficiency from 18.80% to 20.85%, proving that the DARCs strategy can effectively improve the optoelectronic performance of flexible devices.
Article
Full-text available
Conventional solar disinfection (SODIS) processes rely on UVA radiation due to exclusion of shorter wavelengths by common SODIS containers. Because of this, these processes are slow and could be improved by inclusion of UVB radiation, which has been reported to be more effective for microbial inactivation than UVA on a photon basis, but is typically present at lower spectral irradiance. To examine the potential for microbial inactivation resulting from exposure to solar UVB radiation at sea-level, experiments were conducted to define the UVB/UVA action and effectiveness spectra for Salmonella typhimurium LT2, Vibrio harveyi, and Cryptosporidium parvum, which are representative of three of the most prevalent waterborne pathogens globally. For each organism, the action spectrum was similar in shape to its corresponding DNA absorption spectrum, thereby suggesting that inactivation of these organisms by UVB irradiation was largely attributable to DNA damage. Modeling and measurements of ambient solar UVB spectral irradiance were compared, indicating a trend of model over-prediction of spectral irradiance by up to 20% on cloudless days. Effectiveness spectra for organism/location pairs were calculated as the product of the action spectra and calculated spectral irradiance to identify the most effective wavelengths for inactivation. For the organisms studied, maximum predicted effectiveness appeared at wavelengths between 318 and 330 nm. At 320 nm, the simulated inactivation of C. parvum in the top 20-cm of an outdoor swimming pool (mid-latitude location in summer) after one hour of exposure was approximately 6-log 10 units. These results suggest that solar UVB irradiation could yield substantial inactivation of C. parvum in outdoor recreational waters, where these protozoan parasites are responsible for a large fraction of the disease burden among swimmers.
Article
Full-text available
The transition from laboratory research to pilot scale trials can be challenging for novel water treatment technologies. This transition is even more complex for technologies intended for use in a developing country context due to cultural, infrastructural, financial and capacity related challenges. This research looks at the lessons learned from a pilot installation of a continuous CPC solar water disinfection system in a rural community of Kenya. This project was implemented with local and international partners, however the monitoring and evaluation phase collapsed due to the breakdown of these partnerships. A visit to the project site three years after installation revealed significant problems with the system due to drought and flash flooding. A second project phase was funded through crowdfunding in order to rehabilitate the damaged system and provide an alternative water source for the community during periods of drought. Post project evaluation of both project phases showed that the engagement of local implementing partners is essential for ensuring community participation and effective monitoring and evaluation, as the priorities and presence of international implementing partners can easily change in the medium to long term. More external assistance is required for pilot projects using novel technologies than for those using well-established water treatment systems, particularly in terms of operation and maintenance challenges which may arise in the short to medium term. This requirement for external support significantly impacts the sustainability of these interventions. The performance of the continuous flow system while it was in use was found to be satisfactory and feedback from the community regarding operation of the system and quality of water was positive. Both project phases revealed the need for some small design changes, such as inclusion of air-bleed valves, which would significantly improve system operation for future pilot projects. The project experience also illustrated the need for better understanding of the behaviour of both surface and groundwater, given increasingly unpredictable weather patterns as a result of climate change.
Article
The efficiency of two large-volume batch solar reactors [Prototype I (140 L) and II (88 L)] in treating rainwater on-site in a local informal settlement and farming community was assessed. Untreated [Tank 1 and Tank 2-(First-flush)] and treated (Prototype I and II) tank water samples were routinely collected from each site and all the measured physico-chemical parameters (e.g. pH and turbidity, amongst others), anions (e.g. sulphate and chloride, amongst others) and cations (e.g. iron and lead, amongst others) were within national and international drinking water guidelines limits. Culture-based analysis indicated that Escherichia coli, total and faecal coliforms, enterococci and heterotrophic bacteria counts exceeded drinking water guideline limits in 61%, 100%, 45%, 24% and 100% of the untreated tank water samples collected from both sites. However, an 8 hour solar exposure treatment for both solar reactors was sufficient to reduce these indicator organisms to within national and international drinking water standards, with the exception of the heterotrophic bacteria which exceeded the drinking water standard limit in 43% of the samples treated with the Prototype I reactor (1 log reduction). Molecular viability analysis subsequently indicated that mean overall reductions of 75% and 74% were obtained for the analysed indicator organisms (E. coli and enterococci spp.) and opportunistic pathogens (Klebsiella spp., Legionella spp., Pseudomonas spp., Salmonella spp. and Cryptosporidium spp. oocysts) in the Prototype I and II solar reactors, respectively. The large-volume batch solar reactor prototypes could thus effectively provide four (88 L Prototype II) to seven (144 L Prototype I) people on a daily basis with the basic water requirement for human activities (20 L). Additionally, a generic Water Safety Plan was developed to aid practitioners in identifying risks and implement remedial actions in this type of installation in order to ensure the safety of the treated water.
Article
A novel procedure for the simulation of solar water disinfection (SODIS) processes in flow reactors is presented. The modeling approach includes the rigorous description of hydrodynamics, radiation transfer, mass transport and bacterial inactivation phenomena within the reactor by means of a computational fluid dynamics (CFD) software. The methodology has been evaluated in a tubular reactor coupled with a compound parabolic collector (CPC). Velocity profiles have been validated versus theoretical fully developed flow, and radiation fields versus both ray tracing and experimental actinometrical measurements. Incorporation of the solar vector calculation significantly improves the model capabilities for prediction of the potential performance of the SODIS process at different geographical coordinates and operation time. A mechanistic kinetic model was used for the description of the bacterial inactivation rate with explicit radiation absorption effects, coupling the radiation field with the mass balances of viable bacterial species. Model predictions successfully reproduce the experimental data of E. coli inactivation under different irradiances of both simulated and natural solar light with a normalized root mean squared logarithmic error (NRMSLE) of 6.65% and 9.72%, respectively. Therefore, this novel methodology is confirmed as a useful tool for the scaling-up of the SODIS process to large volume systems to be installed in remote communities where safe drinking water is not available.
Article
A new approach is presented for conducting and extrapolating combined environment (radiation plus thermal) accelerated aging experiments. The method involves a novel way of applying the time-temperature-dose rate (t-T-R) approach derived many years ago, which assumes that by simultaneously accelerating the thermal-initiation rate (from Arrhenius T-only analysis) and the radiation dose rate R by the same factor x, the overall degradation rate will increase by the factor x. The dose rate assumption implies that equal dose yields equal damage, which is equivalent to assuming the absence of dose-rate effects (DRE). A plot of inverse absolute temperature versus the log of the dose rate is used to indicate experimental conditions consistent with the model assumptions, which can be derived along lines encompassing so-called matched accelerated conditions (MAC lines). Aging trends taken along MAC lines for several elastomers confirms the underlying model assumption and therefore indicates, contrary to many past published results, that DRE are typically not present. In addition, the MAC approach easily accommodates the observation that substantial degradation chemistry changes occur as aging conditions transition R-T space from radiation domination (high R, low T) to temperature domination (low R, high T). The MAC-line approach also suggests an avenue for gaining more confidence in extrapolations of accelerated MAC-line data to ambient aging conditions by using ultrasensitive oxygen consumption (UOC) measurements taken along the MAC line both under the accelerated conditions and at ambient. From UOC data generated under combined R-T conditions, this approach is tested and quantitatively confirmed for one of the materials. In analogy to the wear-out approach developed previously for thermo-oxidative aging, the MAC-line concept can also be used to predict the remaining lifetimes of samples extracted periodically from ambient environments.
Article
Models that predict sunlight inactivation rates of bacteria are valuable tools for predicting the fate of pathogens in recreational waters and designing natural wastewater treatment systems to meet disinfection goals. We developed biological weighting function (BWF)-based numerical models to estimate the endogenous sunlight inactivation rates of E. coli and enterococci. BWF-based models allow the prediction of inactivation rates under a range of environmental conditions that shift the magnitude or spectral distribution of sunlight irradiance (e.g., different times, latitudes, water absorbances, depth). Separate models were developed for laboratory strain bacteria cultured in the laboratory and indigenous organisms concentrated directly from wastewater. Wastewater bacteria were found to be 5–7 times less susceptible to full-spectrum simulated sunlight than the laboratory bacteria, highlighting the importance of conducting experiments with bacteria sourced directly from wastewater. The inactivation rate mod...
Article
A mechanistic model of the inactivation of Escherichia coli by solar water disinfection (SODIS) technique is presented. Bacterial inactivation by SODIS is commonly attributed to the oxidative stress generated by synergy among solar radiation (UV photons) and mild temperature. Photons may increase the naturally occurring amount of internal Reactive Oxygen Species (ROS), such as hydroxyl radical (HO) and superoxide radical (O2⁻). ROS attacks to different targets inside the cells are one of the main sources of oxidative damage over cells. Besides, photons may damage the two essential enzymes of the defense system against intracellular oxidative stress, catalase (CAT) and superoxide dismutase (SOD). Therefore, the proposed model is a simplified approach of the complex processes occurring inside cells during SODIS, which is based on the photo-induced formation of intracellular ROS and the photo-inactivation of CAT and SOD. The model considers two individual volume units in which the processes are occurring simultaneously: (i) a single cell (mass balances for intracellular ROS and enzymes) and (ii) the reactor (mass balance for bacteria). Kinetic constant from literature were used, meanwhile CAT photo-inactivation kinetic constant was determined experimentally, (1.50 ± 0.04)·10⁷ cm³ Einstein⁻¹. Model regression was done using experimental data of E. coli inactivation by solar disinfection at different controlled conditions of solar irradiance and initial bacterial concentration. The good fit of the simulated and experimental results suggested that the mechanistic process proposed is a realistic approach of the disinfection process. Moreover, simulations of the time profile of intracellular ROS and enzymes involved during bacterial inactivation by SODIS are also presented.
Article
This is the first study that evaluates the efficacy of the photocatalytic disinfection against the waterborne protozoan parasite Cryptosporidium using a combination of TiO2 and H2O2 under simulated and natural solar conditions. Samples of distilled water containing 100 mg/L of TiO2 and/or 50 mg/L of H2O2 were spiked with purified Cryptosporidium parvum oocysts and exposed to solar radiation for 5 h. The oocyst global viability was determined by inclusion/exclusion of the fluorogenic vital dye propidium iodide. A strong decrease in the oocyst global viability was observed in samples containing TiO2 and TiO2/H2O2 under simulated solar conditions (4.16 ± 2.35% and 3.82 ± 4.26%, respectively, vs 90.44 ± 5.87%, initial global viability). Similarly, a drastic reduction in the oocyst global viability was observed under real sunlight (2.29 ± 1.99% and 0.92 ± 0.71% in samples containing TiO2 and TiO2/H2O2, respectively, vs 99.45 ± 0.95%, initial global viability). These results prove the efficacy of the TiO2 photocatalytic disinfection against C. parvum, decreasing the time needed to reach the oocyst inactivation in comparison with exclusive solar disinfection. However, the addition of H2O2 at low concentrations (50 mg/L) did not enhance the TiO2 photocatalytic process against Cryptosporidium.