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Solar-based UV:
Fundamentals and applications
Tamar Kohn Associate Professor
Environmental Engineering Insititute
Solar radiation spectrum
Wikipedia
Solar radiation Solar UV mechanism Example virus Applications Wrap-up
Solar vs lamp UV spectrum
0
20
40
60
80
100
150 200 250 300 350 400
Wavelength (nm)
Rel
ativ
e O
utpu
t (%
)
Low pressure
Medium pressure
Sunlight
UVC
UVB
UVA
Solar radiation Solar UV mechanism Example virus Applications Wrap-up
Comparison of UVC (254 nm) and solar UV (300 nm):
o Energy UVC > solar UV (factor 1.2)
o Absorbance by genome of UVC >> solar UV (factor 125)
Need 150x higher intensity of solar UV for same effect
where we need 40 mJ/cm2 UVC, we need 5000 mJ/cm2 solar UV
0
1
2
3
200 220 240 260 280 300 320
Wavelength (nm)
Abs
orba
nce
(M-1
cm-1
x 10
-3)
Uracil(in RNA)
Thymine (in DNA)
Solar UV is less effective than UVC
E = hν = hc/λ h: Bolzmann constant c: speed of light λ: wavelength
Solar radiation Solar UV mechanism Example virus Applications Wrap-up
Solar UV intensity Solar radiation Solar UV mechanism Example virus Applications Wrap-up
Monthly Mean UVB intensity
http://www.ufz.de/gluv
In Delft (July): ca. 250 mJ/cm2 solar UV per day
20 days of sun (5000 mJ/cm2 solar UV) are as effective as UVC treatment (40 mJ/cm2 UVC)
Dependent on:
o season
o latitude
o weather
o elevation
So why does solar UV disinfection work? Solar radiation Solar UV mechanism Example virus Applications Wrap-up
O2 ROS
O2
ROS O2 ROS
O2
ROS
O2
ROS
Direct inactivation: Absorption of UVB light by DNA/RNA Genome damage
Indirect endogenous inactivation: Absorption of UVB/UVA/(vis) light by internal sensitizers Production of ROS and other transient species Genome and protein damage
Solar UV acts by three different mechanisms:
ROS = reactive oxygen species
Indirect exogenous inactivation: Absorption of UVB/UVA/(vis) light by external sensitizers Production of ROS and other transient species Genome and protein damage
Formation of ROS and other transient species Solar radiation Solar UV mechanism Example virus Applications Wrap-up
Sens
Sens*
1O2
Energy transfer to O2 94 kJ/mol (1260 nm)
H2O2
e- O2•-
Electron transfer to O2
CO3•-, SO4•-
Electron / energy transfer to other water constituents
e- OH•
Internal (endogenous) sensitizers Solar radiation Solar UV mechanism Example virus Applications Wrap-up
Jagger: Solar UV actions on living cells, 1985
Some internal sensitizers absorb light at much higher wavelength than DNA, e.g.: o Riboflavin o Metalloproteins
E.Coli Inactivation occurs at wavelengths beyond UVB
334 nm
365 nm
405 nm
Fluence (MJ/m2)
Surv
ivin
g fr
actio
n of
E.C
oli
320 360 400 440 480
320 360 400 440 480 wavelength
External (exogenous) sensitizers Solar radiation Solar UV mechanism Example virus Applications Wrap-up
One of many possible structures of NOM: Stevenson and Krastonav, 1982
Nitrite / nitrate
Natural organic matter (NOM)
http://techalive.mtu.edu/meec
Triple role of NOM: o Absorption of light, mainly solar UVB o Production of transient species o Consumption of transient species
Which mechanism is important? Solar radiation Solar UV mechanism Example virus Applications Wrap-up
O2 ROS
O2
ROS O2 ROS
O2
ROS
O2
ROS
Direct inactivation: Important for: • All organisms
Indirect endogenous inactivation: Important for: • Bacteria • maybe protozoa Less relevant for: • Viruses (no internal
sensitizers)
Indirect exogenous inactivation: Important for: • Viruses • Few bacteria Less relevant for: • Protozoa • Spores • Many other bacteria
Conceptual model for solar virus disinfection
direct indirect
System dependent Virus dependent
virusbyabsorbedphotonsofmolsdinactivatevirus infectiveofmolsInactivation quantum yield ϑ :
Rate of light absorption Pa : time
virus byabsorbedphotonsofmols
Second-order inactivation rate constant k: time * ionconcentrat ROS
1
Steady-state concentrations of ROS: LROSmol
kinact ≈ ϑ*Pa+ k1O2[1O2] + kOH·[OH·] + kNOM*[NOM*] + kCO3-·[CO3-.] [1/time]
Solar radiation Solar UV mechanism Example virus Applications Wrap-up
Solar disinfection varies between viruses
direct indirect
MS2 phiX174
o Direct inactivation: phiX174 > MS2
o Indirect inactivation: MS2 > phiX174
kinact ≈ ϑ*Pa+ k1O2[1O2] + kOH·[OH·] + kNOM*[NOM*] + kCO3-·[CO3-.] [1/time]
ϑ (mol pfu/ m
ol photons)
k (M
-1s-
1)
1,00E+07
1,00E+08
1,00E+09
1,00E+10
1O2 OH CO3 triplet quantum yield
MS2 phi
1.00E-1
1.00E-2
1.00E-3
1.00E-4
Mattle et al., submitted
Solar radiation Solar UV mechanism Example virus Applications Wrap-up
Modeled inactivation rates and main processes
MS2 phiX174
direct 1O2 OH• NOM*
Example diluted wastewater
Solar radiation Solar UV mechanism Example virus Applications Wrap-up
What happens to the virus?
Virus components Virus life cycle
Replication
Attachment
Entry Release
Genome
Protein
Solar radiation Solar UV mechanism Example virus Applications Wrap-up
Solar radiation Solar UV mechanism Example virus Applications Wrap-up
What happens to the virus?
Indirect (1O2) Direct (UV)
Bosshard et al., AEM 2013
Solar disinfection of bacteria: conceptual model
It’s complicated….
Solar radiation Solar UV mechanism Example virus Applications Wrap-up
Application examples
www.rockymtnhouse.com todosupervivencia.com
Solar disinfection applications: low-tech
Wastewater treatment Drinking water treatment
Solar radiation Solar UV mechanism Example virus Applications Wrap-up
Wastewater treatment
Solar disinfection applications: low-tech
www.rockymtnhouse.com
Anaerobic: BOD and SS removal Biogas formation
Facultative: BOD removal Some pathogen inactivation
Maturation: Pathogen inactivation and removal
2-5 m
1-2 m
1 m
High pathogen removal/inactivation!
o 6 log bacteria
o 4 log viruses
o 1 log protozoa
o 100 % helminth eggs
Solar radiation Solar UV mechanism Example virus Applications Wrap-up
Wastewater treatment
Solar disinfection applications: low-tech
Dandora Pond, Kenya; 160,000 m3/day (2 Mio. Kenyans)
http://www.personal.leeds.ac.uk/
WSPs in Europe and US:
o Germany: 3000 ponds
o France: 2500 ponds
o US: 7500 ponds
www.rockymtnhouse.com
Solar radiation Solar UV mechanism Example virus Applications Wrap-up
todosupervivencia.com
Drinking water treatment SODIS
Solar disinfection applications: low-tech
Used by 5.8 million people in 30 countries
SODIS works best between 35°N and 35°S
Solar radiation Solar UV mechanism Example virus Applications Wrap-up
Drinking water treatment SODIS
Solar disinfection applications: low-tech
Optimal exposure times:
o 6 hours under up to 50% cloudy sky
o 2 days under 100% cloudy sky
o does not perform well during rain Disinfection mechanisms:
o Heating of water
o Indirect inactivation
o BUT: no direct inactivation!
Performance:
www.sodis.ch
Solar radiation Solar UV mechanism Example virus Applications Wrap-up
Drinking water treatment SODIS
Solar disinfection applications: low-tech
Advantages: o Reduces the risk of illness due to contaminated water by 50 -75 % o Simple maintenance and handling o Relies on locally available resources: PET bottles and sunlight o Very low cost Disadvantages: o Not ideal for use by children o Requires availability of PET bottles o Some education necessary o Not suitable for high-throughput treatment o Only works if turbidity < 30 NTU
Educational SODIS theater performance www.sodis.ch
Solar radiation Solar UV mechanism Example virus Applications Wrap-up
Upconversion
Solar radiation Solar UV mechanism Example virus Applications Wrap-up
Solar disinfection applications: high-tech
Sequential absorption of 2 photons leads to emission of shorter wavelength light
Can make UVC from sunlight!
http://www.nature.com/nprot/journal/v8/n10/full/nprot.2013.114.html
Application example:
Prevention of biofilm growth and disinfection of
bacteria on surfaces
Cates et al., Environ Sci Technol 2011
Solar radiation Solar UV mechanism Example virus Applications Wrap-up
Take-home messages
o Solar light «works»!
o Compared to UVC technology, solar UV is less effective, but it can penetrate deeper into the water column
o Sunlight inactivates pathogens by direct and indirect processes
o Their importance depends on the organism and the water composition (NOM!)
o Solar light is used for low-tech water treatment applications
o It is likely that we’ll see high-tech applications in the near future, too