Solar-based UV: Fundamentals and applications · Solar-based UV: Fundamentals and applications...

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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

150 200 250 300 350 400

Wavelength (nm)

Low pressure

Medium pressure

Sunlight

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

200 220 240 260 280 300 320

Wavelength (nm)

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 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

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

Energy transfer to O2 94 kJ/mol (1260 nm)

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)

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

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

Steady-state concentrations of ROS: LROSmol

kinact ≈ ϑ*Pa+ k1O2[1O2] + kOH·[OH·] + kNOM*[NOM*] + kCO3-·[CO3-.] [1/time]

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)

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

Modeled inactivation rates and main processes

MS2 phiX174

direct 1O2 OH• NOM*

Example diluted wastewater

What happens to the virus?

Virus components Virus life cycle

Replication

Attachment

Entry Release

Genome

Protein

What happens to the virus?

Indirect (1O2) Direct (UV)

Bosshard et al., AEM 2013

Solar disinfection of bacteria: conceptual model

It’s complicated….

Application examples

www.rockymtnhouse.com todosupervivencia.com

Solar disinfection applications: low-tech

Wastewater treatment Drinking water treatment

Wastewater treatment

www.rockymtnhouse.com

Anaerobic: BOD and SS removal Biogas formation

Facultative: BOD removal Some pathogen inactivation

Maturation: Pathogen inactivation and removal

High pathogen removal/inactivation!

o 6 log bacteria

o 4 log viruses

o 1 log protozoa

o 100 % helminth eggs

Wastewater treatment

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

todosupervivencia.com

Drinking water treatment SODIS

Used by 5.8 million people in 30 countries

SODIS works best between 35°N and 35°S

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

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

Upconversion

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

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

Solar-based UV: Fundamentals and applications · Solar-based UV: Fundamentals and applications...

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