Final Report: Sequenced Combination of UV LED Wavelengths for Enhanced Inactivation of Waterborne Pathogens

EPA Grant Number: SU835716
Title: Sequenced Combination of UV LED Wavelengths for Enhanced Inactivation of Waterborne Pathogens
Investigators: Elliott, Mark , Sheridan, Charlotte , Clifton, Cheryl , McCandless, Elliott , Uku, George , Waters, Joseph , Zhu, Lian , Voltapetti, Nicole , Das, Parnab , Kung, Patrick , Bedoya, Simon
Institution: University of Alabama
EPA Project Officer: Hahn, Intaek
Phase: I
Project Period: August 15, 2014 through August 14, 2015
Project Amount: $15,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2014) RFA Text |  Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Challenge Area - Water , P3 Awards , Sustainability

Objective:

Ultraviolet (UV) light-emitting diodes (LEDs) are emerging as an energy efficient and environmentally benign alternative to currently employed mercury lamps for disinfection of waterborne pathogens in diverse applications and settings, such as water and wastewater treatment and reuse. LEDs are becoming commercially available that can generate light in the UV range of interest in the optical spectrum where it is most efficient to inactivate microorganisms by different mechanisms. The benefits of LEDs include: energy efficiency, lightness and portability, lack of toxic waste, no formation of disinfection byproducts, low heat generation, redundancy, and the potential for very low cost. Despite the anticipated advantages, many technical questions remain with respect to optimizing UV LED treatment for practical long term use in the field. Additionally, while the cost-to-effectiveness ratio of UV LEDs has improved in the past few years, the market competitiveness has not been clearly established.

In this context, a team of students led this Phase I project to investigate the effectiveness of UV light sources with different wavelengths (from 225 through 370 nm) and their combinations, as quantified by the orders of magnitude of reduction in bacteria and virus indicator population counts. Specific sequences of exposure, could potentially lead to enhanced treatment effectiveness when compared to utilizing the UV light source individually. To do so, the team pooled a multidisciplinary range of skills –from microbiology to optics–, from four academic departments (Civil, Construction and Environmental Engineering; Mechanical Engineering; Electrical and Computer Engineering; and Materials Science), and including both graduate and undergraduate students. A second objective of the Phase I work is to assess the market viability of currently commercially available UV LEDs in the context of other potentially competitive technologies.

The Phase I proposal for this project was the final class project of three students on the team and eight other students have since joined. It is also used as an experimental module for a senior-level, lab-based course in Civil, Construction and Environmental Engineering.

Figure: (a)Schematic of the UV-Visible-Infrared spectrum, with the "germicidal" range indicated. (b) Emission spectra from the UV sources investigated in this study, along with spectral ranges of a few UV sources such as low-pressure and medium-pressure Hg, Xe and currently available commercial LEDs.

Summary/Accomplishments (Outputs/Outcomes):

Through the first 7 months of this project to date, a number of findings of the Phase I research work have been made: (i) in the comparison of the potential efficacy of using UV LEDs and sources with different wavelengths in sequence, (ii) in gaining understanding of the mechanisms of UV-based virus destructions at wavelengths below 235 nm, and (iii) in establishing an objective analysis of cost/benefits of integrating LEDs, which are described in more details below.

  1. Effectiveness of UV sources and sequencing. Our Phase I research thus far has shown that 262-nm LEDs were more efficient than 282-nm units for inactivating bacteria and viruses at a given dose. However, 282-nm LEDs cost about 35% less per unit and emit at higher power than 262-nm, so both the time for a given inactivation and the cost per effectiveness at 282-nm were often higher than 262-nm. Therefore, we are exploring intermediate doses in the 270-275 nm range to determine the most cost-effective wavelength for different test conditions.
  2. UV-based virus destruction mechanisms. Our Phase I research investigated the impacts of <235-nm UV on viruses and bacteria, resulting in a major preliminary finding related to UVbased protein destruction mechanisms. Although dose, i.e. the amount of energy per unit area, has been confirmed as the essential metric for established UV sources that relies on DNA damage, this convention is unclear for the protein destruction mechanisms and virus inactivation. This uncertainty may be driven by the fundamentally different mechanisms by which UV induces DNA-damage and protein-damage.
  3. Phase I Market Research and Implications. UV LEDs offer a great opportunity to improve existing UV-C water disinfection paradigms and to enable future novel and unique configurations. Unfortunately, UV LEDs are currently exceedingly expensive on a $ per watt basis, when compared to other technically competitive relatively higher optical output sources positioned for low flow rate / low processing volume water disinfection. Given this pricing handicap, the implementation of UV LEDs in a wide array of commercial products may remain hindered throughout 2015 and possibly beyond. Furthermore, given this innovation barrier, a well thought out next step would be to build modified test structures incorporating new alternative sources.

Furthermore, given this innovation barrier, a well thought out next step would be to build new test structures based upon new alternative sources to UV LEDs and then compare the inactivation and scalability of systems based upon both types of sources, and determine which arrangement works best for producing 50 gpm modules that meet the requisite inactivation levels while remaining economically viable for multiple end users. With this insight in hand, a more efficient o

Conclusions:

Conclusions:

UV LEDs demonstrate great potential for the production of safe drinking water in an environmentally sustainable manner. However, the price point for UV LEDs is not costcompetitive in the short term. Therefore, in Phase II, in partnership with an industrial partner, we will investigate market-ready alternatives to UV LEDs. These systems should be designed to be modular, so that they can be supplemented with UV LEDs or other targeted wavelengths, if and when needed and cost-efficient. Our Phase II approach (see below) acknowledges the current cost barriers to UV LEDs, while designing for a future in which they supplement and replace conventional sources of UV light.&

Table:&Comparison of our team's proprietary source with commercially available deep UV LEDs emitting in the 250-260 nm range. Also included is a 2009 industry projection of UV LED parameters in 3-4 years.&

Feature

UV LED

2007-08 actual*

UV LED

Projected 2012-13*

UV LED

2015 actual#

Proprietary Source 2015 projected

mW / lamp (output)1

0.36

100

10

1000

Lifetime (hrs)

1,000

10,000

1,000

10,000

Cost ($ / mW)

664

0.10

5

0.10

Flow Rate (Gallons/min)2

0.015

0.015

0.25&

50&

Number of Lamps

201

1

1

1

Upfront Lamp cost ($)

$47,943

$7

$50

$10

1 year cost ($)

Not listed

Not listed

$500

$10

3 year cost ($)

$1,260,063

$21

$1500

$30

1. mW per lamp measured at surface of emitter; 2. flow limited by objective of producing 4 log10&reduction of virus challenge. *Source of these columns: Chatterley, C. and Linden, K. (2010) Demonstration and evaluation of germicidal UV-LEDs for point-of use water disinfection.&J Water Health&Vol. 8:479–86.&#Based on market research.

Journal Articles:

No journal articles submitted with this report: View all 2 publications for this project

Supplemental Keywords:

drinking water treatment, reuse, photonics, germicidal, AlGaIn, LEDs

Relevant Websites:

News article appearing in the Tuscaloosa News Exit

AL.com website Exit

Article in The Crimson White campus newspaper and UA News Exit

International Ultraviolet Association Exit