Final Report: Innovative Ultraviolet Light Source for Disinfection of Drinking Water
EPA Contract Number: 68D01057Title: Innovative Ultraviolet Light Source for Disinfection of Drinking Water
Investigators: Schaefer, Raymond B.
Small Business: Phoenix Science and Technology Inc.
EPA Contact: Richards, April
Phase: II
Project Period: September 1, 2001 through September 1, 2003
Project Amount: $225,000
RFA: Small Business Innovation Research (SBIR) - Phase II (2001) Recipients Lists
Research Category: Watersheds , SBIR - Water and Wastewater , Small Business Innovation Research (SBIR)
Description:
The objective of this Phase II project was to demonstrate the practicality of a new innovative pulsed surface discharge (SD) lamp for ultraviolet (UV) disinfection of water. The SD lamp has high UV efficiency and, unlike mercury lamps, has no mercury or other materials with environmental disposal issues.
Phoenix Science & Technology, Inc., used new pulsed SD UV lamps in a series of UV disinfection tests to extend the Phase I feasibility demonstrations. In collaboration with researchers at Duke University, UV disinfection tests were conducted with the SD UV lamp and commercial low pressure mercury (LPM) and medium pressure mercury (MPM) lamps to provide direct comparisons. Tests included the microorganisms MS2 coliphage, Bacillus subtilis, and adenovirus. A new test configuration called the high intensity (HI) test cell was devised for evaluating the effects of light intensity on inactivation. Initial test set-ups included both a standard collimated beam (CB) and the HI test cell. Inactivation versus UV dose relationships were generated for all three lamps and all organisms. Radiometer and electrical power measurements were taken, and together with UV dose measurements, used to determine the electrical energy per order, a standard figure-of-merit for water treatment. A reactor was designed, built, and tested. Flow-through tests were conducted on MS2 for different flow rates, pulse repetition rates, and reactor designs.
A commercial evaluation included a life-cycle cost analysis for UV disinfection systems using SD and MPM lamps. Processing costs were generated using the inactivation rates demonstrated in this project. Capital and maintenance costs for MPM lamp systems were based on information provided by a commercial UV disinfection equipment company. Capital and maintenance costs for the SD lamp were estimated based on current SD lamp technology.
Summary/Accomplishments (Outputs/Outcomes):
Inactivation versus UV dose relationships were generated for all three lamps and microorganisms. HI test cell experiments were completed for the LPM and SD lamps for the two microbes. The tests results showed that the SD lamp inactivated MS2 and B. subtilis at dose-based rates approximately twice that of the LPM lamp. The rate for MS2 was the same for the CB and HI cell, whereas the rate for B. subtilis was about twice as high for the HI cell compared to the CB. Thus, B. subtilis was sensitive to intensity, whereas MS2 was not. The increased inactivation rate of MS2 coliphage may be due to the relatively high sensitivity of MS2 to the rich short wavelength spectrum from the SD. Reactor tests showed higher than expected inactivation with greater than 5.9 log for clear water and 4.5 log for dark (low UV transmission) water, corresponding to rates approximately five (or more) times higher than LPM. The reactor tests had a different, higher intensity SD pulse condition than the CB and HI cell tests, which may account for the higher rates than expected.
The life-cycle cost analysis indicates that the cost of a commercial SD UV disinfection system is expected to be comparable to, or lower than, that of MPM lamp systems, depending on capital and replacement costs of SD lamps once commercialized.
Conclusions:
The results of this project show that the SD UV lamp is very effective for disinfection of drinking water and can lead to a cost-effective, mercury-free commercial system. Success in ongoing work to increase the SD lamp life will lead to a commercial SD UV lamp water treatment system.