Submitted to: Desalination and Water Treatment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/20/2018
Publication Date: 9/5/2018
Citation: Rasooly, R., Magoz, Z., Luo, J., Do, P.M., Hernlem, B.J. 2018. Sensitive low-cost CCD-based detector for determination of UV-LED water microbial disinfection. Desalination and Water Treatment. 118:120-125. https://doi.org/10.5004/dwt.2018.22667.
Interpretive Summary: Ultraviolet (UV) light is widely used to treat water to kill bacteria and other harmful microbes. Traditionally, UV is made using mercury-containing lamps but mercury is poisonous and can harm the environment. A recent alternative source of UV is the specially-built UV light emitting diode (UV-LED). However, there are no standard methods for comparing the ability of these devices to treat water. We built a small scale flow through UV-LED water treatment device and developed and tested a method using an inexpensive CCD camera and E. coli bacteria that glow green when alive and viewed under purple light. This method is sensitive and compares well against more expensive commercial systems.
Technical Abstract: UV is widely used for bacterial disinfection of water, mainly derived from Low-pressure mercury UV (LP-UV) lamps. However, the United Nations Environmental Programme on Mercury has set the goal to phase out the production of the heavy metal mercury because of its associated hazards. The newly developed UV light emitting diodes (UV-LEDs) have been of great interest as an alternative to LP-UV. However, because of the lack of uniformity in research materials and methods and because no standard methods are available for UV-LEDs, making comparisons is difficult. To overcome some of these limitations we present here a simple low cost new CCD based sensitive method for determination of UV-LED microbial disinfection of water. The system includes a pGlo E. coli cells that express the green fluorescent protein (GFP) which simplifies cell counting and a CCD camera for rapid counting of surviving viable bacteria. The system was tested for UV-LED disinfection using a novel internal reflection UV-LED flow-through reactor. Samples of 200 ml water were spiked with 1,000,000 CFU pGlo fluorescent cells and treated for 4 minutes with different power levels of LED UV. To improve detection at low cell number we used filtration of a relatively large sample volume, the membrane filters were placed on agar plates contains arabinose that regulates the expression of the GFP protein in the live bacterium and their viability was quantified by measuring their fluorescence with a CCD camera enabling detection of very low number of cells (0.62 cells/ml). The number of viable cells decreased with the increased level of UV illumination. At level of 100% illumination the disinfection was ~99.99% and the CCD based detection was in agreement with a commercial detector system. These results demonstrate the potential of the CCD based method combined with fluorescence E. coli to standardize UV-LED water microbial disinfection.