Process Testing for Household Water Treatment Invention Megan N. Heinze, Thomas D. Jacroux, Richard P. Oleksak College of Chemical, Biological, and Environmental Engineering Sponsors: Paul Berg and Jeff Nason BACKGROUND One billion people in developing countries lack access to safe drinking water. A low-cost household treatment device could significantly reduce this number. Ultraviolet light ( nm) disrupts viral and bacterial DNA, making them unable to reproduce. The optimal wavelength for disruption is 265 nm. A variety of UV lamps are available for water treatment. The best choice for here is a low pressure germicidal UV lamp because: A spectral peak at 254 nm, close to optimum High UV efficiency Long lifetime Low power requirement How does UV compare with other potential forms of disinfection for household treatment? Transmittance (T), absorbance (A), and intensity (I) describe the way light passes through a medium. A larger transmittance value (smaller absorbance) means more light reaches the same depth. Transmittance values are measured using a spectrometer. NEW GENERATION DESIGN ACKNOWLEDGEMENTS We would like to acknowledge: Paul Berg for designing the prototype and giving feedback. CH2M Hill for funding the project. Dr. Nason for his continual guidance. UMPQUA Research Company for their timely results. BIOVIR Laboratories for providing MS2 coliphage. Dr. Yokochi for providing essential equipment. Andy Brickman for help with electrical work. Nick Au Yeung for help with UV Vis. Tim Maloney for his expertise in water disinfection. Dr. Harding for organizing the project. RESULTS UMPQUA Research Company OBJECTIVES It was desired to determine the capability of the prototype device by performing an experiment to measure the log reduction of MS2 coliphage depending on the following variables: Exposure time Water depth % Transmittance of water sample Use of hand-crank vs. constant maximum lamp output (DC power supply) METHODS Synthetic water was dechlorinated and the transmittance adjusted to correspond to conditions in developing countries. Coliphage was added to give a final concentration of 10 6 coliphage/mL. Batches were exposed to UV light. Samples were sent to UMPQUA Research Company to determine the final concentration of coliphage. Figure 1: Log reduction of MS2 coliphage is plotted for different exposure times. A DC power supply was used to maintain constant UV output. Liquid levels were constant at a depth of 7.4 cm (corresponding to a 5 L batch) with a transmittance of either 60 or 75% per cm. As expected, lower transmittance resulted in smaller log reduction. At zero exposure time the notable log reduction is thought to have been caused by residual chlorine in the prototype. Figure 3: Comparison of the log reductions with stirring/DC power supply versus hand crank/no stirring. The liquid level was maintained at 7.4 cm with an exposure time of 40 seconds. Trials with stirring produced higher log reduction. Figure 2: Log reduction versus time is plotted for samples of 75% transmittance at depths of 7.4 and 3.8 cm. This shows the effect of depth on log reduction for different exposure times. There is a direct relationship between log reduction and exposure time. Effect of Hand Crank versus DC Power Supply (Replicates) Effect of Liquid Transmittance Effect of Stirred Reservoir Depth UV treatment effectiveness is measured by “log reduction” of microorganisms. The EPA requires a log reduction of 4 for UV treatment (99.99 % removal) of most viruses. MS2 coliphage (used during testing) is a parasite that viruses use as a host to replicate. It is chosen for water disinfection because it is the most resistant to UV radiation and the results are reproducible. Because of its resistance to UV disinfection a log reduction of 2.3 corresponds to the EPA required disinfection above. EPA Standard for disinfection = 2.3 Figure 4: An empirical model was developed relating the required depths to achieve desired log reductions with different treatment times. The equation shown is for a 2.3 log reduction. Original PrototypeNew Design Proposed Improvements Narrow the length to that of the bulb for better intensity distribution. Incorporate reflective surfaces to realize more of the lamp output. Incorporate a mixing device (such as an impeller) to better expose microorganisms to UV light. Based on Figure 4 and estimates of the effects from the above improvements, a proposed device to treat 4 L of water in 40 seconds to a log reduction of 2.3 would need a depth of 13 cm.