Deep UV LEDs for Public Health Applications

Abstract

In 2011, According to the World Health Organization, roughly 768 million people did not use any improved sources for drinking water while 185 million people relied on only regular surface water in order to meet their drinking water needs. The number of people living in slums with no clean water supply is expected to double by 2030 to 2 billion. Each year in U.S. hospitals there are an estimated 1.7 million healthcare acquired infections (HAI) resulting in approximately 99,000 deaths (2007 data). Deep Ultraviolet Light Emitting Diodes (DUV LEDs) technology can help solve these and a variety of other problems related to public health and wellbeing. In contrast to more conventional UV sources, such as mercury lamps, DUV LEDs do not require any warm up time, are toxic chemical free, and possess the capability to be molded into compact systems. The DUV LED diodes fabricated by SET, Inc. are based on III-Nitride Semiconductors ( AlGaN ). These devices are capable of providing spectral power distribution with the peak emission wavelengths from 227 nm to 340 nm. A novel compact low flow water purification unit using DUV LEDs demonstrated a 4.15 LOG reduction of viral MS2 bacteriophage and > 6 LOG (99.9999%) reduction of E.coli at 100mL/min flow and 40mW of optical output power. At higher optical output powers, the LOG reduction begins to saturate and taper off. The water disinfection unit incorporated 20 TO-39 packages and was controlled by a single custom power supply. Arrangement of the LEDs insured minimal to no shadowing of influent water. The germicidal efficacy of the system was further enhanced by photon recycling using UV-reflecting chamber walls and multiple passes through exposed water stream. The water disinfection units are geared towards affordable and durable Point-of-Use (POU) drinking water systems. Current modifications are being made in order to further increase the efficacy of the water disinfection units at higher flow rates and lower power requirements. DUV LED technology was also used to design efficient hard surface microbial disinfection systems. Many microbes have become more resistant to everyday chemical disinfectants. Higher dose and more concentrated chemical solutions are needed to the point that they themselves become toxic for humans. Initial testing has produced visual evidence of microbial inactivation on hard surfaces contaminated with E.coli. Testing involved a single SETi TO-39 package with a wavelength of approximately 275nm. A higher than the 2 LOG reduction at approximately 1 mW optical output power was achieved. Based on these results, a 2nd generation system was designed for portable DUV LED cell phone disinfection containing few separate LED chips at 270-275 nm. Initial testing revealed an almost 2 LOG (99%) reduction of E.coli after 30 minutes of exposure at low microbial influent levels.