The UV disinfection industry has experienced tremendous growth over the last 20 years. The development of new UV technologies over this period is a perfect example of an industry investing to meet market demand – in this case demand for an effective, low cost, and environmentally friendly disinfection technology. The acceptance of UV disinfection at water plants treating in excess of one billion gallons daily is proof that UV is no longer an ‘emerging’ technology, but rather an accepted technology to be used routinely by engineers to safeguard human health. The UV industry continues to change, grow and invent new products and applications. This article briefly explores some of the emerging trends.
Virtually all of the leading innovative, entrepreneurial UV companies have now been acquired by major, multi-product, financially mature industrial groups such as Danaher, Halma, Siemens, ITT and Suez. This has induced market stability and, whilst this will ensure highly professional product offerings and delivery, it also means that many of these newly acquired companies must either become or remain profitable to justify the investment made in them. The regulatory acceptance of UV for treating drinking water (particularly in the USA) and regulatory standards for validating new UV reactor designs all signal a major shift in the acceptance of the technology into the mainstream. The UV industry has experienced double digit sales growth over the last 20 years, and combined annual sales of UV products will soon be in excess of $500M.
The formation of the International Ultraviolet Association (IUVA) in 1999 provides a forum for information dissemination and self-regulation, and the imminent USEPA UV Disinfection Guidance Manual to assist engineers and owners in the design, operation and maintenance of UV systems will further standardize the use of UV.
The use of computational fluid dynamics modeling has vastly improved manufacturers’ ability to predict with confidence the level of treatment required for unique waters using their proprietary equipment. System sizing is no longer a black art, as the selected manufacturer can work with the design engineer to accurately predict treatment levels under varying conditions of water quality and flow. All UV equipment manufacturers will soon use this tool to optimize the dose delivery of their reactors and minimize energy costs. As manufacturers develop and improve optimized reactors, they will then validate the designs using USEPA or European validation protocols. These optimized reactors will be rolled out over the next several years.
Conventional UV lamp technology will also improve. Medium pressure lamps will continue to see gains in energy efficiency, lamp life and power density, with Quartz coating techniques extending lamp life to well over 12000 hours. This approach will remain favored for compact, small footprint installations, particularly retrofit, or where automated wiping is required. Low pressure, high output lamps will also have increasing power, perhaps approaching 1kW, which will decrease the footprint and maintenance requirements for systems using this technology. Lamp disposal will emerge as a significant issue for low pressure UV installations which use many thousands of low pressure lamps.
New UV lamp sources such as light emitting diodes (LEDs) claim to be a technology of the future. The advantages of LEDs are their ability to concentrate virtually all of the electrical power into a very narrow bandwidth of 260 nm to 262 nm, their vastly superior power efficiencies, a very long lamp life (reported to be greater than 100,000 hours) and, because of their point-source nature, they are not restricted to conventional cylindrical designs. Likely drawbacks of this promising technology will be in the power supply drives for the lamps, which remain largely in the concept phase. Other lamp types such as excimer lamps show some advantages, such as being mercury free and having no warm-up time, but are currently limited by low power efficiency and high ballast costs. The excimers are often also more toxic than the elements they propose to replace.
Another interesting technology involves the use of microwaves to energize a UV lamp without the use of electrodes. Developers claim to have produced power outputs of up to 1000 W with similar UV outputs to low pressure lamps, which would dramatically improve the footprint and maintenance of low pressure lamp-based systems. The absence of electrodes also greatly increases the lamp life. This development could well see microwave power supply emerge as the consumable, with the lamp remaining in situ for 4-5 years. The long term effects of using microwaves on sleeve wipers remains unknown.
UV sensor technology has also greatly improved over the last decade, with stable, reliable and germicidally accurate sensors now available and a well regulated calibration protocol now in place. In addition, manufacturers have improved the proprietary control systems for taking information from the sensors, flow meters and other monitoring devices and using this information to optimize the performance of their equipment. They can also interface with the operator at a plant’s control center.
The D10 values* of more and more microorganisms is now known, with the list growing all the time. Most notably, research has confirmed the very low doses required to disinfect Cryptosporidium and Giardia, while also finding several viruses that have an unusually high D10. As new applications for UV are found, new microbes will be added to existing D10 tables.
A major concern to the UV industry is the issue of reactivation – the apparent ability of some microorganisms to repair the damage done to their DNA by UV, reactivating their ability to infect. DNA repair can occur in a closed (dark) system, but is more likely in open systems under direct sunlight (pho6toreactivation). The dose level and lamp type seem to affect the degree of reactivation, with low pressure (single wavelength) UV lamps appearing to be more susceptible to photoreactivation than medium pressure (multi-wavelength) lamps. A much larger research effort into the area of photoreactivation is required and will most likely be forthcoming over the next 5 years.
A significant amount of research has also targeted the question of UV disinfection by-products, specifically the most common water constituents such as chlorine, bromide, nitrate, ozone, NOM**, and iron. At normal UV disinfection doses no significant disinfection by-products have been shown to form. Research continues with more exotic water constituents.