Around the time Galileo Galilei looked through his telescope and first spotted Saturn, another revolutionary idea was being explored when early scientists in 1614 realized that sunlight has powerful chemical properties. That early seed of a theory led researchers to explore the idea through the centuries, leading eventually to today’s ultraviolet disinfection technologies for water treatment.
Ultraviolet disinfection is a key part of today’s municipal and commercial water treatment systems, but the basis for this technology is rooted in discoveries made at a time when fundamental scientific theories were still being solidified and when scientists were sometimes arrested on charges of heresy.
Modern ultraviolet technology stands on the shoulders of flask-wielding experimenters who explored sunlight’s germicidal properties centuries before the germ theory of disease was commonplace.
The history of UV technology starts with Angelo Sala, an Italian physician and chemist. Hoping to show to the world that chemistry had a place in medical science, he started experimenting with powdered silver nitrate (the substance was used on patients at the time as a laxative and as a disinfectant).
“Several of the scientists who were working in the late 1800s shocked me in that they were using what I consider to be ‘modern ideas’ of sunlight,” explains Northwestern University professor Philip Hockberger. “It was humbling to go back and read what they have done. They were really onto something that now maybe we’ll really begin to appreciate.”
Sala realized sunlight turned the light-colored powder black—this discovery also set the stage for discoveries that led to the creation of photographic film.
Sala started out with the idea that chemical reactions could be used to protect people’s health. He couldn’t have known how important his experiment would become to creating a healthier world.
About a century later, in 1801, a German scientist named Johann Wilhelm Ritter built upon Sala’s work and the work of other scientists to set up an experiment to use paper treated with silver chloride to test for invisible rays in the atmosphere. Ritter called them “cold rays” and “deoxidizing rays,” only really understanding these phenomena had something to do with rays that couldn’t be seen with the naked eye. This was the first recorded intentional detection of ultraviolet light.
At the same time, researchers were setting the stage for future ultraviolet applications by establishing what light was actually made up of and how there was much more to light than the visible spectrum.
In 1802, English scientist William Hyde Wollaston showed how light is made up of specific bands of light, building on Isaac Newton’s fundamental observation that visible light is many different colors, and researchers like Joseph von Fraunhofer expanded this idea through the 1800s, cataloguing the wavelengths of hundreds of bands of light and pinpointing which atoms emitted various types of bands.
Scientists grasped onto the idea and development sped forward during the late 1800s. While the US was embattled in its Civil War, European scientists were making leaps toward understanding the complexities of ultraviolet light.
In 1865, Scottish physicist James Clerk Maxwell accomplished his seminal discovery, both a tipping point for the field of photophysics and his own career, by proposing a theory that light, electricity, and magnetism are aspects of the same phenomenon. Maxwell’s equations set up the theory of electromagnetism, which led to essential technologies such as X-ray machines, radios, and, of course, UV lamps.
As fundamental understanding of ultraviolet light became more pronounced in the scientific community, researchers began creating their own artificial ultraviolet lamps to do more experiments, leading to the discovery of unique applications for ultraviolet light.
The first attempts to make lamps created open-arc lamps that also produced UV rays, but the charcoal filament deteriorated quickly. The lamps weren’t made with the specific goal of making artificial UV rays—inventors just wanted lamps for lighting homes and factories. But the carbon arc lamp produced an intense visible light, as well as UV-A, UV-B, and UV-C rays.
Efforts to make a better lamp also resulted in more broad-spectrum bulbs toward the end of the 1800s. Renowned inventor Thomas Edison created a cotton filament lamp that burned longer, didn’t cause carbon monoxide poisoning, and started fewer fires than the fast-burning, loud-buzzing, temperamental open-arc carbon lamps. Tungsten filaments burn even brighter and their light spreads further into the UV spectrum. Inventors created “closed” lamps, made them brighter, and made them safer. Electricity buzzed through the developed world.
Simultaneously, Arthur Downes and Thomas Blunt made a breakthrough for the field of photobiology. They put Pasteur solution in test tubes and were surprised to find that direct sunlight kept the microorganisms (including bacteria) inside the solution from growing for several months. More tests showed specific wavelengths were more effective at killing microorganisms, and violet-blue light was the most effective part of the visible spectrum.
This was significant because scientists were discovering specific methods to kill bacteria at a time when bacteria themselves weren’t fully understood, Hockberger said. “It wasn’t really until the mid-1800s that there was strong scientific validity that bacteria really existed,” he added.
Finally, these discoveries led to UV-specific lamps as the various forms of UV were explored.
The world entered the 20th century awash in light and the promise of discoveries to be made.
UV lamps may have been created for laboratory use, but after a while, people began to recognize that they had immense commercial value. The fledgling beginnings of a water treatment industry began using UV lamps in early forms of disinfection.
The earliest example of this was one of the world’s first water treatment plants, established in Marseilles, France, in 1910. The plant filtered water from the Durance river and used UV lamps as a disinfection method.
Five years later, the US got its first full-scale UV disinfection system for water treatment in Henderson, KY.
But the world was still struggling with waterborne diseases. Cryptosporidiosis and giardia in particular continued to ravage the US and other nations and typically spread via surface water that contained infected feces.
The developments kept coming, but the main device—UV bulbs—stayed essentially the same, getting significantly better as the decades rolled on.
In the 1940s, the invention of neon tubes and low-pressure mercury tubes became an option for UV applications.
The 1970s brought the discovery of disinfection byproducts and concern about treating those byproducts with multi-stage systems. By the 1980s, Canada had created its first UV disinfection system in Tillsonburg, Ontario (ON), for water treatment.
Wayne Lem, municipal market manager for TrojanUV, says TrojanUV was involved in helping create Ontario’s first open-channel UV system. “We developed the first one when UV was used for municipal disinfection,” he says.
By the 1990s, researchers had discovered specific UV doses that could target particularly dangerous disease-causing agents, like Giardia and Cryptosporidium, that can cause outbreaks if spread through a water source. Rates of giardiasis plummeted from the 1970s to 2000s and while instances of the disease still spread via infected water, fewer people than ever are getting sick from it, with 15,000 cases reported in 2012, according to the Centers for Disease Control and Prevention.
“In the early days of UV, it was thought that very large amounts of energy were required to take care of certain microorganisms,” says Steven Day, marketing manager for the UV business unit at Calgon Carbon UV Technologies.
But after an outbreak of Cryptosporidiosis in Milwaukee, WI, in 1993 where 400,000 people were infected and about 60 people died, companies began looking into using UV lamps as a way to treat the parasite that causes the disease, says Day.
The situation in Milwaukee was dire and highlighted how quickly waterborne diseases like Cryptosporidiosis can spread. It was the largest waterborne illness outbreak in US history, and since the 1993 outbreak, Milwaukee’s water utility has invested $417 million in infrastructure, monitoring, and treatment upgrades, the Wisconsin Center for Investigative Journalism reported in 2013.
Several of the city’s pharmacies ran out of antidiarrheal medicine on the first day of the outbreak and emergency rooms were soon overwhelmed with an influx of patients with gastrointestinal issues. Within three days, public health officials issued a boil water advisory when Cryptosporidiosis was pinpointed as the cause, according to the City of Milwaukee Health Department.
Day said Cryptosporidium is invulnerable to chlorine, but specific wavelengths of UV can kill the protozoa. He added that Calgon Carbon filed a patent related to using UV to kill Cryptosporidium after the outbreak.
This shift toward using UV technology for water treatment in the 1990s and 2000s marked an era of safer drinking water, and eventually water quality laws such as the US’s Clean Water Act and the Safe Drinking Water Act made these innovations a requirement in order to reduce instances of water-borne illnesses. UV technology, along with other disinfection methods, makes it possible to meet those water quality standards.
“It’s very important because there are regulations in place, strong regulations, for disinfection and strong enforcement in North America,” says Lem. “Protecting public health is very important.”
The Surgeon General of the Public Health Service authorized the first legislative interaction of the Clean Water Act, called the Federal Water Pollution Control Act of 1948, after a series of environmental and health catastrophes. The dumping of poisonous, inflammable material into Michigan’s Rogue River left the waterway a burning, gaseous inferno. Lake Erie was so polluted the ecosystem collapsed and the lake was left virtually lifeless. The Cuyahoga River in Cleveland looked more like the mythological fire river Phlegethon than a source of drinking water.
While chlorine has been among the go-to methods of disinfection, UV lights were increasingly used through the late 20th Century and are extremely common in drinking water treatment and wastewater treatment processes today. The Safe Drinking Water Act of 1974 specifically pushed US cities to cut back on reliance on chlorine as a drinking water disinfection method due to the discovery of harmful byproducts like trihalomethanes and cancer-causing substances, so UV became a more popular way to provide increased water quality protection while plants reduced their use of chlorine.
So UV technology finally had its long-awaited growth spurt and permeates most areas of the water disinfection industry now as a final polishing step for commercial and municipal water.
Modern UV technology has improved in the past few decades in efficiency, reliability, and power output, but the fundamentals of UV lamps haven’t changed much in recent history, Day says.
“In the last decade, there haven’t been huge changes in the way the system is done,” he says.
The horizontal systems had to have the bulbs submerged and the bulbs had to be protected by another layer, all of which required laborious cleaning, Lem says. Today, maintenance of that system is much easier, he says. “Outside the lamp, there is a quartz sleeve, and it’s important to keep that quartz sleeve clean. You had to lift up the modules or the equipment and manually clean the sleeve,” he says.
The system also had to be kept indoors in the 1980s, but today, UV systems can be placed outside.
But the big change for UV over the past few decades has been how much the bulbs have improved in efficiency, Huynh says.
“One thing that has really changed over the lifetime of UV systems…is really the performance and efficiency of the product,” said Huynh. “If you compare this to a decade ago, the efficiency of the lamps and the ballasts has improved.”
Efficiency has improved with the proliferation of bulbs with different types of pressure—such as the differentiation of low-pressure, high-output lamps for wastewater, and medium-pressure lamps for drinking water, Day says.
Historically, Lem says, UV bulbs only produced about 90 watts. Today, it’s not uncommon to see lamps with 1,000 watts or more.
“You’d need hundreds or perhaps thousands of UV lamps,” just a few decades ago, Lem says. “Every dollar you pay for energy, you get a higher percentage that comes out as UV-C. The lamps are a big improvement today…That translates to much less footprint, [and] much less labor to change lamps.”
Better understanding of UV-A, UV-B, and UV-C wavelengths has helped modern-day water managers choose the best bulbs based on the germicidal properties of the spectrum they’re trying to achieve, Day says. Also the industry’s understanding of how water temperature affects efficiency of lamps has increased in the past decades, making it easier to get the best output from your chosen lamps.
While LED lights haven’t made their grand debut into the UV space properly yet, experts say they expect LED lights to be the next big innovation in the UV industry—although it’s anyone’s guess as to when the technology will permeate the market.
“LED light bulbs have the potential to use a lot less energy,” says Day. He says he looks forward to “the advent of LED technology that can replace these mercury vapor lamps that we’ve been using for years and years.”
Lem says he expects LED lamps will become an eventual innovation within the water treatment industry, but right now they’re only used on a limited basis within the industrial side of the industry.
The efficiency of LED lights could make it possible to do the same job with fewer lamps, which fits into the current industry trend of increasing efficiency and reducing overhead.
“When you look at the adoption of UV tech today in municipal plants, one of the biggest challenges is maintenance,” says Lem. “The trend in UV technology is to provide less equipment.”
But LED technology is still a ways away from being at the level where they could be used on a massive basis for UV disinfection. Right now, LED bulbs aren’t efficient enough to be cost-competitive and still require quite a bit of manual labor to maintain.
“A lot of funding, a lot of research needs to go into the LED space,” he says.
Day says he sees the future bringing more interest in ultraviolet disinfection in international markets. While most of the developed world is already using UV lamps for water disinfection, it’s much more common to see developing nations rely on chlorine alone for water treatment.
“I think it will increasingly be used for disinfection around the world as more of a standard, and it’ll be more pervasive for drinking water disinfection,” he says.
Day says UV technology is currently seeing a “big uptick right now in India, China, and other emerging markets [such as] South America—Brazil, Peru.”
Automation has jumped by leaps and bounds in the water treatment industry over the past 10 years, and there are now machines to automatically clean UV lamps, change lamps, and monitor their usage. However, the advent of artificial intelligence makes it possible to imagine a day in which these systems are self-sufficient and self-monitoring, Huynh says.
“One thing I do see on the horizon is the concept of more advanced automation and artificial intelligence,” he says.
There could one day be automated UV bulb changers with machine learning capabilities that alert the operator when a bulb is declining in efficacy, or the bulb changer could realize a specific bulb is about to burn out and autonomously replace the bulb on its own, shooting off an email to the operator that the new bulb is installed.
Imagine a day where operators can manage water treatment plants across the world from a central location, or where operators can have instantaneous monitoring of the quality of the water at each step in the treatment process through internet-connected remote sensors.
Huynh says remote and automated monitoring and diagnostics could be an integral part of the future of UV technology.
“We really think those type of things will be the future. The majority of UV technology is in municipal space, so less is going on there. In the industrial markets, we really see this going in that direction,” he says.
Lem says states like California are starting to rely more on UV since potable wastewater reuse has become more popular in the drought-ridden state. Other municipalities in the West use variations of wastewater reuse, such as Las Vegas, where 90 million gallons of reclaimed water is sent to the Las Vegas Wash daily to trickle through the wetlands and back to streams to be treated for drinking water, the Las Vegas Sun reported in 2014.
“That’s starting to be common in California, and we see it worldwide since we’re a global company,” he says.
Sometimes to move into the future, one has to remember the innovations of the past. Hockberger says while UV technology has advanced and the water treatment industry has grown by leaps and bounds, there are still areas of the globe that are facing the same problems as these US scientists he studied from the 1800s.
He says there is even a renewed interest in using plain sunlight to disinfect water in some developing nations, but few people realize this idea is hundreds of years old, so they don’t have to recreate the wheel, so to say.“People live all over the world, and many of us struggle with having clean water, so how do we solve that problem?” he says.