A school in Oregon discovers that UV turnkey systems are simple to install and easy to maintain.
By Carol Brzozowski
There are a variety of reasons that can prompt an organization to explore onsite ultraviolet (UV) wastewater treatment. As chlorination falls out of favor, UV treatment stands poised to fill the treatment gap left behind. Now that UV treatment can be incorporated into a turnkey system, its potential seems endless. Whether for a retrofit or a completely new installation, UV treatment has become the weapon of choice for project managers looking to update and streamline their onsite treatment systems.
Across the country, many companies are already experiencing the benefits of turnkey UV treatment systems. For managers at Atlantic Solutions, a Portsmouth, RI, company that designs, installs, and operates decentralized wastewater treatment systems, the decision to try UV treatment was based on its need for an effective, easily installed, and easily maintained solution to reduce fecal coliform counts.
“Maintenance is a huge issue, and anything that can extend the time between required maintenance intervals gives you more reliable results and a more reliable system,” says Bob Johnson, Atlantic Solutions’ vice president.
Barbara Bradley, president of Advanced Onsite System in Escondido, CA, favors UV systems because “you can install them in a parking lot—really, anywhere in the ground,” she says. “It takes up very little room and can be essentially installed with just a valve-cover box over them. This makes them very flexible on where to put them.
David Lowe, an onsite wastewater specialist for H.D. Fowler in Bellevue, WA, says the UV units are requested in septic systems “primarily because of a regulatory trigger when we’re trying to meet a certain treatment level with fecal coliform counts.
“Most of our treatment systems that go in the ground don’t have a problem meeting the organic reduction levels, but it’s the pathogen reduction or the fecal coliform removal that is becoming the critical issue,” he says.
Lowe says UV has become the most popular disinfection method on the market.
“Depending on what part of the country you’re in, chlorine is fading out; but where we work, chlorine is not used for the most part,” he adds.
Lowe outlines UV’s benefits: “There is no residual, and as far as handling the light, you don’t have issues with making sure you have to have rubber gloves or get splashing chemicals into your eye or elsewhere on your body.”
As far as the drawbacks of UV, Lowe says, “You’ve got a fairly sensitive electrical device in a wet space. The bulbs are fragile, so they can be broken. You are dealing with ultraviolet light, so if you look directly at the light there can be some eye damage.”
Power outages also can create a problem, he points out. “People continue to use water during power outages. And if things aren’t installed properly and water gets in where it’s not supposed to be, it can start shorting things out and maybe ruining equipment, depending on how it’s been installed,” he says.
But for service providers familiar with the technology, “It’s pretty much trouble-free,” Lowe notes.
Bright Lights, Big Treatment
Brian Rabe, a senior soil scientist with Cascade Earth Sciences, recently specified the Salcor Model 3G ultraviolet disinfection unit for a retrofit and has been pleased with the results. The UV system was installed last summer as a retrofit into an existing setup at the site of a school located outside of Salem, OR. The high school serves a number of small farm communities and is not located anywhere near a municipal sewer hookup.
Here’s how the system works: The UV light source for disinfection is mounted in a sub-assembly with passage through the top of the riser pipe for servicing. The light source is mounted in the center of an anodized aluminum frame dividing the disinfection chamber in half and is sealed against the inner surface to prevent flow bypass. The system is designed so that wastewater entering one side of the unit flows vertically downward, makes a 180-degree turn, and then flows vertically upward and out of the other side of the unit to give the fluid proper exposure time. A clear, fused-quartz tube surrounding the UV light source controls the lamp surface temperature. A clear Teflon film covers the tube for minimal surface fouling. This combined feature enables the UV light source to operate continuously.
The unit is rated at 3 gallons per minute (gpm) or 4,320 gallons per day for what Jim Cruver, president of Salcor Inc. calls “not-so-clean effluent” with a five-day biological oxygen demand (BOD) and total suspended solids (TSS) of less than 30 milligrams per liter and a 99.9% fecal coliform reduction. The unit is rated at 6 gpm for a “cleaner effluent” of less than 10 milligrams of BOD and suspended solids, Cruver adds. The unit was subjected to NSF Standard 40 tests in combination with 13 different advanced treatment units, prompted by the State of Washington.
The test profile, coupled with a collection of disinfection data not covered by Standard 40, was the basis of protocol developed by the Washington State Department of Health to create a list of approved technologies for new projects. Other states, such as Ohio, Oregon, and Minnesota, are following suit with similar regulatory issues, Cruver notes.
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Photo: Owen Lloyd |
| South Salem, OR, in winter |
The school had been at the site for more than 50 years, and the installation of the UV system was part of a substantial upgrade, virtually a complete replacement of the wastewater treatment system that was serving not only the existing school but new buildings currently under construction, says Rabe. The assembly includes two parallel units, where the flow runs from a single pipe and then splits, going around either side of a “T” configuration to the other side, Rabe says.
Water quality was a primary consideration in the work, Rabe notes. “This all relates to Oregon’s onsite sewage treatment system rules effective in March 2005,” he says. “With those new rules, there came a new treatment standard modeled after treatment standards already in place in Washington.”
Oregon is unique in that it recognizes two different water table environments, says Rabe.
“A lot of states I know view the water table as a water table … period. But Oregon makes a very clear distinction between what is termed a temporary water table and a permanent water table,” he says.
That often draws extensive discussions among hydrologists, geologists, and others about whether such a line can be drawn. Rabe says a simple description of a temporary water table is one that is present on some kind of layer that restricts the flow of water.
“It’s a traffic jam for water molecules; they can’t get through this layer fast enough in relation to rainfall or lateral movement,” he says. “So a water table forms, but during the drier time of the year, it totally disappears, whereas a permanent water table rises and falls with the seasons year-round. They treat the permanent water table with a higher level of protection than the temporary water table when it comes to buffers and setbacks.”
The site on which the high school is located has a lot of gravel on the soil with a network of irrigation ditches, Rabe notes. “In the winter, we get a lot of rainfall around here, and there’s a water table,” says Rabe. “When the summertime hits—just when you think it ought to go down—they turn the irrigation ditches on, and there’s still water being fed into gravelly soils throughout the summer. So the water table then rises and falls but is pretty much consistent throughout the year.
“If we applied the rules strictly, we clearly needed to meet the new treatment standards to be able to work with those soils with that soil environment there,” Rabe says.
Part of those considerations focused on the shallowness of the area.
“The distance from what is deemed the bottom of the treatment zone—the bottom of the trench if it were a standard drain field—to the high point of the water table is really what we have to measure,” Rabe says.
“In the temporary water table, we can basically be just above it, although we can’t go into it. With the permanent water table, we have to have between 1 foot and 2 feet of separation in any amount of the soil.
“In this case, we decided to achieve the higher level of treatment, because without that, we’d have 4 feet of separation, which we did not have. So the other factor that blends into this to help achieve separation is we went shallower in the soil profile, using subsurface drip distribution as opposed to standard drain field distribution.”
The only other options to the UV system would have been ozone and chlorination, Rabe points out. “Working with a system where we are relying on biology and residual effects of chlorine in the environment and the biology to rely on for additional treatment aren’t necessarily very compatible,” he says.
Storage and handling issues, as well as pumps, were other concerns “making it very complex,” Rabe says. Yet based on previous experiences he had with UV in retrofit work, Rabe was somewhat hesitant. But after speaking with Cruver, he saw differences between Salcor’s product and others, he says.
The other project site had been designed to operate on the discharge pipe under pressure, so when the pump came on, the unit had to work at a higher rate given some treatment system complications upstream.
“The lenses would get coated, and there wwas a host of other issues that were probably complicated by the inconsistent water quality ahead of that particular system,” Rabe says. “But in this case, the Teflon coating on the lens and the fact that this was designed to operate on the gravity design system made a lot of sense from a simplicity standpoint.”
By controlling the flow rate upstream of the unit and addressing treatment issues with a secondary treatment system of a recirculating gravel filter, Rabe was able to help create a successful wastewater treatment process onsite that has yielded favorable results on effluent samples. A recent sample posted less than 0.1 per 100 milliliter on fecal coliform, a BOD of 9.8, and TSS of 4.
“That’s helpful in terms of the system having such a high quality and high clarity of water coming through there,” says Rabe. “The lamps have the opportunity to do their job well.”
The school’s onsite wastewater project was financed by a bond measure that was passed to construct new buildings and do improvements.
“System improvements were prompted by documented failure of the previous system, although like a lot of systems built in similar soils, the classic definition of failure where sewage is coming to the ground surface in many cases doesn’t happen in some of these gravelly soils because it is tough to pull that gravel. Although treatment tends to be achieved, it certainly is not at an acceptable level,” Rabe says. “This system is a dramatic improvement in almost every respect over the sewage system that had been serving various parts of the campus for anywhere from 30 to 50 years.”
The Road Ahead
One of the challenges of taking UV to the market is that its initial costs are higher than chlorination, so in areas that are not highly regulated, property owners tend to go for the less expensive route, Cruver says.
“A lot of people are aware of some of the dangers of chlorination from a health standpoint, but some states don’t regulate the chlorinators, so chlorination is done incorrectly,” he says.
“Another problem is a lot of homeowners don’t add the chlorine that’s required, so there’s a public-health problem if they don’t do it.”
Some states, such as Washington, permit chlorination but require dechlorination as well.
“If you do it right, it’s going to be a lot more expensive than ultraviolet,” Cruver notes.
Disinfection standards also drive what type of unit is used, Cruver notes. “UV is not used on everything out there,” he says. “There are a lot of cases where you can depend on the soil to rid itself of pathogens, such as if you’re sitting out in the middle of 160 acres and the soil percolates well but not too well so that it gets into the groundwater. Then it’s perfectly fine to dump it in there with no disinfection.
“But if the groundwater table is high and not too far from the surface and the soil percolates too well—such as in a limestone area where there may be passages—it will get it into the groundwater even though the groundwater might be quite a ways down,” he adds. “Also, if you are near streams or lakes, you do need to disinfect. The states usually have different levels of disinfection, and it’s left up to the design engineers to pick what level is necessary. Many of the projects are reviewed by sanitarians as well; they would have the final say on it.”
Five years ago, UV was considered unique, Lowe says.
“Now it’s so ‘everyday,’ it’s not so unique anymore. It’s pretty much ‘plug and go.’ That’s where the market is now,” he says.
Carol Brzozowski is a journalist in Coral Springs, FL.
OW - January/February 2008
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