Cost-effective disinfection is important to all water treatment plants, but especially for smaller water systems. Low-flow systems (defined generally as 1 mgd or less) looking to UV disinfection have an alternative in a technology from UV Pure Technologies of Toronto, Ontario.

Crossfire Technology places the UV lamps out of contact with the process flow, rather than submerged in the water being treated. The manufacturer states that the system delivers a disinfection dose 2.4 times higher than with a conventional system with the same energy input and cost.

The systems also occupy a small footprint and are designed to be easy to install, start up and service. Mark Houghton, director of engineering sales in Canada for the company, described the technology in an interview with Water System Operator.

wso: What would you say are the main differences between this technology and the kinds of systems most widely used in drinking water treatment?

Houghton: There are three primary differences. While conventional systems have the UV lamps submerged in the water and protected by quartz sleeves, we remove the lamps from the process stream. The bulbs are mounted in air, and the energy is focused on the water column. We also use dual sensors that allow us to monitor both lamp intensity and water quality.
Third, all our models have a self-cleaning mechanism. Self-cleaning is not new and is common on larger conventional systems, but we believe we are unique in offering that capability across the board in our low-flow systems.

wso: What is the flow range that this technology supports?

Houghton: Our systems are modular. The largest module treats 30 gpm. We can multiplex those modules on common headers to meet treatment needs up to 1 mgd.

wso: What makes this technology well-suited to drinking water applications?

Houghton: The dual sensors provide an added layer of safety by monitoring both lamp intensity and energy throughput through the water column, so that we can calculate net UV transmittance. That’s important because the performance capacity of UV systems depends on the UV transmittance of the incoming water. The higher the transmittance, the less energy is needed to achieve a dose that delivers the desired effluent quality.

wso: How do the dual sensors actually work?

Houghton: As we said earlier, our UV lamps are mounted in air. One sensor is aimed directly at a bulb. Because there is nothing but air in the light path, we get an accurate measure of how much energy the bulb is emitting.

Then by having a second sensor aimed at the water column with a bulb on the other side, we can measure the amount of energy coming through the water. That allows the system to calculate net UV transmittance. The system has onboard diagnostics, so that alarms will let users know if they have a lamp problem, or an overheating issue, or a water-quality issue. They don’t need to disassemble the system and go through an iterative process to determine the source of the alarm.

wso: What is the basic structure of the system where treatment takes place?

Houghton: The system sits in a vertical orientation. There are three columns. The outer two columns contain the UV lamps. The center column is a thick-walled quartz pipe through which the water passes. The water never actually contacts the lamps.

An additional benefit of having the bulbs mounted in air is that we can keep them cooled and maintain the optimum temperature by using temperature sensors and blowers, and in some cases by relying on natural convection for cooling. That keeps the lamps at their optimum output even during no-flow or low-flow situations. When UV bulbs are pushed outside their optimum temperature range, their output can drop by up to 50 percent.

wso: What accounts for the increased energy this system imparts to the water?

Houghton: We use low-pressure, high-output lamp technology, which has considerably lower energy consumption than medium-pressure lamps. In addition, there are elliptical reflectors around the outsides of the lamps that help focus all the UV energy on the water column. Having those reflections, we get 2.4 times the UV dose for every watt of input.

The reflectors also help alleviate a problem known in the industry as live transfer, which occurs when particles or pathogen cysts float through the water close to the bulb and their shadow propagates outward. Anything that travels through the UV system in that shadow has the potential to miss being treated. With two bulbs outside the water column and elliptical reflectors surrounding the entire reactor, light enters the water column at every conceivable angle, so there is no risk of shadowing or live transfer.

wso: How does the self-cleaning mechanism work?

Houghton: We run a stainless steel shaft down the center of the quartz column. It has blades similar to squeegees that are torqued against the inside of that column. When the shaft turns, the blades scrape off any scaling. It’s a fairly simple architecture. The cleaning cycle operates every four hours or when the sensors detect a drop in UV energy through the water column.

wso: What is the installation process like for this technology?

Houghton: Because these units take up vertical rather than horizontal real estate, their overall footprint is very small. For installation, we use flex hoses to connect to the castings at the top and bottom of the unit. Just screwing on the flex hoses instead of hard piping makes installation easier.

Startup is very simple — it’s plug and play. The units plug in, they start up, and they’re self-sufficient. There’s no reason for extensive commissioning testing or validation because the units are meant to be fail-safe. They have the dual sensors and the alarms. They come with shutoff valves that will shut the unit off in the event of an alarm that would suggest treatment is not sufficient.

wso: What about ease of maintenance?

Houghton: Another advantage of our technology is that to change the bulbs you don’t have to isolate and drain the system. Because the bulbs are in air, you just open up the system, pull the old lamps right out, and slide the new ones back in.