Ways UVC LED Technology Is Impacting Compact Water Purification Equipment

ByBNW TEAM

Water purification equipment is shrinking.

From countertop dispensers and under-sink systems to RV water lines and smart kitchen appliances, manufacturers want to pack as many treatment features as possible in the smallest amount of space available.

This trend creates new opportunities for ultraviolet technology.

Traditional UV water treatment has existed for decades. The vast majority of systems use mercury-based germicidal lamps operating in wavelengths close to 254 nm. Those systems will remain crucial, particularly in whole-house and high flow rate applications.

Compact equipment requires a different set of capabilities.

Limited space, low-voltage electronics, intermittent water flow, and limited installation space force manufacturers to look at UVC LEDs as a means of adding microbial control to compact water purification products.

Reasons Why Compact Equipment Requires New UV Light Sources

A traditional UV reactor consists of several components: a lamp, quartz sleeve, chamber, power supply, etc.

This setup works perfectly fine in many existing water treatment products. However, it becomes problematic to implement in products where even a single millimeter of space counts.

Consider a countertop water dispenser.

This product already incorporates:

  • Sediment filtration
  • Activated carbon
  • Reverse osmosis
  • Pumps
  • Water tanks
  • Sensors
  • Cooling and heating elements
  • Control electronics

An additional large UV reactor may interfere with design of the rest of the system.

The main advantage of LEDs is the extremely compact light source.

A small LED module can be mounted directly at the water outlet, placed in a small flow chamber or at the last stage of water purification.

This is one of the reasons why UVC LED water treatment is gaining popularity among water purifier manufacturers producing smaller point-of-use products.

Instant On/Off Switching Enables New Control Options

Another feature of LED technology is instant switching.

UVC LED can turn on and off instantly. This ability allows connecting UV system with a flow sensor that turns on the LED once water starts to flow and turns it off as soon as flow ends.

This is useful in equipment where UV treatment operates only during a relatively short period of time.

The examples of such equipment include:

  • Drinking water dispensers
  • Faucet-mounted purification systems
  • Under-sink products
  • Coffee machines
  • Ice makers
  • RV water systems
  • Marine water systems

UV LED treatment can be turned on and off by water flow instead of continuous UV treatment in this case.

This feature enables new design opportunities for low-voltage and battery-operated products.

Compact Size Enables Low-Voltage Applications

Many compact water purifiers work on DC voltage.

Thus, a UVC LED can be designed for popular low-voltage power systems like 12V or 24V.

This increases the compatibility of UVC modules with products that already have DC-powered pumps, sensors, control boards, etc.

For mobile applications, this becomes an essential feature.

An RV, yacht or portable water purifier has its own power system that is different from the electrical system in a whole house UV reactor.

In such cases, a small DC-powered UVC module increases designers’ freedom in design of the whole product.

Small Size Does Not Necessarily Mean Simple Design

The compactness of UVC LED does not mean automatic success in water treatment.

The task of any UV system is delivering sufficient amount of UVC energy to the flowing water.

Thus, the critical parameters are:

  • UVC wavelength
  • Radiant power
  • Irradiance
  • Flow rate
  • Exposure time
  • UV transmittance
  • Water quality
  • Chamber geometry
  • LED position
  • Optical path
  • Thermal management

This is why comparing systems by the electrical power is misleading.

A 4 W electrical system does not necessarily provide 4 W of UVC optical output.

Electrical and optical powers are different characteristics.

UV Dose is More Important than Electrical Wattage

One of the most important concepts for microbial control is the UV dose.

Simplified definition:

UV dose is related to the irradiance multiplied by the exposure time.

If water flows through the chamber faster, it spends less time under UV source.

This means that the increase of flow rate without changing other parameters can decrease the dose provided by the system.

The same concept explains why two water purifiers based on the same UVC LED will demonstrate different results.

One of them has good geometry of the flow chamber with the water passing closely to UV source.

Another has poor geometry, dead zones or optical path that provides less exposure for a portion of water.

The LED is just one of the components.

Water Quality Can Change UV Performance

Another parameter affecting UV system performance is UVT, or UV transmittance.

Clean water transmits ultraviolet energy better than the water with turbidity, suspended particulate matter or certain dissolved substances.

The presence of those substances can also provide shielding of microorganisms from direct exposure.

Thus, UV treatment works best as one of the stages of water treatment instead of filter replacement.

A typical water treatment sequence used in compact equipment is:

Sediment filtration → Carbon or membrane treatment → UVC disinfection

Each stage has a different goal.

The UV LED system cannot physically remove sand, sediment, hardness, heavy metals or most of dissolved chemicals from the water.

Disinfection is the primary purpose of the UV treatment.

Point-of-Use Equipment is a Natural Home for UVC LEDs

One of the most promising fields for UVC LED systems is point-of-use water treatment.

In the last outlet, the flow rates are lower than in the whole-house systems and installation space is limited.

This makes UV systems even more interesting.

Potential locations of UV treatment include:

  • The outlet of an RO purifier
  • Drinking water faucet
  • Countertop dispenser
  • Refrigerator water system
  • Beverage machine
  • Commercial drinking water dispenser

UVC treatment close to the water consumption point may also help manufacturers to control potential microbial growth downstream after previous stages of filtration.

However, the specific design of the UV treatment system depends on the water path, materials and operating conditions.

Thermal Management is Still Critical

LED is compact, but it generates heat.

The high junction temperature can affect UVC output and reliability of the module.

Therefore, a reliable UVC LED system should have a good thermal path, which can include:

  • Aluminum or copper PCB
  • Metal housing
  • Thermal interface materials
  • Heat sink
  • Water contact heat exchange
  • Current control in LED driver

It is especially important in enclosed appliances where air movement can be limited.

In this case, the LED, PCB, chamber and housing should be considered as a single thermal system.

Flexibility of Mechanical Design is Another Advantage of UVC LEDs

Lamps are normally long and tubular.

LEDs do not have such mechanical limitations.

LEDs can be arranged along the water path in different configurations.

The manufacturer may use:

  • One compact LED
  • Several LEDs around the chamber
  • Circular PCB
  • Linear LED array
  • Multi-LED custom array

The optics can be adjusted according to the chamber.

This flexibility allows designing UV treatment around the product and not vice versa.

Validation is More Important Than Marketing Percentages

Water treatment equipment often advertises numbers like “99.9%”, “99.999%” or other values of microbial reduction.

However, those numbers become meaningful only if the test conditions are specified.

Such parameters as target microorganism, water quality, UV dose, flow rate, and reactor geometry can affect performance of the system.

The result obtained at 2 liters/min cannot be automatically taken as a performance level at 5 liters/min.

Commercial development should be based on validation of the finished system at operating conditions.

In the United States, manufacturers developing microbiological water treatment systems should consider standards like NSF/ANSI 55 depending on the product and marketing claims.

The component performance and finished system certification are not the same things.

Future Directions for UVC LED Technology

The rapid research and development of UVC LED technology caused by the improvement of optical output and drop of cost per UV power unit found new applications for UVC LEDs in point-of-use water treatment and is now considered for larger scale water treatment systems.

The immediate goal is not to replace traditional UV lamps.

Instead, UVC LED opens new applications where traditional lamps cannot be used.

These are applications requiring:

  • Small dimensions
  • Low-voltage operation
  • Fast switching
  • Intermittent operation
  • Flexible placement of the LEDs
  • Sensor control
  • Custom integration with the water path

This makes UVC LEDs more relevant to the next generation of appliances.

Engineering a Complete System

Choosing a UVC LED is the first step in the design of the equipment.

Successful design requires integration of optical, electrical, hydraulic and thermal subsystems.

Before starting OEM project, useful information includes:

  • Target flow rate
  • Water source and quality
  • Microbial performance requirements
  • Installation space
  • Input voltage
  • Water pressure
  • Connection size
  • UV wavelength
  • Operating time
  • Thermal conditions
  • Certification requirements

System approach is becoming more important as water purification becomes smaller and more intelligent.

Thus, UVC LED technology not only reduces the size of the UV lamp.

It gives the designers a completely new tool for implementation of the UV treatment in the water purification equipment.

For compact purification equipment, this can be the key aspect.