How to Place Christmas Lights in a Pool Full of Contaminants?

Danilo Bertagna (ESR6)

Hello again! I’m Danilo Bertagna Silva, ESR#6. Today I want to tell you more about my research role in the NOWELTIES project. I’m carrying out the development of ultra-violet light-emitting diodes photoreactor design.

“Ultra-violet light-emitting diodes photoreactor design”… this sounds fancy, but let me break it down to you:

Ultra-violet: this was explained in Camilo’s blog. Ultra-violet is the highest energy constituent of light and it is beyond what our eyes can see. These rays can be very dangerous and are responsible for causing skin cancer, for instance. On the other hand, they are frequently used for sanitation because they can kill bacteria and other pathogens.

Light-emitting diodes: these are the famous LEDs we’ve been using as a replacement for incandescent light bulbs in the past decades. Scientists discovered that some unique materials emit light when an electric current passes through them, and a lot of energy can be saved that way.

Photoreactor: since most people only hear the word “reactor” when Chernobyl is mentioned, it always sounds like something complicated and dangerous. However, a reactor is nothing more than a defined space where a chemical reaction is happening. It can have any shape. It can be a shoe box, an oven, a pipe, a huge tank, a bucket, a petri dish… the prefix “photo” simply means that the reaction needs light to happen.

Design answers these questions: what’s the size of the reactor? What is it made of? How quickly should we add or remove things from it? Should we heat it up or cool it down?

Considering that light is involved, imagine the challenges of someone in charge of illuminating a large swimming pool would have: how much energy should we spend on the lights? How are these lights distributed around the space? Which direction are they facing? Do they need to be on all the time? Should they be submerged or not? Should all lights be of the same colour? And so on and so on…

So this is the point where everything blends together. Although LEDs have been commercially available to illuminate our houses for a while, only very recently, scientists developed LEDs that emit light in the ultra-violet spectrum efficiently. Environmental and chemical engineers were waiting eagerly for this moment because now we can replace mercury lamps, the traditional sources of UV light in the industry, by UV-LEDs.

Why should we bother to do that?

Unlike LEDs, mercury lamps are built from fragile quartz material, demand high voltages, have a short lifetime, and pose a risk of mercury release, a highly toxic substance. Above all that, the most crucial difference between mercury lamps and LEDs for photoreactor design is their dimensions. LEDs can be considered as the typical Christmas lights package: small points that can be arranged in infinite arrays, with each individual source facing any direction in a 3D space. Mercury lamps are much more inflexible: they are cylindrical, and their dimensions vary from centimetres to a few metres. Obviously, the photoreactor design possibilities using LEDs are much larger. And more efficient designs can represent huge shortcuts for more sustainable, energy-efficient processes of water treatment.

Imagine that poor guy, responsible for the swimming pool, having to decide how to illuminate it with Christmas lights, instead of using just one large cylinder? That’s me!!!

The situation gets much more complicated when we consider all the other variables involved in water treatment. Is the liquid in the pool pure water? River water? Domestic wastewater? How does each pollutant present in the pool react when you double the light intensity? Is it worth to spend more energy on it? Can we add something in the pool to make degradation faster? Should we impregnate the pool walls with a catalyst? Is there a risk of creating even more dangerous substances in our process?

These are the questions I have to find the answers to during my PhD.

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