Last month, our WASH 101 series finally got to the fun part of discussing the global water crisis – talking about solutions. And we’re going to continue that conversation over the next few months, with the help of 20 Liters’ Managing Director, Chip Kragt.
In case you’ve missed anything along the way, please take the time to catch up with us… we’ve already talked about each part of the WASH acronym [WAter, Sanitation, Hygiene]. We made sure we understand the shared language of the WASH sector and we’ve touched on some of the disparities that are masked by global statistics.
But assuming that you’re caught up with the conversation, I’ll turn it over to Chip!
Now, in our last post about water sourcing, we gave you this list:
- Physical Intervention: including filtration, adsorption, sedimentation, boiling and distillation
- Biological Intervention: including slow-sand, activated carbon, antimicrobial metals
- Chemical Alteration: including chlorination, flocculation and iodination
- Electromagnetic Radiation: including UV Light treatment
- Sourcing: including rainfall, groundwater, underground aquifers, springs, and human-intervened (bottled, wells or municipal water).
So, let’s keep working from the bottom of the list and let me try to convince you that just leaving water outside in the sunlight is a feasible form of purification.
Electromagnetic Radiation [also abbreviated EM Radiation] can sound really intense and reminds me of something you might find in a grey DeLorean under a clock tower in a lightning storm. But, EM Radiation is just how we describe waves of electric and magnetic fields. [You can find a picture of the full spectrum here.] It includes all visible light, radio waves, gamma rays, and X-rays. Don’t over-think it, the physics aren’t the point here. Just know that some wavelengths on the spectrum are dangerous to living organisms.
It’s time for a vast oversimplification from Amanda, because when you say the word “physics”, I feel out of my depth with science [#istoppedwithchemistry]. So, here’s an example to remind you that we’re all fairly familiar with Electromagnetic Radiation and the damage it is capable of: when you go to the beach, you wear sunscreen [I hope] because UV rays from the sun [a kind of Electromagnetic Radiation] can damage your skin cells and give you a pretty painful sunburn.
Like all living things, bacteria, viruses and protozoa require certain conditions to survive. In this case, we need an adequate temperature range and a limit on our exposure to radiation. But, if our goal is to kill off some living things that make us sick, all we need to do is mess with those variables.
There are two levels of intensity here, let’s cover them individually:
Ultraviolet Germicidal Irradiation (UVGI): High intensity
That’s a mouthful. How does this magic work? Short-wave ultraviolet light reacts with oxygen dissolved in the water to produce oxygen free radicals and hydrogen peroxides that destroy nucleic acids (DNA stuff), killing or inactivating the pathogens. This process can be used to purify food, water or air. Yeah, intense. Crank up the UV radiation and kill off the bad stuff.
However, the ozone layer blocks most of the short-wave UV light from reaching the Earth’s surface, which is great for us because we don’t want the radiation to destroy our DNA. But, if we’re trying to use it to kill the pathogens, we have to use UV-emitting lightbulbs to increase the radiation levels (like mercury-vapor lamps).
Solar Disinfection (SoDis): Low intensity
This one is easier to conceptualize. Just take some clear (not cloudy) water, lay it on a dark surface on a sunny day and let it sit for a few hours. Use exposure to the sun to heat up the water close to boiling (which breaks down pathogens) and use what little UV radiation does reach the Earth’s surface to attack the pathogens.
SoDis is a highly used and highly recommended decentralized, point-of-use treatment option because its inexpensive, flexible and great for areas of the world with lots of sunlight. There are some catches, though. The containers need to be as clean and clear as possible to allow as much sunlight as possible. They also can’t be too big or deep so the sunlight can permeate all the way through.
Why doesn’t this work everywhere and all the time naturally?
The eagle-eyed among you will already be saying to yourselves: “I’ve seen the pictures of the swamps in Rwanda, that water is not clear at all.” And you should pat yourselves on the back. The reason SoDis doesn’t just naturally solve the global water crisis is turbidity. Particulates in the water protect pathogens from exposure.
So, in order for SoDis to work, our first requirement is very low turbidity. This often means we need to utilize another intervention like filtration, flocculation or sedimentation before our EM radiation will be effective.
Our next requirement is lots of sunlight (or just UV radiation). Weak UV sources, cloudy days, cold weather all play a part in keeping the water from heating up (for SoDis solutions) and further diminish the creation of those peroxides we need to destroy the biological pathogens.
If we’re going the more intense route and manufacturing the conditions we need to effectively use EM Radiation utilizing the UVGI approach, we’re going to need steady electricity and a source for UV-emitting lights.
Finally, exposure time is a factor. The intensity of the UV radiation, the depth of the water, and the flow rate of water in moving systems all add variables to the equation. With clear water, passed shallowly across a quality UV-emitting light, it can take as few as 10 seconds to kill bacteria. On the other end, using the SoDis method on a cool, cloudy day too far away from the equator might never get the water warm enough or exposed enough to make any difference. Because of all of these variables, it’s hard to know if you’ve done it long enough without testing.
Arguably, the largest downsides are:
UVGI: often involve technically complicated systems that are electricity dependent and must be carefully monitored both for use and results
SoDis: Weather and water-quality dependent, and you’re still guessing at exposure times unless you periodically test for results.
Have we sparked your curiosity?
That’s your introduction to Electromagnetic Radiation. I believe we covered the basic pros and cons for EM radiation interventions, but if you like to go down rabbit holes, here are some interesting trails to follow: