WASH 101: Biological Intervention – Activated Carbon

May 31, 2019

Posted by Chip, Managing Director

Before we get into today’s post about activated carbon, this is your reminder that you’re joining 20 Liters in an ongoing conversation. So, feel free to go back and catch up with us. We’ve already covered each part of the WASH acronym [Water, Sanitation, Hygiene], made sure we have a shared language, and looked into disparities for vulnerable populations.

Now, we’re working our way through a discussion about various solutions to make dirty water clean. We’ve divided the solutions into a few categories:

Physical Intervention: including filtration, adsorption, sedimentation, boiling & distillation
Biological Intervention: including antimicrobial metals, activated carbon & bio-sand filters
Chemical Alteration: including chlorination & flocculation
Electromagnetic Radiation: including UV Light treatment
Sourcing: including rainfall, groundwater, underground aquifers, springs, and human-intervened (bottled, wells or municipal water).

Today, we’re getting deeper into our conversation about Biological Interventions, moving from a discussion of Antimicrobial Metals into the topic of Activated Carbon.

Activated Carbon or Activated Charcoal

Talking about activated carbon or activated charcoal can get really technical, really fast. So, let’s start at the very beginning and try and take baby steps to keep us all on the same page. So, what is charcoal?

Charcoal is the carbon residue that remains after you remove water and everything else from something that is high in carbon. [One more step back, carbon is a chemical element that is very common in all living things.] And while all life forms are high in carbon, when we’re making charcoal, we stick with plants and trees as carbon sources.

Most commonly, you produce charcoal by heating (but not directly burning) wood or other carbon-rich vegetation in an oxygen-deprived environment. Restricting the oxygen is important because, when present, it bonds with the carbon and we lose most of what we’re trying to produce as carbon dioxide. This production process results in granulated carbon.

Granulated carbon is sticky (or, more technically adsorbent), particularly to non-similar particles.  So, it will cause many different types of particles or impurities from water to “stick” as water is passed through the granulated carbon. This includes sediment, pesticides, radon, oils, solvents, PCBs, nitrates, and chlorine.

But, since the surface area of granulated carbon is limited, you have to pass a very small amount of water across a very large amount of granulated carbon to make sure that all of the impurities are actually caught. To solve this problem, we can “activate” the carbon.

What does it mean to “Activate” Carbon or Charcoal?

There are two main processes for activating carbon. Physical activation: expose the charcoal to really hot gasses (1,100° to 2,200° F) like argon, nitrogen, or oxygen. Or chemical activation: impregnate the wood with certain chemicals (like calcium chloride or phosphoric acid) before turning it into charcoal.

What both of these processes actually do is create pits, divots, channels and tunnels through each grain of charcoal, multiplying the available surface area thousands of times over. In fact, when carbon has been “activated”, a single gram has a surface area of over 32,000 square feet (that’s equivalent to half of a regulation soccer field).

The increased surface area of activated charcoal means that we can pass much more water through the system much more quickly and still effectively purify the water.

There are a number of benefits to using Activated Carbon:

Carbon is literally everywhere and producing and activating it is relatively inexpensive.

Activated carbon is highly effective. It has been proven to remove at least 81 chemicals and the list is still growing. Activated carbon is the only filter medium recommended by the EPA to remove all 32 of their identified organic contaminants.

Reusability is also key. Granulated activated carbon can be “regenerated” by heat treatment. This process removes all the contaminates that it has absorbed, allowing it to be used again. [It is important to note that not all activated carbon is granulated. Many solutions also use powdered activated carbon and that cannot be regenerated or reused.]

Finally, activated carbon’s versatility and broad effectiveness makes it a great solution for industrialized areas where chemical exposure is the key risk factor.

But as always, it isn’t a silver bullet:

While you can make charcoal anywhere in the world, activating it takes some industrial availability. So as usual, this solution can face supply chain issues, particularly in rural communities.

Activated carbon doesn’t remove all impurities. In most forms, activated carbon is not effective against totally dissolved solids and metals [like lead]. And activated carbon doesn’t capture bacteria, parasites, or viruses. This makes it an ineffective stand-alone solution for the 2 billion people worldwide who drink water contaminated with feces.

Furthermore, the fact that activated carbon is so good at removing chlorine from water isn’t always a positive. While this could be desirable in some situations, it increases the likelihood of re-contaminating stored water.

Finally, without testing, the user has very few ways of knowing when the activated carbon is “spent”. Meaning when the pores and channels have been clogged and the carbon is no longer adsorbing impurities. In some cases, the taste or odor of the water may worsen. Most providers just set a recommended lifespan, but have no way of tailoring that to specific water sources.

In a nutshell, activated carbon is a really effective tool, depending on your priority contaminants. So we’ll continue to explore combining activated carbon with other interventions, to create highly effective solutions.

Reading list (for nerds):

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