#6: Activated Carbon Filtration
Here’s where it gets a little complicated. Carbon filters come in many different shapes, forms and sizes. They can be infused with sterilizing agents, they can operate mechanically and chemically, they can remove various different contaminants depending on their form, but the bottom line is that activated carbon is the most effective form of water purification out there. Activated carbon is a form of carbon processed to have small, low-volume pores that increase the surface area available for adsorption or chemical reactions to occur. Adsorption is a chemically reductive process that pulls the negative ions out of water using its positively charged surface. These contaminants collect at the surface of the filter and eventually require it to be replaced.
There are four main types of carbon filtration:
Granular Activated Carbon (GAC)
- How it Works: In comparison to powder activated carbon, GAC pores have a larger diameter and are more loosely organized. Modern GAC products are made from coconut shell, coal, wood, lignite and/or petroleum products. They utilize the process of adsorption to pull contaminants out of water.
- What it Removes: Undesirable taste, odor and color, common disinfection byproducts (THMs), organic contaminants like chlorinated solvents and other industrial pollutants, pesticides, herbicides, insecticides, fungicides, algaecides and select heavy metals such as lead and mercury.
- Advantages: High capacity for the reduction of aesthetic contaminants such as tastes, odors or colors. Serve well as pre-filters to carbon block filters or other purifying methods which more effectively decontaminate water.
- Disadvantages: Because they are not tightly packed together, water is easily able to channel through them, reducing its exposure time to the carbon and lowering the rate of adsorption.
Power Activated Carbon (PAC block)
- How it Works: Pulverized carbon is pressed together to form a highly dense, microporous carbon block. This densely compacted block mechanically filters particles down to 0.5 microns, and then utilizes the process of adsorption to chemically pull contaminants out of water.
- What it Removes: Disinfection by-products (DBPs), volatile organic compounds (VOCs), PCBs, MTBE, lead, chlorine, benzene, chloramines, Giardia, Cryptosporidium, asbestos, turbidity, and particulates.
- Advantages: Carbon blocks don’t allow channeling or bypass as easily as GAC filters, allowing for a greater rate of adsorption.
How it Works: Carbon is impregnated by silver, which is particularly effective at removing bacterial contaminants. Silver exhibits a self-sterilizing property called the oligodynamic effect that, although not fully understood, is recognized as an effective method for controlling microbial growth.What it Removes: Microbes Advantages: Sterilizes water using silver at a level 1000 times lower than an amount toxic to humans.
Bead Activated Carbon (BAC)
- How it Works: BAC is made from petroleum pitch and supplied in diameters from approximately 0.35 to 0.80 mm. Its spherical shape makes it preferred for liquidized bed applications such as water filtration. (Liquidized/fluidized bed: A body of solid particles through which gas or liquid is blown or pumped upwards causing separation and movement; a means of increasing reaction rates.)
- High-fill capability: Due to the spherical shape of BAC, it allows you to fill a container or filter with considerably more carbon than with GAC. This increased density extends the life of the filter.
- High Flowability: The beads’ spherical shape allows for a high flow rate without concern for pressure drops. Both air and liquid move freely through the charcoal beads. This allows for complete contact with the entire surface of the beads.
- Low carbon dust: BAC generates less carbon dust due to a bead formation process that does not use binder.