The main vision behind the MUV Adaptable Water Filter was to design a filter system that adapts first, to water contamination and second to how the user intends to filter their water. We are using some very innovative filter technologies but one that is often overlooked is the Activated Carbon Fiber (ACF). Most people think this is the same activated carbon that is found in most every other water filter on the market but this isn't the case.
Let's review the differences between the two most common filters on the market and why ACF is far superior.
Most Common Activated Carbon Filtration Types
Most filters that use activated carbon are using it in either block format or in granular format. Block Activated Carbon (BAC) is manufactured by fusing together smaller activated carbon particles to form one large solid filter block. The intricate maze developed inside a block of carbon is where the filter action happens. The other common use of activated carbon is granular or powdered activated carbon (GAC or PAC). GAC, PAC and BAC are made from a variety of carbon based materials such as coal petroleum nut shells (coconut is very common) or fruit pits.
Flow Rate VS Effectiveness
Carbon filtration works on the principle of absorption. As water flows through a carbon based filter, contaminants are attracted to and held (absorbed) on the surface of the carbon particles. The structure of these carbon particles is the critical element which determines the effectiveness of the absorption.
Block Activated Carbon filters are most common in pressurized systems (household) and are found in some very cheap low-end water filters. BAC filters are simple to manufacture and because of their overall structure generally ensure that water passes evenly throughout the structure to ensure that the entire surface area of the filter is utilized. Block filters generally have fairly low flow rates since it is hard to draw water through the dense structure of carbon. The positive aspect of the low flow rates is that the water has longer contact time with the carbon. More contact time results in greater filtration. The downside is that the pressure required to force water through the block requires slow flowing and hard to use pumps or extremely slow gravity type systems.
To increase flow rates and lessen the amount of pressure required to move water through the filter, many manufactures use Granular Activated Carbon. Because GAC is a loose material water can flow through it easier which results in higher flow rates at lower pressure. The trade-off however is lower contact time which results in decreased filtration effectiveness. The other problem that can occur in a loose packed material such as GAC or PAC is channeling. Channeling is the result of water creating pathways or channels through the material which reduce water contact with the filter media. As these channels form large amounts of water can pass through these areas and will have very little contact with activated carbon particles therefore reducing the effectiveness of the filter.
Why Activated Carbon Fiber is BEST
Because of the small size of the Renovo MUV filter and the ability to use the MUV in low pressure systems (hydration reservoir, bottle filtration) traditional activated carbon filters wouldn't provide adequate contact time or would restrict the flow too much to be useful. There are many products on the market that still use these types of filters but they are generally only good for slightly improving the taste. We wanted the MUV to provide both a high flow rate and high levels of filtration so we had to consider alternatives such as Activated Carbon Fiber (ACF). The most important aspect of ACF is the mass transfer coefficient is 10-100 times higher than granular activated carbon. This results in absorption rates that are 10-15 times greater than that of granular activated carbon filters. So water can pass through the filter at the same speed of a typical granular activated carbon filter but because of the higher absorption rate the ACF filter can remove 10-15 times the amount of contaminants.
The ACF has a highly structured design similar to a block filter, but it doesn't have the extreme pressure requirements that block filters have because the material is more open and suited for higher flow rates. It also isn't susceptible to channeling that is common in a loose packed material such as granular or powdered activated carbon.
The secret to the increased effectiveness of ACF is at the microscopic level. The reason activated carbon is used for water filtration is because the highly porous surface of the carbon is able to trap and hold onto (absorb) the contaminants in water. If this surface can be made to be more porous, it will perform better. ACF filters have much smaller and better distributed pore structures. For example a typical GAC pore structure will consist of 70% macropores (large pores 50nm or greater) 20% of mesopores (2-50 nm) and 10% of micropores (2nm or smaller). Basically the GAC is primarily composed of pores that are 50 nanometers or larger. An ACF filter is the opposite; 70% of the structure is micropores (2nm or smaller) 20% of mesopores (2-50 nm) and 10% of macropores (50nm or larger). So while the GAC is mostly made of larger macropores the ACF is largely made up of micropores. This larger volume of micropores creates more surface area for absorption.
The Activated Carbon Fiber which we use in the Renovo Water MUV Adaptable Water Filter is far superior to the activated carbon filters found in most any other water filter currently available. ACF has superior flow rates, higher absorption speed and isn't prone to the negative effects of channeling which plague GAC or PAC filters. Because of this the filter can remove more contaminants at better flow rates than anything else. The filters are more costly to manufacture but we consider those increased costs to be a reasonable low price to pay for a vastly superior technology.
For more information on the basics of carbon filtration CLICK HERE