What Affects the Performance of Activated Carbon?
The adsorptive capacity of the carbon is affected by the:
Molecular Size of the Impurity
Concentration of the Impurity
Particle Size of the Carbon
Pore Size Distribution of the Carbon
Temperature and pH of the Solution
The adsorption efficiency of carbon increases as:
Particle Size of the Carbon Becomes Smaller
Solubility of the Molecule Decreases
Temperature of the Solution Decreases
Contact Time Between the Carbon and Solution Increases
Pore Structure Matches Molecular Size of the Impurity
Activated Carbon works best when temperature of the solution is between 40-90 degrees F and when pH is 4-10. Recommended contact time usually ranges from 3 to 30 minutes. In order to achieve this contact time, activated carbon vessels are typically much taller than they are wide. A typical ratio of filter sidewall height to diameter is 2:1.
How Can Carbon Effectiveness Be Extended?
The carbon’s effectiveness will be extended if suspended solids in the liquid have been removed by a sand or multi-media filter before carbon treatment. Otherwise, solids in the stream will become trapped in the carbon pores and cover carbon surfaces so they are unable to attract the maximum number of molecules out of the solution.
The effective life of the carbon can also be extended by periodic backwashing or “air scour”, ( the infusion of pressurized air into the filter ). Backwashing or air scour, agitates the carbon granules, exposing new surfaces that were previously covered by adjacent carbon particles. In instances where oil and grease are to be removed, the life of the carbon can be extended by pre-filtering the liquid with clay platelets treated with quaternary amine. The clay platelets are placed in pressure filters just as is done with the activated carbon.
Used upstream for carbon filter, the clay platelets remove emulsified oil that would otherwise blind or block the pores of the carbon granules. This procedure can extend the life of the carbon by up to seven times. This helps reduce the overall treatment costs, since the clay platelets are less costly than carbon.
To discuss more information regarding Everfilt® Water Filtration Systems, talk with an Everfilt® Applications Engineer: 1.800.360.8380 / everfilt@everfilt.com