Adsorption Influence Factors & Applications
Adsorption Influence Factors & Applications
ADSORPTION INFLUENCE FACTORS
As with almost all water treatment methods and unit processes, three key factors play a very important role in controlling the degree to which the adsorption process succeeds or falls short. Some of the same factors that govern aeration effectiveness also come into play in the adsorption unit process. Three vital factors include:
Temperature
In general, lower temperatures favor the adsorption process, while higher water temperatures are likely to cause desorption, or the “dumping” of already removed constituents. Where water temperature goes up (seasonally) by 20°F in an operating system, the adsorbent medium may “kick off” the very contaminant that the unit was originally installed to remove. Generally, the most efficient temperature range for adsorption is from 40° to 55°F (4.4°-12.8°C).
pH
Most organics (nonpathogenic) in water are more soluble on the alkaline side than on the acid pH side, indicating better organics adsorption at the lower pH values. Similarly, chlorine and chloramines are more effectively removed by activated carbon below pH 7.0 value.
Contact time (flow rate)
This is extremely critical in adsorption, as the amount of “dwell time” water spends passing through the adsorbent medium bed is a measure of effectiveness. To achieve proper contact time, the unit design calls for well-controlled service flow rates. To this end, downstream flow control devices for any adsorption system are considered a must by practitioners of this technology. Where the water supply to be treated may have a summer/winter water temperature swing, the system must also take this into consideration.
ADSORPTION APPLICATIONS AND ADSORBENTS
In domestic water treatment, the question usually is, “Where are with what adsorbent medium can correction of adverse water characteristics be accomplished?” The adsorption process for home, farm, and business is useful for getting rid of many unwanted water constituents, including some that may be on the potentially hazardous side. This technology is employed for:
- Improving taste and removing odors.
- Decolorization of water.
- Radon and chlorine reduction and removal.
- Removal of organic (nonpathogenic) substances.
- Synthetic organic compounds removal (such as pesticides).
- Selective reduction and removal of inorganic substances (such as fluorides and arsenic).
To accomplish the above, a wide choice of adsorbent media is available, including:
- Granular, powdered, and block-activated carbons.
- Activated alumina products.
- Ion exchange resins.
- Dissimilar metal alloy materials.