Powdered Activated Carbon: General Information

Powdered Activated Carbon (PAC) has long been employed as a treatment option because to its convenience of usage and cost savings. PAC can be used dry or as a wet slurry (a combination of carbon and water). The primary drawback of powdered activated carbon is that it cannot be revived after usage and can be difficult to dig out of water treatment reservoirs. "However, the low capital cost associated with PAC feed system combined with the ability to apply PAC seasonally or for periodic issues can make it an economic alternative based on an annualized cost."

PAC can be kept wet or dry

Dry is normally held in compact 55-pound bags, but wet is delivered and stored in a massive slurry. If maintained in a slurry condition for an extended amount of time, PAC can solidify. To prevent this from happening, periodic mixing is essential. When PAC is expected to be used more frequently, it is stored in a wet slurry, and when it is expected to be used less frequently, it is stored dry. Dry storage is less costly, and dosages are more precise. When transporting dry PAC into silos, the facility must account weight gain owing to adsorption of moisture from the air.

The essential design parameters for a PAC feed system are as follows:

Design flow rate influences dosing needs, storage vessel size and quantity, and feed equipment amount and size.

Influence target and background concentrations The DOC determines the PAC dosage required.

Treatment goals include identifying target pollutants, determining target effluent concentrations, and determining dosage and equipment size.

Coal, coconut shell, and wood are examples of PACs.

Seasonal/periodic vs. continual application

Contact time and mixing - quick mix (often referred to as "PAC will remain in suspension through the rapid mixer"), flocculation basins, sedimentation

The influent concentration, residence period, external mass transfer, adsorbate characteristics, and other pollutants other than the target molecule all have an effect on the powdered activated carbon. "Increasing the PAC dose will lower the reactor effluent concentration as more adsorbate can be removed from solution." However, the percentage drop in effluent concentration is not proportionate to an equivalent percentage increase in PAC dosage. For high TOC water (TOC = 10 mg/L), a dosage of 5 mg/L can provide a 40% reduction in influent geosmin concentration, but it requires around 17 mg/L of PAC to accomplish 90% removal. Chlorine, various disinfectants, and unexplained pollutants have been reported to take up adsorption sites, reducing the PAC adsorption capacity for target chemicals. This might result in a high concentration of the target molecules in the effluent. Increasing contact time improves removal efficiency. A minimum of 15 minutes of contact time is advised, but longer may be required and helpful to attain the PAC's entire adsorption capacity. Before installing a new feed system, jar tests are often performed to see how effective the powdered activated carbon will be.

Powdered activated carbon is a proven, cost efficient treatment option. Please speak with us if you should have any questions. Thank you.