AVOID COMMON ERRORS
Plants potentially can compromise the life and efficiency of their GAC by making some all-too-frequent mistakes:
• Installing an activated carbon system based on process assumptions without an actual pilot test. Any trials should include appropriate comprehensive sampling and analysis so that the pilot can be meaningful and not simply raise more questions because insufficient results were obtained. Often the analytical costs will be the most significant portion of the pilot-plant costs.
• Leaving spent carbon online for an excessive amount of time to save on change-out costs. This can make the spent carbon unsuitable for reactivation due to contamination level and calcification.
• Overlooking the potential need for prefiltration. Undissolved contaminants and solids may limit access to the carbon and greatly reduce bed life. So, pretreat such streams to allow the activated carbon to focus on adsorption rather than having to contend with scaling or deposits.
CONSIDER SOME SUCCESSFUL RECENT APPLICATIONS
One prominent chemical maker sought a cost-saving alternative to wastewater disposal. Specifically, it was looking for a way to reduce the organic chemical content of its process wastewater so that water could go to a water treatment unit at the plant. After evaluating the available options, the site installed a modular carbon-adsorption system configured as two adsorbers with connected piping; each adsorber contains 20,000 pounds of GAC and treats up to 100 gpm. Instead of using virgin carbon, the plant reduced its carbon footprint and costs by purchasing a large volume of reactivated-grade carbon and implementing an ongoing protocol for spent-activated-carbon reactivation by the carbon manufacturer. The chemical maker leased the carbon adsorption equipment from the carbon vendor, which also provided field service personnel for equipment maintenance and troubleshooting (Figure 1).
A major international chemical manufacturer wanted to reuse its process wastewater, so it could decrease its raw water intake from a nearby river and reduce its discharge volume to a local wastewater treatment plant. A principal concern was whether carbon adsorption could adequately purify the wastewater, which contained organic contaminants detrimental to the final product. After a trial test proved satisfactory, the plant decided on a modular carbon-adsorption system configured as two adsorbers with connecting piping, with each adsorber containing 20,000 pounds of GAC and treating up to 100 gpm. The purified wastewater was recycled to the process.
ROBERT DEITHORN is business unit product director for Calgon Carbon Corp., Pittsburgh, Pa. E-mail him at email@example.com.