Activated carbon (both powdered activated carbon (PAC) and granular activated carbon (GAC)) has been applied for a long time in water and wastewater treatment due to its large surface area for adsorption (Tri, 2002; Jafarinejad, 2015e). Powdered activated carbon has a diameter of less than 200 mesh (Tri, 2002). Activated sludge treatment with PAC is similar to the conventional AS process, but in this process, PAC is added into the aeration tank or mixed liquor. The removal of contaminants is achieved and enhanced by a combination of biodegradation and adsorption (Tri, 2002; IPIECA, 2010). A schematic of a typical powdered activated carbon treatment (PACT) process is shown in Fig. 6.6. Most of the PAC is recycled with the activated sludge, but the system requires a continuous makeup of fresh carbon. The PACT process is generally used for petroleum industry wastewater in those cases where stringent standards must be met for certain contaminants (IPIECA, 2010). According to Tri (2002), the PACT process could generally remove organic compounds more efficiently than what would be expected from either biodegradation or adsorption alone. The dosage of PAC and the mixed-liquor-PAC-suspended-solids concentration are related to the sludge age as follows:

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Figure 6.6. Schematic of a typical powdered activated carbon treatment (PACT) process.

Modified from IPIECA, 2010. Petroleum Refining Water/Wastewater Use and Management. IPIECA Operations Best Practice Series, London, United Kingdom.