Water Treatment Facilities

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Most water treatment facilities today utilize granular activated carbon (GAC) as a filter media to remove dissolved organic carbon (DOC) and other constituents from influent water. The large, adsorptive surface area that activated carbon provides allows DOCs to constantly have an area to contact and adsorb. However, as DOC collects onto the GAC, the overall surface area reduces, and blockages occur in the filter that generate head-loss and reduce the efficiency of GACs removal. At this point in the process, water treatment plants (WTP) typically send the “spent” carbon to a facility for thermal regeneration.
Thermal regeneration of activated carbon is a procedure in which the spent carbon loaded with organic and inorganic particles undergoes a staged heating procedure. This procedure follows two stages: pyrolysis and oxidation (Cannon, Snoeyink, Lee, & Dagois, 1994; Guo & Du, 2012). Pyrolysis initiates the regeneration of the activated carbon by introducing the spent carbon to an inert gas environment. Once in the environment, it is heated to temperatures ranging from 650°C to 850°C to vaporize trapped water, volatize any volatile organic compounds, and reduce nonvolatile organics to char (Cannon et al., 1994). Oxidation then exposes the GAC to steam, carbon dioxide, or both simultaneously. Again, the environment is heated to a temperature range of 650°C to 950°C to gasify the char and internal surface area of the GAC to allow for adsorptive characteristics to regenerate (Cannon et al., 1994).
Regenerated GAC characteristics are affected through temperatures and parameters used during thermal regeneration, and thereby require tailoring to achieve optimal results. Using mild conditions for thermal regeneration will not eliminat...

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...he material introduced has typically high affinities towards various other minerals. One study utilized iron-modified activated carbon to determine efficiency at adsorbing arsenic (Chen, Parette, Zou, Cannon, & Dempsey, 2007). Within the study, it concluded that iron impregnated activated carbon not only had high affinity towards arsenic, but lasted up to 200 times longer bed life in comparison to the virgin carbon (Chen et al., 2007). However, this increased lifespan is potentially caused by the impregnated iron overtaking many of the internal pores of the activated carbon, essentially cutting those surface areas off from contact. As a result, this would reduce overall organic adsorption through activated carbon (Chen et al., 2007; Yin et al., 2007). Overall, impregnated GAC would have to strike a balance to optimize the effective removal for both DOC and metals.

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