Activated Carbon

Activated carbon has long been used as an effective means of removing organics, chlorine, chlorates, other chlorine compounds and objectionable tastes and odors. The organics removed include pesticides, herbicides and industrial solvents for which activated carbon has diverse capacity. Typically, carbon filters are operated at a flow rate of 1 -2 gpm/ft3 of activated carbon.

Since chlorine is removed from water by the carbon, extra care is required from here on to protect against bioburden growth. Carbon beds themselves are good breeding grounds for bacteria. To keep the system in check, a recirculation system as depicted in Fig. 3 is recommended. The constant recirculation avoids water stagnation and reduces viable bioburden growth.

Figure 3. Activated Carbon.

Activated carbon is manufactured by heating selected grades of coal or other higher carbonaceous material in the absence of oxygen. This "activation" process burns out impurities and produces a honeycomb-like structure containing millions of tiny pores. The structure provides a large total surface area that enables the carbon to adsorb (attract and hold to the surface) large quantities of contaminants. Chlorine, or its related elements, are first adsorbed on the surface of the pores where they react with the carbon to liberate chloride. Because of this reaction and deterioration of chlorine, the capacity of activated carbon for chlorine removal is exceedingly high. In addition to chlorine removal and adsorption of organics, the granular carbon is an effective filter. Although removal of turbidity will shorten the carbon life by blocking pores, the carbon will function as an excellent filter. Particle removal down to 40 microns can be achieved with freshly backwashed beds of carbon.

Carbon beds are backwashed to remove carbon fines and suspended matter which have been filtered by the bed. Backwashing does not regenerate the carbon. Sanitizing and some degree of regeneration can be effected by passing low pressure steam or hot water through the carbon bed. The degree of regeneration is limited and the carbon must be replaced periodically (once every 1-2 years). Steam is of course more effective than hot water for sanitization, but it does cause some carbon degradation.

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