Adsorption with activated carbon, made from bituminous coal, of soluble organic compounds (SOCs) to purify surface and ground water is a proven technology, as discussed by Stenzel [Chem. Eng. Prog., 89 (4.), 36-43 (1993)l. The less-soluble organic compounds, such as chlorinated organic solvents and aromatic solvents, are the more strongly adsorbed. Water containing 3.3 mg/L of trichloroethylene (TCE) is to be treated with activated carbon to obtain an effluent with only 0.01 mg TCEL. At 25oC, adsorption equilibrium data for TCE on activated carbon are correlated with the following Freundlich equation:

q = 67 c^0.564            (1)

where

q = mg TCE/g carbon and c = mg TCE/L solution. The TCE is to be removed by slurry adsorption using a powdered form of the activated carbon, with an average particle diameter of 1.5 mm. In the absence of any laboratory data on mass-transfer rates, assume that the rate of adsorption for the small particles is controlled by external mass transfer with a Sherwood number of 30. Particle surface area is 5m2/kg. The molecular diffusivity of TCE in low concentrations in water at 2S°C may be determined from the Wilke-Chang equation.

(a) Determine the minimum amount of adsorbent needed.

(b) For operation in the batch mode with twice the minimum amount of adsorbent, determine the time to reduce the TCE content to the desired value.

(c) For operation in the continuous mode using twice the minimum amount of adsorbent, determine the required residence time.

(d) For operation in the semi-continuous mode at a feed rate of 50gpm and for a liquid residence time equal to 1.5 times that computed in part (c), determine the amount of activated carbon to give a reasonable vol% solids in the tank and a run time of not less than 10 times the liquid residencetime.