Question

A wastewater containing 150 mg/l chlorobenzene is treated in a laboratory adsorption unit using a PVC column, 1.0 inch internal diameter, to an effluent concentration of 15 mg/l . Service times, and throughput volumes at specified depths and flowrates associated with a breakthrough concentration of 15.0 mg/l are given in table 1.

table1 : result of adsorption column experiment

Loading rate,gpm/ft²   Bed depth,ft Throughput volume, gal Time, hr

loading rate gpm/ft2	bed depth ft	throughput volume, gal	time, hr
2.5	3.0	810	980
	5.0	1750	2230
	7.0	2910	3440
5.0	3.0	605	420
	5.0	1495	1000
	9.0	3180	2185
7.5	5.0	1183	452
	9.0	2781	1075
	12.0	4000	1564

1) is the attainable effluent concentration satisfactory from a regulatory standpoint?

2) determine the Bohart-Adams constant ( K,N₀ and x₀) for each hydraulic loading.

3)base on data derived above design an adsorption column 2.0 ft internal diameter to treat a wastewater flow 5,000 gal/d containing 150 mg/l of CB. The attainable effluent concentration is 15 mg/l and it is desired to operate the column for 90 days(8 hourslday,7 days/week) before reching exhaustion.

4)calculate the yearly carbon requirements in cubic feet.

Answer 1

a) No, According to regulatory limits the concentration of chlorobenzene should not be more than 0.1 mg/l whereas in the effluent it is 15 mg/l therefore, it is not agreeable from the regulatory point of view also.

Where, C₀ and C_t (mg/L) are the influent and effluent dyes concentration. k_ab (L/mg ^.min) is the kinetic constant, F (cm/min) is the linear velocity calculated by dividing the flow rate by the column section area, Z (cm) is the bed depth of column and N₀ (mg/L) is the saturation concentration. The validity of this model is limited to the range of conditions used.

ln 15/150 = ln 15-ln 150 =2.70 -5.010 = -2.30

F =     flow rate /column section area

cross sectional area = pi r^2 = 3.14 * 0.041*0.041 =0.0052 Ft^2 = 4.83 cm^2

F = 2.5/4.83 = 0.517 cm/min

z values at 2.5 = 91.44cm, 152.4cm, 213.36 cm

suppose, for the first z value we calculate -2.30 = 0.517/91.44 Kab No

Kab No = 406.79