Exercise #4: Activated carbon treatment
1. Your factory produces a waste containing 1,4 dioxane that you must treat before discharge.
You have decided to use activated carbon for this purpose. You perform laboratory–scale tests to see how well the 1,4 dioxane in your waste will adsorb to the activated carbon you will use.
You put 0.5 liters of wastewater containing 2500 mg/L of 1,4 dioxane into 6 separate containers. Each container holds a different amount of carbon (GAC). After equilibrium is established, you measure the 1,4 dioxane concentration that remains in the liquid in each of the containers (Cf). The data you collect are in the table below.
a. Find the Freundlich isotherm constants (K and 1/n) for your waste and the carbon you used. Include the isotherm plot you used to determine these values. Hint:Use Excel to make a table of your data and follow the methods described in class (and in the text) to make a graph of log(Xeq/M) versus log Ceq.
b. You produce 8000 L of waste containing 2500 mg/L of 1,4 dioxane each day. You are required to reduce the 1,4 dioxane concentration to 1 mg/L before discharging your waste. How much carbon would need to be used each day to treat your waste?
2. There are two types of waste: 1) Wastewater with dissolved polychlorinated biphenyls (PCBs), and 2) Wastewater with dissolved heavy metals and particulate matter. For which of these two wastes would activated carbon adsorption be more appropriate? Fully explain why it is more appropriate and why the other waste is less appropriate.
3. You must deal with wastewater containing two dissolved chemicals. For each case (a and b), determine which chemical will i) adsorb more strongly and ii) which chemical you might expect to see later in the effluent at high concentrations. Fully explain your reasoning. Use the Freundlich parameters provided in the table below.
a. 2,4 Dichlorophenol and 1,1,2–Trichloroethane
b. Phenol and Hexachlorocyclopentadiene
Compound 1/n K (mg/g)(C–units)1/n
2,4 dichlorophenol 0.15 157
1,1,2 TCA 0.60 6
hexachlorocyclopentadiene 0.17 370
phenol 0.54 21GAC (mg) Cf (mg/L)
25 2340
100 1940
200 1550
300 1260
400 1060
500 900
