ENE 802:Physicochemical Processes in Environmental Systems

Fall Semester 2003 Dr. S. Masten

Homework due: October 25, 2003

1. Water flows through an aquifer at a rate of 1.5 foot per day. The porosity (Vw/Vtot) of the aquifer is 0.30 and the density of the aquifer solids is 2.5 kg×L-1. The fraction of organic matter of the aquifer solids is 0.4.

A river contains a suspended solids concentration of 5 mg/L.

Calculate the fraction of benzo[a]pyrene that is truly dissolved in each of the waters assuming a Kd of 10,000 (mol×kg-1/ mol×L-1). Determine Kom for benzo[a]pyrene for the aquifer solid.

Hint: read over Sections 11.2 to 11.4 (pp. 258-272) in SGI (1st ed) (Section 9.2, pp 280-291 in SGI, 2nd ed.). For the next questions, review pages 276 to 280 in SGI (1st ed); pages 310-313; 316-318; 321-325 in the second edition.

(a) Calculate the percent change in the Kom for benzo[a]pyrene upon a temperature increase from 10 to 25 oC.

(b) Calculate the Kom (25 oC) for benzo[a]pyrene in sea water (30,000 mg/L salinity).

2. 2-Methylisoborneol (MIB), a metabolite of algal production, is a common taste- and odor-causing compound in surface waters. Adsorption on activated carbon is one treatment option. A series of batch adsorption equilibrium tests were performed using powdered activated carbon (PAC) as the sorbent. Plot the data according to the Langmuir and Freundlich isotherms. Choose the isotherm that is "most closely linear". The water of the Foulsmelling Reservoir has an MIB concentration of 1.5 m g/L. The treated water is to have a MIB concentration of 0.030 m g/L and:

a) Determine if the desired effluent quality can be achieved by adsorption.

b) Determine the adsorptive capacity (x/m) of the carbon at this level of effluent quality.

c) Determine the ultimate capacity of the carbon for this water (i.e., x/m for Co).

d) Calculate the values for the constants from the isotherm.

Flask No. / Initial MIB conc. (Co)
(m g/L) / Equilibrium MIB conc. (Co)
(m g/L) / PAC Dosage (Do) (mg/L)
1 / 1.0 / 0.01 / 20
2 / 1.0 / 0.05 / 10
3 / 1.0 / 0.10 / 7
4 / 1.0 / 0.50 / 2
5 / 5.0 / 1.0 / 10
6 / 5.0 / 2.0 / 6
7 / 5.0 / 3.0 / 3

3. A batch adsorption study was conducted to investigate the removal of TOC from an water from the Grand River. The initial study indicated that the adsorption isotherm could be described by a Freundlich isotherm where :

The water treatment facility operates at a flow of 2 mgd. The water has an initial TOC of 8 mg/L, which must be reduced to 0.5 mg/L prior to disinfection to ensure that the concentration of DBPs are below regulatory limits. The carbon selected for use has an apparent density of 35 lb/ft3 and a packed density of 30 lb/ft3. The value of the overall mass transfer coefficient has been found to be 1050 lb/min· ft3 at a temperature of 70 oC.

Using the Mass Transfer Approach developed by Weber (1972) to design an activated carbon, fixed bed, continuous-flow adsorption column for these specifications. Determine the height and diameter of the column, the depth of the adsorption zone, the percent saturation and the TOC application rate.

4. A leaking underground storage tank results in the release of 5,000 gal of tetrachloroethylene (PCE). Soil borings in the unsaturated zone have revealed a concentration of 12,000 mg PCE/kg soil. Assume that:

(a) the soil contains 0.5 organic matter (fractional mass basis),

(b) the soil has a porosity of 0.25, a particle mass density of 2.5 g/cm3 and a moisture content of 10%,

(d) the temperature of the soil is 15 oC,

(e) that free product is present

(f) equilibrium conditions exist

(g) free product is present

(h) the D Hse for PCE is the same as the D Hse for TCE

Estimate the concentration of PCE in the pore air, dissolved in the pore water, sorbed onto soil organic matter. Estimate the mass of soil that is contaminated.

5. A chemical manufacturing company produces a variety of polycyclic aromatic hydrocarbons (PAHs), including fluorene. In a trucking accident involving a shipment of fluorene across the Deep Gorge Bridge, a 900 kg quantity of product spilled into a seep-fed wetlands at the bottom of the Gorge. The deep and narrow conditions of the gorge inhibit air circulation above the relatively well-mixed waters of the small wetlands. The seep that feeds the wetlands is near its center and outflow occurs only by seepage return to the subsurface along its perimeters. You are asked to perform an analysis of the potential distribution of fluorene in this system if equilibrium conditions are attained. The following issues are of specific interest:

(a) The acute aqueous-phase toxicity limit of the Gorge Lake fiddler toad is 100 m g/L fluorene. Is the fiddler toad in immediate danger of chemical poisoning

(b) Discounting degradation and wash-out, determine what percentage of the total mass spilled into the lake will eventually be taken up by its sediments.

Your staff has compiled the following data for the system:

Phase volumes (estimated):

Water: 25,000 m3

Sediment: 1200 m3; r (sediment) = 1200 kg/m3

Biota: 10 m3

Air in the gorge above the wetlands: 125,000 m3

Temperature, T: 25 oC

Hint: See the fugacity paper by Mackay and Paterson (1981).