Question: Water treatment

Q1. Balance the oxidation-reduction reaction for the oxidation of methyl tert-butyl ether (MTBE) [(CH₃)₃COCH₃] using (a) hydrogen peroxide and (b) ozone.

Q2. Can nitrate (NO₃^-) be reduced to nitrogen gas (N₂) under aerobic conditions? For this problem, assume the following conditions are applicable for aerobic fresh water: [NO₃^-] = 10^-2 M, P_N2 = 1 atm, [H⁺] = 10^-7 M, and [O₂(aq)] = 8.24 mg/L (2.58 x 10^-4 M) at 25 C.

Q3. (Modified) Given below are some data from Wattle and Butterfield (1944) on the inactivation of E. coil with free chlorine at 2 C and pH 8. Fit the data to the Chick-Watson model.

Q4. What is the mass concentration of 1 μM concentrations of the following DBPs: chloroform, bromoform, dibromchloromethane, bromodichlorobromethane, monochloroacetic acid, and monobromoacetic acid?

Q5. Using the McCabe-Thiele graphical method, determine the number of equilibrium stages required to strip chloroform from an influent concentration of 200 μg/L to its treatment objective of 5 μg/L in a countercurrent, packed tower at 5 C. Assume clean air enters the tower and S = 3.5.

Q6. (Benjamin & Lawler) A gas stream containing 3% ozone by volume is bubbled into a water column as part of a disinfection strategy. K_H = 0.011 M/atm and K_La = 18 h^-1 for ozone in the system. The gas transfer process is limited by interfacial transport (i.e., kinetically or microscopically limited). Ozone dissolved in water is unstable. The kinetics of decomposition are complex, but under some circumstances, the rate can be approximated as first-order with respect to dissolved ozone. The first-order rate constant is pH-dependent and, at pH 8.0 and 25 C, is 12 h^-1 in the system of interest.

a) Find the steady-state concentration of dissolved ozone in the reactor if it is operated with no flow of liquid.

b) Find the steady-state concentration of dissolved ozone in the effluent if the reactor is operated as a CFSTR with a 15-min hydraulic retention time.

Q7. The results of a mineral analysis of a raw water are as follows: Ca²⁺ = 88 mg/L, Mg²⁺ = 29 mg/L, Na⁺ = 18 mg/L, HCO₃^- = 135 mg/L, Cl^- = 60 mg/L, SO₄^2- = 180 mg/L, CO₂ = 4 mg/L, pH 7.4. Determine the doses of softening chemicals required so that the finished water contains ≤ 50 mg/L Ca hardness (as CaCO₃) and ≤ 20 mg/L Mg hardness (as CaCO₃). Perform your calculations using:

a) Reaction stoichiometry/manual calculation, with the aid of a bar graph for the water constituents.

b) Lawrence-Caldwell diagram. Include a diagram showing your construction lines.

c) MINTEQ. Include a printout showing program results.

Q8. Determine the Freundlich and Langmuir parameters for the data given below. You may use linear regression, and plot C/Q versus C for the Langmuir equation and log Q versus log C for the Freundlich equation.

Adsorption isotherm data: Carbon type, F-400; chemical, tetrachloroethene; temperature, 13.8 C. Isotherm Data:

Q9. Determine the Freundlich isotherm parameters for tetra-chloroethene (PCE) using Polanyi potential theory and compare the parameters with those determined in Q8. Use Cargon F-400 GAC and a water treatment temperature of 13.8 C. For PCE, the following properties at 13.8 C are given: V_m = 102.4 mL/mol, ρ_l = 1620 kg/m³, and C_S = 347.0 mg/L.

Q10. Calculate the dosage of activated carbon to reduce an influent concentration of 300 μg/L of chloroform to 100 μg/L (treatment objective) using powdered (PAC) and granular activated carbon (GAC). Assume for the GAC and PAC process that the carbons are saturated at the influent concentration and treatment objective, respectively. Given: Q = 10 mgd.

K = 159(μg of chloroform/g of activated carbon)(L/μg)^0.625

How long will the GAC last if the filter density ρ_F = 0.37 g/cm³ and EBCT = 15 min?

Textbook - Crittenden et al., MWH Water Treatment Fundamentals and Design 3/e.