1. Sulfate (molecular weight = 96g/mole) from an acid mine treatment pond leaves

1. Sulfate (molecular weight = 96g/mole) from an acid mine treatment pond leaves via an
outlet stream at a concentration of 275 mg/L. The outlet stream flows into a small river
with a flow of 30 cfs upstream, 37 cfs downstream, and a background sulfate
concentration of 17 mg/L. Please answer the following.
a. What is the concentration of outlet stream sulfate in moles/L and equivalents/L?
b. What is the concentration of sulfate in the river immediately downstream of the
confluence with the outlet stream in mg/L?
2. One oxidation treatment process uses light and hydrogen peroxide to generate the
highly reactive hydroxyl radical (OH•), which can be used to degrade certain PFAS
“forever compounds”, but not others. A very recent paper by Zhang (2023
Environmental Science and Technology: so recent no volume has been assigned) report a
second order rate constant between OH• and the PFAS, perfluoro(2-
ethoxyethane)sulfonic acid (PFSA with a k = 1.2 x 10 7 L/mole-second), while this radical is
less reactive with 4.8-dioxa-3H-perfluorononanoic acid (DPFA with a k = 5 x 10 5 L/mole-
second). Suppose your UV-hydrogen peroxide system generates a constant output
(steady-state) of this radical at a concentration of 3 x 10 -14 moles/L, please answer the
following.
a. What is the pseudo-first order rate constant for the degradation of both
compounds at this OH• concentration?
b. What are the half-lives for these two compounds?
c. Suppose you have to treat these two compounds such that they both must not
exceed the 50 nM water quality standard. If both compounds have a starting
concentration of 1µM how long (in hours) will it take each to reach this
concentration? For the slower reacting compound is the time needed to achieve
the water quality standard a reasonable time from a design perspective?