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Tetrachloroethylene Biochemical Oxygen Demand problem

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BOD: Biochemical Oxygen Demand
BOD5 is the total amount of oxygen consumed by microorganisms during the first five days of biodegradation

BOD5 = (DOi - Dof)/(P) this is the five-day BOD of a diluted sample
Where DOi = the initial dissolved oxygen (DO) of the diluted wastewater
DOf = the final DO of the diluted wastewater, 5 days later
P = the dilution fraction = (volume of wastewater)/(volume of wastewater plus dilution water)
A standard BOD bottle holds 300 mL, so P is just the volume of wastewater divided by 300 mL

A cubic meter of a gravel-and-sand aquifer has been contaminated with 20 L of tetrachloroethylene. If the amount of tetrachloroethylene dissolved in aquifer water is 20 percent of its aqueous solubility,
a) How much tetrachloroethylene is dissolved?
b) How much remains as undissolved DNAPL mass?
c) If the aquifer has a gradient of 0.001, use porosity and hydraulic conductivity data for gravel-and-sand aquifers to estimate the average linear velocity of the groundwater.
d) How long would it take to remove the tetrachloroethylene?

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Solution Preview

a) The solubility of PCE in water is 215 mg/L. Multiply this by the 20L.
b) PCE has a density of 1.6 g/cc. 1 L = 1000 cc. So to get the total PCE, multiply 1.6 g/cc x 20000 cc/ 20 L = answer in g. Convert to mg, then subtract the amount dissolved (answer in a) from this ...

Solution Summary

Tetrachloroethylene Biochemical Oxygen Demand problem.