Please Help! A small community water well has become contaminated with a chlorin
ID: 2085994 • Letter: P
Question
Please Help!
A small community water well has become contaminated with a chlorinated solvent believed to be perchloroethylene (PERC, molar mass of 166). We wish to design a facility to treat 50 gpm of this water using air stripping to bring it to EPA drinking water standards. The well water is currently testing at 100 ppm (by weight) of the PERC and the EPA drinking water standard is 5 ppb. A consultant has recommended a column that is 2 feet in diameter and packed with 10 mm ceramic Raschig rings that is operated with a gas flow of twice the minimum rate.
Please calculate the required air flow rate, the height of the packing required and the pressure drop that is seen for the gas flow in the column.
Assume the entering gas and liquid streams are at 20 C and 1 atm.
Data: Phase equilibrium relation for PERC between air and water y = 471x
Explanation / Answer
Tetrachloroethylene is also known as perchloroethylene - hence the common acronyms PCE or PERC.
This chemical is a chlorinated solvent.
PCE is used commercially as industrial degreasers, spot removers, and in dry cleaning.
PCE is not a natural chemical, it is manmade.
Exposure typically occurs via drinking contaminated water. PCE typically gets into drinking water aquifers when it is improperly disposed of, and is able to leach into groundwater.
PCE can also be inhaled. The chemical is a Volatile Organic Compound (VOC) which means it readily vaporizes.
Chronic PCE exposure can cause damage to the liver, the kidneys and the central nervous system. It may also lead to increased risk of cancer.
The MCL for PCE is 5.0 ppb (5.0 grams per billion grams of water).
Well No. 4 in Chubbuck has tested positive for tetrachloroethylene. The source of the PCE contamination is unknown at this time.