“I just have a small amount of acid; I’ll just pour it down the drain with plenty of water.”

We hear this from time to time and it’s not compliant or the safest thing to do.

• If you’ve been doing it for a while, take a look at your sink fixtures.  A little green are they?  The same stuff that turned the metal green could be in someone’s lungs.
• If you pour the acid all at once – you are just liable to create an acid geyser that will come back at you.

Okay, so you’re just going to dribble a little bit of acid at a time and run the faucet.  How much is “plenty” of water?  Let’s say you have 1 liter of 1 Molar (1 Normal) Hydrochloric Acid which will pH at 1.0.  To meet Environmental Protection Agency requirements, you must get that up to a pH of 2.0; to meet the requirements of the local water authority (Atlanta Watershed District) you need to get it up to 5.0 at the point it enters the sewer system.

(Most research buildings on campus have “acid dilution tanks”, these help but, they are really only handle small amounts of acid at a time).

pH is a log scale so pH of 1 is 10 times as strong as pH 2 which is 10 times as strong as pH 3…   You need to get your 1 liter of acid to a pH of 5 – how much water do you need:

• 99,999 liters (a little over 25,000 gallons). At the flow rate on most laboratory sinks it will take a little over 83 hours of constant running to get that much water.  Cost to Georgia Tech in water and sewage fees about $1000.

Compare that with the 15 minutes it takes to process the acid for pick-up by the hazardous waste folks and the $2.50 it costs to dispose of it properly. So a small amount still needs to be properly disposed of.