Neutralization of Acidic Wastewater Flashcards
What does the phrase “acid mine drainage” mean as it pertains to the NPDES permit?
Acid mine drainage is defined as mine drainage which, before any treatment, either has pH of less than 6.0 -OR- a total iron concentration of equal to or greater than 10mg/L (PPM).
What does the phrase “alkaline mine drainage” mean as it pertains to the NPDES permit?
Alkaline mine drainage is defined as mine drainage which, before any treatment, has a pH equal to or greater than 6.0 -AND- a total iron concentration of less than 10mg/L.
What is pH?
It is an expression of hydrogen ion concentration of water and is a measure of acidity or alkalinity of water. The acceptable pH range in the NPDES permit is 6 to 9. If the pH is above 9.0 it is too alkaline for aquatic life and for recreational use of a stream.
Why is the drainage from a coal mine normally acidic?
Sulfurous compounds in coal and other toxic overburden react with atmospheric oxygen and produce compounds which make water acidic when dissolved.
What are some of the problems with acidic water?
It interferes with growth and propagation of aquatic life. Low pH (acidic) water increases corrosive action on iron, steel and concrete. It also affects the taste of water when it is used for drinking.
What is the normal method of raising the pH of acid mine wastewater?
The most common method is chemical neutralization by use of sodium hydroxide, soda ash, or lime.
What are the items one should consider when using chemicals for neutralization of acidic wastewater?
One should be careful in choosing the proper dosage, the method of chemical feeding and the mixing of chemical with water. Many serious injuries have occurred while treating acidic wastewater, usually to the eyes. Therefore, proper safety precaution should be provided and utilized.
What is the practical way to choose the proper chemical dosage for neutralization of acidic wastewater?
Run a bench test on small volume of the waste to be treated. Find the proper amount of chemical for that volume. Then calculate the amount of chemical needed for the entire volume of pond water.
The operator determined it takes 20 grams of lime for one gallon of water to raise the pH of acid mine waste from 5.2 to 6.5. How many tons of lime will be needed to raise the pH to 6.5 if the total volume of pond water is estimated at two million gallons?
20g lime for 1 gallon H20 2,000,000 gallons x 20 g = 40,000,000 grams 40mil/1000 = 40,000kg x 2.2 (conv kg to lbs) = 88,000 lbs
88,000 lbs / 2000 lbs (conv lbs to tons) = _________ tons
44 tons
