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The use of which substance can be very effective for removing soluble organic contaminants if used in conjunction with coagulation, sedimentation, filtration and disinfection?

A. Potassium permanganate
B. Anionic polymer
C. Sodium hydroxide
D. Activated carbon

Answer: D. If used along with other processes — like activated sludge, enhanced primary treatment, filtration and final disinfection — activated carbon can effectively remove soluble organic material from wastewater. Powdered activated carbon (PAC) can be added to the influent where it adsorbs organic contaminants. As it does so, it settles in clarifiers with other solids and is removed. The use of PAC requires a constant feed as a slurry. Be careful: PAC dust can be explosive.

Granular activated carbon, or GAC, can be used in filtering as a layer of media or in a separate contact unit where soluble organic material is adsorbed and removed. As the GAC continues to adsorb organics, it becomes exhausted and measurable COD begins to rise in the effluent. At that point, the GAC can be removed from the filter, dried and regenerated by heating in a furnace. The organic material is released during heating and is destroyed in an afterburner; the GAC can then be reused.


To prevent splashing acid on yourself or the surrounding area when preparing dilutions of acid in a laboratory, the following safety rule of thumb should be followed:

A. Always pour the dilution water into the concentrated acid solution.
B. Rapidly add the entire amount of required acid to a small amount of heated dilution water, then top off with cold water.
C. Add equal amounts of the dilution water and concentrated acid in a separate container simultaneously.
D. Always pour the acid slowly into the dilution water.

Answer: D. Always pour the acid slowly into the dilution water. To avoid harm to yourself and others working in the lab, remember: Do it like you ought-er, add the acid to the water! If water is added into a concentrated acid solution, a violent reaction can take place, causing the water and acid to splatter and splash out of the container. When working around lab chemicals, or any chemicals, always wear proper personal protective equipment. This includes acid-proof aprons, chemical-resistant gloves, and eye and face protection.

About the author

Ron Trygar, a certified environmental trainer, is the senior training specialist for water and wastewater programs at the University of Florida TREEO Center. He has worked in the wastewater industry for more than 30 years in a variety of locations and positions. He holds a Florida Class A wastewater treatment operator license and a Florida Class B drinking water operator license.


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