Maintaining your education is important, especially in a career that demands licensing exams. Prove you’re an expert operator by answering these questions and others from our Exam Study Guide Series.


Welcome back to TPO magazine's Exam Study Guide Series, which offers a pair of water/wastewater study questions each week with in-depth explanations of the answers. We covered a set of wastewater and drinking water treatment questions last week on the topics of RBC Unit Operation; and Water Hardness Testing. This week, you can test your knowledge about power outage procedure, and ion exchange softening.

Wastewater Treatment Sample Question:

The operator of the RBC treatment plant experiences a citywide power failure at the facility, and standby generator power is unavailable. Local emergency management officials determine the power will be restored in 36 to 48 hours. What should the operator do to protect the growth on the media and the RBC units themselves?

Related: Study Guide: General Knowledge

A) Immediately wash the attached growth off the RBC discs with a power washer

B) Manually rotate the RBC drum one quarter of a turn every four hours to prevent the slime growth from only growing on the bottom portions

C) Manually rotate the RBC drum completely until power is restored to maintain compliance with permit requirements

Related: Exam Study Guide: Chlorine Cylinder Emergency Leak Repair

D) Drain the RBC tanks and flush with fresh water.

Answer: The answer is B, manually rotate the RBC drum one quarter of a turn every four hours to prevent the slime growth from only growing on the bottom portions. If power will not be restored before about four hours, the RBC shaft should be rotated manually to ensure even slime growth on the discs. Rotating the drum one quarter of a turn every four hours is recommended to even the pattern of the attached growth. This should be done in the safest manner possible.

If the RBC drum is not rotated, and the slime growth has only continued to grow on the portion that remained submerged, the weight and balance of the drum will be very uneven. If the weight of the growth is not heavy enough to prevent the rotation completely, the unit will struggle to reach the apex point of the rotation and then will move very quickly toward the bottom causing excessive strain and wear on motors, gear boxes, RBC drum shafts and bearing mounts.

Related: Exam Study Guide: RBC Unit Operation; and Water Hardness Testing

Keep the biomass wet by hosing the slime growth occasionally, but do not wash off (or pressure wash) the media. You’ll need the active biomass to treat all the wastewater that will come rushing in once power is restored to the city and sewage pump stations.

One other note: ensure standby generators at the treatment plant are working in good order and capable of keeping critical unit processes functioning. 

Water Treatment Sample Question: 

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What is a disadvantage of ion exchange softening?

A) The amount of land space needed to build the plant

B) The complexity of the operation and amount of training needed

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C) Disposal of the spent brine and rinse waters

D) Excessive operation and maintenance costs

Answer: The answer is C, disposal of the spent brine and rinse waters. Ion exchange softening is a relatively straightforward process of water softening and capable of reducing the finished water hardness to zero. The process consists of Service, Backwash, Brine and Rinse stages.

A disadvantage of the process is figuring out what to do with the spent brine and rinse waters. These are considered industrial strength wastes since the amount of total dissolved salts (TDS), conductivity and pH can be very high. Discharging these wastes into a sanitary sewer for treatment at a municipal wastewater treatment plant is a common practice, especially if the utility owns both the drinking water and wastewater treatment plants. However, the operator of the wastewater plant must be made aware of these discharges since it may affect the biological processes used. Slug loads of high pH, conductivity and saline water can negatively affect the bacteria used for secondary treatment, so it is imperative these industrial wastes be controlled to prevent plant upset.

The ion exchange drinking water treatment plant may have to apply for an industrial waste discharge permit from the receiving utility to accept the spent brine, backwash and rinse waters.


About the author: Ron Trygar is the senior training specialist for water and wastewater programs at the University of Florida’s TREEO Center. Previously, he was the wastewater process control specialist at Hillsborough County Public Utilities in Tampa, Florida. He has worked in the wastewater industry for more than 30 years in a variety of locations and positions. Trygar became a Certified Environmental Trainer (CET) in 1998 and has since provided training for associations and regulatory agencies such as Florida Department of Environmental Protection (FDEP); Florida Water and Pollution Control Operators Association Short Schools; USABlueBook; Florida Water Environment Association sponsored training events; and local school environmental programs. Working alongside the FDEP Northeast District, Trygar helped begin the Florida Rural Water Association and FDEP joint operator certification review classes that are still given around the state today. He holds a Florida Class A wastewater treatment operator’s license and a Florida Class B drinking water operator’s license.


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