Exam Study Guide: Internal Process Equipment; and Reverse Osmosis Chemicals

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.

Exam Study Guide: Internal Process Equipment; and Reverse Osmosis Chemicals

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Welcome back to TPO magazine's Exam Study Guide Series, which offers a pair of water/wastewater study questions with in-depth explanations of the answers. Last time, we covered a set of wastewater and drinking water treatment questions on the topic of Identifying Water and Wastewater Treatment Processes. This time, you can test your knowledge about internal process equipment, and reverse osmosis water treatment chemicals.

Wastewater Treatment Sample Question:

This unit process uses internal equipment called flights, chains, shoes, baffles and sumps. Can you identify the unit process?

A) Sequencing batch reactor (SBR)

B) Membrane bioreactor (MBR)

C) Primary settling tank (PST)

D) Moving bed bioreactor (MBBR)

Answer: The answer is C, primary settling tank. Primary settling tanks are commonly rectangular in shape, and have two sets of long chains that move through the action of sprockets, chain drives and motors. Flights are made of either some type of durable wood or newer composite plastic material and are connected to the chains. The flights span the width of the tank and when they are along the bottom of the primary basin, they slowly move settled solids toward a sludge pump sump. As they reach the surface of the tank, they slowly collect and move floatable solids and grease and scum toward scum skimmers. The shoes are small pieces of metal or durable material attached to the flights that will stand up to the wearing of being scraped along the track that supports the flights.

The other three (incorrect) choices are more modern modifications of the activated sludge process.

Water Treatment Sample Question: 

What purpose does adding a dosage of 2 to 5 mg/L of sodium hexametaphosphate (SHMP) play in reverse osmosis water treatment?

A) SHMP inhibits the precipitation of calcium sulfate on the membrane

B) SHMP will reduce the amount of dissolved hydrogen sulfide gas that must be de-gasified

C) SHMP will eliminate the need for degasification after membrane treatment

D) SHMP will eliminate the need to provide corrosion prevention in the distribution system

Answer: The answer is A, SHMP inhibits the precipitation of calcium sulfate on the membrane. The source water to a membrane (reverse osmosis) water treatment plant can contain calcium carbonate and calcium sulfate in solution. These compounds can cause significant scaling to occur on the membrane if not controlled. Reducing the pH with an acid will help keep the calcium carbonate from becoming a problem by keeping the alkalinity in the bicarbonate form, which is more soluble. The calcium sulfate, however, can continue to precipitate (form scale) over a wider pH range. The addition of sodium hexametaphosphate (SHMP) inhibits both calcium carbonate and calcium sulfate from becoming crystallized and forming the scale on the membrane surface.

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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