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 topics of Indicator Organisms; and Iron Contamination. This time, you can test your knowledge about the purpose of screens, and different forms of iron.
Wastewater Treatment Sample Question
What is the purpose of using screens, grit chambers or comminuters for preliminary treatment in a water resource recovery facility?
A. EPA regulations regarding debris classification
B. Debris reuse and recycling
C. Protect equipment downstream
D. Protect collection system flow measurement devices
Answer: Raw wastewater contains many things such as debris, trash, sand, gravel, eggshells and many other materials that if not removed may cause damage and excessive wear to pumps and equipment throughout the treatment facility. Therefore, the answer is C. This material may also settle out in some downstream units and fill in valuable tank space. As much grit and debris as possible must be removed to avoid these problems. Having this knowledge allows the operator to understand the treatment process and reasons plants are designed this way.
Water Treatment Sample Question
What form of iron passes through a sand filter and typically causes dirty water complaints from customers?
A. Ferrous bicarbonate
B. Ferric hydroxide
C. Insoluble iron
D. Fe(OH)3
Answer: The correct answer is A. Public water supplies that utilize groundwater as their source typically have to combat with high iron levels in the raw water. Raw groundwater with high concentrations of soluble ferrous bicarbonate will appear clear until the soluble iron is oxidized by dissolved oxygen and/or chemical oxidant. To reduce discolored water complaints, iron, should be completely oxidized and removed at the treatment plant. Ferrous bicarbonate that passes through the treatment plant and distribution system may become oxidized inside the customers residence and cause staining on laundry and fixtures.
About the authors: Rick Lallish is the Water Pollution Control program director at the Environmental Resources Training Center (ERTC) of Southern Illinois University Edwardsville. He provides training for entry-level operators in the wastewater field and operators throughout the state looking to further their education. Lallish was also named the 2017 Illinois Operator of the Year and 2018 president of the Illinois Association of Water Pollution Control Operators.
Drew Hoelscher is the program director of drinking water operations at the Environmental Resources Training Center in Edwardsville, Illinois.
