Exam Study Guide: Organic Loading Rates; and Ion Exchange Softener Math

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 with in-depth explanations of the answers. Last time, we covered a set of wastewater and drinking water treatment questions on the topics Automatic Composite Sampling Devices; and Chemical Solution Math. This time, you can test your knowledge about organic loading rates and ion exchange softener math.

Wastewater Treatment Sample Question

How do you express the organic loading rate on a trickling filter?

A. Pounds of BOD per square foot of media per day
B. Pounds of BOD per cubic foot of media per day
C. Pounds of BOD per 1000 square feet of media per day
D. Pounds of BOD per 1000 cubic feet of media per day

Answer: The answer to this question is D. The organic loading on a trickling filter is an important factor for the proper operation of trickling filters. Simply put, it is the amount of organic matter (BOD) fed to the trickling filter per day. We express this as pounds of BOD per thousand cubic feet of media per day or pound of BOD/1000 ft³ per day. 

Factors to be aware of when dealing with organic loading on a trickling filter are: 1. all the surface area of the media is taken into account from the surface to the bottom (i.e. the volume of media) and 2. do not take into account the recirculation flow, as the formula only takes the flow and BOD concentration into account.

Water Treatment Sample Question

How many gallons per minute of raw water should flow through the ion exchange softener?

Raw water flow rate = 550 gpm

Raw water hardness = 425 mg/L as CaCO3

Desired finished water hardness = 165 mg/L as CaCO3

A. 165
B.. 213.5
C. 336.5
D. 425

Answer: The correct answer is C. Ion exchange softeners produce a zero hardness water, which creates a corrosive water. To help prevent corrosive water from entering the distribution system, an operator blends the softener effluent with bypass water. Bypass water is the portion of raw water that does not flow through the softener as part of the treatment. The bypass water eventually mixes with the softener effluent to create the desired finished water hardness. Typically, the division of the raw water into bypass water and softener water is after the pressure filter but before the softener. An operator can choose to adjust the desired finished water hardness by manipulating the control valve associated with the bypass water. 



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.



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