Exam Study Guide: Sewers and Hydrogen Sulfide

Exam Study Guide: Sewers and Hydrogen Sulfide

[Editor’s Note: We’ve enhanced our Exam Study Guide Series to give you more of the content you love. Instead of two short questions per month on the topics of water and wastewater treatment, you’ll now find a pair of study questions every week with high-quality explanations from our expert contributor Ron Trygar of the University of Florida’s TREEO Center. Make no mistake, this will be an excellent resource going forward. Ron is the real deal — check out his bio at the end of this week’s quiz.]

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 ongoing Exam Study Guide Series.

This week, we’ll cover two questions about water entering sewers through ground-level drainage, and the behavior of hydrogen sulfide. Take a look at the multiple-choice quiz questions and answer explanations below.

1. Water that enters a sewer line through surface, or ground-level drainage sources such as broken clean-outs, service laterals and unsealed manhole covers is known as what?

A) Inflow

B) Infiltration

C) Exfiltration

D) Effluent

The answer is A, inflow. Rainwater or groundwater entering a sanitary sewer system is generally termed Inflow and Infiltration, or I&I. Inflow is the direct flow of stormwater intrusion into a sanitary sewer from ground level openings in the sewer lines. Common entry points are broken or deliberately opened clean-out caps in residential property, illegally plumbed sump pump discharge lines or rain gutter downspouts, poorly sealed manhole covers, cross-connected storm water drain pipes and cracked or broken lateral lines from homes to the main sewer line.

Infiltration, on the other hand, is when water in the soil/ground water table leaks or seeps into the sewer lines through cracks or breaks in the sewer line itself or through open pipe joints.

Exfiltration is the opposite kind of problem. That's when sewage leaks from the interior of the sewer line to the outside of the pipe, contaminating the soil or water that it enters.

Effluent is the common term used for treated wastewater from a treatment plant, but could also mean the flow of water out of a basin, pipe or other treatment tank or structure.

2. Which statement shown below regarding hydrogen sulfide is correct?

A) Hydrogen sulfide causes corrosion due to the development of high pH conditions

B) The lower the pH of the sewage, the higher the potential for hydrogen sulfide to be present

C) Using acidic chemicals in lift stations is a method of preventing hydrogen sulfide formation

D) Hydrogen sulfide is lighter than air and will accumulate in the upper parts of manholes

The answer is B, the lower the pH of the sewage, the higher the potential for hydrogen sulfide to be present. Hydrogen sulfide is a deadly gas commonly found in sewage collection systems, wastewater influent treatment structures, empty treatment tanks that contain decomposing organic matter, manholes, vaults and other confined spaces. Hydrogen sulfide is about 2 ½ times heavier than air and can usually be found near the bottom of the locations previously listed.

This colorless gas can be described as having a rotten egg odor, and in high enough concentrations, it can deaden the victim’s sense of smell, giving a false sense of safety by the lack of a strong odor. Methods of controlling hydrogen sulfide in wastewater include adjusting the liquid pH with a basic chemical like sodium hydroxide, magnesium hydroxide or sodium hypochlorite (bleach). Hydrogen sulfide gas in moist environments like manholes and lift stations creates sulfuric acid (low pH condition) which is very corrosive to metal and concrete structures.

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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