By Cassie McClure
Published in Las Cruces Bulletin on 9.16.22
For nearly a year, Las Cruces Utilities (LCU) has been conducting a new pilot study to see how they can continue and expand the mitigation of odors from wastewater that travels miles through sewer pipes and ends up at the Jacob A. Hands Wastewater Treatment Facility (JHWWTF).
“Ironically, fresh wastewater doesn’t really smell,” said LCU Deputy Director Wastewater Laura Montoya. “Wastewater starts to gain odor as it travels through the collection system; the farther it has to travel to the treatment facility, the more it’s going to stink. The wastewater can be really ripe when it gets to JHWWTF.”
Montoya explained that the study was not only to help expand odor control throughout the city but to determine the best locations to build odor control sites that can keep the chemical process stunted enough not to produce the smell as it goes to the plant.
Montoya and her team started the work of the new study at Well 33 – which links to the wastewater pipes nearby – by introducing magnesium hydroxide, which raises the pH of the water above 7. At that point, hydrogen sulfide (H2S), the chemical which emits the typical and toxic sewer smell, cannot be produced.
“Bacteria in wastewater need some sort of oxygen source to survive. When wastewater is fresh, the bacteria will use the gaseous oxygen dissolved within it in an aerobic process which doesn’t stink,” she said. “When this oxygen is used up, the bacteria will anaerobically metabolize sulfates (SO4), releasing the sulfide (S) ion, which bonds with the hydrogen (H) ions in water and ultimately forming hydrogen sulfide (H2S) gas which smells like rotten eggs. The magnesium hydroxide raising the pH eliminates excess hydrogen ions, thereby inhibiting the formation the H2S gas.”
Montoya explained that much like our gut has no oxygen, the smell at the toilet is from our bodily waste that is coming from our anaerobic metabolism.
“We haven’t gotten rid of H2S completely out of our wastewater system, but it's dropped significantly,” she said. “Our focus is decreasing it as it comes our way. We have pipes stretching for miles, from out to Sonoma and even from NASA, so as it travels, it increases H2S. Our plan in the future might be to put a full odor control site on that side of town to mitigate the H2S.”
For her employees, the buildup of that H2S is also a work hazard that, if it can decrease, will add to the overall safety of workers. “It’s toxic, and if you’ve been around the smell long enough, you get desensitized to it, and you can’t tell how concentrated it is,” she said. “While we don’t have a lot of locations where our crew are exposed to it, in other locations like in the sewers in New York City, sewer gas is a real danger.”
Montoya sees that long-term odor control sites would be something for the Wastewater line of business to budget and plan. She said, “For me, it’s taking the science and seeing how it solves problems in the real world and how to accomplish the goal.”
LCU – Your Utility Connection. Customer Central can be reached at 575-541-2111 from 8 a.m. - 6 p.m. Monday through Friday. LCU provides clean, safe, and reliable services to Las Cruces residents and businesses. Learn more at: las-cruces.org/180/Utilities
For emergencies, call Dispatch at 526-0500.
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PHOTO 1: A magnesium hydroxide delivery at Well 33 overseen by LCU Wastewater Maintenance Worker Erik Medrano. This chemical is used for an odor control pilot study where LCU is investigating mitigating chemical reactions wastewater has as it travels through the sewer pipes.