Last week, we shared an invite to tour the city’s wastewater treatment plant, which is about to get a $152.7 million upgrade that will double its treatment capacity.

We had no idea what to expect in terms of audience interest, but all tickets were reserved within a day.

We started our tour on Wednesday with a one-hour presentation from Chris Earl and Matt Webster, the facility’s manager and assistant manager, respectively.

Here are some things we learned about the plant:

• When people hear that the plant will double its capacity, they might wonder about the smell that it will generate. Staff actually expects the odor to be much less noticeable thanks to an upgraded influent building (where raw sewage enters). With advanced air filtration, Earl says you’ll be able to walk by the facility without noticing the smell.

• The wastewater treatment process relies on nature’s little helpers — billions of microorganisms, which staff manipulate to speed up natural processes. “We like to say we’re farmers,” Earl told our tour group.

• 9/11 affected the treatment process. Until then, the plant used chlorine gas to treat wastewater. While chlorine is a common industrial chemical, it could also be used in a chemical attack, so federal officials implemented stricter safety precautions. The inspection and security requirements became cumbersome, which is partially why the facility switched to UV light as an alternative.

• The five-person maintenance team that manages the wastewater plant also oversees 62 lift stations around town.

• Before deciding to expand the wastewater treatment plant, staff considered sending more wastewater to a regional facility near XNA run by NACA. However, the cost of building the infrastructure to pump wastewater there would have exceeded the cost of upgrading the city’s centrally located plant. The NACA facility serves several cities, and wastewater from residences and businesses south of Highway 102 in Bentonville is already sent there.