What’s that smell in Portland? Blame it on an $11.4 million upgrade and an aging aeration system at the East End Wastewater Treatment Plant.

The project has been going on for about a year and won’t be done until next year. But people throughout the city noticed a spike in foul odors in recent weeks as the Portland Water District, which operates the plant, began to transition to the new equipment and as one of the plant’s old aerators malfunctioned.

Inadequate aeration of the sewage in open tanks at the plant coincided with the warmest and most humid months of the year, when odor complaints tend to increase, said water district spokeswoman Michelle Clements.

“We just have a lot of things happening at once,” Clements said about the cause of the odor. “It’s pretty clear this construction is a factor. We’re doing everything we can to minimize that (smell).”

Scott Firmin, director of wastewater services, said the plant typically operates with two of three aeration basins and uses the third when demand peaks. Equipment malfunctions and a 36-year-old aeration system are making it difficult to infuse enough oxygen into the wastewater, which is necessary to eliminate odors, he said.

This photo taken from a drone shows the East End Wastewater Treatment Plant, which is getting an $11.4 million upgrade.

This photo taken from a drone shows the East End Wastewater Treatment Plant, which is getting an $11.4 million upgrade. Photo by Bill Lord/Maine HDTV Photo by Bill Lord/Maine HDTV

The East End treatment plant has been located since 1979 at the base of Munjoy Hill, then a run-down, working-class neighborhood. The area has since become one of Portland’s most expensive places to live. The facility treats roughly 20 million gallons of wastewater a day.

Complaints about sewer odors spiked last month, and the smell was particularly strong Monday.

Tiffany Crockett, who was making art Tuesday on Munjoy Hill, said the smell, though not totally obnoxious, was noticeable more than a mile away at the University of Southern Maine on Bedford Street, where she takes art classes.

“It smelled like waves of poo,” joked Crockett, who did not lodge a complaint. “It was coming in waves, just like the ocean.”

SURGE IN COMPLAINTS THIS SUMMER

The water district received 33 formal complaints in July about the sewage odor through its online “Odor Monitoring” portal, according to data provided by the district. That is far more than the five complaints received in June and the 13 complaints it received in July 2015.

While odor complaints in the past were mostly filed by residents living on the East End, in recent weeks complaints to the water district and to the city’s online complaint page, SeeClickFix, have been more widespread. Beginning in late June and continuing through July and August, the odor has been reported on Munjoy Hill, Bayside, India Street, downtown and the Back Cove.

Two residents of St. Lawrence Street on Munjoy Hill said the smell was especially offensive on Monday night and Tuesday morning.

” ‘Tremendous’ is the word I would use. It was a tremendous odor,” said Chris Smith, whose friend filed an online complaint with the city Tuesday. “It was so bad I had to close my windows.”

Sewer smells have been an issue in the past. In 2012, the district brought in an expert to help identify the source of foul odors, and the aeration system was identified as a contributing factor.

Clements said the district has taken extra steps to address the odor issues associated with the construction project.

Inadequate aeration of sewage in open tanks at the East End Wastewater Treatment Plant coincided with the year's warmest and most humid months.

Inadequate aeration of sewage in open tanks at the East End Wastewater Treatment Plant coincided with the year’s warmest and most humid months. Derek Davis/Staff Photographer Derek Davis/Staff Photographer

The plant is no longer accepting waste from private septic haulers in Portland, sending them instead to Westbrook, as a way to reduce the demand on the aeration equipment. The district also has purchased and installed two temporary aerators, and it has fast-tracked the upgrade, which is a month ahead of schedule, Clements said.

The district began testing the new equipment, called a train, in the first of three basins this week, she said.

“We anticipate that once we get this first train up and running, this should minimize some of the worst odors,” Clements said. “It’s a much more effective and efficient system, it’s just a matter of getting that first train up and going.”

The Munjoy Hill Neighborhood Organization posted a message for residents Tuesday saying the intensity of the odor should decrease in the coming days, although there still may be odors from time to time until the project is done in the fall of 2017.

Hill residents such as Andy Jennings were relieved to hear that the problem was being addressed.

“Fortunately, it’s not something that happens very frequently,” said Jennings, who lives on St. Lawrence Street.

PLANT’S AERATION SYSTEM MODERNIZED

Aeration is a critical step in treating wastewater. After entering the treatment plant, wastewater is screened to remove debris, such as sticks and trash, and other inorganic material. Wastewater is then moved to a series of covered tanks, designed to allow the solids to settle to the bottom. Those solids are later removed, processed, treated and typically recycled as inexpensive organic fertilizer.

After the sediment is removed, the water is aerated, a process that involves the circulation of oxygen to encourage the growth of microorganisms that consume more than 90 percent of the remaining organic material. A lack of oxygen can lead to increased odors, said Firmin, the wastewater director.

From there, the water is clarified one more time, disinfected and discharged into Casco Bay.

Clements said the old aeration system, which uses fans on the surface of the water, has reached the end of its useful life. The new system uses three diffusers that inject oxygen into the water from the bottom of each tank.

Successful – and odorless aeration – relies on an abundant supply of oxygen.

“In that part of the process, air is essential, so covering it is not really an option,” she said.