The city plans to spend $3.2 million for odor control at the Moccasin Bend Sewage Treatment Plant.
A second $198,606 contract is to study how to reduce the city's water bill at the sewage treatment plant and make better use of sewage effluent.
Jerry Stewart, plant manager, said the contract with Haren Construction Company will use a biological scrubbing process to clean portions of the plant and hold down bad smells. He said it will also help with corrosion control and make the plant safer for employees.
Councilwoman Deborah Scott said a more pressing problem is that of odors downtown, which she said are mainly caused by the city's aging combined sewers. She said a survey was taken of smell complaints and most were about downtown problems.
She said of the $3.2 million in work, "I don't think it's a panacea for downtown."
Mr. Stewart said it would cost at least $400 million to separate all the city's combined sewage lines.
He said one step being taken by the city is that when a road is under construction crews take the opportunity to install trap basins that help dampen odors. But he said just about five percent of lines have the device, which costs between $3,000-$5,000.
Another method being studied is to carry out periodic jet cleaning of the combined lines.
Councilwoman Sally Robinson said the city has "a couple of big stinky problems" - referring to the treatment plant and the combined sewers. She said, "We need to deal with both of them."
Mr. Stewart said the treatment plant now "is in the middle of a national park." He said there are many more visitors to Moccasin Bend and homes are being built closer.
He said the city's water bill with Tennessee-American Water is $235,000 a year.
The treatment plant uses eight million-10 million gallons of water a month.
He said the study will look at whether the city could make better use of the effluent, but he said it never will be drinking water.