After an $11.7 million renovation, the Chelsea Wastewater Treatment Plant has greatly increased its capacity and is now better equipped to better mask sewage odor.

The treatment process is not significantly different, according to John Hanifan, Chelsea’s city manager, who said water treated by the plant and discharged into the environment has always met state standards.

Among the improvements to the plant are a new enclosed headworks, where the gray water initially collects, a new oxidation ditch, where microorganisms consume waste in the water, and four new enclosed biosolid storage tanks, each with the capacity of 250,000 gallons. Both the headworks and the biosolid tank have a carbon filter system that allows for less odor.

An additional selector tank was also added, which will help the plant to use fewer chemicals for phosphorus reduction.

“The selector tank is an "anaerobic" environment, which allows the micoorganisms to work better and so there is biological reduction of phosphorous,” said Hanifan.

One of the main improvements to the plant was its enhanced capacity. Before the improvements, the plant was able to treat 1.1 million gallons a day. That total now stands at 1.8 million gallons a day.

“During peak flows, we had storm water (around) 1.8 million gallons,” said Hanifan, adding that operators at the plant had been skillful in working to store and treat that amount, and the plant had not had a spill that released untreated sewage.

“If we are running consistently over capacity, (we run the risk of) sewage (backing up) in homes, or the discharge of raw sewage in the creek.… We want to make sure that is never an issue,” said Hanifan, adding that that when officials applied to the state for a loan to make improvements, they had to demonstrate that they were at or above capacity at the plant, and that it had outlived its useful life.

They secured a State Revolving Loan Fund at 2 percent interest to make the renovations possible. Payback is in 20 years, at about $750,000 per year.

“Two percent was a fantastic rate,” said Hanifan, who said that the renovations were completed in May.

This video on the city's website explains the sewage treatment process and improvements to Chelsea's plant.

Alana West is a freelance reporter for AnnArbor.com. Reach the news desk at 734-623-2530 or e-mail news@annarbor.com.