PENN TWP — Ten years after opening, the Saxonburg Area Authority's sewage treatment plant off Renfrew Road still has room to serve more customers.

Paul Cornetti, authority manager, said the average daily flow actually has been shrinking since 2011 due to sewage line replacements.

“If there's not a tight seal, then rain water can get in,” he said.

The former treatment plant on Dinnerbell Road in Jefferson Township — which serviced 1,125 residential and business customers in Saxonburg, Clinton Township and Jefferson Township — put out a daily average of 534,000 gallons.

After the new plant was operational with the initial addition of 1,785 Middlesex and Penn customers, the flow exceeded an average of a million gallons daily. Eventually, another 243 customers connected.

After peaking at 1.2 million gallons in 2011, the plant's daily flow fluctuated slightly through 2014 with an overall drop to 788,000 gallons last year.

Cornetti said the authority spent nearly $2 million replacing lines in the system, which reduced the amount of rainwater seeping inside loosened seals.

“You can see the effect it had,” he said.

Cornetti said the plant, which would not need major upgrades for two decades, is equipped to handle pending development in the authority's coverage area.

“Based on growth trends, we're over 20 years,” he said.

There are 125 new connections pending in various developments.

Another 520 new customers will be added to the system once the Middlesex Crossing along Route 8 and subsequent phases of the Weatherburn and Blackhawk housing plans in Middlesex are completed.

The $11 million plant was part of the authority's $63 million expansion into Penn and Middlesex.

A decade later, the treatment plant still does not stink.

The absence of odor in most areas of the plant is due to the use of an aerobic wastewater treatment system in which oxygen is injected into the tanks.

As the sewage enters the plant, inorganic material such as plastic is filtered out.

“We pull out all the inorganic solids,” Cornetti said.

The sewage is then sent into the oxidation ditch, a circular concrete tank divided by three concentric rings, where microscopic organisms break down carbon-based material.

The treated sewage is separated into liquid and solid matter. That liquid is disinfected by ultraviolet light and discharged into Connoquenessing Creek.

After being separated from the water, the solid waste undergoes another separation in which more liquid is extracted to be sent through the treatment process a second time.

The dry material is hauled to a landfill.

Since the plant capacity has not been reached, one of its two settling tanks remains empty.

Cornetti said the tanks are rotated each year between being used and sitting idle.

He said the only chemical added to the process is aluminum sulfate six months a year.

“It reduces our phosphorus,” Cornetti said.