June 2006, Vol. 18, No.6

Plant Profile

Johnstown Wastewater Treatment Plant

PlantProfileMapJune06

Location: Johnstown, Pa.
Startup date: 1961
Service population: 60,000
Number of employees: 16
Design flow: 12 mgd (45,000 m3/d)
Average flow: 8 to 10 mgd (30,000 to 38,000 m3/d)
Peak flow: 27 mgd (102,000 m3/d)
Annual operating cost: $5.7 million 

 

The Johnstown Wastewater Treatment Plant provides wastewater treatment to 20 municipalities and more than 60,000 people in the greater Johnstown, Pa., area. The plant provided primary treatment from the time of its construction in 1961 until 1992, when an activated sludge secondary treatment system was installed as part of a $30 million upgrade.

The upgrade was conceived in 1976, when the U.S. Environmental Protection Agency (EPA) ordered it, but the project was delayed indefinitely following the catastrophic flood of July 19 and 20, 1977. Finally in 1987, EPA and the city negotiated a consent decree to install secondary treatment. Johnstown delegated the construction and financing project to the Johnstown Redevelopment Authority, which bought the plant in October 2004 and operates it for the city.

Today, influent enters the headworks through a 60-in. (1500-mm) pipe that can handle flows as high as 27 mgd (102,000 m3/d). Typical plant flow ranges between 8 and 10 mgd (30,000 and 38,000 m3/d). From the headworks, the flow passes through a 0.375-in. (9.5-mm) mechanical bar screen to an aerated grit basin where inorganics settle out. Settled material is washed and deposited into a dumpster along with the mechanical bar screenings for landfill disposal.

Raw influent flows from the aerated grit chamber to an onsite pump station. Four 100-hp (75-kW) pumps move the flow to an aeration tank. The secondary process is a pure-oxygen activated sludge system. Due to the small size of the site, the aeration tank is one-fifth the size necessary to properly treat sewage utilizing atmospheric air for aeration, so pure oxygen is used to accelerate the activated sludge process. The plant uses about 5 to 10 ton/d (4.5 to 9 tonne/d) of cryogenically produced liquid oxygen — depending on the water temperature. Tanker trucks deliver the oxygen to the plant regularly.

Following aeration, four rectangular clarifiers that were converted from primary to secondary clarifiers and a 110-ft-diameter (34-m-diameter) circular clarifier that was built during the upgrade to secondary treatment allow solids to settle out further. Effluent from the secondary clarifiers then flows to three chlorine contact tanks and is discharged to the Conemaugh River.

Solids Handling
Before the secondary treatment upgrade, the plant relied on vacuum filters and a natural gas incinerator to convey and dispose of primary sludge. The ash, which amounted to approximately 30% of the original sludge volume, was disposed of at a landfill. Now, all of the sludge at the plant comes from the secondary treatment system.

The upgrade to secondary treatment initially included incineration as the ultimate disposal method, but the multihearth incinerator installed for the task could not maintain pace with the plant’s secondary sludge production.

Sludge is wasted from the secondary system to a gravity thickening tank, and then pumped to holding tanks. From these holding tanks, the sludge travels to one of two 7.2-ft (2.2-m) filter belt presses. After the thickened sludge dewaters to 17% to 20% cake, it travels to a pugmill, where it mixes with cement-kiln dust, a byproduct of the cement production industry. The high-alkaline cement-kiln dust lime-stabilizes the sludge to produce Class B biosolids. The plant produced and land-applied 22,000 ton (20,000 tonne) of Class B biosolids in 2005.

Extra Work
In addition to upgrading the plant to secondary treatment, the $30 million renovation budget included about $7 million to upgrade the main interceptor line that runs through Johnstown. This main interceptor serves the city of Johnstown and 19 municipalities that are tributary to the system. Three of these systems are combined sewer systems; this, along with other infiltration and inflow problems, surcharges the plant during wet weather periods. The Redevelopment Authority currently is taking the lead in a concerted effort of all of the municipalities to reduce wet weather flows.

To further increase plant treatment capacity and efficiency, construction of another 110-ft-diameter (34-m-diameter) circular clarifier is slated for this year.