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The Metropolitan Syracuse Wastewater Treatment Plant (Metro) provides high quality treatment for 270,000 people and many industrial and commercial customers in the City of Syracuse and some areas outside the city in Onondaga County. Metro treats an average of 84 million gallons per day. Full secondary and tertiary treatment can be provided for up to 126 million gallons per day. Metro has a total hydraulic capacity of 240 million gallons per day during wet-weather events such as rainstorms.

Wastewater treated by Metro

Major upgrades of treatment at Metro mean improved water quality in Onondaga Lake.

Wastewater reaches Metro from a number of sources. The largest is the Main Interceptor Sewer (MIS) that runs north-south through nearly the center of Syracuse. The MIS is 90-inch in diameter.

The Harbor Brook Pump Station contributes 30 million gallons per day (MGD) to Metro. In addition, the Ley Creek, Westside, and Liverpool pump stations convey wastewater to Metro.

This influent enters a diversion structure that can channel wastewater to either of the two grit-removal facilities at Metro. An overflow structure prevents any flooding at the treatment plant in case of an emergency.

Preliminary treatment

The first step in treating the sewage at Metro is the removal of sizable objects. The wastewater flows through large racks with spaced steel bars, and debris that cannot fit through the spaces is caught on the racks. This material is removed and disposed of.

Inside a grit chamber

The wastewater next enters the grit chambers. Sand, stones, and other small bits of solid waste are removed there. Wastewater then flows through screens where additional debris is removed.

Influent pumping

Since water always flows downhill naturally, it is easier to manage the wastewater if it flows by gravity through Metro. The low-lift pump station raises the incoming wastewater to such a level. The station has five centrifugal pumps rated for 600 horsepower. The pumps' speeds vary depending on the amount of wastewater entering the plant. Each pump has the capacity to handle 60 MGD—for a total of 240 MGD for the low lift pump station.

The wastewater is discharged from the lift station to a 90-inch diameter force main that is 820 feet long. At an average rate of 84 MGD, the flow is 2.2 ft/sec.

The wastewater is treated in stages—three times—
before it is disinfected and discharged to Onondaga Lake.
The treatment stages are named primary, secondary, and tertiary.

Primary treatment

In the first stage of, treatment process, solid particles settle from from the water. The wastewater's velocity is slowed to permit the solids to settle. The solid material falls into a trough at the bottom of a tank. This mixture of solids and wastewater is pumped to thickeners where the amount of water is substantially reduced. This material is then disposed of.

At this stage, too, oils and grease are skimmed from the surface of the water.

Primary clarifiers

Primary clarifier tank. Settling takes place here.

Treatment starts in the primary clarifiers. They are 135 ft in diameter, have a 10-ft side wall depth, and can hold 1.07 million gallons.

Bypass flows

After primary treatment, any flow greater than 66 MGD/side (126 MGD total) is sent to the by-pass chlorine contact tanks for disinfection. This facility consists of two rectangular tanks (31 ft by 100 ft by 20 ft deep). If flow is 126 MGD, the contact time is 13 minutes.

Secondary treatment

Aeration area

The next stage of wastewater treatment provides a controlled environment where bacteria come in contact with the organic matter. An iron salt is added to improve removal of phosphorus.

Aeration tanks mix the water and provide sufficient contact time to decompose and the organic material and allow it to coalesce for later removal from the water. Metro has eight aeration tanks, 100 ft by 130 ft by 14.2 ft deep. Each holds 1.4 million gallons.

Secondary clarifiers hold the water to permit the solids to settle. In this process, the biosolids are moved to the center of the tank, and most of this material is pumped to the thickeners. Each of the four secondary clarifiers are 170 ft square by 11 ft deep. They each hold 1.83 million gallons.

SEPS has four pumps, rated at 500 horsepower

Treatment is not yet finished, however.

Tertiary treatment—state of the art

In January 2004, Onondaga County WEP put into service a new pump station that will pump secondary-treated wastewater to the tertiary process. Known as the SEPS (Secondary Effluent Pump Station), it now pumps a peak flow of 126 MGD to a new state-of-the-art tertiary treatment process for year-round removal of ammonia.

Removing ammonia

Effluent flow through the BAF cross gallery

Ammonia in high concentrations can be lethal to juvenile fish and other aquatic animals. The concentration of ammonia discharged from Metro is now being reduced significantly, after startup in January 2004 of the biological aerated filter system (BAF).

Ammonia is removed from the wastewater using a process developed by I. Krüger, Inc. that uses a biological aerated filter (BAF) called Biostyr.

At Metro, the BAF process consists of eighteen individual cells, each with a capacity of about 273,000 gal. The cells are filled with billions of polystyrene beads that are 0.14 inch in diameter. These beads provide a huge surface area on which grow nitrifying bacteria, and these bacteria convert ammonia to nitrate and nitrite. The BAF process lowers ammonia below 1 mg/L.

Disinfection of the discharge water

Following the BAF process, the treated water passes through an ultraviolet light disinfection system. UV light provides a chemical-free way to disinfect wastewater by altering the genetic material in bacteria, viruses, and other micro-organisms so that they no longer can reproduce. UV light provides an environmentally safe way to disinfect wastewater.

UV disinfection lights being readied for testing, Jan 2004

The UV system consists of 308 high-intensity germicidal lamps that are submerged in an open channel. As the wastewater flows past the lamps, the micro-organisms are exposed to a lethal dose of UV energy. The intensity of the UV lamps can can be varied to deliver between 840 and 2400 watts.

Biosolids

The biosolids and associated liquid—products separated through primary, secondary, and tertiary treatment—are thickened to reduce the liquid content. A polymer is added to the mixture to promote settling of the solids.

The three thickening tanks are 65 ft in diameter and 12 ft deep. Each holds 298,000 gallons.

Biosolids digestion

Digesters

The thickened biosolids are kept heated between 90-95°F and mixed. A byproduct of this process is methane gas, which is used to fuel the boilers that heat the digesters and the buildings at Metro.

The plant has three primary digesters that are 100 ft in diameter with walls 27.5 ft high. They each hold 1.6 million gal.

Biosolids dewatering

The digested biosolids are treated with a polymer to promote further separation of solids and the water. The biosolids are then pressed on a belt filter to produce a cake. Most of this material is converted to an agricultural fertilizer using the N-Viro™ Soil process. The product is used by farmers throughout Central New York.

See more on biosolids and their use.

Future treatment improvements

Many improvement projects have been completed and are resulting in measurably better water quality. The largest and most significant upgrade in treatment is the advanced ammonia and phosphorus removal facilities.

Phosphorus

Phosphorus is a nutrient that aids algae growth. In limited quantities, algae is beneficial, but in high concentrations it can cause many problems. An over-abundance of algae is unsightly, leads to odors, and, most importantly, when it dies it sinks to the bottom of the lake and decomposes using precious dissolved oxygen in the process. The oxygen is critical to fish and other aquatic life.

Thus, more phosphorus leads to more algae—which leads to less oxygen.

As with ammonia, the concentration of phosphorus in Metro's discharge has been declining over the past several years because of Onondaga County's operating changes and pretreatment efforts. With the addition of the Advanced Ammonia and Phosphorus Removal Project, future water quality will be even better.