Theresa Street Facility

Underneath and throughout Lincoln are 840 miles of sanitary sewer lines and 14 pumping stations that keep the wastewater flowing to two municipal treatment plants. The Theresa Street Plant sits on 51 acres along Salt Creek in the north central section of the City. As Lincoln expanded to the east, the Northeast Wastewater Treatment Plant was constructed just south of Interstate 80 and east of Highway 77. The Theresa Street facility has a maximum capacity of 24.5 million gallons per day and on an average day presently treats about 18 million gallons of wastewater. The Northeast facility presently treats about 6.5 million gallons per day. That adds up to 24.5 million gallons of water per day running through the two treatment plants - enough to fill Holmes Lake in 3 and one-half days.

How Wastewater Treatment Is Done at the Theresa Street Facility

Technology gives us the capability to treat wastewater so that the processed water can be safely returned to the environment. At the Theresa Street Plant, the activated sludge process and trickling filter system is used for the treatment of wastewater.

The activated sludge process gives the best results of all treatment methods. Wastewater passes through two complete stages of treatment and is also disinfected with chlorine. The simplified chart at the right and the description omit many of the technical terms and engineering processes involved. However, they will give you a general understanding of how wastewater is treated at the Theresa Street Plant.

• A.   Preliminary Treatment Area - When wastewater enters the plant, it is passed through mechanical screens and grit chambers. Large pieces of debris are caught by a bar screen, and grit (such as sand and gravel) is settled out. The materials removed are hauled by truck to the landfill.
• B.   Primary Settling Tanks - Wastewater flows into six large primary settling tanks capable of holding more than 614,000 cubic feet of wastewater. It is retained in the tanks for approximately 3.7 hours to allow solids to settle to the bottom. The solids and floating scum are removed by mechanical scrapers and diverted to scum pits.
• C.   Secondary Aeration Tanks - Air is pumped into tanks which receive the partially treated wastewater from the primary settling tanks. The wastewater, which contains countless microscopic organisms, and the air are mixed together mechanically. The mixture of air and organisms causes the pollutants to decompose.
• D.   Trickling Filter Train - Wastewater from Primary Settling Tanks One and Two flows to eight 1-19 foot diameter trickling filters. The trickling filters have rock media, tile under-drains and mechanically sealed rotary distributors. The effluent flow from trickling filters goes to =5 Final Clarifier (Secondary Settling Tank).
• E.   Secondary Settling Tanks - Wastewater from the secondary aeration tanks flows into four secondary settling tanks (a fifth settling tank receives flow from the trickling filters), holding more than 508,000 cubic feet of water. After approximately 3.5 hours, the water leaves these tanks with more than 90% of the original pollutants removed.
• F.   Final Contact Basin & Chlorine Treatment - Before the water is released into Salt Creek, it is disinfected with chlorine. Baffled chambers hold the water long enough to give the chlorine time to act.

The sections above describe basic treatment methods. However, large amounts of sludge which have been removed from the wastewater must still be processed. Here is how that is done:

• G.   Anaerobic Digesters - Sludge removed in the primary treatment process is pumped into a large tank called an anaerobic digester. The sludge decomposes in the tank before being pumped through the sludge tank and on to the filtering process.
• H.   Air Flotation Tanks - In these units, waste activated sludge from the secondary treatment process is concentrated with water and air under pressure. Sludge is forced to the top of each unit where it is removed by mechanical scrapers, pumped through the sludge tank and on to the final filtering process.
• I.   Belt Filter Press - The function of the belt filter press is to provide de-watering for the sludge. Raw and waste-activated sludge is pumped to the belt press from the primary settling tanks and the DAF units. The sludge is mixed with a chemical solution and fed onto belts that allow the water to drain, leaving the sludge to be pressed into a 'cake' (de-watered sludge). This 'cake' is carried from the belt filter press discharge by conveyors which drops it into an awaiting truck for disposal.

Supporting Services

The Theresa Street Plant was designed for an average daily flow of 30 million gallons per day and a peak stream flow of 61 million gallons per day. There are dozens of support activities performed daily to be certain the wastewater treatment processes are properly accomplished.

For example, a laboratory is staffed with chemists and technicians who conduct continuous tests as a quality control measure. Activities such as maintenance and repair of the system are carried out routinely by Theresa Street Plant technicians and craftsmen.

An Invitation

We want you to know as much as possible about the Theresa Street Water Pollution Control Plant and how it operates. Group tours of the treatment facility are available. Simply telephone or write us. We want you to see for yourself that you truly can take your sewer service for granted.