Town of Speedway, Indiana

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The Speedway Wastewater Treatment Plant is a Class IV treatment facility with a design flow of 7.5 million gallons per day (MGD), a primary treatment capacity of 11.25 MGD, and a peak secondary treatment capacity of 8.9 MGD. The treatment process consists of the following: influent cylindrical fine screen, grit collectors, primary clarifiers, oxygen activated sludge, secondary clarifiers, nitrification towers, chlorination and de-chlorination. Solids handling consists of anaerobic digestion and belt filter presses for dewatering.

The sewer system is 85% sanitary and 15% combined. Inflow and infiltration is a problem and the combined sewers add a significant amount of stormwater to the system. Because of this, a combined sewer overflow (CSO) is located at the headworks to the treatment plant. Whenever the flow exceeds the plant primary capacity of 11.25 MGD,  a portion of the wastewater stream discharges out the CSO in order to protect plant equipment and optimize treatment efficiency.

The treatment process begins when the flow passes through the cylindrical fine screen. This screen removes the large material such as cans, bottles, etc. from the waste stream.

The flow volume is then measured by means of a 36-inch parshall flume and ultrasonic flow meter. A pH meter is installed at the flume to contiuously monitor the pH. The wastewater enters a wet well where it is pumped to the grit tanks.

In the grit tanks, the flow velocity is slowed down so the heavier grit material such as sand, rocks, etc. can settle out. The settled grit is then pumped to a grit separator that separates the water from the grit material. The water flows back to the head of the plant to be treated and the grit is collected in a dumpster and disposed of in the landfill.

After grit removal, the wastewater flows to the primary settling tanks. In these tanks the flow velocity is slowed further, causing the lighter material to float to the top and the heavier material to settle to the bottom. The floating material (scum) is collected and sent back to the head of the plant to be removed by the cylindrical fine screen. The heavier material (sludge) is collected and pumped to the anaerobic digester for further treatment.

Now that primary treatment has been accomplished, the primary effluent flows to the oxygen activated sludge process (Unox). In this process, the most important treatment takes place. Microorganisms (bugs) are utilized to absorb and break down the waste materials in the wastewater. This is accomplished by providing the bugs with food (organics in the wastewater) and oxygen, which is generated onsite by the Pressure Swing Adsorption unit (PSA). The PSA unit takes atmospheric air and separates the oxygen from the nitrogen. The nitrogen is vented to the atmosphere and the oxygen is sent to the Unox tank to be used by the bugs. Mixers in the Unox tank keep the contents suspended to better convey the waste material and oxygen to the bugs. As the bugs multiply, they become over populated and some of the bugs must be removed from the system (wasted) daily in order to maintain a controlled environment. This wasted material is pumped to the waste sludge holding tank to be thickened.

After treatment in the Unox tank, the flow goes to the final settling tanks. Here the bugs settle to the bottom leaving a clear liquid at the top. The clarified effluent continues downstream for further treatment. The settled bugs are returned to the Unox tank or removed from the system.

The wastewater is now ready for ammonia removal in the nitrification towers. In the towers, a fixed plastic media is used to grow a special type ammonia-removing bacteria. The wastewater is pumped to the top of the towers where it is distributed across the surface of the media. As the water trickles down through the media, the bacteria convert the ammonia to nitrates.

The wastewater now flows to the chlorine contact tank for final treatment. In this tank, chlorine is added to kill the pathogenic bacteria. The chlorine is then removed using sulfur dioxide after which the effluent is discharged to Eagle Creek.

The solids (sludge) that have been removed from the wastewater during treatment must now be processed. Solids handling is accomplished in two phases. First, the sludge is treated in the anaerobic digester by heating it up to about 95 degrees and holding it for at least 15 days. During this process pathogen reduction takes place as the sludge is converted primarily to methane, carbon dioxide, and cellular material, thus rendering the sludge relatively stable. The digested sludge (biosolids) is then dewatered with a belt filter press and pumped to a storage building. The biosolids are then utilized on farm land as a fertilizer and soil conditioner.