Treatment

Treatment Plant Process

Influent wastewater enters the facility through a 42″ diameter interceptor sewer located on Erie Street. Wastewater then flows through an Aerated Influent Channel, where it is metered by an open-channel Influent Flowmeter, then flows to the Grit and Screenings Building. The wastewater passes through a Mechanical Bar Screen that removes debris and other trash, which may harm the downstream processes. The wastewater then passes through Aerated Grit Channels to remove grit, sand, and other inorganic material from the waste stream. The grit is collected by chain and bucket grit collectors, where it is transported, washed, and dewatered by the Grit Screw Conveyor and discharged into a dumpster for disposal. The wastewater then flows to the Aeration Tank for secondary biological treatment.

Secondary treatment at the facility consists of a three-concentric-channel Aeration Tank followed by settling in the Final Clarifiers. The aeration tank contains a colony of microorganisms, known as “mixed liquor.” These microorganisms convert the biodegradable organic material in the wastewater into carbon dioxide, water, and additional cell material. Rotating discs in the channels provide oxygen to the system necessary to sustain the colony and maintain the activated sludge-wastewater (mixed liquor) mixture in suspension. Varying dissolved oxygen levels in each of the channels provide nitrification as well as organic solids removal. A flow control structure located in the center island of the aeration tank maintains a consistent water depth in the channels. Water Pollution Control Facility

After remaining in contact with the activated sludge for at least 24 hours, the wastewater flows by gravity to the Final Clarifiers for settling. There are two clarifiers, each measuring 75 feet in diameter. Here the activated sludge is separated from the wastewater by gravity settling. Effluent wastewater flows over the weirs to proceed on to disinfection, while the activated sludge is collected in the clarifiers and flows by gravity to a common sludge well located in the Clarifier Building.

Telescoping sludge valves regulate the amount of sludge transported. A portion of the sludge is returned to the aeration tank by the Return Activated Sludge (RAS) Pumps to seed influent wastewater and maintain a healthy microorganism colony. Sludge that is not returned to the aeration tank is removed by Waste Activated Sludge (WAS) Pumps, which pump the wasted sludge to the sludge storage tank for further processing and disposal. Both RAS and WAS Pumps are located in the basement of the Clarifier Building. Grease, scum, and other floatable solids are removed from the clarifiers by scum baffles and surface skimmers and collected in troughs. A Scum Pump Station collects the grease and scum and transports it to the sludge holding tank for further processing.

The effluent from the final clarifiers flow through a 36″ conduit to the Chlorine Contact Tank for disinfection. Chlorine is introduced to the wastewater through diffusers and the chlorine and wastewater remain in contact for a sufficient time to provide bacteriological kill. The chlorine remaining at the end of the tank is then removed by the addition of sulfur dioxide. The disinfected effluent then passes over the Post Aeration Unit for final aeration and is metered by the Final Effluent Metering Flume prior to discharge to Little Yankee Run. Final plant effluent (water) is recycled for process operations to minimize operational costs.

Information provided by WCPF Design Engineers, ms consultants, inc.

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City of Hubbard
Municipal Building

220 West LIberty Street
Hubbard, OH 44425
P 330.534.3090
F 330.534.8441

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