The treatment process begins when wastewater enters the facility through a 72-inch diameter pipe. It flows through channels and passes through mechanical bar screens which remove debris from the water. This debris, or "screenings," is rinsed and de-watered before being transported to the City Landfill.

The wastewater is then pumped uphill to the grit removal and pre-aeration facility , where grit (inorganic solids like sand and eggshells) is removed. Air is also added at this stage to "freshen" the wastewater and support the micro-organisms it contains.

After leaving the grit tanks, wastewater flows to the primary clarifiers. These tanks, whether rectangular or circular, allow wastewater to settle due to the slowing flow, enabling solids (sludge) to be removed from the bottom and scum to be skimmed from the surface.

The wastewater leaving the primary clarifiers is piped to the flow distribution box.

From there, it flows to the aeration tank influent channel, or a portion may be diverted to the flow equalization tanks. These tanks help regulate the flow of wastewater during high-flow periods by holding excess water, which is later released back into the influent channel when incoming flow decreases, ensuring a consistent flow through the treatment process. Later, as the incoming wastewater flow drops off, the equalization tanks are drained back to the influent channel at the beginning of the treatment process. This allows for a more consistent flow through the facility. 

Wastewater that is not diverted to the equalization tanks leaves the flow distribution box through the aeration tank influent channel. The first portion of the channel is underground. After surfacing at the influent end of the aeration tanks, vigorous mixing units prevent solids from settling in the channel. Valves located along the channel allow wastewater to flow into the aeration basins.

Four blowers supply air to the aeration tanks, pumping it through air diffusers mounted on piping grids at the bottom of the tanks. This air supplies oxygen to the micro-organisms responsible for converting the suspended solids in the wastewater into settleable solids. The diffused air also mixes the wastewater and helps to regulate the water temperature.

After the micro-organisms in the aeration tanks have converted the suspended solids into settleable solids, these solids settle out into secondary clarifiers. In addition to removing a portion of the solids from these tanks, pumps and piping are provided to return the remainder of the solids back to the aeration tanks. This ensures a healthy population of micro-organisms in the aeration process.

Although the wastewater looks good as it flows over the weirs from the final settling tanks, the wastewater treatment process isn't finished.

The process continues in the aqua cloth filters. In these filters, water flows through a layer of cloth to finish removing suspended particles of impurities. From there, the effluent flows to the chlorine contact chambers for disinfection. Liquid sodium hypochlorite is added to the effluent to ensure the removal of pathogenic (disease causing) bacteria.

Before the disinfected effluent can be discharged, the oxygen level of the water is boosted by allowing the water to flow over steps (cascades). Next, the effluent flow is treated with sodium bisulfite to ensure minimum chlorine residual. After measuring the amount of flow, the final treated effluent travels through a short pipe to South Buffalo Creek.

Biosolids Thickening Process

The settled solids (sludge) that are removed from the primary clarifiers are pumped to the sludge receiving and blending tanks. Here, the sludge from the T.Z. Osborne Facility is mixed using coarse air diffusers located at the bottom of the tanks. 

The combined sludge (or biosolids) is then pumped to the gravity sludge thickeners. These tanks operate the same as Primary Clarifiers, which allow the solids to settle to the bottom, thereby producing a thicker sludge. This thickened sludge is then pumped to the sludge holding tanks where a mixing system keeps the sludge mixed.

Sludge Dewatering

The City incinerates sludge in a fluidized bed incinerator. Before incineration can take place, the sludge (which is 96 to 98 percent water), must be de-watered. The first step in this process is to mix a polymer solution with the liquid sludge. The polymer is a flocculant. This means the polymer is used to "charge" the sludge particles, so they will tend to clump, or floc, making it easier to separate the solids from the water. After being treated with polymer, the sludge is pumped into centrifuges where centrifugal force is used to remove the excess water from the sludge. This drier sludge is referred to as sludge cake. Although the sludge cake is still about 70 percent water, it is now ready for incineration.

Sludge Incineration

After dewatering, the sludge is burned in a fluidized bed incinerator. This incinerator has one hearth which is equipped with openings to allow air to be blown through the hearth. The flow of air raises and suspends a layer of sand above the hearth. The sand is heated to approximately 1400°F. As the sludge is pumped into the incinerator, it comes in contact with the fluidized bed of hot sand and instantaneous evaporation, then combustion occurs. The same air flow that suspends the sand blows the ash out of the incinerator and into the air scrubbing system where the ash and some of the fine sand is removed. A sand silo provides "make-up" sand to replace what is removed with the exhaust from the incinerator.

Incinerator Ash Disposal

Water containing ash and sand from the incinerator air scrubbing system is pumped to the ash clarifier. After the ash and sand mixture is allowed to settle in the clarifier, it is pumped to the ash press, where porous fabric belts are used for dewatering. The dewatered ash and sand mixture is hauled to the City's landfill for disposal.