Downstream of the grit chamber, raw wastewater will blend with returned activated sludge (RAS) in a mixing chamber. The mixture of aerated wastewater and sludge is known as mixed liquor.

The mixing chamber is the first of three structures plumbed for metal salts (Alum) application. Metal salts react with phosphates in the wastewater to form insoluable precipitates. The mixed liquor is then piped to a splitter box.

In the splitter box, the mixed liquor flows over 120° v-notched weirs, allowing the operator to divide flow to the oxidation ditches for secondary biological treatment in which mixed liquor is aerated for secondary biological treatment. It is operated with high sludge ages, which are conducive to both the nitrification process and the aerobic stabilization of the suspended solids carried in the biological reactor. The mechanical components of the system are inherently simple in design, using VFD motors to drive vertical impeller type mechanical aerators for balanced and throttled air delivery. Mixing and constant movement of the mixed liquor keeps solids suspended. The sludge mixture produced during this oxidation process contains an extremely high concentration of aerobic bacteria, most of which are near starvation. This condition makes the sludge an ideal medium for the destruction of any organic materials in the mixture.

Mixed liquor, then pass over the effluent weirs in the oxidation ditches and into a weir box, where Alum is introduced at a rate controlled by chemical feed pumps located in the laboratory building. This weir box is also plumbed to deliver polymer if it is needed in the future to aide flocculation. From the weir box mixed liquor travels into the center feed clarifiers for sludge settling. Sludge is drawn off the bottom of the clarifiers through its ports in a sludge collecting ring and hydraulically pushed over v-notched telescoping valve. Scum is skimmed off the top of the clarifier, near the perimeter. The sludge and scum is mixed in a control box chamber located between the clarifiers and will flow by gravity into the RAS/WAS wet well adjacent to the headworks building.

The clarifier control box has three separate chambers, one for effluent flow, a second for sludge collection, and a third chamber for scum collection and draining of the clarifiers.

RAS pumps equipped with VFD’s return sludge to the mixing chamber through piping equipped with a magnetic flow measuring device. A constant speed waste activated sludge (WAS) pump with timers will deliver waste sludge to the 18 million gallon sludge storage lagoon north of the headworks building. Supernatant from the sludge storage lagoon decants to the RAS/WAS wet well by means of manually operated sluice gates positioned at various elevations.

The effluent from the clarifiers travels to the transfer box. From this point, sluice gates can control flow into one of four different flow patterns which are dependent on surface water discharge limits.

UV disinfection is the primary mechanism for the inactivation/destruction of pathogenic organisms to prevent the spread of waterborne diseases to downstream users and the environment. This UV disinfection system transfers electromagnetic energy from a mercury arc lamp to an organism’s genetic material (DNA and RNA). UV radiation penetrates the cell wall of the pathogenic organisms, destroying the cell’s ability to reproduce.

The cascades are the final stage of treatment, which increases the treated water’s dissolved oxygen content. This is accomplished by allowing the water to run down over a series of steps and blocks. The agitation is enough to bring the dissolve oxygen content backup to ensure that plenty of oxygen will be available for fish and other aquatic life upon its discharge.