Caroline County Regional
Wastewater Treatment Plant
UPPER POLECAT CREEK FACILITY
PLANT DESCRIPTION
This plant has a
treatment capacity of 0.5 mgd (500,000 gallons per day) and is designed to produce a high
quality treatment plant effluent. All flows are concentrated
within the collection system and flow by gravity or are pumped under pressure to the
treatment plant. After the wastewater enters the treatment plant
collection wet-well it is pumped to a flow meter and enters the preliminary treatment at
the influent bar screens.
PRELIMINARY TREATMENT
The headwork’s of
the treatment plant consists of a pair of manually cleaned bar screens in the influent
channel. The bar screens retain any solids which are larger than
their openings and prevents their accumulation in the downstream process. The
captured material is then removed from the screens by raking and is deposited temporarily
in a container before ultimate disposal by burial in a landfill.
SEPTAGE RECEIVING STATION
A septic tanker will
connect a discharge hose to this station and the contents are automatically screened and
discharged into one of two 20,000 gallon tanks to be continuously aerated.
The septage can then either be pumped into the headwork’s of the plant or
directly to the digester.
This mechanical device
consists of a cylindrical fine screen with a screen basket, rotating rake, cleaning comb,
screw conveyor, dewatering screw, screening press with drive unit and housing complete
with hinged and gasketed cover with vent, tank spray wash system, quick coupling inlet,
motorized inlet valve, outlet connection, and liquid level sensing system.
BIOLOGICAL/CHEMICAL TREATMENT
The majority of the
treatment at the plant is accomplished by using biological and chemical modification of
the activated sludge process. The basic components of the system
consist of a biological reactor (oxidation ditch), the final settling tanks and the
pumping and piping system needed to return the settled sludge from the final tanks to the
biological reactor.
After preliminary
treatment, the incoming wastewater is dosed with magnesium hydroxide (alkalinity
adjustment) then discharged to the reactor together with a continuous recycle flow of
return activated sludge. Inside the reactor, the biologically
active growths in the return sludge (bacteria and other organisms) are contacted with the
organic pollutant material in the sewage, and act to utilize the waste and reduce them to
inoffensive end products. Oxygen from the mechanical aeration
devices must be added to the reactor to promote growth of the bacteria and to maintain
circulation and suspension of the activated sludge/sewage mixture. The
primary reactions occurring in the reactor result in the stabilization of both organic
matter (BOD reduction) and nitrogen compounds (nitrification).
Flow from the reactor (a mixture of treated sewage and the
microorganisms known as mixed liquor) then passes on and through to a splitter box where
the sludge is dosed with aluminum sulfate for phosphorus reduction, then on to the final
clarifier settling tanks. In these units, the activated sludge
particles settle to the bottom of the tanks by gravity, and the clarified effluent
overflows to the next processing stage. As the sludge
concentrates near the tank floor, it is continually remove by mechanical sludge collectors
and pumped back to the reactor to perpetuate the biological treatment process.
Any floating matter is also simultaneously collected and removed to prevent it from
being released with the effluent. Effluent from the clarifiers is
then processed through an up flow sand filter to further remove solids and produce an
excellent final effluent.
DISINFECTION
Disinfection is the
selective destruction of waterborne disease-causing organisms, and is an essential final
stage at all wastewater processing facilities. At the Caroline
County plant, disinfection of the final settling tanks effluent is accomplished by
Ultraviolet Light Open Channel Contactors (UV System). The
essential components of this system are to deliver high doses of ultraviolet light to the
final plant effluent for a sufficient time for disinfection to occur. The
UV system includes facilities in a reaction tank, UV light source and associated hardware.
EFFLUENT DISPOSAL
The overflow from the UV
contact tank flows through a flow measuring/effluent reuse chamber and finally over a
series of post-aeration cascade steps (which raise the dissolved oxygen concentration of
the plant effluent) and is the final step in the treatment process. The
effluent flows through a 24 inch diameter outfall pipe and is released to the waters of
the Polecat Creek.
SLUDGE HANDLING
More activated sludge is
produced by the biological growth in the reactor tank than is needed to maintain the
process. Although most is returned from the settling tanks to the
reactor for process control, some must be wasted or permanently removed from the system. This waste activated sludge is composed of light biological solids,
has high water content, and is basically stable or digested due
to the long detention times in the biological reactor. Waste
sludge is pumped to the aerobic digester to further stabilize and gravity thickens prior
to discharge to the sand drying beds or processed through a belt filter press.
Sludge remains in the drying beds until it is dried and manually removed to a large
dumpster and hauled to a landfill for burial. Belt press solids
are also contained in a dumpster and disposed of at a landfill.
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