Raw Sewage Pumping:
The raw sewage pump station is a cast-in-place concrete structure with a wetwell capacity of 5,500 gallons. The station consists of 3 submersible, 2-speed pumps; each rated for 580 gpm @ 1,200 rpm and 1,380 gpm @ 1,800 rpm; with a firm pump station capacity of 2,450 gpm with 1 pump out of service. The pumps discharge to an open channel upstream of the screening facilities.
Raw Sewage Flow Measurement:
Raw sewage flow is currently measured by a magnetic flow meter, which provides a continuous record of influent flow.
The screening system consists of a 2" manually cleaned, coarse bar screen, located in a channel downstream of raw sewage pumping. Screenings are periodically transported to a licensed landfill. Effluent flow from the bar screen discharges to the aerated grit chamber.
Grit Removal Facilities:
Removal of grit and other settleable inorganic solids is accomplished with a 10'-10" x 10'-3" x 10'-0" deep aerated grit chamber located northwest of the manual bar screen. The grit is removed by 1 air lift pump which transports the solids into the hopper of the grit washer. The grit washer dewaters the grit and discharges the solids to a container for transportation to a licensed landfill. The compressed air required for the grit facilities is provided by 2 positive displacement blowers each with a capacity of 62 cfm @ 4.5 psig. Wastewater from the grit chamber flows to the Parshall flume and flocculation tanks.
There are 2 flocculation tanks, with a volume of 10,770 gallons each. The basins were originally designed to improve the settling characteristics of solids in the primary clarifiers with the addition of the ferric chloride. However, the ferric chloride feed point has since been relocated to the trickling filter effluent to promote the removal of solids and phosphorus in the final clarifiers. Since the flocculation facilities are no longer required in this treatment scheme, the flocculation mechanisms were removed. As there is no method for bypassing the flocculation tanks, aeration diffusers were installed to prevent solids from settling in the bottom of the tanks.
Two rectangular primary clarifier basins, 50'-0" x 16'-0", are located southwest of the laboratory building. The primary clarifier water depth varies from 10'-0" at the inlet end to 5'-6" at the outlet. A third settling tank can function as either a primary or secondary clarifier. Screened and degritted raw sewage enters the primary clarifier inlet channel through 2 16" diameter inlet pipes. The wastewater flow is split equally to each of the 2 (or 3) primary clarifiers through multiple inlet ports. Heavier solids settle to the bottom of the clarifier and are moved towards the sludge hopper at the south end of the clarifier by the sludge collector flights. Floating solids rise to the top of the liquid as scum and are moved to the scum pipe by the sludge collector flights as they return to the north end of the tanks. Sludge is removed from the sludge hopper through 6" diameter sludge withdrawal lines. Sewage flows over the primary clarifier effluent launders and out through a 16" diameter effluent pipe to Trickling Filter Wetwell No. 1.
Trickling Filter Pumps:
There are 4 trickling filter feed pumps; the vertical, non-clog pumps each have a rated capacity of 620 gpm @ 51' TH, 620 gpm @ 41' TH, and 240 gpm @ 39' TH. Typically, trickling filter feed pumps No. 1 and No. 2 take suction from wetwell No. 1 and discharge to Trickling Filter No. 1, while trickling filter feed pumps No. 3 and No. 4 take suction from wetwell No. 2 and discharge to Trickling Filter No. 2.
There are 2 trickling filters measuring 31' x 26' deep, containing synthetic media constructed from corrugated rigid PVC sheets. Wastewater is distributed over the top of the media via rotary distributors. The media provides a minimum of 31 ft2 of surface area per cubic foot of media, with a total volume of 38,500 cu. ft. The trickling filter effluent flows to the secondary clarifiers.
Two rectangular tanks, 50'-0" x 16'-0", at a depth varying from 5'-6" to 10'-0" are located southwest of the laboratory building. A third tank can be used as either a primary or secondary clarifier. Secondary clarifier effluent flows through a 20" diameter pipe to the chlorine contact chamber.
Chlorine Contact Chamber:
Chambers No. 1 and No. 2 have capacities of 13,400 and 13,800 gallons, respectively. The chambers are operated in parallel depending on the quantity of flow passing through the plant.
The chlorination equipment includes the following: 1 gas chlorinator, 2 chlorine leak detectors, 2 chlorine scales with 2-1 ton container capacity, 2 gas masks with 15 minute air tanks, a 1 ton container lifting bar, and trunnions for storage of 2 - 1 ton containers. Chlorinated wastewater flows to the plant effluent pumping wetwell.
Effluent Pumping System:
The effluent pumping system consists of 2, 2-speed, effluent pumps and discharge force main. The effluent pumps have a capacity of 1900 gpm @ 52' TH and a capacity of 950 gpm @ 20' TH. The pumps discharge the treatment plant effluent to the Shiawassee River through a 16" diameter ductile iron force main.
Automatic Sewage Samplers:
There are 3 automatic composite type sewage samplers measuring plant influent, primary effluent, and final effluent. The samplers are the vacuum lift type. Each sampler is equipped with a refrigerator for preserving the samples collected. Dissolved Oxygen, Fecal Coliform, Total Residual Chlorine and pH samples are collected as grab samples after disinfection at wet well 3.
Chemical Feed Systems:
Chemical feed consists of ferric chloride for phosphorus and suspended solids removal. The chemical feed system consists of a 6,000 gallon chemical storage tank, a 150 gallon chemical day tank, a transfer pump rated at 30 gpm @ 10' TDH, and 2 positive displacement type chemical feed pumps with a capacity of 25 gph @ 50 psig. Ferric chloride is fed to the trickling filter effluent splitter box while the trickling filter feed pumps are running.
The primary and secondary clarifier sludge pumps are progressive cavity type; each pump has a rated capacity of 100 gpm @ 5' TH. The pumps take suction from the 5 settling tank sludge hoppers and discharge to the batching storage tank.
Sludge Conditioning System:
The lime stabilization system consists of a liquid lime storage tank, day/feed tank, batching storage tank, and the east conditioning tank. Lime stabilization is operated in a batch mode. Sludge is pumped from the batching storage tank to the east conditioning tank where liquid lime is added to achieve a sludge pH of 12 and mixed for a minimum of 2 hours. The stabilized sludge is then pumped to sludge storage tanks.
Sludge storage consists of a 225,000 gallon concrete tank. Currently, liquid sludge is hauled, via tanker truck, by contract sludge haulers to selected farm land for subsurface disposal on a semi-annual basis.