Upper Hocking Water Pollution Control Facility

The Treatment Plant

The Upper Hocking Water Pollution Control Facility (UHWPCF) is designed for a peak hour capacity of 8.0 Million Gallons per Day (mgd).  Flow equalization at the plant reduces the peak capacity to 6.0 mgd through the biological treatment system.  The average day capacity of the facility is 2.0 mgd and the plant is designed for 2.0 mgd incremental expansions up to 8.0 mgd.  The UHWPCF is designed to intercept flows from several existing separate sanitary sewered areas before they enter the combined sewer system.  The facility will also be able to accept flow from new development in the US Route 33 Corridor.

National Pollutant Discharge Elimination System (NPDES) Permit

Effluent from the Upper Hocking Water Pollution Control Facility discharges to the Hocking River in accordance with the NPDES Permit issued by the Ohio Environmental Protection Agency.  Discharge limits were developed based on chemical and biological data and modeling and in accordance with the Hocking River Total Maximum Daily Load Report as developed by the Agency.

Monthly Average Effluent Limits are

Total Suspended Solids (TSS)   12 mg/l
Carbonaceous Biochemical Oxygen Demand (CBOD) 10 mg/l
Ammonia Nitrogen 1.0 mg/l (summer) 3.0 mg/l (winter)
Disinfection (summer only)
    Fecal Coliform 1,000/100 ml
Dissolved Oxygen (DO) Minimum 6.0 mg/l
treatment plant schematic

The Treatment Process

Upper Hocking Pump Station—Five pumps, each with variable frequency drives are sized to accommodate dry weather and wet weather flows. The peak capacity of the pump station is 8.0 mgd. The facility includes odor control and emergency standby power facilities.

Force Mains—Two force mains, a 14-inch line and an 18-inch line, each approximately 14,300 feet long, are used to convey flow from the pump station to the UHWPCF. The two lines provide capacity for peak flow and maintain minimum scouring velocity at low flow.

Preliminary Treatment— Preliminary treatment is sized for a peak flow of 8.0 mgd and consists of two cylindrical drum screens with 2 millimeter perforations. A washer/compactor at each screen is used to process the screened material for landfill disposal. 

Equalization— A one-million gallon circular equalization tank (EQ) is used to limit the peak flow to the biological process to 6.0 mgd. Screened flow in excess of 6.0 mgd is diverted to EQ. After the wet weather flows subside, flow from the EQ is pumped into the aeration system influent. The EQ tank is equipped with a pumped jet mixing system. 

Aeration— There are three Vertical Loop Reactor™ (VLR)  tanks   with a total process volume of 866,000 gallons. Each tank has a surface  type disc aerator and coarse bubble diffusers at the tank floor level. Three    process air blowers with variable  frequency  drives supply air   to the    VLRs. The VLRs can operate in parallel or in  series and    have internal mixed liquor return capibility.

Membranes—  Following aeration in the VLRs, liquid solids separation takes place using hollow-fiber membranes. There are three membrane tanks, each with 17 racks of membranes. The ultrafiltration membranes have a pore size of 0.1 microns. Three membrane feed pumps with variable frequency drives supply mixed liquor from the VLRs to the membrane tanks. Scouring air is provided by three blowers with variable frequency drives. To prevent solids from clogging the membranes, scouring air and mixed liquor are introduced at the tank floor directly below the membrane racks. Three filtrate pumps pull clear liquid through the membranes and discharge it to disinfection. The system uses sodium hypochlorite and
citric acid for periodic cleaning cycles.

 

 

Disinfection— A horizontal, low-pressure, high-output ultraviolet light system provides disinfection. There is a single channel with two banks of bulbs per module for a total of 48 bulbs. A constant water surface elevation is maintained by an effluent weir.

Post Aeration— A minimum dissolved oxygen concentration of 6.0 mg/l is maintained by a step-aeration system that is located just downstream from the disinfection system. Treated effluent is conveyed to the Hocking River through a 36-inch outfall pipe.

Phosphorous Removal— While there is no phosphorous limit in the NPDES permit, alum or ferric chloride is available for phosphorous
removal, in order to keep the effluent level around 1.0 mg/l.

Solids Reduction— In the Cannibal® sludge minimization system, the destruction of biological solids is accomplished through an interchange of mixed liquor flow between the VLR activated sludge process and specially controlled sidestream bioreactors called interchange tanks. Air is provided to the tanks by two constant speed blowers and coarse bubble diffusers. A decanter in each tank is used to thicken solids with the recycle being returned to the VLRs. The oxidation reduction potential (ORP) of the interchange tanks is carefully controlled by the extent of aeration provided, thereby minimizing biological solids yield. Mixed liquor is processed through a 0.25 millimeter wedgewire cylindrical drum screen, and then through grit cyclones to further reduce solids yield from the biological system by removal of inerts and non-readily degradable “trash” solids. The solids from the screen are processed through a washer/compactor and the grit is dewatered by gravity for landfill disposal.

 Residuals Storage— Solids are wasted from the interchange tanks to a residuals storage tank. The residuals storage tank is aerated with a constant speed blower and coarse bubble diffusers. A decanter is used to thicken the solids.

 Dewatering— Waste solids are dewatered with a high-solids, horizontal, solid-bowl type centrifuge. Dewatered solids are conveyed to a dumpster for landfill disposal. The dewatering system includes variable speed sludge feed pumps and liquid polymer feed units.