- Sanitary Engineer
- Wastewater Operations
Danbury Township Wastewater Treatment Plant Overview
The wastewater entering the Danbury Wastewater Treatment Plant is treated in an aerated facultative lagoon system. Within the lagoons two types of microorganisms, aerobic and anaerobic, use the pollutants in the wastewater as food. The aerobic microorganisms live in the upper water level of the lagoon. They are maintained by a variable supply of air injected into the lagoons. These organisms will use pollutants suspended in the lagoon water as food.
Anaerobic microorganisms exist in the sludge layer in the bottom of the lagoons. Anaerobic microorganisms live in the absence of air utilizing the sludge layer as food. The sludge layer consists of settled pollutants of the wastewater, byproducts of the aerobic microorganisms, and dead organisms and algae. Together the aerobic and anaerobic microorganisms reduce the pollutants in the wastewater and sludge in the lagoon bottoms.
Danbury Township Wastewater Treatment Plant Components
Receives pumped wastewater from both sides of the peninsula and directs the wastewater through a fine screen and into an aerated grit tank to remove grit and debris. From there the water is directed to any of the three lagoons or combination of the three. Normal operation is to direct all flow to Lagoon Number 1 for series operations.
The three lagoons in the system each have a volume of 24 million gallons and a water depth of 17 feet. They are constructed on one of the few areas on the peninsula having a deep clay stratum. The clay forms an effective seal for the lagoon contents.
Efficiently distributes air throughout the lagoons to meet the oxygen requirements of the aerobic microorganisms. The equipment is a membrane diffuser system manufactured by Environmental Dynamics Inc.
Four positive displacement air blowers are located in the Blower Building on top of the dikes. The blowers compress air forcing it through the aeration equipment into the lagoons where it will provide oxygen for the aerobic microorganisms.
Actiflo system manufactured by Kruger further enhances the treatment process by using a polymer and alum for the removal of phosphorus
Adds chlorine to the treated water after it has passed through the treatment plant to kill any disease-causing microorganisms remaining in the treated water.
Injects bi-sulfite into the water following chlorination to remove any remaining chlorine before discharge into the Sandusky Bay.
Sludge storage lagoon
Provides a means to store sludge from the Actiflo process which is later land applied in accordance with all EPA regulations.
Contains an administration office, wastewater laboratory, chlorination room, repair shop, and storage areas.
Additional Plant Information
The plant has the capacity to treat an average sewage flow of 3.8 million gallons per day with a strength of typical domestic sewage. The plant is capable of providing the treatment required by the Ohio Environmental Protection Agency even when one of the lagoons is out of service.
The pipes handling the flow through the plant are so arranged that all raw sewage pumped to the plant must pass through the lagoons. It is not possible to pump sewage to the plant and then directly to the Bay. All flow must pass through the lagoons to reach the plant outfall which discharges to Sandusky Bay.
The aerated facultative lagoon system was chosen over more conventional treatment systems because the construction cost and operating cost are approximately one-half those of a conventional system.
Portage-Catawba Island Wastewater Treatment Plant Overview
The Portage-Catawba Island Wastewater Treatment Plant incorporates a Cyclic Activated Sludge System (CASS) as the biological treatment unit. This type of batch reactor facility is easily operated and provides a high degree of operator flexibility. A number of processes and unit operations are combined into the same structure to reduce the capital and operating expenses associated with wastewater treatment. The dual basin CASS plant provides hydraulic and organic load equalization, satisfaction of carbonaceous and nitrogenous oxygen demand, filamentous sludge bulking control mechanisms, substantial denitrification and associated alkalinity recovery, phosphorus removal, solids-liquid separation and substantial stabilization of the sludge.
The wastewater treatment plant is designed to treat an average daily flow of 1,340,000 gallons per day (GPD) and a peak hydraulic flow of 3,800,000 GPD. As flows approach peak rates, the cyclic activated sludge system automatically operates on a High Flow Cycle which provides the necessary flow equalization for operation during these periods. This type of plant generates a quality of effluent which is only achieved in conventional activated sludge facilities with substantially more equipment and capital cost.
Design & Impact
The plant was designed by the engineering firm of Finkbeiner, Pettis, and Strout, Limited. The facility provides a high level of wastewater treatment to reduce the pollution load on the sole-source water aquifer serving the Catawba Island Peninsula. Treatment efficiency also contributes positively to the overall improvement in water quality of the drainage basin of the Great Lakes.
Wastewater Treatment Plant Components
The heart of the treatment facility is the Transenviro Cyclic Activated Sludge System (CASS). This technology incorporates fed-batch reactor activated sludge processing using sequenced periods of aeration and non-aeration which permits the use of a single vessel to accomplish both biological degradation reactions and solids-liquid separation. CASS is a fill-and-draw activated sludge system which uses an initial captive selector to favor concurrent nitrification-denitrification, biological phosphorus removal and to maximize initial enzymatic storage of the soluble organics in the wastewater by the activated sludge.
Aeration & Filtration
This inlet reaction area enhances sludge settling and controls the growth of filamentous bacteria. During the period of a cycle, the liquid volume inside the vessel increases from a set minimum operating bottom water level in response to a varying inflow rate. Aeration and mixing ceases at a predetermined period of the cycle's operation to allow the biomass to flocculate and settle under quiescent conditions. After a specific settling period the treated effluent is removed using a VARI-SKIM solids excluding surface skimmer which returns the liquid leveling the vessel to the minimum operating bottom water level after which the cycle is repeated. Solids are wasted from the two basins as required to maintain the biomass at manageable levels. The facility operates with timed sequences which accomplish fill-aeration, fill-settle, effluent removal and fill-idle. Continuous inflow is accommodated at all times. The treated effluent flows to the chlorine contact tank at the end of each cycle.
The Grit Building houses a perforated screen and vortex grit removal tank through which the raw sewage passes prior to flow splitting for the cycle activated sludge basins. Alum is stored in the Grit Building in the event that a precipitant is required to augment the biological phosphorus removal. A Chlorine Contact Tank/Equalization Tank is provided for chlorination and aeration of the effluent before it is dechlorinated and discharged into Lake Erie. A 20 inch outfall sewer carries the treated effluent about 1,000 feet offshore for discharge to Lake Erie. A Blower Building is provided which houses the Cyclic Activated Sludge Basin blowers, the Sludge Storage Tank blowers, the emergency power generator, the motor control center and cycle control center for the automatic operation of the treatment plant.
Stabilized sludge is then stored in three aerated Sludge Storage Tanks and then transferred to a Sludge Truck Fill Station for hauling to OEPA approved land application sites.
Buildings are simple, but aesthetically pleasing with earth-tone colors blending with the natural surroundings.
Additional Plant Information
- Aeration: Three positive displacement blowers, each 1100 scfm with 60 horsepower motors for Sludge Storage Tanks.
- Aeration: Three positive displacement blowers, two 1150/767 scfm with 75 horsepower two-speed motors and one 1150/575 scfm with 75 horsepower two-speed motors for the CASS system
- U.S. Patent Numbers 4663044, 4693821,4891128, 5013441
- Chlorine Contact Tank: One 24 feet by 40 feet by 11feet SWD chlorine contact tank with a total volume 79,000 gallons, detention time 15 minutes at peak flow
- Design Flow: 1.34 Million gallons per day (MGD)
- Design Peak Flow: 3.80 MGD
- Equalization Tank: One 26 feet by 40 feet by 10 feet SWD equalization tank with a total volume 78,000 gallons
- Grit Removal: One vortex grit tank
- Raw Wastewater Pumping: Three 1,500 GPM at 54 foot TDH and 40 HP
- Screening: Perforated screen with emergency bypass bar rack
- Sludge Storage Tanks: Three tanks; each tank 42 feet by 56 feet by 14 feet SWD
- Construction: $27,523,136
- Equipment: $450,000
- Issuance: $375,000
- Land, Rights-of-Way, Appraisal: $2,700,000
- Miscellaneous: $399,482
- Net Interest: $1,303,839
- Technical Services: $4,871,5200
- Total Project Cost: $37,622,977