Welcome to the virtual tour of Springfield’s Wastewater Treatment Plant. In addition to this site, the plant proudly gives tours to small groups of students, businesses, organizations, and individuals from around the city. If you would like to schedule a tour of the facility or have questions about the processes on this page, please call the plant at (937) 324-7626.
- 1. Influent
- 2. Bar Screens and Grit Basin
- 3. Primary Settling Basins
- 4. Trickling Filters
- 5. Complete Mix Activated Sludge
- 6. Secondary Clarifiers
- 7. Disinfection Basin
- 8. Emergency Effluent Pump Station
- 9. Post-Aeration and Dechlorination Basin
- 10. Mad River
The flow enters the headworks of the plant through one 84-inch and one 48-inch interceptor. The 84-inch interceptor has two automated sluice gates and a side-mounted combined sewer overflow (CSO) screen with an attached bending weir. The 48-inch interceptor comes into the plant downstream of the CSO. The WWTP plant flow is normally between 10 and 18 MGD and the plant’s peak flow is 36 MGD. However, during storm events the flow to the plant can increase to 60 to 90 MGD. Any flow above 36 MGD is bypassed though the CSO screen to Mad River.
There are two control gates that allow flow into the plant. These gates are controlled by the SCADA system through the use of various level detectors and flow meters that prevent flooding and process washout. In the event the flow increases to exceed the hydraulic capacity of the plant, the sluice gates will start to close and the flow in the influent chamber will rise. When the flow in the chamber rises, a programmable logic controller (PLC) will activate the CSO screen mechanisms and bending weir allowing the excess flow to enter the 100 MGD bypass sewer through the screening mechanism. The screenings will proceed on into the plant.
A septic dumping station is located at the beginning of the plant. Registered septage haulers and RV users can use this station. In 2007 there were 12 registered septage haulers that used the septic dumping station. Septage is dumped directly into an 84-inch influent sewer. Septage is regulated under an administrative memorandum (61.4) allowing only for residential septage. The memorandum permits trucks of 4,000 gallon capacity or smaller with no side discharge. Each registered user is only permitted to discharge up to 12,000 gallons per day. During 2007 the WWTP received over 5.5 million gallons of septage. The septage is randomly sampled and analyzed for metals and the acceptance of septage has had no adverse effect on the plant. Since the WWTP is sitting in a valley, the odors from the septage are confined to the plant’s preliminary and primary treatment area.
Bar screens remove solid waste and debris larger then the opening of the screen. Grit basins remove rock, sand and silt by slowing the velocity of the flow stream so the grit will drop to the bottom of the tank.
The two Hycor bar screen channels and aerated grit basins were built in 1972. Each channel was designed to handle 25 MGD with a combined flow of 50 MGD. However it has been found that the pipe feeding the two channels has a low spot in it that lets grit and stone settle. Every time the flow is increased above 24 MGD the bar screens were blinded by grit and stone. For this reason the plant is set up to take a maximum of 23 MGD though one Hycor bar screen channel and any flow above 23 MGD will go to the Dorco bar screen and Detritus tank.
The two Hycor “Climber” screens that were installed in the 1988 project replaced the Dorr-Oliver back rake screens that were installed in 1972. The two Hycor screens are front rake cleaning type with 1-inch bar openings. The screens are sitting in a 3-foot wide channel with a maximum channel depth of 7.5 feet and normal operating depth of five feet. The velocity with one channel open and with a flow rate of 25 MGD is 2.6 fps. The Hycor Bar Screen is locally controlled by its own control system; it monitors level and function and controls the screen frequency.
The bar screens dump screenings into a dewatering screw conveyor press. The press advances the screenings through a closed trough to a pressing area, where they are washed. The organic wash-off is piped back into the influent channel and the screenings are manually incinerated.
The screenings are incinerated in a gas-fired incinerator. The incinerator has three burners and has an effective load capacity of 50 cu ft. The unit can be fired by sludge gas (methane) or natural gas. A mechanical gas blower is used to increase the burn rate for large volumes of screenings. The ashes from the screenings are removed by the shift operator each shift and are disposed of by landfill.
The flow that passes through the Hycor screen then flows into the Aerated Grit Basin (AGB). Each screen has it own basin, which is 47 feet long, 22 feet wide and has 17 feet of sidewall depth.
Three 20 HP 125 cfm positive displacement blowers are used to aerate the grit tank. This keeps the organic material suspended from the grit. Only two blowers are used at any given time. Grit is collected on the bottom of the tank and moved to a pit by an auger.
The grit is removed from the basin three times per week by a grit elevator. The grit elevator is a series of buckets on a chain going from the bottom of the grit basin to the grit washer in the AGB machine room. The grit is washed and then dumped into a roll-off for disposal at the local landfill.
The 1935 Dorco Detritus system is the unit used to handle the excess hydraulic flow during storm events. The system is designed for a hydraulic flow of 35 MGD. The screenings from the Dorco bar screen as well as the screenings from the dewatering auger are manually incinerated. The Dorr Oliver classifier is 29 feet by 29 feet with a five-foot sidewall depth. The classifier removes the grit from the Detritus system to a storage pit. The storage pit is manually cleaned and added to the roll-off.
There are three primary settling basins at the plant. Primary settling basins remove settleable solids (raw sludge) and the skimming of scum from the flow stream. The sludge-collecting unit consists of a set of plows in the bottom of the tank. The plows move at the rate of 10 fpm. The plows push the primary sludge to a sludge collection hopper near the center of the tank.
The Primary Clarifiers have a 90-foot diameter and a 10-foot sidewall water depth. The water depth at the center is 13.7 feet with a radial slope of approximately one in twelve inches. The design flow capacity for these clarifiers is 37.5 MGD, however the rate is limited to 36 MGD peak and 34 MGD sustained due to the bottlenecks downstream of the primaries. The total volume of the tanks is 1.4 million gallons.
An average of 88,775 gallons of raw sludge is removed from the primary clarifiers daily through 6-inch and 8-inch lines with Monyo progressive cavity pumps to the anaerobic digestion system. The progressive cavity pumps are controlled by the PLCs. Each primary can be pumped at a minimum of 4 minutes to a maximum of 15 minutes each hour and the start time for each tank is offset by 20 minutes. The operators take samples of the raw sludge and gauge the thickness of the sludge. He then adjusts the pumping minutes to maintain the thickest sludge and not more then one to one-and-a-half feet of sludge in the primary clarifiers. The average primary sludge is 3.1 percent solid, with 75 percent volatile. A monthly average of 2,663,242 gallons of primary sludge are pumped to the primary digesters.
The skimmers collect grease off the surface and fill a grease pit, which is decanted automatically and pumped to the anaerobic digester at least once per day, however during storm events the frequency will increase. The build up of grease is a problem in the raw sludge pumping system. The plant annually cleans the primary clarifiers and pressure washes the sludge lines from the center of the primaries to the inlet of the raw sludge pumps with the Service Department’s flusher truck.
The Primary Effluent Pump Station has four vertical pumps, two rated at 15 MGD, one 12 MGD and one 8 MGD, that pumps the flow to the trickling filters. The system is automated in conjunction with several level detectors that automatically control the starting and stopping of the pumps. The SCADA system will increase the pumping capacity if the level in the PEP pit surpasses 6.9 feet and lower the pumping capacity when the influent flow rate drops below preset points. The PEPs pit has a recirculation valve that maintains a liquid level of no less then 6.5 feet. The recirculation valve gets its PEPs pit makeup water from the secondary clarifiers effluent channel.
Trickling filters are a type of fixed-film reactor. They work by passing wastewater though a fixed media by rotating arms that distribute the wastewater evenly across the top of the media. The media has a biological film that comprises of a diverse population of living organisms. The wastewater comes in contact with the biological organisms that consume the soluble organic material from the wastewater. The biological organisms are predominately aerobic that absorb oxygen from air circulating though the media. As the organisms die off they will slough off the media and continue through to the CMAS system.
The two trickling filters are each 200 feet in diameter with a WesTech distribution system. The filters have 8-foot depth of limestone media with a design surface area loading of 398 gpd/sqft. Each filter has four distribution arms with a rotary distributor and is hydraulically driven by the PEPs pumps.
The trickling filters are designed for a loading of 25 pounds of C-BOD/day/1000 cuft and a hydraulic load of 541-gpd/sq ft peak at 34 MGD. The average loadings are 239 gpd/sqft. In 2009 the trickling filters removed an average C-BOD of 33 mg/L, with a removal efficiency of 46%. With an average loading of 67 mg/L of C-BOD to each filter and an average flow of 17 MGD, the filters have an actual loading of 15.5 pounds of C-BOD/day/1000. This leaves about 40% of loading capacity left. The filters are annually flooded for 24 hours in an effort to control the filter fly population.
The Trickling Filter effluent goes to a diversion structure where it is mixed with the return activated sludge. The 54-inch Trickling Filter Bypass enters at this chamber.
The effluent from the trickling filter diversion structure enters the Trickling Filter Effluent Pump station. The station has three open three-flight screw pumps that lift the sewage into the CMAS basins. The screw pumps are 42 feet in length and 8.2 feet in diameter. The pumps use 150 HP motors and rotate at 28 RPM. Each pump is rated at 31.4 MGD.
The Complete Mix Activated Sludge (CMAS) system removes soluble, suspended solids and ammonia by exposing the waste to organisms that will feed on it. Air is blown into the tank to keep the waste mixed with the organisms and to add oxygen to the water.
The CMAS system consists of four aeration basins, five centrifugal blowers and 200 coarse bubble diffusers per basin.
The basins are 105 feet by 105 feet with 15-foot side water depth. The volume of one aeration basin is 1.23 million gallons. The plant design is to have one blower for each basin in service plus one backup. Each basin is capable of independent operation for seasonal flexibility.
The blowers are multi-stage centrifugal blowers rated at 300 Hp with an output of 4700 scfm each. Each blower has a throttling valve before the blower to adjust the actual scfm output. Through trial and error, it has been determined that the process can run with half of the design aeration, which saves on maintenance and electric usage. The plant was designed to have two basins on line during the summer and three basins during the winter. With a lower Return Activated Sludge (RAS) rate the plant is still able to handle the treatment of the flow and lower the electricity usage. The design for the Sludge Retention Time (SRT) is 4.8 days in the summer and 9.2 days in the winter. To be at the design SRT the MLSS in the summer would be 700 mg/L and 1200 mg/L in the winter. The plant has been running at an average of 1300 mg/L MLSS with all four basins in service in the summer and an average of 1770 mg/L MLSS in the winter.
The Complete-Mix Activated Sludge process handles slug loads better then the typical activated sludge system. This is achieved by having the identical concentration of activated sludge throughout the tank. A disadvantage is that a C-MAS system is prone to filamentous bulking and hydraulic short-circuiting. This plant has never had a problem with either of the two. The effluent from the trickling filters is mixed with Return Activated Sludge and then sent to the CMAS system. Each of the CMAS basins has its own influent line feeding into the bottom on the side away from the basins effluent. Air is added to the system to keep the D.O. above 1 mg/L. The biological floc consists of bacteria, protozoa, rotifers, and nematodes. The floc is used to reduce the carbonaceous BOD and oxidize ammonia content of the sewage. Bacteria make up about 95% of the activated sludge biomass. These organisms grow in the wastewater by consuming bio-degradable materials such as proteins, carbohydrates, fats and many other compounds. A sign of a healthy floc is the present of higher forms of animal life like Protozoa & Rotifers.
The secondary clarifiers allow floc from the CMAS system to settle out of the flow stream and return it back to CMAS to maintain the bio-mass and to remove the bio-mass that is not needed.
There are two square secondary clarifiers, measuring 140 feet on each side with a 10-foot side water depth. The floc-collecting unit consists of a set of plows. The plows push the secondary floc to a floc connection trough near the center of the tank. There is an average of two feet of floc in the bottom of the secondary clarifiers. The secondary clarifiers were installed in the 1961 upgrade. They were designed to be used with only trickling filters. In 1988 the plant was changed to an advanced secondary plant with the addition of the Complete-Mix Activated Sludge process.
The design detention time for two secondary clarifiers is 168 minutes. At a plant average flow of 15 MGD, the secondary clarifiers detention time is 281 minutes and at the peak-sustained flow of 34 MGD, the detention time is 124 minutes. Each clarifier has a Return Activated Sludge (RAS) line, which comes from the floc connection trough of the secondary clarifiers though a flow meter and throttling valve. The RAS is set to flow at 70% of the plant influent. It is adjusted automatically by the SCADA system by modulating an automatic valve. Each of the two RAS lines has a flow meter. The plant tries to maintain a two to three foot sludge blanket in the secondary clarifiers and a 70% flow rate can maintain that level. The weir overflow rate at average flow of 15 MGD is 13,393 gpd/ft and 30,357 gpd/ft at the peak sustained flow of 34 MGD. The wasting rate is determined by the amount of Mixed Liquor Settleable Solids in the CMAS basins. If the Mixed Liquor Settleable Solids imhoff cone test reads above predetermined limits the operator starts the WAS pump and set its speed at either 30% or 50% of its rated pumping capacity.
The WAS pumps are on a VFD and are set at either 30% (45 gpm) or 50% (75 gpm). The plant removes an average of 7900 pounds of solids from the CMAS system per day. The channels and weirs of the secondary clarifiers build up with algae and are manually cleaned on a regular basis.
The flow is disinfected during the months of May though October. Disinfection kills harmful microorganisms that live in water. Liquid sodium hypochlorite (bleach) is added in small amounts.
Flow continues to the chlorine contact basin. The basin is a rectangular shape measuring 109 feet long and 49 feet wide with 10.4-foot side water depth. There are four sets of flow-mixing wooden baffles in the basin. The plant feeds liquid sodium hypochlorite with up to two tube type peristaltic pumps. Liquid hypochlorite is stored in five 2200-gallon tanks. The PLC controls the pump feed rate based on the flow meter at the chlorine contact effluent weir. The plant feeds at an average rate of 2 to 3 mg/l. The design detention time through the tank is 22 minutes. The detention time at average flow of 15 MGD is 36 minutes and 16 minutes at the peak sustained flow of 34 MGD. An ultrasonic flow meter measures flow going over a 21-foot cipolletti weir.
The emergency effluent pump station is only used to keep the plant in service when Mad River floods to a point that the plant can’t discharge by gravity. There are three 16.5 mgd pumps in the chlorine contact basin that discharge into the effluent diversion structure. Only two pumps can run at a time with one backup pump. The pumps can be controlled manually or by the SCADA system.
The final stage of the flow is through the dechlorination and post- aeration basins. Air can be blown into the flow to add oxygen to the water. This keeps the waters down stream of the wastewater plant able to support aquatic life.
Sodium bisulfite is added to remove chlorine residual left over from the disinfection process.
The two basins are 46 feet long, 15 feet wide, with a 14-foot side water depth. Each basin has a coarse bubble diffused aeration system.
The plant feeds liquid sodium bisulfite with one or two tube type peristaltic pumps. The liquid is stored in two 2800-gallon tanks. The PLC controls the pump feed rate based on the flow meter at the chlorine contact effluent weir. The plant feeds at an average rate of 1 to 2 mg/L.
There are three 50 HP centrifugal blowers that are controlled by an inline dissolved oxygen meter. PLC logic operates the blowers to prevent D.O. levels from dropping below the 5.0-mg/L minimum requirements. Design detention time for both basins is 19 minutes. The detention time at average flow of 15 MGD is 32 minutes and 14 minutes at the peak sustained flow of 34 MGD.
Effluent is discharged into Mad River at a point approximately six-tenths of a mile downstream from the confluence of Mad River and Buck Creek. The plant does testing upstream on Mad River, Buck Creek and downstream testing on Mad River.
Mad River is a cold-water stream flowing from Logan County, to downtown Dayton, where it meets the Great Miami River. Buck Creek flows from west side of Springfield and takes flow from Clarence J Brown Reservoir. It then flows through the center of Springfield and joins with Mad River about a mile upstream of the plant. Both rivers have very different loading on them and the plant samples before the confluence of the two rivers.
The plant’s final effluent limits are set by the Ohio EPA to protect the receiving stream from pollutants of raw wastewater. The Dissolved Oxygen yearly limit is 5.0 mg/L. The plant monitors the effluent DO continuous and will run post air blowers as needed. The plant also has yearly limits on Oil & Grease, max limit of 10 mg/L, pH, max of 9.0 min of 6.5. We have seasonal limits for concentration and loading for TSS, Ammonia, and CBOD. There are summer limits for Fecal Coliform and total chlorine residual. We also report the following but have no limits for: Water Temperature, Flow, Total Nitrogen Kjeldahl, Total Nitrite Plus Nitrate, Total Phosphorus, Free Cyanide, Nickel, Silver, Zinc, Cadmium, Lead, Chromium, Copper, Dissolved Hexavalent Chromium, and Mercury. The operator does a good job at keeping this plant within the NPDES limits. The times when the plant violates its permit is usually from mechanical breakdowns. Any violations have been for short durations with a total of six violations for 2006, 2007, and 2008. There was one for TSS, three for low DO, and two for high total chlorine residual.