WPCF Treatment Process
Preliminary / Primary
The raw flow enters the plant through 3 main lines or interceptors. A 54” (South) enters from the south side of Muncie. A 60”(Main) enters from the center of town and a joint 30” /42” (North) enters from the north and west side of town. The North interceptor is a separated sanitary line as opposed to the Main and South which are both combination lines with associated Combined Sewer Overflows (CSO’s).
The 3 flows combine into a single 48” line that enters 2 channels for screening, the first plant process. 2 Aquaguard fine screen units remove debris from the stream and the debris is then washed and compacted for disposal. The flow then enters a large raw sewage wet well. From this well , it is pumped by a combination of 3 20” and 1 16” Wemco Hydrostal raw sewage pumps to a higher elevation which allows the raw wastewater to flow by gravity for the remaining processes until it reaches the tertiary plant. After the raw flow is pumped to the higher level, it runs through a Parshall flume for flow measurement. The flow then enters 2 Eutek head cells for grit removal. The head cells separate the water from the grit using centrifugal force, and the grit is dewatered, washed and conveyed for removal/disposal. The screened and de-gritted flow then travels to 2 140’ diameter primary clarifiers. These tanks settle approximately 60% of organic solids present in the wastewater, and the settled solids are pumped to anaerobic digesters. A primary pump station is used for this process which includes 3 primary pumps (2 Wemco centrifugal & 1 Lobeline positive displacement) as well as 1 Gorman Rupp pump to drain the tanks for maintenance and 1 Wemco scum pump to convey fats and greases (scum) that float to the top of the tanks. The ‘scum’ is pumped to a ‘scum drum’ that is also located in this building to separate the scum for disposal.
At this point, the primary effluent from the 2 tanks flows into a control structure and is combined with return activated sludge (RAS). This mixture is referred to as ‘mixed liquor’. 8 control gates associated with 4 mix basins are manipulated to modulate the ratio of RAS to primary effluent, balancing the amount of mixed liquor loading that is conveyed to the 4 aerator basins downstream.
The mixed liquor is divided between 4 3 pass aerators with fine air diffuser for dissolved oxygen (D.O.) transfer and mixing. The air pumped to the aerators is conveyed by 3 Hoffman centrifugal blowers. The microorganisms present in the RAS have been mixed with the primary effluent in the control structure and now this combination will flow through the aerators with D.O. present. The majority of the bacteria is absorbed/stabilized as well as removal of carbonaceous BOD and nitrogen ammonia. By the end of the aeration process, the mixed liquor flows into 6 (4 circular & 2 rectangular) secondary clarifiers. The solids present are now allowed to settle to the bottom of these clarifier tanks to be wasted (WAS) to anaerobic digesters or to be returned (RAS) to the mixing basin for reincorporation with the primary effluent. The remaining water in the clarifiers has now reached a level of treatment (after disinfection – Apr./Nov.) suitable for discharge to the receiving stream. Approximately 90% of the T.S.S., BOD & NH4 has been removed. Although this effluent can be discharged in its present state, a tertiary process is available and used to further increase/enhance the water quality before discharge.
The effluent from 4 of the 6 secondary clarifiers flows through a contact tank and then flows to another basin where the remaining 2 secondary clarifiers join the mix. From this point, the effluent from all secondary clarifiers flow through a disinfection channel (disinfection is required from April to November). From here the flow enters a pumping basin where 3 200 hp Flygt submersible pumps convey the water to an elevation that allows it to flow through influent channels to all or some of the 6 mono media filters. The flow passes through and is filtered of remaining fine solids through the media and discharges into a large clear well. An overflow weir allows the filtered flow to pass onto the tertiary effluent channel. As filters need cleaning, an air/water backwash process occurs and the wash water from the wash cycle is collected in a large basin (surge tank) for reintroduction to the head works. The filtered flow passes through a tertiary effluent channel, over a 7’ weir for final flow measurement. Final sampling takes place and the treated effluent discharges into the West Fork of the White River.