The Lower Meramec River WWTP is designed to treat the plant influent quantity of flows and water quality in order to meet the effluent water characteristics established and required by law. The process was developed to address the governmental requirements of discharge standards; the projected influent flow to the plant and variable loadings that will occur; the special issues (noise, odor, visual aesthetics); and MSD’s extensive experience in operating and maintaining the other existing treatment facilities in the St. Louis metropolitan area.

Preliminary treatment includes influent screening and grit (sand, small rocks, etc.) removal. Self-cleaning fine screens are installed as the wastewater flows into the plant. Solids (screenings) from this process are discharged into a washer/compactor and are washed and pressed before discharge to a conveyor and into a hopper. From the hopper the screenings are dropped into a truck and hauled to a landfill or other disposal location.

Grit will be removed by settlement in the Primary Clarifiers. The grit is then separated from the sludge allowing more consistent and higher efficiencies of the process. The sludge is thickened in gravity thickeners before the process of drying the sludge (called dewatering).

Primary clarifiers are used to let the remaining solids settle to the bottom of the structures to make sludge. Submerged wiers will be used to minimize odors. Sludge is pumped from the primary clarifiers back to the grit removal units and gravity thickeners. Scum and other floating material is removed from the surface of the clarifiers using surface skimmers with water sprays. The scum flows into a hopper on the outside of the clarifier and is transferred to the scum concentrator in the Process Building where it will be dropped into a truck and hauled to a landfill or other disposal location.

Secondary treatment utilizes trickling filters and secondary clarifiers.
Large pumps lift the treated primary effluent water to the top of the trickling filter structures. The trickling filters are covered to contain odors. The trickling filters contain a plastic filter media. The water gravity flows down over the filter media allowing microorganisms to collect on the media and consume most of the organic matter in the wastewater. Large blowers force air across the media to increase oxygen for the microorganisms.

From the trickling filters the treated water flows on to the secondary clarifiers. Here the remaining solids are allowed to settle to the bottom for a second time. Scum removal is similar to the primary clarifiers. Resulting sludge is returned back to the degritting units with the primary sludge. The treated water (effluent) then flows out of the plant by way of the plant outfalls.

 The plant effluent will flow over a mile and one-half to the Mississippi River at the confluence of the Meramec River by way of an underground pipe. A smaller portion of the plant effluent will flow through a disinfection process to the present Meramec Lagoon outfall of the wetland preservation area. That discharge will help preserve and enhance the ecology that has developed around the existing Lagoon discharge on the District’s property.

Solids handling includes sludge thickening, sludge storage and blending, sludge dewatering, and sludge cake storage and truck loading facilities. 

Dilute, degritted primary and trickling filter sludge flows by gravity after degritting to the gravity sludge thickeners. These sludge thickeners are covered to control odor. Thickened sludge is pumped to the storage/blending tanks. The purpose of these storage/blending tanks is to provide storage that effectively allows separation of the liquid process from dewatering and also to provide a uniform flowrate and concentration of sludge to the final dewatering process.

Sludge is then dewatered using machines called belt presses. Each belt press is sized to handle 2,000 lbs. per hour. The presses will be located in the Process Building and will discharge directly to trailer trucks for disposal.

The loaded trucks will then transport the sludge cake for disposal offsite.

The entire layout of this new plant has been done to minimize the potential for odor generation.