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WRH Construction out of Amana, IA is building a new wastewater treatment plant for the city of Grinnell. The project is approximately fifty percent complete. Work will continue through the winter in the buildings that are enclosed by the time weather makes outdoor work not possible.
The city's current trickling filter treatment system will be replaced by an aerobic digestion treatment system. The city has been planning for this project for several years as the current plant is unable to meet current EPA and DNR standards.
In the current system, wastewater arrives at the plant and basically goes through a three-step process. Step 1: screenings and grit removal take place; this removes any solids from the wastewater. Step 2: the water enters the trickling filter where micro-organisms that are attached to rock consume organic material remaining in the water. Step 3: the water goes through the final clarifier before discharge into Sweetwater Creek.
The new plant will use an aerobic digestion treatment system. The treatment process in the new plant will have four basic steps. Step 1: wastewater enters the new headworks building where screenings and grit removal take place, again to remove any solids. Step 2: the water enters new oxidation ditches where micro-organisms consume remaining organic material. Rather than being attached to rock, the micro-organisms in the new system are freely moving around aided by paddles. Step 3: the water is sent into a new UV building for disinfection. Step 4: the water goes through the final clarifier before discharge into Sweetwater Creek.
The new plant is projected to be complete by Fall of 2019.
The new circular final clarifier is to the far left.
The aerobic digester is the rectangular structure in the middle of the photo.
The footprint for the new blower building is just to the left.
The new oxidation ditches