The Rio Dell wastewater system serves approximately 1,100 customers, and consists of a network of wastewater collection pipes, manholes, clean outs, and pumps that convey wastewater to the treatment plant located at 475 Hilltop Drive.  The City of Rio Dell WWTP utilizes an aerated activated sludge process to provide secondary treatment of wastewater.  In 2013 The City completed a major plant upgrade which replaced the old conventional Wastewater plant with the new Activated Sludge Process to address nutrient removal.  The project also included construction of the flood irrigation field located in Metropolitan.

Since the plants construction the City has received several awards. 

2010 Project of the Year, Solids and Disinfection Project Upgrade- Presented by American Society of Civil Engineers, San Francisco Section

2013 Water/Wastewater Project of the Year- Presented by American Society of Civil Engineers, San Francisco Section

2013 Project of the Year Environment Category- Presented by Sacramento Chapter of the American Public Works Association

2014 Engineering Excellence Award- Presented by American Council of Engineering Companies

2014 Wastewater Plant of the Year- Presented by North Coast Section of the California Water Environment Association

Raw sewage from the south and north mainlines enter the WWTP headwork’s and flows through a ¼ inch opening automatic bar screen provided by Headworks, and grit removal system from Smith and Loveless, which discharges into the influent pump station wetwell.

Wastewater is then pumped to the WWTP biological treatment tank provided by Aero-Mod Inc.  At the biological treatment tank, the wastewater splits into two treatment trains at the selector tank; each train provides two-stage aeration and biological denitrification.    There are two secondary clarifiers where the activated sludge biomass is separated from the secondary effluent.  Secondary effluent is chlorinated then passes through the chlorine contact basin prior to dechlorination before either discharge to the Eel River (October-May) or the flood irrigation fields (May- October).


The solids removed from the wastewater are stored and thickened in two aerated digesters and subsequently dewatered with an Aero-Mod Tritan belt filter press .


The dewatered bio solids are processed through an indirect sludge dryer made by Therma-Flite, which produces a Class A bio solids that the City is able to give away to residents as a soil amendment.  If any residents would like to pick up any of the bio solids to use for their yards or gardens please call the treatment plant at 707-764-5754 to arrange a time.