Wastewater Treatment Process

Plant Overview

The Yuba City Wastewater Treatment Facility, originally built in 1975, was redesigned in 2003 to treat an average flow of 10.5 million gallons per day (MGD) with an average organic loading of 44,000 lbs/day biological oxygen demand (BOD) and 16,000 lbs/day total suspended solids (TSS). Yuba City’s current average daily flow is about 6.5 MGD. The redesign of the facility will enable Yuba City to provide wastewater treatment for projected growth over the next ten years. It is a Class IV Wastewater Treatment Facility with a pure oxygen activated sludge process designed to handle high and variable BOD loads from local food processing facilities, commercial facilities and residential areas. The facility consists of three main treatment processes – Primary Treatment, Secondary Treatment and Bio-solids Treatment.

Primary Treatment consists of bar screens to remove large objects such as plastics, metals, rags, and paper from the influent wastewater, an aerated grit chamber to remove grit (sand, cinder, bone chips, seeds, coffee grounds, eggshells etc.) from the influent wastewater flow, and primary clarifiers to remove approximately 26% to 30% of the Biochemical Oxygen Demand (BOD) and 60% to 70% of the total suspended solids (TSS).

Secondary Treatment consists of a High Purity Oxygen (HPO) activated sludge process to remove the remaining BOD through the biological process and secondary clarifiers to allow the bacteria used in the process to be recycled within the facility.  Secondary effluent is disinfected with chlorine followed by de-chlorination and then discharged into the Feather River or percolation ponds located on the east side of the Feather River in the river flood plain.

Biosolids Treatment consists of rotary drum thickening (RDT), anaerobic digestion, and finally belt press dewatering.  The bio-gas (methan) produced from the anaerobic digestion process is recyled and used as a fuel source to operate the plant boilers.