Jennings Secondary / Tertiary Treatment Facility

Wastewater pond

Treatment Facilities

In 1969, the City purchased property along the San Joaquin River and began developing what is one of the largest pond system in the US. This new system is called the Jennings Secondary Treatment Facility.

The secondary treatment process biologically treats clarified wastewater. The wastewater is treated in facultative ponds and stored for irrigation. It is then blended with seasonal cannery waste and applied with biosolids from Sutter to the ranch at Jennings.

Tertiary Biological Nutrient Removal & Membrane System

The City of Modesto spent a decade and over $130 million on a state-of-the-art Tertiary Biological Nutrient Removal (BNR) and Membrane system to meet the stringent effluent limits required by the State of California.

The Tertiary plant takes clarified wastewater from Sutter and screens it through fine screens designed to remove small particulate material in order to protect the membranes. After the wastewater has been screened, it moves on to the BNR (Activated sludge) system  which removes dissolved organic waste, ammonia, and nitrate. The activated sludge process uses dissolved oxygen to grow microorganisms that particles are then filtered out using membrane filters with a 0.04µm pore size. While virtually all wastes are filtered out during this process, viruses are still able to pass through the membranes, thus requiring the water to be disinfected. The filtered water is then disinfected using ultraviolet light and is now safe to be recycled for beneficial use. 

As partners in the North Valley Regional Recycle Water Project, our tertiary recycled water supply provides a new source of water for agricultural customers in the Del Puerto Water District (DPWD). These customers have been severely impacted by drought and environmental restrictions on pumping water from the Delta.

  1. 1 a large pipe feeds wastewater into an enclosed quarter inch screen filter to remove any remaining solids
  2. 2 Two large pipes deposit the filtered solids into a bin where workers collect and dispose of them
  3. 3 large pools of wastewater filled with micro organisms that consume all organic matter in the water
  4. 4 Micro organisms are kept in a nearly oxygen free environment where they must utilize nitrates (NO3) in the waste to make oxygen leaving Nitrogen (NO2)
  5. 5 bubbles are blown into the wastewater to increase the activity of the micro organisms
  6. 6 The heavily oxygenated wastewater is then transported slowly down large pools to a filtration system
  7. 7 .08 micron filters remove all of the active liquor from the treated water
  8. 8 A large series of pipes transports the treated water to a UV room for further processing
  9. 9 Green UV lights provide the final level of treatment for the wastewater