Virtual Plant Tour


Virtual Treatment Plant Tour

New: Join Us for a Virtual Tour and Q&A!
Where does all that toilet paper go? What happens to coronavirus and other pathogens in our wastewater? How can each of us help protect our sewer system and our environment? Join us for a virtual tour and Q&A to learn even more about what it takes to clean millions of gallons wastewater every day. Register for an upcoming Q&A session.


Note: For best performance, please use the latest version of the internet browser on your computer, phone, or tablet.



Located in Martinez, Central San’s treatment plant cleans an average of 35 million gallons of wastewater per day.  

Wastewater travels through Central San’s 1,500 miles of sewer lines, finally arriving at the plant’s headworks to begin treatment. Most of the wastewater is treated to a secondary level, disinfected by ultraviolet light, and then discharged into Suisun Bay.

Below you will find 360 degree photos of each stage of our treatment plant process. You will also find an audio tour for each section.

In blue boxes to your right (if you are using a computer), or at the very bottom of the page (if you are using a phone or tablet), you will find a few short videos of our treatment plant and other parts of our system. 

We hope you enjoy your tour!



Wastewater, which is generated by homes and businesses located throughout Central San’s service area, flows through a collection system of underground pipes to our wastewater treatment plant in Martinez.

The first process area that the wastewater encounters upon reaching the treatment plant is known as the headworks. Wastewater also enters the headworks via septage trucks, or “honey trucks.” These trucks deliver their wastewater directly into our system by pumping their contents into holding tanks below ground.

This combined wastewater flow is screened to remove large objects.


Primary Treatment

Primary sedimentation is a simple process found in most wastewater treatment plants. It serves to remove substances in the wastewater that are lighter or heavier than water.

The primary sedimentation tanks mirror a natural physical process, similar to when a swiftly moving river flows into a tranquil lake. As the water slows, grease, plastics and other light substances collect on the water’s surface while heavy substances sink to the bottom as sludge. The difference from nature is that, in the primary sedimentation tanks, we can mechanically collect and remove the bottom sludge and the floatable materials, known as scum.


Secondary Treatment

Secondary treatment is a biological process that removes dissolved and suspended solids from the wastewater. Bacteria ingest the solids, then form a floc that will settle out in the secondary clarifiers. 

To aid the growth of the bacteria, oxygen is pumped into these tanks, which are aptly named “aeration tanks.” The oxygen is converted from heat captured from our furnace. 

Most of the bacteria that settle out of the process are pumped back into these aeration tanks and mixed with the incoming primary effluent to begin another cycle of secondary treatment. A much smaller portion are sent to our furnace for incineration.


Secondary Clarifiers

Water from the secondary treatment tanks is pumped to our secondary clarifiers. The clarifiers function much like our primary sedimentation tanks, allowing the heavy floc to settle to the bottom.  

The water that rises to the surface of these clarifiers has over 95% of the impurities removed.


Ultraviolet Disinfection 

Ultraviolet (UV) light kills bacteria and viruses in wastewater by destroying their cellular material, thereby preventing reproduction. Unlike chlorine, UV leaves no residual in the wastewater that can affect the receiving waters and marine life in them.

Once the water has been treated with ultraviolet light, the majority of it is pumped out to Suisun Bay where it is safely returned to the environment as final effluent.


Filter Plant & Recycled Water

The Filter Plant is used to further treat our final effluent for use as recycled water in various capacities. Approximately 600 million gallons per year are treated to this tertiary level through additional filtration and disinfection.

This recycled water is distributed and used for landscape irrigation, industrial processes, and plant operations.


Solids Building

The Solids Building is where we treat the solids that are removed from the wastewater during the treatment process. This building houses our two furnaces, which reduce an average of 200 tons of solids a day into approximately 14 tons of sterile ash. This ash is trucked offsite and used as a soil amendment.



Thank you for taking a virtual tour of Central San’s treatment plant and processes. We hope you enjoyed it! If you have additional questions, please contact Ben Lavender,