Virtual Plant Tour – San Andreas Sanitary District

San Andreas Sanitary District’s Operators are responsible for maintaining 18.61 miles of sewer pipes. That’s 98,249 feet. These pipes transport 250,000 gallons of raw sewage to the treatment facility daily. The Operators then direct wastewater through physical, biological and chemical treatment processes in order to remove all oxygen demand and all disease-causing organisms. After verification for compliance to stringent laboratory standards, the treated water is discharged to either the North Fork Calaveras River or to sprayfields where the cleaned water eventually evaporates.

Wastewater leaves residential and commercial establishments the same way. Waste from toilets, sinks, shower, laundry and so on is carried through a system of sewer pipes that connect to larger pipes, called interceptors, which deliver wastewater to the treatment plant for processing. Each step of the treatment process will be described in the following slides.
The Plant Headworks is where raw wastewater from the entire city enters the plant. Heavy Grit and Debris settle out in the bottom of the Grit Channel. The large solids that do not settle out in the Grit Channel are removed by a Mechanical Bar Screen, seen here in the background.
The Primary Clarifier is a large tank where the wastewater is caused to slow down enough so that the suspended solids in the water can either sink to the bottom as sludge, or float to the surface as scum. The sludge and scum are then skimmed off and pumped to the Anaerobic Digester for further treatment.
The Trickling Filter is a form of biological treatment where micro-organisms break down the fine dissolved solids in the wastewater that flowed from the Primary Clarifier.
The Process Feed Pump Station moves the wastewater to the next step of the treatment process, at the other end of the facility.
The Aeration Basins are another form of biological treatment. Billions of micro-organisms greatly reduce toxins such Ammonia which can be extremely toxic to fish and other wildlife.
The Secondary Clarifier is a large settling tank in which the solids from Aerations Basins can settle out and be returned to the process. The clear water then continues on to Tertiary Filters.
The Tertiary Filters remove the very fine particles that made it through the previous treatment stages. Once the water has been filtered, it is chlorinated to kill harmful pathogenic bacteria.
The Chlorine Contact Chamber provides sufficient detention time for chlorine to kill pathogenic organisms before being released back to the environment. The fully treated water is then discharged to the North Fork Calaveras River, or to on-site Spray-Field Irrigation systems. When Discharging to the North Fork Calaveras River, the chlorine is neutralized to prevent contact with any wildlife.
During the summer months, water is pumped to spray fields where sprinklers like this one release the clean water back to the environment
The Gravity Thickened Aerobic Digester, or G-TAD, is an aerated solids holding tank in which microorganisms help to significantly reduce the volume, odor, and pathogenic organisms within the solids that were removed from the wastewater. These solids are then dewatered with a Belt Filter Press.
The Belt Press is a specialized machine designed specifically to dewater bio-solids by squeezing the bio-solids at high pressure. The bio-solids that were removed from the water leave the belt-press ready for drying beds and eventual disposal.
Our entire facility is closely monitored 24 hours a day by an advanced computer system called SCADA (Supervisory Control and Data Acquisition). This is the nerve center of the treatment plant. If any malfunctions, errors, or treatment problems are detected, the system will automatically notify the On-Call Operator by telephone.
The entire facility is equipped with backup power generators such as this one. In the event of a power outage, the plant is still required to treat dirty wastewater effectively. After all, the sewer doesn’t stop when the power’s out!