Partially treated wastewater containing
organic matter is now sent to the
aeration tanks where biological
organisms use the residual impurities as
food. Mechanical mixers supply oxygen
for the bacteria. Plant staff monitors
the process and incorporates control
strategies to maintain the correct
balance between food and
microorganisms. Another name for this
process is called “activated sludge”.

 

 

 

The pumped wastewater is sent to three primary sedimentation tanks. Here gravity separates heavier solids (sludge) and floatable ludge (scum). Once these materials are separated the wastewater flows to a secondary process for further treatment. The primary treatment
removes approximately 50% of the impurities in the wastewater. Rotating arms collect the sludge and they are removed for further processing.

 

The treatment plant incorporates a high strength bleach (Sodium Hypochlorite) to disinfect the clean water leaving the secondary Clarifier. This chlorinated
water is sent to a holding chamber for an hour to kill any pathogenic organisms.Plant Laboratory staff continually monitor effluent standards to conform to the
Federal Clean Water Act levels. After disinfection the wastewater is then sent to the San Francisco Bay.

 

Approximately 200,000 cubic feet of digester gas is produced each day. Thisgas supplies the fuel for two 350-kilowatt engine generators. These generators provide approximately 90% of all treatment plant’s electrical needs. The exhaust from the engines provide heat for the sludge digesters.

 


All stabilized digested sludges are then dewatered through the use of special chemicals (polymer) and the use of mechanical squeezing. The 2% digested sludges are converted to a 17% sludge.
These dewatered sludges are then solar dried and stored prior to removal to beneficial reuse or landfill.

 


All residual solids (sludges) that have been captured during the primary sedimentation and activated sludge process are sent to sludge digesters for approximately 16 days. Five digesters are heated and mixed to stabilize the sludges prior to dewatering operations.

 

The treatment plant receives 15 million gallons/day (MGD) of wastewater. Following the removal of grit and debris, influent pumps raise the water prior to the treatment process. Two 15 MGD electric pumps and two 50 MGD diesel driven pumps are used.

 

In the secondary clarifiers the activated sludge settles out. The clean water is removed from the top and sent on for disinfection. The settled sludge is returned back to the aeration system to
process more wastewater. The excess sludge (waste activated sludge) is removed from the system for further processing.

 


Some treated wastewater is chlorinated a second time prior to being sent to Skywest Golf Course. Each month approximately 8 million gallons of treated wastewater is sent for irrigation purposes.