When you flush a toilet in the city of Lodi, you don’t normally think about where that water is headed. But it all ends up in the channels, holding tanks and pump systems at the White Slough Pollution Control Center. It’s a wastewater treatment plant that can clean up to 8.5 million gallons of sewage each day.
“When you think about it, every process is just about taking solids out of water and disinfecting the pathogens,” said Larry Parlin.
The process starts when raw sewage travels from the homes, businesses, schools and churches of Lodi and flows into the main line at the center. The water contains everything you think it might, including toilet paper, human waste, dirt and garbage.
The first job is to filter the large debris out using two large rotating band screens. The water and small grit runs through the screens, while the debris is lifted out. That debris is compacted, dried, and disposed of in a dump site.
Next, the water runs through a wide shallow grit chamber, forcing the flow to slow down and let bits fall to the bottom. That process continues in the primary tank.
Scrapers travel the bottom of the tank to move heavy grit to a trough to empty later.
The settled water is carried to the secondary tank where natural bacteria break down any solids. Bubbles float them to the surface, where sprayers push the sludge to a trough on the side.
From here, the water goes to a circular tank, where it settles further and more debris is skimmed off the top.
At this stage the water is clean enough for agricultural use. But it goes through a series of ultraviolet light to disinfect it enough for flows to the river.
All that sludge they took out earlier goes into a huge anaerobic digester to be broken down and later disposed of at the landfill.
— Source: White Slough Pollution Control Center