Wastewater Treatment Plant Virtual Tour

Wastewater first passes through an aboveground headworks where the volume is measured and a portion can be diverted to the underground treatment facilities, otherwise, the flow goes to a second aboveground headworks. In both headworks, large solids, which would interfere with pumps and other equipment are removed using mechanical bar screens. Screenings removed from the wastewater are hauled to a landfill for disposal.

The wastewater flows through primary settling tanks, known as "primaries". Six primaries are located aboveground and two underground.

Primary treatment consists of holding wastewater for about two and a half hours to allow heavy particles to settle to the bottom as "sludge" and light particles to float to the top as "scum".

During rain storms and daily peak flow periods, primary treated wastewater is diverted to underground equalization basins. Here, up to 2.8 million gallons of wastewater can be held until the peak period passes. Equalized primary wastewater is pumped to the secondary treatment process.

Wastewater treated in the aboveground primaries can either be pumped to the secondary process or flow to the equalization basins.

Sludge is collected and pumped to a cyclone degritter which removes heavy grit particles such as sand, egg shells, and coffee grounds. Grit is hauled to a landfill for disposal.

Degritted primary sludge is concentrated in gravity thickeners until it contains about 5% solids and 95% water.

Thickened primary sludge is anaerobically digested just as people digest their food. Here methane forming bacteria feed on sludge contained in a tank devoid of oxygen. The digesting sludge is heated to an average of 98 degrees Fahrenheit to speed up the process that takes anywhere from 12 to 25 days.

Methane gas, produced during digestion, is burned to heat the digesters or used to generate electricity. Any remaining gas is burned in an excess gas burner.

Digested sludge, or biosolids, is dewatered using a high speed centrifuge. The centrifuge spins the water from the biosolids until a cake containing 20 to 25% solids remains. Depending on the season, the biosolids are hauled to a landfill where they are used as daily cover or to a site where they are beneficially reused as a soil amendment.