Have you ever wondered, “where does the water go from there”? Maybe you think that once the water goes down the drain it’s gone forever, but that’s not the case! Modern technology allows us to give contaminated water a second life, which is important in a changing world where fresh water is becoming scarce. Here in Napa County, wastewater is treated, recycled and reused to irrigate parks, golf courses, fields and vineyards. Some of this water is even used to restore wetlands and replenish water diverted farther up the Napa River.
The Napa Sanitation District (NapaSan) maintains more than 270 miles of underground sewer lines that carry wastewater from homes and businesses throughout Napa to the Soscol Wastewater Recycling Facility off Soscol Ferry Road. It is the largest wastewater treatment plant in the valley- it recycles 740 million gallons of water each year. Some of the recycled water goes through an additional treatment process so it can be used for irrigation and landscaping throughout the valley while the rest of the treated water is returned to the watershed, replenishing surface water in the wetlands on the southern portion of the Napa River. The health of our watershed depends upon effective wastewater treatment and recycled water. If contaminants are left in the water when it is returned to the watershed, it can be toxic for people, animals, and the environment. Wastewater (also known as sewage) was once dumped straight into the Napa River. This made the water toxic, resulting in massive fish kills and an unbearable stench that convinced the community to change the way wastewater was handled. In 1945, Napa residents came together to create the Napa Sanitation District and change the health of our local waterways through their mission to "collect, treat, beneficially reuse, and dispose of wastewater in an effective and economical manner that respects the environment, maintains the public's health and meets or exceeds all local, state, and federal regulations".
Today’s water treatment plants create clean water and clean energy: Modern, state-of-the-art facilities allow us to not only remove harmful contaminants from the water, but also to produce biosolids (soil-like byproduct of sewage treatment) that can be used to fertilize fields, generate energy from captured methane gas, and recycle water for agriculture and irrigation. Recycled water is especially important because it allows cities to conserve the drinking water supply, particularly in drought years. During a drought, decreased snowfall and rain results in less water supplied to cities and greater dependancy on groundwater. Using recycled water in the dry season allows us to avoid using potable (drinkable) water for irrigation and avoid tapping into limited groundwater storage. In Napa County, 80% of groundwater use is for agricultural purposes. Using alternative water sources like recycled water for agriculture helps increase water security for famers. When recycled water is used to irrigate parks, vineyards, fields, and golf courses, more potable (drinkable) water and groundwater is available for homes, farms, businesses.
So how do we make the water from our toilet clean enough to be reused, recycled, or returned to the Napa River? First, wastewater received by the treatment plant is sent through screens to remove any rocks, grit, or garbage that is sent down the drain. This debris is the only part of the water treatment process that doesn’t get recyled; everything caught by the screens is sent to the landfill. Next, the water goes into a clarifier tank, where solids are separated from the water. Large rotating arms at the bottom of the tank sweep away heavier particles in the water that sink, while another set of arms on top of the water remove lighter solids that float. The sludge of solids swept from the top and bottom of the tanks goes on to a giant egg-shaped tank called a digester while the mostly clarified water is sent to the aeration basin.
A digester is just like an enormous, 74 foot tall stomach where bacteria in the 1.3 million gallon tank 'digest' or eat the sludge to convert solid waste into methane gas and biosolids. This bacteria particularly loves to eat the the fats, oils, and grease (FOG) that is skimmed from the wastewater- so much so that NapaSan accepts thousands of gallons of FOG from local food service facilities to add to the digester to speed up the conversion of the solid waste and increase methane production. The resulting methane gas is captured and then powers the plant, saving electricity and lowering the cost to treat the water. Each day 115,200 cubic feet of methane is produced by the digester, producing 1,377 mega watt hours of power a year. That’s almost half the total energy used to power the plant! The biosolids produced by the bacteria are rich in nutrients such as nitrogen, phosphorus, and potassium and are used to fertilize fields like those that grow alfalfa and sorghum for cattle off of Jamieson Canyon Road. This incredible process not only produces its own energy, but it also diverts waste from the landfill and returns nutrients to the land.
While the solids waste is being processed in the digester, the water from the primary clarifier tank is sent to the aeration basins so that any dissolved solids in the water can be removed. The aeration basins bubble up with oxygen and billions of microrganisms that eat the dissolved solids in the water. The water travels to a secondary clarifier tank to remove waste from the microrganisms and comes out clear. In the wet season, clean water is simply disinfected and returned to the Napa River. During the dry season, water is run through sand filters to remove any remaining fine particles before being disinfected with chlorine and sent out to vineyards, parks, fields, and golf courses to be reused. In American Canyon, treated water is used to recharge the wetlands that were once converted to salt ponds along the Napa Bay and River Trail.
75 years ago, wastewater nearly destroyed the Napa River and its ecosystems. Increased environmental awareness has helped us develop a truly extraordinary system that helps our watershed thrive. Watch the videos below in our Go Deeper section to see for yourself how dirty water is made clean, and how recycled water is helping to preserve our watershed and the Napa Valley way of life.
Check us out! Books and resources available from the Napa County Library:
1). How Water Gets from Treatment Plants to Toilet Bowls by Megan Cooley Peterson
2). Toilet: How it Works by David Macaulay
3). Save The Planet: Keeping Water Clean by Courtney Farrell
4). Water by Jen Green
5). Why Should I Turn Off the Tap? by M.J. Knight
Go deeper! Explore these great resources online:
NapaSan Wastewater Treatment Brochure
Watershed Explorers: Amercian Canyon Wastewater Treatment Video
NapaSan Tour of Soscol Wastewater Recycling Facility
NapaSan Recycled Water Video
Napa Recycling Trash Talkin' with NapaSan
Click on the images below to learn more: