Did you ever wonder what happens to the water that swirls down the drain when you take a shower or flows into the sewer after a heavy thunderstorm?
Twelve billion gallons of wastewater are dumped in oceans and estuaries every day in the United States alone. With that much water you could take a 3,000-year-long shower or fill more than half a million swimming pools!
A better (and much more practical) option is recycling that water for anything from watering crops to reclaiming wetlands to flushing the toilet. We hear about recycling cans, bottles, and paper all the time – but water recycling is just as important. The world is filled with over 7 billion people who need a fresh supply of water, but this year drought gripped 80 percent of the world’s (and 60 percent of the U.S.’s) agricultural lands. Water recycling plays a growing role in making sure people get enough water to drink, clean, grow crops, and run factories. It means cities in drought don’t have to bring in as much water from outside or take the salt out of seawater (desalination) for their water supply.
The big question is, how can you take sewage and transform it back into usable water? Let’s follow rain runoff as an example. When it rains, water is funneled down storm drains into the sewer, where it flows along until it reaches a water treatment plant for recycling. First, large debris like dirt, leaves, trash, and rocks are taken out. The water can filter through screens (like the ones on your windows) or sit in large tanks where heavy debris settles to the bottom as sludge and grease and oil float to the top where they can be skimmed off.
The water is then sent to secondary cleaning to remove smaller leftover waste and pollutants – stuff like soap, food, and chemicals. Most water recycling centers use microscopic organisms like bacteria to break down and eat any sugars, fats, or other waste left in the water. Bacteria in your local wastewater treatment plant could be enjoying the fruits of your dishwashing labor right now. In some plants, water is trickled through a special filter that’s coated with a thin film of bacteria. The bacteria digest waste as it passes by, and cleaner water comes out the other side. In other plants, the water is put into pools, where special floating mixers keep the bacteria well supplied with oxygen and fresh debris to break down.
This step in water cleaning can even be used for environmental conservation. Marshes and swamps clean dirty water in nature through bacterial breakdown, like the pools used in wastewater plants. Artificial wetlands can not only help clean our sewer water, they provide a habitat for wildlife.
After the bacteria have done their job, the water gets filtered and disinfected with special chemicals or UV light to remove anything living that’s left over. Water that’s been through secondary treatment is clean enough to be used where it won’t come in extensive contact with people (or human food and homes). For example, it’s used for the irrigation of nonfood crops, refilling dangerously low lakes or wetlands, or cooling and heating at factories.
Even after all that work, the water’s not quite ready for general human use. For this, wastewater plants use several final rounds of cleaning (sometimes this is called “polishing”). The water goes through more microorganism treatment (often with special chemical-eating bacteria), filtration, and chemical treatment to remove leftover particles, or chemicals like nitrogen and phosphorous. The water is disinfected one more time and is now ready for many new uses. This water that’s been cleaned (at least) three can be used to water golf courses, lawns, and food crops. It can also supply fire-safety sprinkler systems, toilets, car washes, and artificial snow machines.
As you can imagine, recycling water has its hurdles. It’s a long and complex process, and a special system of pipelines is needed to make sure water that’s not clean enough doesn’t make it into the drinking or food-crop water supply. In addition, water from farm runoff is often filled with fertilizer chemicals even after cleaning – bad for the human use, but great for watering crops – so it needs to be directed back to farms.
However, one of the biggest hurdles is the word “wastewater” itself. Who wants to ski in snow or eat lettuce that’s been watered with “waste” water filled with chemicals, dirt, and decomposing food? Of course, that’s not the case – you now know that wastewater goes through a rigorous cleaning process before it’s sent back out into the world. In fact, recycled wastewater is often cleaner than well water, and recycling water prevents the flow of waste into oceans and rivers, making the rest of the water around us cleaner as well. Many water treatment advocates are coming up with new names to make wastewater reuse sound more pleasant, like reclaimed water (you could even call recycled water “vintage”).
Recycling water, whatever name you call it by, is the opposite of waste – it’s a vital part of making sure humans have the reliable supply of fresh water we need to survive.