Written by Andrew Toth, PE
Environmental Engineer, Burns & McDonnell
This morning, like most mornings, I flushed the toilet. I took a shower, put on clean clothes (taken out of the washing machine just last night), and ate my breakfast on clean dishes (I ran the dishwasher while I was sleeping). Each of these activities produced wastewater. A toilet flush, a 10-minute shower, a load of laundry, a load of dishes—I likely produced between 30 and 80 gallons of wastewater before I even got to work! In fact, the average American produces 88 gallons of wastewater per day. When you consider how many people there are in the United States, this can add up: in the US alone, we produce 12 billion gallons of wastewater every day. That’s almost 50,000 Olympic-style swimming pools! That’s an American football field filled to a depth of almost 17 miles!
All this wastewater must go somewhere. Have you ever thought about what happens to all this wastewater each day?
When you flush your toilet, wastewater (which we call “sewage”) flows from the toilet to the sewer pipe under the street in front of your house. A huge network of sewer systems crisscrosses our nation—more than 1.3 billion miles of sewers!
Some sewage flows by gravity (i.e. downhill), while some sewage is pumped to its destination. The destination is a Wastewater Treatment Plant (WWTP).
Environmental Engineer, Burns & McDonnell
This morning, like most mornings, I flushed the toilet. I took a shower, put on clean clothes (taken out of the washing machine just last night), and ate my breakfast on clean dishes (I ran the dishwasher while I was sleeping). Each of these activities produced wastewater. A toilet flush, a 10-minute shower, a load of laundry, a load of dishes—I likely produced between 30 and 80 gallons of wastewater before I even got to work! In fact, the average American produces 88 gallons of wastewater per day. When you consider how many people there are in the United States, this can add up: in the US alone, we produce 12 billion gallons of wastewater every day. That’s almost 50,000 Olympic-style swimming pools! That’s an American football field filled to a depth of almost 17 miles!
All this wastewater must go somewhere. Have you ever thought about what happens to all this wastewater each day?
When you flush your toilet, wastewater (which we call “sewage”) flows from the toilet to the sewer pipe under the street in front of your house. A huge network of sewer systems crisscrosses our nation—more than 1.3 billion miles of sewers!
Some sewage flows by gravity (i.e. downhill), while some sewage is pumped to its destination. The destination is a Wastewater Treatment Plant (WWTP).
image from Real Tech Water
The first step of a WWTP is called the “headworks.” In the headworks, solid objects are removed from the sewage. All sorts of items are removed here: everything from big pieces of wood to little pieces of corn.
After the headworks, we let nature work for us: sewage is sent to basins (sort of like huge bathtubs) where we pump air into the sewage. Bacteria live in these basins. The bacteria use the pumped air to breath, and they literally eat the gross stuff in the sewage. That’s right: you flush your toilet, and we feed the contents to bacteria. These bacteria consume what is in the sewage and convert it to less-harmful substances. In between eating sessions, the bacteria make lots of babies. As these bacteria babies begin to fill up our basins, we must remove a portion to make room for more incoming sewage. The bacteria we remove from the basins is attractively called “sludge.”
Sometimes the sludge, which contains valuable things like nitrogen and phosphorus, is used as fertilizer on farmland. Sometimes the sludge is put into a process called “digestion.” The digestion process is a lot like your stomach: more bacteria go to work “digesting” the contents of the sludge. And just like our stomachs, the bacteria create gas. Unlike our own farts, however, we build special structures to capture these bacteria farts because we can use the gas as a fuel source called “biogas.”
What is left is liquid, and that is sent to a disinfection process. Disinfection kills—or disables—any harmful pathogens and viruses still left in the sewage. If a human or animal were to come into contact with this treated sewage, we don’t want them getting sick, and that is why disinfection is so important! Typically, the disinfected wastewater is then released to a water body, such as a nearby river or stream.
Now keep in mind, this is a general overview—some sewage requires further, more complex, processing. But you start to get the idea: it is a massive undertaking to properly dispose of the contents of your morning stool. Each part of this system, from the pipes that convey it to the pumps that pump it to the plants that treat it, requires constant attention and maintenance. And our system is not in good shape: the American Society of Civil Engineers (ASCE) report card gives our wastewater treatment system in the US a resounding “D+.” At this point, the EPA estimates that we must spend upwards of $300 billion to meet current and future wastewater treatment demands in this country. Where will that money come from? That’s a good question! The honest answer is that we don’t really know. Some funding comes from the federal government, some from the local government. One federal program called the Water Infrastructure Finance and Innovation Act (WIFIA) will provide approximately $1 billion dollars to local communities which will themselves invest approximately $2 billion. While this is a great start, it is still just a drop in the proverbial wastewater bucket.
Our hope is that illustrating exactly how involved and important clean water and wastewater systems are in your own life will increase appreciation and gratitude for the water that you use on a daily basis. What would we do without wastewater infrastructure and treatment? Alarmingly, still more than half of the world's population does not have access to safe sanitation facilities.
After the headworks, we let nature work for us: sewage is sent to basins (sort of like huge bathtubs) where we pump air into the sewage. Bacteria live in these basins. The bacteria use the pumped air to breath, and they literally eat the gross stuff in the sewage. That’s right: you flush your toilet, and we feed the contents to bacteria. These bacteria consume what is in the sewage and convert it to less-harmful substances. In between eating sessions, the bacteria make lots of babies. As these bacteria babies begin to fill up our basins, we must remove a portion to make room for more incoming sewage. The bacteria we remove from the basins is attractively called “sludge.”
Sometimes the sludge, which contains valuable things like nitrogen and phosphorus, is used as fertilizer on farmland. Sometimes the sludge is put into a process called “digestion.” The digestion process is a lot like your stomach: more bacteria go to work “digesting” the contents of the sludge. And just like our stomachs, the bacteria create gas. Unlike our own farts, however, we build special structures to capture these bacteria farts because we can use the gas as a fuel source called “biogas.”
What is left is liquid, and that is sent to a disinfection process. Disinfection kills—or disables—any harmful pathogens and viruses still left in the sewage. If a human or animal were to come into contact with this treated sewage, we don’t want them getting sick, and that is why disinfection is so important! Typically, the disinfected wastewater is then released to a water body, such as a nearby river or stream.
Now keep in mind, this is a general overview—some sewage requires further, more complex, processing. But you start to get the idea: it is a massive undertaking to properly dispose of the contents of your morning stool. Each part of this system, from the pipes that convey it to the pumps that pump it to the plants that treat it, requires constant attention and maintenance. And our system is not in good shape: the American Society of Civil Engineers (ASCE) report card gives our wastewater treatment system in the US a resounding “D+.” At this point, the EPA estimates that we must spend upwards of $300 billion to meet current and future wastewater treatment demands in this country. Where will that money come from? That’s a good question! The honest answer is that we don’t really know. Some funding comes from the federal government, some from the local government. One federal program called the Water Infrastructure Finance and Innovation Act (WIFIA) will provide approximately $1 billion dollars to local communities which will themselves invest approximately $2 billion. While this is a great start, it is still just a drop in the proverbial wastewater bucket.
Our hope is that illustrating exactly how involved and important clean water and wastewater systems are in your own life will increase appreciation and gratitude for the water that you use on a daily basis. What would we do without wastewater infrastructure and treatment? Alarmingly, still more than half of the world's population does not have access to safe sanitation facilities.
(image from WHO Progress on Safe Treatment and Use of Wastewater Report)
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