OK,
I’ve looked all over, and I can’t find it, so I’m posting it here: When you flush the toilet, where does all the sewage go? How do they filter out the bad crap and clean out the water? Where do they put all the solid stuff?
And while we’re at it: Aren’t we rapidly running out of space to put all our garbage? I mean, doesn’t every person generate something like a ton of garbage every year? Where does all this stuff GO???
Thanks! 
Greg
The ultimate destination of sewage depends on where you live. In the country, septic tanks are common, where solids settle and are slowly digested by bacteria and water filters into a leach field. In the city, all waste water, including rain runoff goes to sewage treatment, or water quality control plants. There, solids are settled out and usually incinerated and the water is treated and released into the watersystem, usually an river or bay. The effluent is cleaner than the body it’s discharged into, and although it may not meet drinking water standards, is pretty darned close in most locales. At least in California.
I’m not sure if your “everywhere” included the Encyclopædia Britannica, but it has a decent overview of sewage and the index at the bottom of that page will allow you to look at the entire cycle of water supply and distribution.
When you’re done there, you can stay in Britannica.com and look up “trash” or"landfill."
That depends, Greg. Are you have a septic system, city sewage, or an outhouse?
The outhouse explanation is easy. It goes to the bottom of the hole and stays.
A septic system is a little more complicated. When you flush the waste is carried out of the house through a pipe (or series of pipes). Outside the house those pipes, now underground and preforated, continue to carry your waste. This is known as the septic field. The length of the septic field is dependant on many factors, but it is usually alot of pipe. Some of the liquid waste leaches out of the pipe and is cleansed by the gravel and dirt surrounding the septic line. The remaining liquid and all solid waste is deposited in the septic tank where it is broken down by anaerobic bacteria. If your bacteria go on a hunger strike you get to call a specialist to have your septic tank dug up and pumped out.
With a sewer system your waste is piped out of your house and into a bigger pipe, usually at the street. It mixes with the waste of your friends and neighbors as it journeys through progressively bigger pipes to the wastewater treatment plant. At the treatment plant various methods are used in sequence to clean the water, including sand, gravel, filters and chemicals. The cleansed water then comes back to your house so you can drink it.
Hrumph, buncha succinct typist. But I’m the only one who covered outhouses!
Wait a second! Not so fast! One respondant said that once the waste water is treated, it is sent back to your house, purportedly in an endless cycle, for drinking and general use. Another respondent claims it isn’t. What’s the deal?
Here’s something that amazes me about this topic: it’s kinda hard to believe that the water from a city of, say, five million residents can be effectively purified to almost natural, um, purity. I mean, we’re talking about millions of trips to the restroom every day, along with everything that goes down the toilets with it, flushed back to the treatment center. Add to that sundry solvents and chemical from industrial operations, farm runoff, etc., and you’re talking a staggering amount of gunk. These treatment centers must be immense and the smell atrocious! YUCK!
Most of it goes into landfills. Giant oceans of trash. Some of it is incenerated to create electricity. Some of it is recycled, but most of it goes in the good ole city dump. Some municipalities send their garbage out of town, and in some instances, out of state to dispose of it. The landfills are huge. Massive.
Where does it “go?” My mother thinks that once you throw it away, it goes to the landfill where it gently bio-degrades into the earth from whence it came. Not so. Your garbage, in its plastic bag will be around much longer than you are. In fact, some students of archaeology are now digging in landfills to research eating habits during the second world war. Newspapers are totally readable, food matter is still recognisable . . . just like the garbage from 1940 was thrown away yesterday. They theorize that because the weight of the garbage above pushes out all of the air that microbes and bacteria cannot decompose the trash. We’re leaving quite a boon for the archaeologists of tomorrow.
Again, it depends on where you live.
I take it you’ve never had the experience of driving by one such treatment plant. I assure you, the smell is all it’s cracked up to be. I used to work half a mile down river from a sewage treatment plant, and believe me, I was constantly aware of the stench.
The plant six or so had large, bubble-topped tanks that sewage was pumped into. The floatsam was scraped off the top, the solids disposed of, and the liquid was sent through very fine filters. Then the water was heavily chemically treated, and dumped into the river to continue the beatiful “circle of life.”
Fishermen loved it. In colder weather, the water coming out of the plant was warmer than the river, and the fish flocked to it.
If you live in Pacific Grove, Ca, it often flows right into the bay.
Otherwise it travels in its own little pipe to a sewage treatment plant with filters out things & the rest of the water is dumped into the sea.
Had a neighbor once in the 70s who used to have human shit fertilizer that he bought, it was dry, it stunk but boy did things grow well with it. However, I did eat the vegetables ugggggggh!
Finally, something I have an answer to – at least for the US –
Lissa was right about decomposition (or the lack thereof) in modern landfills. The study she was talking about was a part of the Garbage Project at the University of Arizona – I’ll see if I can find a link.
As for garbage generation, I think the most current average I’ve heard from the EPA is 4.3 lbs per day per person, which equals about 1500 lbs per year. Concern about a lack of landfill space was a hot topic in the early 1990s (and led to the creation of the particular governmental agency I work for.) In the years since, we’ve found that we don’t really have a “landfill crisis” – most places in the US have many years of available space in their existing landfills, and room to build new ones if need be. The densely populated east coast states often have to export their trash to other states to be landfilled because they just don’t have the space (or any appropriate space) to put another landfill.
That being said, landfill siting and construction is difficult and expensive. Many people feel that we can do much better things with our trash – source reduction, reuse, recycling and composting – than entomb it in the earth.
If you want to know at least one of the ultimate destinations for human waste recovered from sewage treatment, look up milorganite.
And start looking at your local produce section funny…
I understand about my human waste going from a pipe under my house to a bigger pipe under the street, and eventually to the treatment plant.
What I need to understand is, what powers that movement? Just gravity? So all the pipes are installed on a carefully-planned slant to facilitate the flow, even under level streets? That’s a hard concept for me to grasp.
Or is water pumped through the sewers to provide a current? What kind of water is this?
5, if you want find your local college library, they might have the complete map of you city sewage system for you to look at.
They have pumping stations that pump it to the cleaning plant.
milorganite, yeah, thats the stuff my neighbor put on his plants. gross.
Ah, sewage…
First, sewage (or “wastewater”) from your home is a mix of effluent from all the outgoing pipes (toilet, sinks, showers, washing machine, etc.).
(1) If you have a septic system, then it goes to a septic tank which is essentially a large concrete box where bacteria get some time to digest all the organics. Then, the overflow (hopefully mostly clean water) goes out a pipe and to a leaching field (a series of perforated pipes) that puts the water back into the ground. Something to keep in mind if you also get your drinking water from a well on your property!
(2) If you’re on a town sewer system, then it goes through a force main and a series of pump houses to a treatment plant (at least in developed countries…otherwise it probably just goes to the nearest river). At the treatment facility, there are a series of cleaning steps. The amount of cleaning varies from community to community (based on how much money they have and how clean they need the wastewater to get before they discharge it).
First, there is a big screen to remove floating debris, dead bodies, etc. (some sewer systems also handle stormwater from the streets, etc…a bad design, but oh well). That junk gets disposed like a solid waste (landfill, incinerate, etc.).
Next, there is “primary treatment” which is a big settling tank. Heavy stuff sinks to the bottom and is scraped out and collected. Light stuff floats to the surface and is also collected aside. The partially clean water moves on to the next stage. (hang on a moment for the “sludge” treatment)
Next, there is “secondary treatment” which is usually some kind of biological process (“activited sludge”, “trickling filters”, etc.) that gives microorganisms some time to digest the organics that made it through the first stage. Again, some sludge is collected in a “clarification tank” (another settling tank).
Next, if the town is rich, there is “tertiary treatment” which can be another kind of biological or other fancy way to get more organics out of the flow.
Finally, there may be some disinfectant step is done (like chlorination or UV light) to kill all the bacteria/viruses. If it was a chemical step like chlorine, then there is a dechlorination step to neutralize that before the water is discharged.
Lastly, the cleaned water (I wouldn’t drink it directly!) is discharged to a river, ocean, or something for the last step…dilution.
All the sludge that was collected can be treated in various ways…an additional biological digestion (often under anaerobic conditions), composting, landfilling, etc.
Garbage (solid waste) that is not recycled is typically landfilled or incinerated. Many parts of the country have enough landfill space for quite a while, but some regions…like the Northeast, are running out fast. Cecil has some info on this if you check the archives.
Yes, “staggering” is a good word for the volumes being handled as well as the smell (although there are ways to control that (enclosed tanks, etc.). Treatment plants cost millions of dollars to build and maintain. Thus, the large tax bill.
It’s certainly better than what used to be done (direct discharge to the nearest body of water)…just ask people around Boston Harbor (who recently got a new multi-million dollar treatment facility on Deer Island).
oops! make that “multi-billion” dollar!
I’ve been waiting for this question to come up from my very first day at the SDMB, since I work at a Municipal Waste Water Treatment Facility. And Phobos beats me to the punch. So I’ll elaborate a little on some of the details.
Wastewater Treatment Facilities (WWTFs) are usually situated in lower lying areas near a convenient ocean or river, so they have a place to discharge the Final Effluent (FE) and to maximize gravity feed to the plant. My WWTF only does primary treatment, (solids removal) and can actually operate for many hours without power, relying on gravity to push the water through the whole process. Of course, all areas of a city cant be at a higher elevation, so the collector mains in low lying areas feed into “Lift Stations” where the wastewater is pumped to a higher level again before continuing down the pipe.
Side note: In a sewer main turds don’t float. They bounce.
Removal is the name of the game, and every WWTF operates under a permit issued by the EPA which specifies physical and chemical parameters that the FE must meet prior to discharge into the receiving water body. The two most critical parameters are Suspended Solids and Biochemical Oxygen Demand (BOD). In addition, temperature, pH, dissolved oxygen, fecal coliform densities, oil and grease, cyanide, disinfectant residual, and dissolved metals are routinely monitored. I personally perform analyses for all of these parameters, except metals.
Sludge is probably a bigger concern than the water itself. Water goes away after it is treated, but you still have to deal with the sludge. There’s many ways to handle it, but the big idea is to de-water it, so it takes up less space. I’ll describe my plant.
It starts out as “wet sludge” which looks like mud and is about the consistency of tomato sauce. Then it becomes thickened into the consistency of spaghetti sauce in another process. Chemicals are added to make it clump together, then water is squeezed out of it on a moving belt press. It looks like damp, dirty cardboard, and is called “cake sludge”. At this point, it is still about 70% moisture by weight and it can be trucked to a landfill or a composting facility.
But that 70% water still weighs a lot and takes up a lot of room. So we burn it in a huge incinerator which reduces the volume by a factor of 10 or 15, and take the ash to the landfill. That way we drive only 1 dumptruck load to the landfill each day instead of 15.
Doctor Jackson wasn’t incorrect when he said the water is purified and sent back to your house. He just skipped over the part about the hydrogeologic cycle. However, the concept of returning FE from a WWTF right back to a drinking water treatment plant isn’t new. There was (is?) a very high profile project in the San Diego area, and another one in Florida I believe, where treated wastewater is discharged directly into a reservoir, where it would eventually be treated and turned into drinking water. I’m pretty sure the San Diego one failed miserably before it ever got off the ground, due to overwhelming opposition from the citizens. No matter how strong and reliable the technology might be, the thought of drinking treated wastewater was too much for the people to handle.
[sub]I won’t even apologize for being so lengthy. I might not get another chance.[/sub]
All this talk of sewage is making me wonder… Just how much sewage is produced in a day in the world? If you figure 5 billion people going to the bathroom at least once a day… wow! I wonder if it will ever reach a crisis point where there is just too much sewage accumulating!
honkytonkwillie Sorry to steal your thunder! (I too have been waiting for a question from my field of work…although I deal more with haz waste than wastewater.) Anyway, you provided some excellent details.
DaveRaver it’s millions of gallons per day per city. I didn’t find an exact figure on this.
My college professor joked about how it seems illogical that we start with something that is about 95% solids (poop) and then make it about 3% solid (wastewater) and then spend tons of money to struggle it back to 70%.
Wow, who’d of thought there’d be this many people so eager to post about doo-doo! Well, OK, this IS the web, so maybe that’s not surprising, but the eagerness to post esoteric technical facets to doo-doo management is probably unique.
Since phobos and honkytonkwillie have covered most of it, I don’t have much to add, but I’m going to ramble for a moment anyway. Mostly, I just want a chance to be able to mention my favorite euphamistic sewage/environmental technical term. Maybe it’s just me, but I love the term ‘floatables’ which is the image-inspiring word they use in technical documents to describe certain kinds of water pollution from sewage. I hope I don’t need to go into any more detail on what it means. Other than to say, there are still places in the U.S. where raw sewage can wind up in rivers – mostly older cities whose sewer system is connected to storm drains and therefore gets overwhelmed during rainstorms, leading to overflows. So you could possibly have a floatable sighting, depending on where you live (ooh!) Though thanks to Deer Island and it’s cousins, it’s much rarer than a couple decades ago.
Oh, and in case anyone cares, to address a minor part of tsunamisurfer’s post there are limits to the amount of industrial solvents and chemicals that businesses can send (legally) into the sewage pipe; these limits are in fact there in large part so that the sewage plant won’t be overwhelmed by something it can’t deal with.
There is an old saying, *** Shit always flows down hill***