How Does Sewage Treatment Work?

Sewage treatment turns out to be a somewhat less nasty business than you probably thought















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Smith packs us back in his pickup and we drive to a parking lot and a box truck with a picture of a fish on it. The three guys in the truck are going to TV a pipe: Mike is preparing the camera and the screens in the back of the truck while Wayne and someone who introduces himself only as "the Rev" open the manhole, popping the cover off easily with a metal hook. Wayne and the Rev then retrieve the camera from the truck. With six tiny rubber wheels and an inquisitive single eye, it looks a bit like the Mars rover vehicle, only tiny and dangling at the end of a wire. When they come back to the manhole Wayne and the Rev are shocked to find it suddenly filled with sewage. This kind of backup indicates a block in the 6-inch pipe at the bottom of the manhole, though it drains away as fast as it backed up.

A few moments of observation shows two things: The backup comes and goes rhythmically, meaning there's a pump station upstream that sends a pulse of wastewater every couple of minutes, and the blockage is a bunch of pieces of some solid substance that nobody can identify. Out come spoons--hooked, perforated shovels on the end of 12-foot handles. Wayne, Robert Smith, and Eddie, another supervisor who has arrived, take turns scooping, pushing things back and forth between rushes from the pump and pulling them out with an awkward hand-over-hand motion that keeps the gunk barely balanced on the edge of the spoon unless you knock the handle against an overhanging tree branch. It's like using an iced-tea spoon to fish olive pits out of a bleach jug at the back of a cupboard. "And people think it's Ty-D-Bol that keeps their bathrooms clean," Wayne says.

The stuff turns out to be congealed grease, and pieces of it are sufficiently solid--and sufficiently far up the 6-inch pipe--that they block the progress of the camera every time the Rev dangles it down there and tries to get it running. The vacuum nozzle can clear the manhole but can't pull grease out of the pipe and it resists everything else they've got, so the crew finally gives up on TV-ing that pipe for the day, until they can clean the pipe--possibly by using a bucket truck (which feeds a cable past the debris and drags a bucket from one manhole to the next, pulling before it the kind of grit and large debris flushing just doesn't get) or possibly by sending someone down there in the hope that a simple scoop into the pipe will clear the debris. (Sending someone down a manhole, though it's only about 8 feet deep, requires confined spaces training, extra supervision, and ventilation equipment--sewer gas contains methane and hydrogen sulfide, and it has killed workers as recently as 2008.)

Smith shows me video footage from another TV-ing expedition that shows long traverses down shiny pipes half full of dull gray water. The color makes sense--much more of it comes from your washing machine and shower than from your toilet. "First thing people say is 'Eew,'" Smith says; "they think I'm walking around in feces." But even the wastewater filling up the manhole that day smelled more like runoff than poop.

Though most blockages are caused by grease or roots, the talk naturally turns to memorable clogs, and I hear about mops, golf clubs, firewood, riprap, and even a refrigerator that have had to be pulled out of manholes. Once a carpet remnant created a block so nasty it took most of a day to clear out. If you're on call and someone calls in a spill, especially one where the overflow is making its way toward a waterway, then it's showtime. "You go running after it like it's a Russian spy," Wayne says. "You chase the spill, pulling hose, four, five, six miles." First the crew finds the end of the spill in the waterway--where the water is still clean--and sets up a block using hay bales, which both dam the flow and filter any water that might trickle through. A pump immediately starts channeling the polluted water into the nearest downstream manhole. And while a crew works on clearing the clog itself, other crews chase the spill, hosing down the sides and bottom of the stream. You can tell when untreated wastewater has hit a stream, Smith says, by the powdery-looking buildup it leaves: "It looks like gray dust in the water," coating the rocks and sticks. The hoses clear the scum off the bottom and stir up the mud. "That muddy water acts like a glue to that stuff--it piggybacks on the mud." Then you pump it out at the end of the spill. "After we go through, that creek looks like nothing ever hit it. It's pretty neat."



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  1. 1. quincykim 02:36 PM 7/5/10

    Excellent article, kudos to SA for reprinting it. I've been studying water and wastewater treatment with an eye toward employment. The more I learn, the more impressed and fascinated I am by the ingenuity that had made WWTPs amazingly efficient and virtually smell-free, producing very clean water. It's unfortunate that most people can't or won't ever visit one of these high tech plants to see how much they aren't like you'd expect, and how sensible it is to re-use tertiary treated water.

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  2. 2. lwinn 04:48 PM 7/5/10

    Recycled water is the only thing that makes sense in a space colony. Of course, you could reduce all the water in sewage to hydrogen and oxygen, then burn it, if you have enough energy. I'm always looking for alternative concepts. Got ideas?

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  3. 3. rstorey 05:56 PM 7/5/10

    Excellent article, with information that should be, but is generally not, understood by citizens. Many still protest the fees they must pay for wastewater treatment as part of their utility bill. I hope this lengthy article can be condensed into newspaper features and municipal handouts to better educate citizens about a vital service. The city of Arcata, CA, has a very interesting wastewater treatment system that may warrant the attention of the author and readers. Link: http://www.cityofarcata.org/departments/environmental-services/water-wastewater/wildlife-sanctuary

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  4. 4. Wayne Williamson 06:23 PM 7/6/10

    one of the best articles i've read in along time....contained both historic and current detail...thanks Scott for your effort...this should be one of the main articles in sciam...not just a link to the side...then again 11 pages might be to much for most;-)

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  5. 5. lowndesw 05:22 PM 7/7/10

    The four letter word for this stuff is actually an old acronym from the days of sail. When guano (bird droppings) was discovered in huge quantities on pacific islands and transported back in bales in the cargo holds of wooden sailing ships, any stored in the very bottom would get wet, give off methane gas which would be ignited by any sailor with a candle doing inspections. Several ships were lost before survivors told of huge explosions and fires that happened during inspections and the problem and mystery was resolved. Thereafter, maritime laws required all guano bales be marked "Store High In Transit".

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  6. 6. Quinn the Eskimo 01:42 AM 7/8/10

    Question; Does it make sense to pump city water from wells (from the aquifer) use it, treat it, and dump it in the river-shed?

    A rural home pumps from a residential well, uses it, treats it and returns it to the ground. Not a river headed for the Gulf of Oil.

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  7. 7. akmangalick 01:57 AM 7/8/10

    I agree wholeheartedly with several others here that this was a fascinating and well-written article. Who knew sewage treatment could be so interesting?

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  8. 8. wongxinwei 12:06 AM 7/10/10

    A well written story on the history of used water distribution and treatment around the world. Ending off with a a fine and entertaining write up on the process of water reclamation. I love the point which says that what the used water treatment plant is doing is in fact mimicking what the river is doing, just quicker!

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  9. 9. wongxinwei 12:07 AM 7/10/10

    A well written story on the history of used water distribution and treatment around the world. Ending off with a a fine and entertaining write up on the process of water reclamation. I love the point which says that what the used water treatment plant is doing is in fact mimicking what the river is doing, just quicker!

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  10. 10. mm in reply to lowndesw 12:09 AM 7/13/10

    This is hogwash, or perhaps a good example of the word it purports to define. See the Etymology section of http://en.wikipedia.org/wiki/Shit, which shows the origins going back to Roman times.

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  11. 11. mm 12:19 AM 7/13/10

    This text was meant to reply to the comment on the origin of the s-word, not a comment on the article or reply to any of the other comments:

    This is hogwash, or perhaps a good example of the word it purports to define. See the Etymology section of http://en.wikipedia.org/wiki/Shit, which shows the origins going back to Roman times.

    The article itself was wonderful, a fascinating read, with a mind-boggling amount of information I could hardly wrap my mind around (though Mr. Huler's style certainly was as clear as . . . triple-treated waste water!).
    I live in flat Phoenix and I'm really wanting now to know how our system works. And all the other infrastructure we ignore but wouldn't want to be without these days.

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  12. 12. huler 05:34 PM 7/13/10

    Thanks for the kind words; mm, you beat me to the punch on the etymology. And in answer to Quinn, no, I don't think that makes sense; surface water -- like water from a reservoir -- basically just makes its way to the ocean through the city and its residents. That's where it was going anyhow, so wastewater generated by a community with surface water as its source can reasonably be released back into the stormwater system -- the riverbasin from which it emerged.

    Aquifer water is on the same journey, but it may take much longer, and continued pumping from an aquifer can deplete it; using septic systems to replace wastewater from such systems into the aquifer is probably a wiser move. Just the same, in my experience most houses on pumps -- using aquifer water -- are also using septic systems too, so the wastewater just trickles back into the ground.

    There's a long chapter in "On the Grid" about stormwater -- much current stormwater treatment is about keeping it where it lands and helping it soak into the earth, instead of using curb and gutter to sluice it into creeks. It has a job to do as part of the hydrological cycle, and we do ourselves and the planet no favors by getting rid of it so quickly.

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  13. 13. eco-steve 05:46 PM 7/20/10

    Many sewerage treatment stations only work at around 15% efficiency, because the operators cut the electricity supply to aerators and turbines to reduce expenses. The liquids that are then put into rivers are therefore a serious cause of pollution.
    Pyrolysing sewerage is a new, simpler and cheaper technique that should totally replace traditional plant. See www.eprida.com for more details.

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  14. 14. Neptunerover 07:41 AM 7/25/10

    How sewage treatment works in this country is so complicated! Why all the bother?
    They've got it figured out in Kibera; who needs sewers? Just poo in a bag and throw it in the street!

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  15. 15. cwclark 01:34 AM 8/14/10

    Thank you for this article; it has been a wonder to me that we honor or police and firefighters (rightfully so) but never give a second thought about those water and wastewater professionals who also keep us safe and healthy day in and day out. This too is a dangerious profession, there are more people who die in water/wastewater industry than in the police/fire profession. Again, kudos, keep up the good work.

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  16. 16. huler 03:45 PM 8/14/10

    @cwclark: I did not know that -- do you have a source for that statistic? It's important and I will share it. Thanks for your kind words.
    Scott

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