One day I pulled over on a main highway to watch a sewer crew fix a leaky pipe using what's called cured-in-place pipe: A long liner impregnated with resin is pushed into a pipe by water, then they pump steam through the pipe to harden the resin, and presto--the pipe is, though slightly narrower, all but new. The crew runs an auxiliary pipe while they fix the leaky one. Workers can find leaks by stopping up pipes with sandbags, pumping smoke down a manhole, and then seeing where the smoke starts creeping out of the ground. Clearly, people have thought about this stuff a lot.
"It gets in your blood," said a senior engineer and inspector named Dave, who managed a construction site near my house. I had stopped by a sewer truck to watch a couple of guys hose out a pipe, which they followed to a manhole at the backyard boundary of a few properties. "I don't like the looks of that," one had said when, spooning out grit from the hole, he unearthed pieces of clay pipe. Rather than dig on several people's private property, the city decided to abandon the line running between the houses and reroute the flow to the end of the street, where it could join a larger main and head downhill. But since the flow had to go downhill, the engineers had to get wastewater to flow away from the manhole in a different direction. That meant, simply, digging a deeper trench in the direction they wanted it to go. They had to do the same thing on the line that received the new flow, so they were digging on two streets for a few weeks, and I occasionally stopped by.
I watched them carefully lower new green PVC pipes and check the slope. They use a laser to measure, with a sort of bull's-eye target at the end. The red dot right in the center means the pipe has the right slope. "We used to run string lines, length by length," Dave told me. "This makes it easier. A lot easier." They lay pipe on a bed of gravel, supporting it with rocks and pieces of brick to maintain the slope, unlike water pipe, which, under pressure, can just be laid in a trench and buried. Any pipe below 12 feet has to be ductile iron, to support the weight of the earth on top; same with any pipe that crosses a creekbed, hangs under a bridge, or does anything but lie directly on the earth. Even though sewer pipes start out low and have to keep going lower, in a city with no subway system there's not much other infrastructure in the way; 12 feet is fairly deep for Raleigh.
The Neuse River Wastewater Treatment Plant, southeast of Raleigh, discharges most of the 40-plus million gallons of water it treats every day in a state bordering on potable. Spread over 300 acres (and surrounded by 1,200 acres of farm fields for application of biosolids), the plant is big enough that to see it you have to tool around in a van; you can't walk it like you can the water treatment plant miles upstream. Superintendent T. J. Lynch started my tour with a drive to the headworks, where screens and vortex filters remove the floating junk and grit from the outflow of the twin 72-inch trunks flowing in from the sewer system. The floating stuff is more obvious, but Lynch emphasizes the basins that settle out grit: In a process heavy on pumps and pipes, grit is anathema. "Think about sand," he says. "It's abrasive. It will literally wear out your equipment." They fill three Dumpsters a day with grit and the debris caught by screening, all of which goes to the landfill.
Remarkably, though the air has a certain tang, it doesn't stink. "Ninety-nine-point-nine percent of it is just water," Lynch says. "We've just got to get that 0.1 percent out."
Outside the headworks Lynch points to a concrete basin almost the exact size and shape of a baseball field, sloping downward from the outfield to a low point at home plate: a 32-million-gallon equalization tank. The sewer system does not have water towers or storage tanks to accommodate regular fluctuations in wastewater volume (flow peaks at breakfast time and again just after midnight), so it stores water in the equalization tank during periods of high flow and, especially, storms: Lynch says, "It's not uncommon for us during a heavy rain to see our flow double." The equalization tank gives Lynch a place to put that excess flow. When the flow slows down again, he uses four enormous screw pumps to push the water to the top of the slope on which the plant is built--the rest of the way through the plant, gravity does the work. He shows off the pumps proudly. They're called "vertical turbine solids-handling pumps," but he notes that they use technology roughly unchanged since the time of Archimedes: turning screws to lift water.
See what we're tweeting about
16 Comments
Add CommentExcellent 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.
Reply | Report Abuse | Link to thisRecycled 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?
Reply | Report Abuse | Link to thisExcellent 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
Reply | Report Abuse | Link to thisone 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;-)
Reply | Report Abuse | Link to thisThe 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".
Reply | Report Abuse | Link to thisQuestion; Does it make sense to pump city water from wells (from the aquifer) use it, treat it, and dump it in the river-shed?
Reply | Report Abuse | Link to thisA 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.
I agree wholeheartedly with several others here that this was a fascinating and well-written article. Who knew sewage treatment could be so interesting?
Reply | Report Abuse | Link to thisA 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!
Reply | Report Abuse | Link to thisA 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!
Reply | Report Abuse | Link to thisThis 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.
Reply | Report Abuse | Link to thisThis 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:
Reply | Report Abuse | Link to thisThis 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.
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.
Reply | Report Abuse | Link to thisAquifer 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.
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.
Reply | Report Abuse | Link to thisPyrolysing sewerage is a new, simpler and cheaper technique that should totally replace traditional plant. See www.eprida.com for more details.
How sewage treatment works in this country is so complicated! Why all the bother?
Reply | Report Abuse | Link to thisThey've got it figured out in Kibera; who needs sewers? Just poo in a bag and throw it in the street!
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.
Reply | Report Abuse | Link to this@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.
Reply | Report Abuse | Link to thisScott