To find out what happens in these pipes, I talked to Raleigh's dean of pipage, sewer collection superintendent Hunter "Gene" Stanley. "We're not like New York City," Stanley says right off. "Some of those you can drive a truck through." New York has a combined sewer system that has to be prepared to move the billions of gallons of water that a major storm could dump on the city, not just the comparative trickle of sewage the city generates daily. Combined systems manage overflows with relatively simple mechanical junctions called regulators: basically weir dams in pipes or junction boxes. A weir is nothing more than a low barrier for steering water. When flow is routine, the dam routes it through pipes to the treatment plant; during large rain events, the flow of mixed stormwater and wastewater rises high, overtops the weirs, and flows directly through outfalls to rivers or lakes. Such an event is called a CSO, or combined sewage overflow. New York dumps about 40 billion gallons of CSOs into its rivers and harbors every year.
But before you draw too much comfort from Raleigh's system having to convey only sewage (the plant treats about 45 million gallons per day that are generated by the 400,000 or so customers connected to the system; it's rated for 60 million gallons, and it's being expanded to 75), consider this: The increase in flow caused by nothing more than rainfall and street flow coming in through manhole vents in low-lying areas can nearly double the flow to the treatment plant. Really? "Oh yeah, oh yeah," Stanley says. "A thousand gallons a day [per manhole] if it rains all day." Add in leaky joints, cracks, and holes made by thirsty tree roots, and you can have significant water infiltration during rainstorms. Though catching and correcting the breaks and overflows are an unavoidable part of his job, Stanley stays focused on preventive maintenance.
Stanley grew up in rural North Carolina and has called his preventive maintenance management "an ol' country boy work system"--he copies pages from the map book of his system and gives them to his crews. When the crew has flushed and inspected every line on the map, it comes back. The department logs its maintenance in feet per day, and it likes to reach 300,000 feet per month if it can, meaning that every pipe in the system gets a look-see once every few years. GIS keeps the maps updated, of course, but Stanley's system has been working since they were using nothing more than blueprints and as-built surveys; finding that what's an 8-inch pipe on the map is really a 6-inch is just part of keeping on top of things. That's why you carry different-size saw blades in your truck.
Stanley says a sewer is a simple thing: The pipe needs to drop about half a foot per 100 feet of length, a slope of 0.5 percent, which is fast enough to keep everything moving, but not so fast that the liquid races away from the solids. Bigger pipes--30 inches or larger--can slope even less. But they all must flow downhill, powered by gravity, which is why sewer pipes so commonly crisscross the stormwater drainages: Raleigh Public Utilities Department director Dale Crisp calls all the sewers that run in a particular drainage a "sewershed," which for a while became my favorite new word.
Of course, if wastewater pipes followed only natural gullies, the mains would eventually have to parallel the river, and for many reasons, from aesthetics to the catastrophic results of a spill, nobody wants that. The system generally moves downhill, but pipes sometimes need to cross rises. So the city has more than 100 lift stations, where the contents of pipes are pumped to join other flows or where wastewater from lowlying areas collects in sumps. When the water gets high enough, it trips a float valve and a pump clicks on and lifts it up a hill--kind of like your toilet, only this float valve starts the flush instead of stopping it. I visited one lift station, a 10- by 20-foot rectangle of electrical boxes that look like a central air-conditioning system behind chain-link fences between two houses, controlling an underground sump; even when it's pumping, if you were more than 10 feet away you wouldn't hear it. The station has a backup pump and a generator to power it, plus a little antenna to send information back and forth to the supervisory control and data acquisition (SCADA) system at the treatment plant; that's plenty of equipment, but just the same, if you weren't looking for it you wouldn't know it was there. A much larger station sits on the trunk line, giving a lift to pretty much all of Raleigh's waste on its way to the plant. It's underneath a highway on-ramp, and though some people suggested I could find it by following my nose, it didn't smell when I went out to visit it.
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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