From the digesters we drive to the dewatering building--just as at the water treatment plant, the wastewater plant uses belt presses to squeeze the water out of the last, bug-eat-bug stage of the sludge. Enormous screw conveyors grind big pieces of the dewatered stuff along like the mixers in an industrial bakery. Lynch hands me a piece of what they call cake. It has no odor at all and feels a lot like inch-thick rubber, the kind used under playground equipment. Polymers are introduced to help coagulation and add to the rubbery feel. "Don't forget to wash your hands," Lynch says.
We leave the sludge and return to the water. Primary treatment is mechanical--settling; secondary treatment is biochemical--activated sludge digestion. Tertiary treatment combines mechanical and photochemical: The water flows to a dozen deep sand filters, which remove the remaining fine particles. The final hurdle the water clears is ultraviolet treatment. We walk over to a small, low concrete building, in front of which Lynch pulls up a flat piece of aluminum to reveal a 4- or 5-foot-wide channel of water flowing smoothly past banks of green-glowing UV lamps. They look much like fluorescent lights, though they have a self-wiping mechanism to keep them clean. "It doesn't kill [pathogens]," he says of the light. "It just scrambles their RNA. Sterilizes 'em." He mentions in passing an open concrete channel between the filters and the UV treatment, in which tilapia swim. "It keeps the duckweed down," he says. Once fish are swimming in your treated sewage, you've got to feel like you're getting the job done.
Out behind the UV building we finally reach the finished product: the effluent, flowing out in strong wide arcs into a canal from a dozen UV channels. The water seems to have a greenish tinge, but when Lynch fills a little water bottle and holds it up it looks utterly clear. Then we drive down toward the end of the line, where the effluent enters the Neuse River. There, in a tiny green glade at the bottom of the hill, the river bends into a cove, near the bank of which a few surface bubbles give away the presence of the underground pipe. Lynch says if you didn't know where the pipe was you could follow shad upstream to find it: "The water's warm and highly oxygenated," so the fish love it.
Lynch says the river is the natural place for the water anyhow. Every drop of Raleigh water comes from the Neuse watershed and ought to return there. "All we're doing," he says, "is what a river would do." That is, rivers are naturally self-cleaning, and the Neuse would absorb waste, given time and distance. Waste on the ground would be dispersed by rain and the water would be filtered through the earth, entering the groundwater system clean; matter that made it to the stream would become waterlogged and sink. "On the rocky bottom, bacteria live," he says, that feed off the nutrients in waste. "What happens in our plant is the exact same thing that happens in a stream. That's exactly where the process came from. We've just concentrated it," Lynch says. "It might take the river a couple hundred miles to accomplish what we do in a couple days." We've been talking about sewage treatment for 2 hours--about dewatered cake and grit screens and activated sludge and UV filters--and suddenly I understand.
What the river does is exactly what a sewage plant does, and until around World War I most people didn't really think plants were needed at all. It was understood that watercourses were to some degree self-cleaning, that "the solution to pollution is dilution." But as populations increased, especially downstream, dilution stopped offering much of a solution. Chicagoans felt great about their famous flow-reversal of the Chicago River, sending their sewage into the Mississippi instead of into their own water supply of Lake Michigan. Predictably, the people of St. Louis were not as delighted. Their expression of dissatisfaction eventually landed them in front of the Supreme Court. Raleigh itself was sued in the late 1940s by downstream neighbor Smithfield. Smithfield won, and in 1956 Raleigh's first sewage treatment plant opened, treating 12 million gallons per day. The current plant replaced it in 1977; it's expanded since, and now it's expanding again.
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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