How is sewage water treated

Even though water is not always available in the needed quantity and quality for all people everywhere, people have learned to get and use water for all of their water needs, from drinking, cleaning, irrigating crops, producing electricity, and for just having fun.

How about a refreshing cup of reclaimed wastewater? No, we're kidding. You probably don't drink much reclaimed wastewater although some people do - see below! But reclaimed wastewater has many uses, with more promise of usage in the future. Skip to main content. Search Search. Water Science School. Wastewater Treatment Water Use. Water Use Information by Topic Learn more. Water Quality Information by Topic Learn more.

Below are other science topics associated with wastewater treatment water use. Date published: August 30, Filter Total Items: 1. Loading Close. Do Not Show Again Close. Treatment Steps. Step 1: Screening and Pumping The incoming wastewater passes through screening equipment where objects such as rags, wood fragments, plastics, and grease are removed.

The material removed is washed and pressed and disposed of in a landfill. The screened wastewater is then pumped to the next step: grit removal. Another effective physical water treatment technique includes aeration. This process consists of circulating air through the water to provide oxygen to it. Filtration, the third method, is used for filtering out all the contaminants. You can use special kind of filters to pass the wastewater and separate the contaminants and insoluble particles present in it.

The sand filter is the most commonly used filter. The grease found on the surface of some wastewater can also be removed easily through this method.

Biological Water Treatment This uses various biological processes to break down the organic matter present in wastewater, such as soap, human waste, oils and food. Microorganisms metabolize organic matter in the wastewater in biological treatment. It can be divided into three categories:. Secondary treatment removes most of the solids present in wastewater, however, some dissolved nutrients such as nitrogen and phosphorous may remain.

It's much like the stormwater system, if every ravine in every drainage basin remained piped and they all came together in one place before entering the Neuse. To find out what happens in these pipes, I talked to Raleigh's dean of pipage, sewer collection superintendent Hunter "Gene" Stanley.

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 , 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.

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 , 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 feet of length, a slope of 0. Bigger pipes 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 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 by 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.

Stanley hands over a laudatory profile of Raleigh's sewer maintenance department in a recent issue of Municipal Sewer and Water magazine, then hands me off to Robert Smith, a sewer monitoring supervisor and asks him to show me around. First things first: We walk the yard, checking out trucks. Sewer guys basically do three things: They perform maintenance, they respond to crises, and they "TV" pipes, sending tiny little vehicles with cameras on them up the pipes to check both their condition as part of general maintenance and whether the crews who claim to have recently maintained them have actually done so.

Smith shows off the department's various trucks. Rodder trucks have a spool of linked rods, a sort of long chain that the workers feed into a manhole and then rotate, just like someone cleaning roots or a clog out of your drain at home. Some rodders have cutting blades or spiral grabbing implements to clear roots or debris. Flushing trucks carry enormous water tanks to feed high-pressure hoses with spinning heads on the end: Workers feed the hose into the system, usually past the next manhole, and then turn on a pump.

Water pressure starts the head spinning, spraying water at thousands of pounds of pressure per square inch back toward the truck as the truck pulls back the hose, scouring the pipes along the way.

Standard now is the combination truck, which carries tanks of water for flushing and a garbage-truck-size tank for postflush water, which the truck vacuums up with a huge tube that hangs from a derrick over the cab like an elephant's trunk. The driver eventually empties that tank onto a pad in the parking area, Smith explains; water drains off into the sewer system and the cleaned-out debris--tampons, bricks, gravel, roots, supposedly flushable materials--gets loaded into a dump truck once a week and sent to the landfill.

Smith marshals those vacuum trucks when Raleigh has a sewage overflow, too. Another truck he calls a blockbuster has a water hammer--a pipe that uses water to rhythmically pound and break up large blockages. Finally, he shows me a sort of souped-up golf cart that provides access to the many parts of the system that, because they follow ravines rather than roads, are not easily reached by regular trucks.

But we're standing in a parking lot while people are out in the field, rodding sewers. Our first stop is a highway off-ramp, where two flush trucks and a pickup are parked behind orange cones. Several men wearing hard hats, green mesh vests, and rubber-palmed gloves manage a hose coming off a spool on the back of one of the trucks and running to a manhole 20 feet down a steep ravine.

A hundred yards away, two guys stand at another manhole looking out for the spinning head of the water jet, which Smith says is called a Warthog. Once it's past, the guys still at the truck turn on the jet and the spool to start reeling it back in. Over the roar of the truck engine Smith explains that on the way out the head sprays as a sort of presoak; "on the way back, it's like a broom. It looks like you sprayed foam on that pipe.

Where the vacuum trucks can't reach a manhole, the crew flushes debris downstream to one the truck can reach. That's sewer flushing, and the sanitation department does it all day long. Ever since the Hamburg sewers first captured tidal water and then released it all at once to flush out debris, the basic idea hasn't changed much: You use water to flush, you use rods or hooks to attack clogs, and, as Ed Norton sang, you keep things rolling along. 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 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. 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 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. 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.

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. It's pretty neat. 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.