How it works: Sewage big city

The pipe from which pours the contents of a powerful jet of sewage collector.

Aerotanks SWTP.
So let's start. Water, dilute soap and shampoo, street dirt, industrial waste, remnants of food, as well as the results of digestion of food (all of it gets into the sewer, and then - to the treatment plant) have a long and thorny path before it will return to Neva and the Gulf of Finland. Begins this way or in a lattice gutter, if it happens on the street or in a "sewer" pipe, if it is about the apartments and offices. From the not very large (15 cm in diameter, all probably seen them at home in the bathroom or toilet room) sewage pipes water mixed with waste falls into larger obschedomovye pipe. Several houses (and street drains in the surrounding area) are merged into the local watershed, which in turn are grouped into areas sewer and then - in the sewer basins. At each stage of the pipe diameter increases with sewage and tunnel collector he has already reached 4, 7 m. On such a hefty tube dirty voditsa slowly (by gravity, no pumps) comes to aeration stations. In St. Petersburg, there are three large, fully ensuring the city, and several smaller ones in remote areas such as Repino, Pushkin or Kronstadt.
Yes, about the treatment facilities themselves. For some it may be a reasonable question: "Why do treat the wastewater? Neva bay with all endure! "In general, the way it was before, and, until 1978 virtually no waste water purified and immediately fell into the bay. Gulf of them somehow recycled, coping, however, with the increasing flow of sewage each year worse. Naturally, this situation could not affect on the environment. Most got our Scandinavian neighbors, but also the neighborhood of St. Petersburg also experienced the negative impact. And the prospect of a dam across the Finnish forced to think about what the city waste-millionth together happily swimming in the Baltic Sea will now hang between Kronstadt and the (then) Leningrad. Overall, the prospects for eventually choke sewage nobody rejoiced and the city water utility in the face gradually began to solve the problem of wastewater treatment. Almost completely solved it can only be regarded as the last year - in autumn 2013 was launched the main sewer north of the city, and the amount of treated water has reached 98, 4%.

Pools sewerage on the map of Saint Petersburg.
Look at the example of South-West Wastewater Treatment Plant, as there is a clearing. Reaching the bottom of the reservoir (bottom right is on site treatment facilities) water powerful pumps rises almost 20 meters high. This is to ensure that the dirty water through the stage purification by gravity, with minimal involvement of the pumping equipment.
The first stage of treatment - the lattice, which is large and not very rubbish - any rags, dirty socks, drowned kittens, lost mobile phones and wallets with other documents. Most of the collected goes straight to the dump, but the most interesting findings are in a makeshift museum.

Pumping station.

Pool with filth. View from outside.

Pool with filth. View from inside.

In this room are set lattice, catching large debris.

Over the cloudy plastic can be seen assembled array. Stand and paper labels.

Brought water.
And the water is moving on, the next step - the sand trap. The task of this stage - to collect coarse impurities and sand - all that passed by lattices. Before the release of the sand traps in the water add chemicals to remove phosphorus. The water is then sent to the primary clarifiers, which are separated suspended and floating matter.
Primary clarifiers are completing the first stage of treatment - and partly mechanical - chemical. The filtered and separated the water does not contain debris and solids, but it is still not fully most useful organic, and home to many microorganisms. From this, too, need to get rid of all and start with organic ...

Sand traps.

The design in the foreground moves slowly along the pool.

Primary clarifiers. The water in the sewage at a temperature of about 15-16 degrees, from its active steams as ambient temperature is below.

Biological process takes place in the aeration tanks - these are hefty bathrooms, which is filled with water, and air is pumped trigger "activated sludge" - a cocktail of protozoa, sharpened on the digestion of just those chemical compounds from which you want to get rid of. Air is pumped into the Tenke, needed to increase the activity of microorganisms in such conditions they are almost entirely to "digest" the contents of the bath for five hours. Next biologically treated water is sent to the secondary settling tanks, where it is separated from the activated sludge. Il again sent to the aeration tanks (except surplus that burn), and the water gets to the last stage of purification - UV treatment.

Aeration tanks. The effect of "boiling" due to active pumping of air.

Dispatching. From the height of the entire station can be seen.

Secondary clarifier. The water is somehow very attracted birds.
On the southwest treatment facilities at this stage also conducted a subjective quality control purification. It looks as follows - cleaned and disinfected water is poured into a small aquarium, which sit several cancers. Crayfish - being very fussy on the dirt in the water react immediately. Since emotions crustaceans people have not yet learned to distinguish, using more objective assessment - ECG. If suddenly a few (protection against false positives) cancers experienced a lot of stress, so that the water is not so urgently need to understand which of the cleaning steps has failed.
But this situation is an emergency, and in the ordinary course of things already clean water is sent to the Gulf of Finland. Yes, about cleanliness. Although cancers in such water and there are microbes, viruses, all of it removed, drinking it is still not recommended. Nevertheless, the water fully complies with environmental standards HELCOM (Convention for the Protection of the Baltic Sea from pollution), which in recent years has had a positive impact on the state of the Gulf of Finland.

The ominous green light disinfects water.

Cancer detector. By armor attached no ordinary rope and cable that transmits data on the state of the animal.

I will say a few words about the disposal of all that is filtered out of the water. Solid waste is transported to landfills, dumps, but everything else is burned at the plant, located on the territory of treatment facilities. In the furnace sent dewatered sludge from the primary clarifiers and excess activated sludge from the secondary. The combustion takes place at relatively high temperatures (800 degrees) to minimize the harmful substances in the exhaust. It is surprising that the total volume of the factory premises stove occupies only a small portion, about 10%. All of the remaining 90% given the huge system of various filters, screening all possible and impossible harmful substances. At the plant, by the way, to adopt a similar system of subjective "quality control". Once the detector is no longer protrude crabs and snails. But the principle of action in general is the same - if the content of hazardous substances at the outlet of the pipe is above the allowable, the body responds immediately clam.


Purge valve of the recovery boiler. Purpose is not clear, but as impressive look!

Snail. Above her head tube from which water drips (to shellfish not bent before the time), and next to another, with slightly dilute the smoke from the chimney.

P.S. One of the most popular questions asked by the announcement: "Well Th there with the smell? Stinks, huh? "Smell I was somewhat disappointed even icon smile How it works: Sewage big city sewer crude content (in the first photo), almost no smell. At the station the smell, of course, present, but very mild. Most of all (and this is already being felt!) Stinks dewatered sludge from the primary clarifiers and activated sludge - what goes into the oven. Therefore, by the way, and they began to burn, polygons, which were brought before the sludge was allowed so very unpleasant smell to the surroundings ...



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