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| PMI109C - Population connected to waste water collecting systems and waste water treatment plants, counties and localities |
| Definition |
Sewage system: all constructions and facilities used for wastewater collection and transport (sewerage network), for wastewater treatment (wastewater treatment plant) and for their discharge into a natural receiver. The sewage system is collecting, transporting, treating and discharging urban wastewater and/or industrial wastewater and/or rainwater.
Wastewater treatment plant: all construction and facilities achieved for decreasing or removing the pollutants existent in wastewater in such a way as to obtain treated water proper to be discharged or reused. Usually, a treatment plant has one ore more treatment steps: primary (mechanical), secondary (biological) and tertiary (for nitrogen and phosphorous removal).
Urban wastewater treatment plant: a treatment plant for urban wastewater, formed generally from a mixture of domestic and industrial wastewater.
Industrial wastewater treatment plant: a treatment plant for treating the industrial (and possibly some domestic) wastewater in a proper manner to be discharged into an urban sewerage network or directly into a natural receiver or to be reused.
In the primary treatment step there takes place mainly a suspended solids removal process. It is achieved mechanically, by sedimentation and sludge removal. Fine suspended solids are removed by mechanical and chemical techniques using different chemical reagents for precipitation - flocculation. This way suspended solids are settled together with chemical precipitate and the sludge is removed. Most parts of the primary treatment facilities accomplish also the flocculation process, removing all substances less dense than water (oils, greases, plastics, wood pieces, etc.). Together with a large part of suspended solids, in this step part of the organic substances existing in wastewater is also removed.
In the secondary treatment step biodegradable organic matter is mainly removed. The bacteria in activated sludge consume it in their metabolism. This process can take place in the presence of oxygen (in aerobic conditions, the process being named bio-oxidation) or in oxygen absence by anaerobic fermentation. In this step are also removed very fine divided suspended solids (colloids), which have not been removed in the previous step and also part of the substances containing nitrogen and phosphorus (nutrients).
The tertiary (advanced) treatment mainly achieves the removal of nutrients (substances containing nitrogen and phosphorus). The nitrogen containing compounds are removed usually using the procedure named nitrification?denitrification, consisting in biological oxidation of all nitrogen variety existing into wastewater to nitrates, which are reduced in the second phase (also by microorganisms, in absence of oxygen this time) to elementary nitrogen escaping from treated wastewater. In the same time there are removed a part of substances containing phosphorus. If necessary to remove more phosphorous compounds, this can be done by chemical precipitation.
Public water supply system refers to public water distribution network, operated by specialized units in water abstraction and distribution. |
| Periodicity |
Annual |
| Data sources |
The statistical survey on population connected to waste water collecting systems and waste water treatment plants details |
| Methodology |
The statistical survey covers the town halls of the localities that have sewerage systems. |
| Responsible person |
Anastasiu Daniela, e-mail: daniela.anastasiu@insse.ro, int. 2184 |
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