All the wastewater collected via tunnel collectors is pumped into the wastewater treatment plant\u00a0by using three pressure pipes.<\/p>\n
Mechanical treatment<\/span><\/h2>\n\n\n\n![\"\"](\"https:\/\/www.tallinnavesi.ee\/wp-content\/uploads\/2017\/05\/7570_20170527-1024x683.jpg\")
Screenhouse<\/strong>
\nBy using 6 mechanical screens, larger debris (screenings)\u00a0are removed from the incoming wastewater, which then\u00a0are washed, pressed and taken to the landfill.<\/p>\nGrit traps<\/strong>
\nGrit that has\u00a0been\u00a0carried into sewerage with storm water\u00a0is removed from wastewater, sediments from the grit traps\u00a0are also taken to the landfill.<\/p>\nPrimary sedimentation\u00a0tanks<\/strong>
\nIn primary sedimentation tanks, sedimentation is used to remove suspended solids (raw sludge) from wastewater. Fats and oils floating on surface are also removed here.\u00a0Raw sludge that was removed is then\u00a0directed to the sludge treatment process.<\/p>\n<\/div>\n<\/div>\n<\/div>\nChemical and biological treatment<\/span>
\n<\/strong><\/h2>\n\nAdding special water treatment chemical (coagulant)\u00a0![\"\"](\"https:\/\/www.tallinnavesi.ee\/wp-content\/uploads\/2017\/05\/7646_20170527-1024x683.jpg\")
\n<\/strong>For better phosphorus\u00a0removal, coagulant is added. Coagulant is a substance that\u00a0aggregates around\u00a0tiny particles, making them\u00a0larger and heavier, and\u00a0easier to remove from water.\u00a0
\n<\/strong><\/p>\nAeration tanks<\/strong>
\nNow the wastewater is conducted to the aeration tanks where nitrogen compounds are removed\u00a0from wastewater biologically (i.e.\u00a0with a help from bacteria). By using diffusers in the bottom of aeration tanks, large quantities of air is blown through the wastewater, and by\u00a0adding\u00a0also methanol,\u00a0an effective biological treatment is ensured.<\/p>\nSecondary sedimentation tanks<\/strong>
\nWastewater and the bacteria (activated sludge) is conducted to the secondary sedimentation tanks where\u00a0activated sludge is separated from wastewater. Some of the sludge is returned to aeration tanks,\u00a0while the excessive part\u00a0of activated sludge (excess activated sludge) is directed to the\u00a0sludge treatment<\/strong>.<\/p>\n<\/div>\nTreated effluent pumping station<\/span><\/h2>\n\nThoroughly treated effluent is\u00a0pumped via deep-sea outlet nearly 3 km away into the Bay of Tallinn.<\/p>\n<\/div>\n
Sludge treatment<\/span><\/h2>\nMixed sludge storage<\/strong>
\nIn the sludge storage, the raw sludge removed from the primary sedimentation tanks is mixed with the\u00a0excess activated sludge removed from the secondary sedimentation tanks.<\/p>\nDigesters<\/strong>
\nMixed sludge is heated up to\u00a037 o<\/sup>C and pumped into digesters\u00a0for\u00a0anaerobic fermentation\u00a0(stabilisation). This process produces biogas that is used for heating the plant facilities.<\/p>\nSludge dewatering<\/strong>
\nStabilised sludge is pumped into centrifuges to remove excessive water. Before dewatering, a special chemical (flocculant) is added to sludge to facilitate the process. Dewatered sludge is taken to compost fields.<\/p>\nMaking the compost soil<\/strong>
\nOn the compost fields, dewatered sludge is mixed with peat. It takes 6-8 months for the compost soil to ripen, during that time the compost is periodically mixed. Compost soil that is ready gets distributed.<\/p>\n\u00a0![\"\"](\"https:\/\/www.tallinnavesi.ee\/wp-content\/uploads\/2017\/05\/7649_20170527-1024x683.jpg\")
\n<\/strong>Did you know that …?<\/span><\/h2>\n
Grit traps<\/strong> Primary sedimentation\u00a0tanks<\/strong> Adding special water treatment chemical (coagulant)\u00a0 Aeration tanks<\/strong> Secondary sedimentation tanks<\/strong> Thoroughly treated effluent is\u00a0pumped via deep-sea outlet nearly 3 km away into the Bay of Tallinn.<\/p>\n<\/div>\n Mixed sludge storage<\/strong> Digesters<\/strong> Sludge dewatering<\/strong> Making the compost soil<\/strong>Screenhouse<\/strong>
\nBy using 6 mechanical screens, larger debris (screenings)\u00a0are removed from the incoming wastewater, which then\u00a0are washed, pressed and taken to the landfill.<\/p>\n
\nGrit that has\u00a0been\u00a0carried into sewerage with storm water\u00a0is removed from wastewater, sediments from the grit traps\u00a0are also taken to the landfill.<\/p>\n
\nIn primary sedimentation tanks, sedimentation is used to remove suspended solids (raw sludge) from wastewater. Fats and oils floating on surface are also removed here.\u00a0Raw sludge that was removed is then\u00a0directed to the sludge treatment process.<\/p>\n<\/div>\n<\/div>\n<\/div>\nChemical and biological treatment<\/span>
\n<\/strong><\/h2>\n
\n<\/strong>For better phosphorus\u00a0removal, coagulant is added. Coagulant is a substance that\u00a0aggregates around\u00a0tiny particles, making them\u00a0larger and heavier, and\u00a0easier to remove from water.\u00a0
\n<\/strong><\/p>\n
\nNow the wastewater is conducted to the aeration tanks where nitrogen compounds are removed\u00a0from wastewater biologically (i.e.\u00a0with a help from bacteria). By using diffusers in the bottom of aeration tanks, large quantities of air is blown through the wastewater, and by\u00a0adding\u00a0also methanol,\u00a0an effective biological treatment is ensured.<\/p>\n
\nWastewater and the bacteria (activated sludge) is conducted to the secondary sedimentation tanks where\u00a0activated sludge is separated from wastewater. Some of the sludge is returned to aeration tanks,\u00a0while the excessive part\u00a0of activated sludge (excess activated sludge) is directed to the\u00a0sludge treatment<\/strong>.<\/p>\n<\/div>\nTreated effluent pumping station<\/span><\/h2>\n
Sludge treatment<\/span><\/h2>\n
\nIn the sludge storage, the raw sludge removed from the primary sedimentation tanks is mixed with the\u00a0excess activated sludge removed from the secondary sedimentation tanks.<\/p>\n
\nMixed sludge is heated up to\u00a037 o<\/sup>C and pumped into digesters\u00a0for\u00a0anaerobic fermentation\u00a0(stabilisation). This process produces biogas that is used for heating the plant facilities.<\/p>\n
\nStabilised sludge is pumped into centrifuges to remove excessive water. Before dewatering, a special chemical (flocculant) is added to sludge to facilitate the process. Dewatered sludge is taken to compost fields.<\/p>\n
\nOn the compost fields, dewatered sludge is mixed with peat. It takes 6-8 months for the compost soil to ripen, during that time the compost is periodically mixed. Compost soil that is ready gets distributed.<\/p>\n\u00a0
\n<\/strong>Did you know that …?<\/span><\/h2>\n