9. Waste Water Management
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9. Waste water management 9A. Present Situation Please complete the following table providing the most recent data that is available: Indicator Unit Year of data Percentage (%) of total annual generated waste water load, connected to waste water 100 % 2015 collecting system + urban waste water treatment plants (UWWTPs) 1 No of wwtp Total Design Capacity (p.e) 170,333,090 p.e 2014 Total Load Received by WWTP (p.e) 14,485,000 p.e 2014 Total annual generated waste water load of 289,700 p.e 2014 the city (in p.e.) Treatment level which is applied in each Stage 3 treatment uwwtp: secondary or more stringent; in this (chemical and 2014 case, type of treatment: nitrogen and/or phosphorus removal, disinfection etc. biological) Describe the present situation in relation to waste water management, including any relevant disadvantages or constraints resulting from historical, geographical and/or socio-economic factors which may have influenced this indicator area. Where available, information/data should be provided from previous years (5 – 10) to show trends. Describe the current general features of waste water treatment according to national requirements and the requirements of the Urban Waste Water Treatment Directive (UWWTD, 91/271/EEC). Include data and a short explanation for the following specific indicators. Provide explanation in the case of missing information. 1. Provide an indication of the fraction (%) of the total annual generated waste water load of the city coming from population and from idustry (also specifying type of industry, when information is available); The most advanced treatment level at UWWTPs (primary treatment, secondary treatment, tertiary treatment; 2. Proportion (%) of total annual generated waste water load, not connected to waste water collecting systems, and explanation of the type of waste water treatment applied to this fraction (reference to individual or other appropriate systems, i.e., IAS); 3. If the city is located in an EU Member State include data on waste water treatment obligations according to the UWWTD (based on city's size and nature of the area of discharge); 4. Waste water collecting systems: main type of collecting system (combined/separated) and annual proportion (%) of COD-loads discharged via storm water overflows; 5. UWWTPs: Organic design capacity (p.e.), most advanced treatment level, annual incoming and discharged loads (t/a) of BOD5, COD, Ntot and Ptot and treated waste water amounts (m³/a) of all UWWTPs serving the city. If the city is located in an EU Member State, indicate whether the UWWTP complies with the treatment requirements under the UWWTD; 6. Annual amounts of generated sewage sludge (t/a) and description of treatment/disposal pathways (% of total amount). 7. Provide data on annual energy consumption for wastewater treatment in Kwh/year/p.e., if available. Further information (e.g. on energy efficiency at UWWTPs, treated waste water re-use, economic sustainability, use of integrated constructed wetlands or other GI/nature-based solutions) is highly appreciated. (max. 600 words & 5 graphics, images or tables) The sewerage system of Tallinn consists of 21 separate (wastewater only) and seven combined (wastewater and stormwater) catchment areas (Figure 1). Proportionally, the combined sewerage system covers ca 35% of the territory of Tallinn, which means that ca 35% of stormwater passes through the wastewater treatment station. The combined sewerage system is mainly located in the older districts of Tallinn, such as City Centre and Northern Tallinn (Figure 2, Section 9B). Figure 1. System of stormwater catchment areas and stormwater outlets in Tallinn The wastewater is directed to the Tallinn (Paljassaare) wastewater treatment plant that is located on the Paljassaare peninsula in Northern Tallinn (Figure 2). The water is directed from the wastewater treatment plant to a distance of 2.8 km from the coast and a depth of 26 metres in the Tallinn Bay. Tallinn also accepts and treats the wastewater of neighbouring local authorities (4% of volume). Figure 2. Tallinn wastewater treatment plant (middle) is surrounded on two sides by the Paljassaare special conservation area (left and front) that belongs to the network of NATURA 2000 sites 100% of the wastewater generated in Tallinn is treated. 99.8% of the population of Tallinn have joined the public sewerage system, but in the case of the remaining 0.2%, this is not economically practical. They are obliged to collect wastewater in liquid-proof tanks from which it is discharged into the sewerage system. The quantity of wastewater passing through the treatment equipment is 41-57 million m3 per year, depending on the quantity of stormwater that has flowed into the combined sewerage system. The pollution load of Tallinn has decreased in the last decade (Table 1). In 2014 it was 289,700 population equivalents, ca 73,000 (25%) of which comprised industry. Table 1. Pollution load in the last 10 years (in population equivalents) Year 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 351,683 313,334 311,017 329,367 295,467 308,833 272,383 282,567 311,542 289,700 Mechanical and chemical-biological treatment technologies are used at Paljassaare wastewater treatment plant. The mechanical treatment part consists of mechanical grids, sand traps and primary settlement tanks. The biological treatment of wastewater uses aerotanks, secondary settlement tanks and a biofilter (purification level III). A methanol station, air blowers and coagulation assembly support the technological processes. Approximately 0.3% of the wastewater entering the treatment plant has passed through a preliminary purifier (mainly an oil, sand or grease trap). The designed parameters of the treatment plant are as follows: wastewater reception volume 127.75 million 3 m /y; BOD7 – 10,220 t/y; suspended solids – 17,885 t/y; Ntot– 2190 t/a; Ptot – 328.5 t/y. The wastewater treatment plant has achieved high purification efficiency: 98% for BOD7, 97% for suspended solids, 84-86% for total phosphorus, and efficiency of nitrogen separation with a biofilter of 80-90% (Table 2). Table 2. Purification efficiency of Tallinn wastewater treatment plant from 2005-2013 Year Suspended solids BHT7 Ngen Pgen in out standard in out standard in out standard in out Standard mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l 2005 202 5.0 15 41.0 13.2 10 6.76 0.96 1 2006 232 4.9 15 47.6 10.9 10 7.65 0.98 1 2007 343 9.6 15 206 3.9 15 42.8 9.1 10 6.66 0.94 1 2008 334 9.1 15 197 3.7 15 42.1 9.9 10 6.12 0.96 1 2009 349 9.2 15 223 3.7 15 47.0 10.0 10 6.88 0.97 1 2010 366 10.5 15 207 4.1 15 48.5 11.9 10 6.82 0.97 1 2011 350 9.3 15 195 3.3 15 44.7 11.1 10 6.24 0.92 1 2012 312 7.4 15 161 3.0 15 42.7 6.3 10 5.57 0.76 1 2013 363 6.0 15 193 3.3 15 48.8 7.5 10 6.70 0.45 0.5 The treatment of wastewater in Tallinn complies with the requirements of the Urban Waste Water Directive (92/271/EEC): - all wastewater in Tallinn is treated chemically and biologically (stage three treatment); - the indicator of the total phosphorus exiting the Tallinn wastewater treatment plant complies with requirements (<1 mg/l in residential settlements of more than 100,000 people); - since the launch of a denitrification biofilter in 2011, the indicator of the total nitrogen exiting the treatment plant has also complied with requirements (<10 mg/l in residential settlements of more than 100,000 people). In addition to the Urban Waste Water Directive (92/271/EEC), the indicators of the wastewater exiting the treatment plant also comply with the recommendations of the international HELCOM committee. The share of stormwater in the overall pollution load was studied in 2012. COD in stormwater has not been studied, but the indicators of the remaining components are as follows: BOD – 0.049%; suspended solids – 24.9%; Ntot – 0.026%; Ptot – 0.046%. 27-30 tons of sludge is generated at the treatment plant each year. Since 2003 the sludge has no longer been deposited in landfill, but is mixed with peat and composted instead. The resulting compost is used as a fertiliser in landscaping and as a ground filler. 23-27 thousand tons of compost is made each year. Figure 3. Sludge composting facilities at Paljassaare wastewater treatment plant The biogas generated in the methane tank is used to heat the plant’s own buildings. 100% of the biogas is used in winter and 20-30% in summer; the surplus is burnt in a residual gas burner. Irrespective of investments made in Tallinn’s wastewater treatment system, it has been impossible to achieve the good status of the coastal waters of Tallinn by 2015. These waters form part of the Baltic Sea ecosystem, where water exchange occurs every 25-30 years on average. Since water exchange between the open sea and coastal waters is good, the status of the coastal waters does not depend on pollution coming from land alone, but also on the status of the open sea. HELCOM has developed recommendations for achieving the good status of the Baltic Sea and found that achieving it throughout the sea – including coastal waters – will probably occur by 2021 considering the implementation of the measures known today. Figure 4. One of the most popular beaches in the city, which has been awarded the Blue Flag eco-label, is located at Pirita on Tallinn Bay 9B.