Waste Water Treatment
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Section 09: Wastewater management 9 A. Current situation In the Ruhr Area, special legislation provides for water management associations, which are substantially focussed on wastewater treatment. Municipalities and the industry are legally instituted members. The Emschergenossenschaft is responsible in the north of Essen, and the Ruhrverband in the south (Figure 9.1). According to the regulations under water legislation, the City of Essen is obliged to collect, transport and dispose of wastewater. Wastewater disposal obligation in the area of the City of Essen section 535353 and section 545454 of the State Water Law for North RhineRhine----WestphaliaWestphalia (LWG NW) City of Essen Ruhrverband (RV) Emschergenossenschaft (EG) City of Essen Ruhrverband (RV) Emschergenossenschaft (EG) (collecting and (purifying and (purifying and feeding in) transporting) feeding) in) Disposal contract City of Essen Stadtwerke Essen AG Water (SWE) management (operational sector) EG Coordination planning, construction, Drainage operation (statutory sector) Lease contract RV Entwässerung Essen GmbH (EEG) Owner of public sewer network Fig.: 9.1: Wastewater disposal obligation in the area of the City of Essen (source: Rademacher / City of Essen) (1) For the year 2013, water consumption in the City of Essen came to around . 34.2 million m³, which then becomes wastewater from around 574,000 persons, industry and business. Around 4.4% of water consumption related to industry, 6% to the public sector, and 89.6% to residents and SME. 1 1 Data from Stadtwerke Essen AG 1 a) As of 30 June 2014, the population of Essen was around 574,000 persons, of whom 99.5% are connected to the sewer system that transports the wastewater to wastewater treatment plants. 2 b) The Ruhrverband operates four wastewater treatment plants in the Essen municipal area, where the wastewater from this catchment area is treated, together with partial flows from other communities. The Essen wastewater produced in the Emscher region is treated at plants run by the Emschergenossenschaft in Bottrop and Dinslaken (Emschermündung). The urban wastewater treatment plants are all biological treatment facilities. The wastewater from the residents is treated 100% in wastewater treatment plants with more extensive processes (nitrogen and phosphor elimination). 3. The EU Urban Wastewater Treatment Directive 91/271/EEC (UWWTD) is complied with. Only in rural areas outside the cities there are isolated buildings for which connection to the public sewer system would be associated with disproportionately high costs. In these areas, private wastewater treatment plants and septic tanks are used. In 2012, only 0.5% of residents were not connected to the public sewer system, and disposed of their wastewater at 871 small wastewater treatment plants and 95 septic tanks. 4 Sewer network Public sewer network 1,643 km (Stadtwerke Essen AG / Entwässerung Essen GmbH) Total length 1,447 km 107 km Fig. 9.2: of which 89 km Combined sewer system Data on wastewater systems, without Sewage system wastewater treatment plants Rainwater sewer system (sources: Stadtwerke Essen AG, Road construction authority City of Essen City of Essen) 26 km Rainwater sewer system Other facilities Public network (Stadtwerke Essen AG / Entwässerung Essen GmbH) 62 3 Rainwater retention basins 1 Rainwater overflow basins 41 Rainwater treatment basins 329 Rainwater overflow drains 23 Sewer feed systems 12 Floodwater and wastewater pumps Culverts Road construction authority (City of Essen) 6 Pumping plants 3 Separators 5 Rainwater retention basins approx. 51,000 Gullies The discharge quality of wastewater treatment plants in Germany is subject to the strictest stipulations of the Wastewater Ordinance. Furthermore, EU Urban Wastewater Treatment 2 Data from Stadtwerke Essen AG 3 Data from Ruhrverband and Emschergenossenschaft 2010 4 Data from Stadtwerke Essen AG 2 Directive 91/271/EEC requires that urban areas with a population equivalent (PE) in excess of 2,000 must collect wastewater in sewer systems and subject it to biological treatment. In addition, urban areas with over 10,000 PE, and which are located in the catchment area of sensitive regions, require a third treatment step for nitrogen and phosphor elimination. The City of Essen is in the drainage area of the North Sea, which is listed as a sensitive region in the EU Urban Wastewater Treatment Directive. On the basis of planning certification calculations, a total COD load of around 1500 tpa can be estimated, which during rainy weather is discharged into receiving waters through the combined sewer overflows of Essen's sewer system (672 tpa from the Essen catchment areas of the Ruhrverband wastewater treatment plants, and 829 tpa from the Essen catchment areas of the Emschergenossenschaft wastewater treatment plants). 5 Fig. 9.3 Visit to a plant operated by the Association (source: Emschergenossenschaft) At 6 central wastewater treatment plants, with a total treatment capacity for a population equivalent (PE) of 4.1 million and nitrogen and phosphor elimination facilities, an average of 614 million m³ of wastewater from the City of Essen (around 34.2 million m³) and the neighbouring municipalities were jointly treated between 2009 and 2011, and discharged into 5 Data from Ruhrverband and Emschergenossenschaft 3 the Ruhr river and the Emscher river. The total wastewater load of these wastewater treatment plants came to an average population equivalent of 3.2 million (Fig. 9.4). The incoming and discharge loads in terms of COD, total nitrogen and total phosphor can be found in Fig. 9.5. The requirements of Directive 91/271/EEC are thus fulfilled. 6 Of which Wastewater Design Of which residents Wastewater treatment capacity Connecte connected of City of volume plants Catchment (PE) d PE residents Essen (1,000 m³) Operator Essen- 32,916 7,743 Burgaltendorf Ruhr 44,200 46,857 2,946 Ruhrverband Essen- 65,548 28,294 Kupferdreh Ruhr 96,000 114,185 8,477 Ruhrverband Essen- 54,295 41,094 Kettwig Ruhr 100,000 54,713 7,319 Ruhrverband Essen-Süd Ruhr 135,000 125,445 119,433 116,974 13,685 Ruhrverband Emschergenosse Bottrop Emscher 1,340,000 1,112,493 711,720 376,924 139,440 nschaft Emschermün Emschergenosse dung Emscher 2,400,000 1,652,566 1,652,566 415,624 nschaft 4,115,200 3,106,259 2,462,750 571,047 587,490 Fig. 9.4: Capacity of the wastewater treatment plants for draining the City of Essen and total load of municipal wastewater volume of the City of Essen, approx. 34.2 million m³ (according to water consumption data provided by Stadtwerke Essen AG, 2013); (source: compiled based on master data from wastewater treatment plants of Ruhrverband (2013) and Emschergenossenschaft (2012); population and wastewater volume for Essen (based on water consumption) according to details from Stadtwerke Essen AG, 2013; PE = population equivalent, R = residents) Discharge load Incoming load (t/a) (t/a) Measurement of Number of Design capacity COD N P COD N P PE plants (PE) tot tot tot tot Up to 100,000 3 240,200 6,776 808 134 408 142 11 > 100,000 3 3,875,000 96,110 9,557 1,490 16,300 3,910 313 Total 6 4,115,200 102,886 10,365 1,624 16,708 4,052 324 Fig. 9.5: Incoming and discharge loads of the wastewater treatment plants at which Essen's wastewater is treated. (averages 2011-2013) (source: compiled based on data from the Ruhrverband [2013] and Emschergenossenschaft / averages 2011-2013) The sewage sludge produced at the six wastewater treatment plants where wastewater from Essen is handled totals 74,850 tonnes dry weight p.a. (from Essen approx. 14,116 tonnes dry weight p.a.), and is stabilised by means of decomposition. The sludge gas produced during this process is largely used for operational purposes. Under the respective plant- specific boundary conditions, the economically useful energy content of the sewage sludge is thus recovered. (2) 6 Data from Stadtwerke Essen AG, Ruhrverband and Emschergenossenschaft 4 The Emschergenossenschaft 7 and the Ruhrverband (3) burn 100% of the sewage sludge they produce. Modern filtration technology ensures that the requirements of pollution control legislation are reliably complied with at the incineration plants. Supplementary information on the environmental performance of the wastewater management system (energy efficiency etc.) will follow in chapter 9B. 9 B. Results achieved in the past In recent years, a wide variety of measures have been implemented, optimising both the wastewater treatment process and wastewater drainage. Particularly in the field of wastewater treatment and its subsequent discharge into the receiving waters, the measures were triggered by the increasingly strict requirements of the standards pyramid of water-related legislation. EU (Water Framework Directive / Flood Risk Management Directive) Germany Water Resources Law , Waste Water Charges) State (State Water Legislation City of Essen (Drainage and Drainage Charges Statute) Fig. 9.6: Standards pyramid of water-related legislation (source: Rademacher / City of Essen) In 2012, the city administration of Essen set up a new technical department for "Water Management". This department handles the areas of sewage removal, flood protection, rainwater management, water body development, and water authority. This should allow optimisation effects to be achieved, e.g. through the bundling of responsibilities and technical competence, a reduction of interfaces, and the networking of municipal and statutory tasks. Stadtwerke Essen AG has invested approx. € 259 million in public wastewater infrastructure over the last 10 years. The investments were largely made in sewer renewal work, water body protection, new construction and access work, and in the municipal wastewater treatment plants. (4) 7 Emschergenossenschaft data 5 Conversion of the Emscher system as a regional key project – the return of the Blue Emscher Fig. 9.7: Biodiversity increases through the progress of natural succession, thus increasing ecological value (source: Emschergenossenschaft) With the end of mining subsidence, the laying of underground sewers along the open sewage channels in the Emscher system commenced in the 1990s.