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Discussions and debates on municipal sludge management in Lübeck

Image 1 The medieval city of Lübeck hosted the PURE project workshop on Sustainable Sludge Handling on 7-8 of September 2011. The role of the organiser was taken by one of the project partners, Sewage Management Facilities Lübeck, Entsorgnungsbetriebe Lübeck (EBL). The workshop gathered about 70 experts from around the Baltic Sea region, among which were the PURE partner organizations, delegates from associated partner organisations and many external stakeholders. The wide range of interested parties demonstrates the importance of environmentally sustainable, economically efficient and legally allowed sludge management – essential part of modern waste water treatment.

Political and economical aspects

Dr Jan-Dirk Verwey, managing director of the hosting organisation EBL, reminded the participants of the seminar of the two tracks of activities in PURE project – reducing the phosphorus load and developing sludge handling, from which the latter would be in focus now. In his short presentation about EBL and its sludge treatment and disposal methods Mr. Verwey mentioned an interesting fact concerning biogas production for generating electricity and heat: EBL is able to supply its waste water treatment plant with energy the whole year around. He also reminded that the changes in German national energy regime after the Fukushima nuclear power catastrophe are making sewage sludge a precious source of energy in the future.

Image 2 Juhani Anhava’s (Pöyry Finland Oy) overview of PURE Project findings in sludge handling in the Baltic Sea region had economic, legislative and technical aspects. According to a Finnish study, the management of sludge comprises as much as 50 % of the whole costs of waste water treatment. There are political dimensions to the sludge handling issue not only in differing legislation, energy strategies and sludge handling costs, but also due to the fact that most of
the world’s mineral resources of phosphorus are in Morocco, in currently politically turbulent North Africa.

Dr Tim Evans, Convenor of the European Committee for Standardisation’s Technical Committee on characterization of sludges (CEN/TC 308), brought into the focus the significance of an accurate and unbiased assessment of the risks connected to the use of sewage sludge. He emphasized the difference between experienced hazards and calculated risks, the latter being the only reliable basis for control measures. The following discussion concentrated on various substances present in municipal sewage sludge and how to deal with them versus nutrient recycling.

Real-life examples and future prospects

The seminar continued with examples of sludge handling practices in Germany: Mr Enno Thyen presented the case of Lübeck, Siegrid Mayer – of Bremen and Dr Karl-Georg Schmelz – of Bottrop. The latter two waste water treatment plants are serving metropolitan areas with 1-3 million inhabitants but having very different sludge management strategies because of local circumstances. Dr Jörn Einfeldt from PIK gave examples of sludge treatment processes in small and medium sized plants of the Schleswig-Holstein region.

Image 3 The case examples showcased that many things, such as location of the waste water treatment plant, transportation costs, quality of incoming waters, used nutrient removal technology, legal restrictions concerning sludge disposal, availability and price of conditioning agents etc. shape the sludge handling strategy of each waste water treatment plant. The speakers considered flexibility of any sludge handling system to be important for taking into account the possible future changes of national energy, waste or nutrient policies. Regular upgrading of the system is needed to keep pace with the changing circumstances: the German examples gave an impressive picture of the active development work that is going on in the sector.

The last part of the seminar was comprised of the examples of various innovative approaches to sludge treatment and disposal. Dr Klaus Nickel talked about ultrasound disintegration of waste activated sludge, which is one of the pre-treatment technologies to anaerobic digestion and aerobic sludge stabilization with the objective to increase energy efficiency. Sebastian Petzet from the Technical University of Darmstadt introduced possible methods of phosphorus recovery from ashes of the incinerated sewage sludge, emphasizing the importance of mono-incineration as well as mono-landfilling for future recovery. Kimmo Palmu told about a possible future sludge treatment option – highthermal carbonization (HTC) to biochar and studies of the properties of “Terra Preta” soils in Amazonia.

PURE partners’ experiences and future planning

Workshop’s second day took place at the Lübeck waste water treatment plant and consisted of several types of activities for the project partners. At first, the representatives of the project partner waste water treatment plants presented their activities, focusing on sludge handling. The Gdansk and Szczecin partner WWTPs told about their new incineration facilities and Kohtla-Järve partner about their composting process and challenges with the energy-consuming hygienisation and chemical consumption in dewatering.

Image 4 The three investing partners of the project, Brest, Jurmala and Riga water utilities, told about the on-going implementation of the PURE project and other modernisation projects as well as on-going investigations concerning sludge related challenges. During the workshop the sludge issues were further discussed between the water utility partners and experts from EBL and Pöyry. Future activities in PURE sludge handling workpackage will be training sessions Finland to assist future planning of sludge management and preparation of a publication on best sludge handling practices.

PURE Database development was presented in the partner meeting by Mariehamn town. Here special attention was paid to the importance of involvement as many users as possible, which will enable having more comprehensive and up-to-date information. Project administration and communication matters were discussed in smaller groups. An excursion around the Lübeck plant was given to the participants with an opportunity to get familiarized to e.g. with 2-step filtration, CHP and chamber filter presses.

Photos by Lotta Ruokanen, HELCOM