The theoretical work presented here analyses various process chains for the energetic utilisation of municipal sewage sludge in their energy and greenhouse gas balance taking into account the hydrothermal carbonisation (HTC), based on the operating data of an HTC pilot plant. In the comparison with reference processes for sewage sludge dewatering (centrifuge, chamber filter press) the HTC with this offers energetic advantages with the treatment of digested sludge through high energy credit notes in the incineration and relatively small additional expenditure if the process can be operated via waste heat. For raw sludges without digestion the HTC offers no advantages as the energe tic advantage of the high calorific value are balanced out through additional outlays (natural gas, increased return loading). Decisive factors with the energetic evaluation of the HTC process are here the internal heat management and the biogas yield from the HTC process water. To be noted is, however, that the refractory COD in the process water can lead, via the return loading of the wastewater treatment plant, to considerably increased COD discharge values, which the introduction of an HTC in many cases would prevent. Along with the energy balance the HTC technology for sewage sludge should therefore be comprehensively evaluated in large-scale trials in order to investigate more accurately the economic efficiency and environmental relevance of the process.

Remy, C. , Boulestreau, M. , Warneke, J. , Jossa, P. , Kabbe, C. , Lesjean, B. (2015): Evaluating new processes and concepts for energy and resource recovery from municipal wastewater with Life Cycle Assessment.

p 10 In: IWA Cities of the Future Conference – TRUST2015. Mülheim an der Ruhr, Germany. 28-30 April 2015


Energy and resource recovery from municipal wastewater is a pre-requisite for an efficient and sustainable water management in cities of the future. However, a sound evaluation of available processes and pathways is required to identify opportunities and short-comings of the different options and reveal synergies and potentials for optimisation. For evaluating environmental impacts in a holistic view, the tool of Life Cycle Assessment (LCA, ISO 14040/44) is suitable to characterize and quantify the direct and indirect effects of new processes and concepts. This paper gives an overview of new processes and concepts for upgrading existing wastewater treatment plants towards energy positive and resource efficient wastewater treatment, based upon an evaluation with LCA using data from pilot and full-scale assessments of the considered processes.

Lesjean, B. , Kabbe, C. (2015): Key Outcomes of FP7 Project P-REX.

p 25 In: WssTP Water Innovation Europe 2015. Brussels, Belgium. 24-26 June 2015

Lesjean, B. (2015): Green Jobs with Phosphorus Recycling.

p 7 In: WssTP Water Innovation Europe 2015. Brussels, Belgium. 24-26 June 2015

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