Towards the energy-optimized wastewater treatment plant of the future - Development and model-based integration of innovative treatment technologies for transformation processes
The municipal „waste water treatment plant (wttp) of the future" will not only cater to today’s requirements for nutrient removal. In many cases, further processing steps regarding the elimination of micropollutants and/or pathogens will be included. At the same time the wwtp of the future will recover the energy contained in the wastewater as well as material resources as far as possible. Therefore it is necessary to critically analyse best practices and use new technologies.
Municipal wastewater is a potential source of energy and valuable materials. The energy of organic compounds in municipal wastewater is approximately 155 kWh/(PE•a) at a load of 110 gCOD/(P•d). Depending on effluent quality requirements, applied process technology and equipment, the recoverable electrical energy by anaerobic sludge digestion is currently in the order of 7.7 to 18.9 kWh/(PE•a). However, the average power consumption of wastewater treatment plants is 34.0 kWh/(PE•a) on average in Germany.
Besides effluent quality requirements, other requirements and claims increasingly affect everyday plant operation and make the use of new technologies attractive.
The research project E-Klär develops strategies in order to use energy and other resources present in wastewater most efficiently and to reduce energy consumption of next generation wastewater treatment plants. A methodology will be developed that will help to transform existing plants into energy-optimised, resource-protecting and economically feasible plants through a plant specific step-by-step process. The strategies to be developed focus on an extensive nutrient removal alongside with a reduction of micropollutants and pathogens.
The project will result in innovative process chains using new methods which are conceived and tested in their interactions with each other and with best practices processes. In addition, innovative approaches to integrated material and energy flow modeling will be developed for the whole wastewater treatment plant, so that after calibration on representative facilities it is possible to compare various wastewater treatment plant concepts in terms of energy, resources and costs. Based on this, practical recommendations for the transformation of current wastewater treatment plants in more energy-efficient future concepts are developed in an interdisciplinary transferable methodology.
Fig. 1: Key activities and aims of E-Klär
Within the first subproject (SP I: “Design“) research will focus on technical questions regarding innovative processes and their interdependencies among each other as well as with established technologies. Thereby all relevant process steps of the next generation wwtp will be considered. Options of an extensive carbon recovery and utilisation will be investigated to improve the energy balance of the next generation wwtp. Conventional processes for nitrogen removal affect the energy balance negatively due to the oxygen demand for nitrification on the one hand and the carbon demand for denitrification on the other hand. Therefore research will be carried out to close knowledge gaps with respect to how to include autotrophic processes into the next generation wwtp. Additionally, processes for the elimination of micropollutants and for disinfection will be considered and further developed with focus on energy optimisation.
Alongside with energy the potential of substance recovery is relevant for wwtp regarding resource conservation. This subproject focusses on recovery of phosphorus and other resources such as metals or cellulosic fibres from wastewater. The results of these proven and technically innovative processes will form the basis of the conceptual subprojects SP II ”Operation“ and SP III ”Transformation“.
The objective of subproject II "Operation" is the development of a modular simulation tool that allows the modelling of the entire wwtp by using a holistic approach. This approach involves the connection of various process steps of the wwtp, the integration of material and energy flows as well as the description of annual costs as time series and as a forecasting tool. By using a holistic and systematic approach to model the entire wwtp - including its numerous individual process units and the complex interactions between energy and material flows - it is possible to identify optimisation potentials derived from the interaction of production, distribution and utilisation of energy and other resources. On the one hand, particular emphasis is given to the modelling of time series of material, energy and cost characteristics of different wwtp concepts over the period of the transformation process (static). On the other hand, emphasis is also given to the dynamic modelling of relevant process variables (forecast) to support the wwtp operation in terms of an energy-optimised plant operation. All in all, subproject II "Operation" forms a link between subproject I and subproject III. The innovative treatment processes of subproject I “Design” will be integrated as individual process modules into an enhanced plant-wide modelling approach of the entire wwtp.
The objective of subproject III (“Transformation”) is to develop and test a sequential approach for deriving and evaluating long-term transition strategies for wwtp in terms of energy efficiency, economic viability, flexibility and lock-in situations. Eventually, conclusion will be drawn to improve strategic investment decisions of municipalities that are willing to improve on wwtp’s energy-efficiency.
As a first step, long-term development targets of energy-efficient wastewater treatment plants will be defined and solutions that are more robust towards varying frame conditions will be identified. This step will be done with the help of scenarios that contour possible states of future frame conditions. The second step outlines transformation pathways towards those “robust target-plants” that consist of a sequence of investment decisions. Here, the aim is to specify those critical investment decisions that most strongly influence the investments that follow afterwards and may reduce adaptability of the treatment plant in a critical way. Based on this, solutions to reduce path dependency and to improve overall adaptability of those critical decision points will be compared.
This sequential approach will be applied on selected wastewater treatment plants of the Ruhrverband. Finally, recommendations will be made for operators of wwtp to approach energy efficiency of wwtp in a most adaptive and economic way.
The subproject III „Transformation“ is based on the model delivered by subproject II “Operation”. The enhanced plant-wide modeling approach that will be developed during subproject II will be used to deduce the robust target-plants. Furthermore, the model of subproject II will be applied in order to analyse the transformation paths of the wastewater treatment plants. The innovative treatment processes delivered by subproject I “Design” will be seized indirectly as they are incorporated in the enhanced plant-wide modeling approach and thus will be recognised when applying the sequential approach.
The following figure shows the breakdown of all subprojects into individual work packages (WP). Highlighted names stand for the responsible institutions in every work package.
Fig. 2: Work packages of E-Klär subprojects