To sustain good harvests, each year more than one million tonnes of mineral phosphorus have to be imported to the European Union (van Dijk et al., unpublished data), while the potential to recover and recycle this essential resource remains untapped or is just inefficiently used as in the case of sewage sludge, manure and food waste. In recent years various technical solutions have been developed to recover phosphorus providing mineral compounds suitable as raw material for fertiliser production or even as ready-to-use fertiliser. Regarding the implementation of these technologies, operational benefits for plant operators like the water utilities in the case of P recovery from wastewater and/or sewage sludge are the strongest argument for their market penetration. Without the provision of direct operational benefits, implementation needs to be motivated or even enforced by suitable and reliable policies. In order to realise a circular economy, it is important not just to focus on the recovery itself. The recovered materials need to match the requirements and needs of their intended users. Therefore, full value-chain solutions have to be promoted instead of isolated technology-focused approaches. Following our principles of sustainability and resource efficiency, the assessment of innovations must also include their environmental impact. This review provides an overview of recently developed and promising technologies for phosphorus recovery from wastewater and discusses aspects regarding their wide-spread application, along with their limitations. It will focus on recovery and recycling from sewage sludge. Not only the technologies themselves, also the recovered materials and their valorisation options are addressed. Results of the EU FP7 funded project P-REX entitled 'Sustainable sewage sludge management fostering phosphorus recovery and energy efficiency' and other recent initiatives will be included. Since innovation always needs an enabling environment for market penetration, barriers set by the existing legal framework and measures to resolve them will be reviewed. Finally, Goethe's words are true more than ever: 'Knowing is not enough, we must apply! Willing is not enough, we must do!'

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.

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.

Being a measure to counteract an increasing water scarcity in multiple regions of the world, water reuse is the subject of numerous investigations. The pan-European project DEMOWARE aims at tackling barriers related to water reuse to support further applications. At the project site of Braunschweig in Germany wastewater is reused historically to irrigate agricultural fields. Against the background of an ongoing debate in Germany to establish a legal basis for water reuse, options for a disinfection of secondary treated wastewater were tested at the wastewater treatment plant Steinhof. This thesis investigates the disinfection performance of two pilot scale plants (performic acid (PFA) dosage and UV irradiation) against the background of the compliance with wastewater-related standards, especially DIN 19650 and a WHO guideline regarding wastewater reuse. In order to meet recommendations of the latter, a noro- and rotavirus removal of 1.5 log was recommended by (1) for the site of Braunschweig. E. coli, intestinal enterococci (IE) and Clostridium perfringens were analyzed regarding their abundance and log removal concerning physicochemical properties. Serving as indicator organisms, they were related to the log removal of noro- and rotavirus. Differing doses were tested. The impact of the contact time was investigated for PFA by the presence or absence of sodium thiosulfate (STS) in the sampling bottles whereat the presence of STS terminates the disinfection process. The application of STS in the PFA sampling bottles caused a performance difference of 1.32 log for E. coli, 0.78 log for IE and 0.28 log for C. perfringens. Hence, the PFA reaction was not completed at the effluent sampling spot of the reactor (stirrer tank) and the determined minimum contact time of 3.5 min is not sufficient for PFA to develop its complete disinfection performance. The disinfection reactor did not provide the minimum recommended RT (10 min). Possibly, short circuits and zones with limited substance exchange occur. For full scale implementations, the PFA contact basins need to be designed carefully. A flow channel as used at full scale reference applications is preferable here. The PFA plant showed break-ins of the disinfection performance (to values < 0.5 log) for definable and indefinable reasons. Hence, its disinfection performance is not constant. Further investigations are necessary. Of the 3 doses per method deployed, a UV dose of 44 Wh/m³ and a PFA dose of 2 ppm (= 10 min, without STS) is proper to achieve quality class 3 of the DIN 19650 which is required for the present conditions and applications in Braunschweig. The requirements for a noro- and rotavirus removal of 1.5 log units according to the WHO guideline can be satisfied by a dose of 2 ppm of PFA and 35 Wh/m³, respectively, using an evaluation based on the mean value of the disinfection performance (both PFA and UV). By the application of a threshold-based evaluation the requirements are not satisfied for UV irradiation. Regarding PFA dosing, a dose of 2 ppm is sufficient as long as a sufficient contact time (= 10 min) is provided. The order of sensitivity against the disinfection methods was found for both UV irradiation and PFA dosage the same: E. coli > E. cocci > C. perfringens. Clostridium being used as an indicator for endospore-formers showed a remarkably lower sensitivity against both methods. A doseperformance-linearity can be suggested for the present range of dosage for E. coli and IE. C. perfringens does not show a correlation between the PFA/UV dose and the disinfection performance.

Commercialisation of nutrient recovery technologies are progressing across Europe, with a contract signed earlier this year to recycle phosphorus from 60,000 tons of sewage sludge ash. This article looks at progress and options from other companies against market barriers such as raw material prices and legal frameworks.