Wastewater treatment plants (WWTPs) require an urgent transition from a linear to a circular economy operation/design concept with a consequent resource recovery and more sustainable waste management. Natural resources have to be preserved, and wastes have to become an opportunity for recovering resources and materials (water reuse, energy, sludge reuse). However, the transition toward a circular economy is a complex and long process due to the existence of technical, economic, social and regulatory barriers. These existing barriers are critical challenges for a modern and sustainable WWTP concept. The recovery of resources must be considered a strategic target from the earliest process-design phase. In this context, the European Union’s Horizon 2020 project “Achieving wider uptake of water-smart solutions—WIDER UPTAKE” aims to overcome the existing barriers (technological, regulatory, organizational, social and economic) toward the transition from a linear to a circular economy model for WWTPs. This study is aimed at increasing the awareness of the existing barriers to a circular economy and summarizes the key contributions of the WIDER UPTAKE project in terms of water reuse, sludge reuse and nutrient recovery.

Lined permeable pavements (LPPs) are types of sustainable urban stormwater systems (SUDs) that are suitable for locations with low infiltration capacity or shallow groundwater levels. This study evaluated the hydrological performance of an LPP system in Norway using common detention indicators and flow duration curves (FDCs). Two hydrological models, the Storm Water Management Model (SWMM)-LID module and a reservoir model, were applied to simulate continuous outflows from the LPP system to plot the FDCs. The sensitivity of the parameters of the SWMM-LID module was assessed using the generalized likelihood uncertainty estimation methodology. The LPP system was found to detain the flow effectively based on the median values of the detention indicators (peak reduction = 89%, peak delay = 40 min, centroid delay = 45 min, T50-delay = 86 min). However, these indicators are found to be sensitive to the amount of precipitation and initial conditions. The reservoir model developed in this study was found to yield more accurate simulations (higher NSE) than the SWMM-LID module, and it can be considered a suitable design tool for LPP systems. The FDC offers an informative method to demonstrate the hydrological performance of LPP systems for stormwater engineers and decision-makers.

Population growth, climate change, and unsustainable water use have prompted the exploration of alternative solutions for sustainable water management. While significant advancements have been made in resource recovery technologies from wastewater, the large-scale implementation of these systems and associated impact on the environment and society are still far from full realization. This paper reviews the scientific state-of-the art on resource recovery in the water sector with respect to the four pillars of symbiotic circular economy solutions, consisting of technological processes, final applications, business models, and stakeholder involvement. A systematic and transparent literature review has been carried out, showing that a variety of technologies for recovering water, materials, energy, and nutrients have been proposed and tested, but widespread application is constrained by multiple barriers. These include the technical limitations of existing recovery processes, financial obstacles, and the difficulties associated with integrating technologies into existing value chains. This work emphasizes the need for additional research on novel approaches to promote alternative business models and bottom-up involvement of stakeholders, from public and private organisations to local communities, in the planning and implementation of resource recovery systems in the water sector.

The present study introduces the SWMMLIDopt tool that aims to optimize the implementation of low-impact development (LID) measures for stormwater management. The developed tool utilizes the capabilities of the stormwater management model (SWMM) and provides a user-friendly interface for conducting multi-objective optimization of the selection and placement of LID measures in urban catchments. The features and capabilities of the developed optimization tool are demonstrated on two urban catchments in Northern Europe, Norway and Finland. The catchments exhibit different catchment sizes and characteristics, complexities and constraints demonstrating the flexibility of the tool. The selection and placement of LID measures within the study catchments were optimized according to two criteria: (1) minimizing the peak flow and (2) minimizing the cost. The generated Pareto-fronts for the study catchments allow for the evaluation of optimal scenarios based on the trade-offs between the two selected criteria. The results obtained using SWMMLIDopt demonstrate its efficacy in optimizing LID measures in urban stormwater management that will aid practitioners in designing cost-effective and climate resilient infrastructure.

A novel approach for resource recovery includes forward osmosis (FO) as a concentration step in municipal wastewater treatment. The current study investigates different pre-treatment strategies including biological treatment with a moving-bed bioreactor (MBBR) at different loading rates and particle removal by filtration and sedimentation. Membrane performance and recovery potential for energy and nutrients were investigated in laboratory-scale FO experiments in batch mode using pre-treated municipal wastewater as feed and 35 g/L NaCl as a draw solution. Initial water fluxes were in the range of 6.3 to 8.0 L/(m²·h). The baseline fluxes were modelled to account for flux decline due to concentration effects and to enable the prediction of flux decline due to membrane fouling. Fouling-related flux decline varied from 0 to 31%. Both organic fouling and precipitation of CaCO₃ and CaHPO₄ were identified by using SEM–EDS. High-rate flushing resulted in complete flux recovery under most conditions. Scaling could be avoided by lowering the pH. Two operation strategies were tested to achieve this: (1) applying a bioreactor with a low organic loading rate to achieve high nitrification, and (2) adding a strong acid. A low organic loading rate and the use of additional particle removal were efficient measures that reduced organic/particulate fouling. The recovery potentials for COD and phosphorous in FO concentrate were close to 100%.