Scaling up water solutions I

Industry is one of the largest water users in Europe next to agriculture and households. Circular water concepts are already implemented in industry, but the European Commission (EC) is giving specific attention to ‘Water Smart Industrial Symbiosis (WSIS)’ in which economic value and increased sustainability is created by introducing circular symbiotic arrangements between industry and water service providers. This approach will also enhance the opportunities for recovery and reuse of water embedded resources (energy, materials) and stimulate new circular business arrangements. In the EC funded ULTIMATE project we have looked into the potential of WSIS in different industrial settings. ULTIMATE has developed nine lighthouse WSIS cases In Europe, the UK and Israel, where ULTIMATE has successfully connected the water sector with the agri-food, chemical, petrochemical, biotechnology and beverage industries, and established 24 different pilot plants and three control- and monitoring systems. In addition, six concept/feasibility studies were conducted and three Greenfield assessments have been carried out to show the replication in other industrial settings. Six case studies are planning full scale implementation of the demonstrated solutions. In total 31 novel circular water technologies have been successfully tested and demonstrated, enabling water reuse, heat recovery and reuse, biogas production and utilisation, energy efficiency, and material recovery. In addition to these technological innovations, digital support tools and social innovations have been applied. Digital support tools identify symbiotic opportunities, enhance the design and operation of industrial symbiotic schemes, and assess their long-term viability, improving cross-domain interaction, resilience, replicability, transferability of solutions. Social innovations support the involvement of stakeholders, policy and governance recommendations and new business tools and arrangements. The positive experiences from ULTIMATE and take up of innovations and approaches, showing the potential to achieve a water smart industrial symbiosis, will also contribute to achieving a water smart society.

1. Introduction Hydrogen sulfide (H₂S) poses significant challenges in sewer systems, contributing to odor, corrosion, and safety risks. Traditional chemical treatments, while effective, often rely on costly and non-sustainable materials. This study explores an innovative circular economy approach for sulfide control by utilizing a thermochemically-regenerated multifunctional coagulant using drinking water sludge (DWS) as feedstock to simultaneously achieve odor control in sewer systems and phosphorus control in primary clarifiers. The benefit of introducing a multi-mineral DWS (enriched in calcium, iron, aluminum, silica as main key constituents ) also arguably extends further downstream, e.g. by enhancing activated sludge settleability and anaerobic digestion, as reported in some (isolated) previous studies. In our work, we compared this novel coagulant against nitrate as alternative treatment agents for sewers and against iron as alternative coagulant for chemically-enhanced primary clarification. The research was conducted using a novel sewer physical twin (SPT) system that replicates real-world sewer conditions, bridging the gap between lab-scale concepts and practical applications. By focusing on biofilm dynamics, wastewater characteristics, and economic viability, this study aligns with key themes of circular water systems, climate resilience, and stakeholder engagement. 2. Materials and Methods The study utilized three parallel SPT systems to evaluate the effects of DWS, a commercial iron coagulant, and nitrate on sulfide control, biofilm behavior, and wastewater properties. DWS, rich in ferric iron and aluminum, and the commercial ferrous iron product, were dosed during the first stage of experiments. In a subsequent stage, nitrate was introduced following iron treatment to investigate synergistic effects on biofilm disruption and sulfide control. The systems were operated under dynamic conditions for over 300 days, simulating real sewer hydrodynamics and including recovery periods between treatments to evaluate system resilience. 3. Results and Discussion The results demonstrate the effectiveness of DWS in reducing sulfide and phosphorus levels, with up to 63% inhibition of sulfate reduction and 67% soluble phosphorus removal, outperforming the commercial iron product under similar conditions. The systems exhibited rapid recovery following iron treatment, with sulfide levels returning to baseline within five days, demonstrating the reversible nature of sulfide inhibition by DWS and the commercial iron product. In contrast, recovery from nitrate treatment was slower, with sulfide concentrations remaining suppressed for over 30 days due to biofilm disruption and iron release. The application of DWS also increased inert suspended solids, which, while presenting sludge handling challenges, offers opportunities for enhanced CEPT (via ballasted flocculation in the primary clarifier) and methane generation in downstream anaerobic processes. Nitrate addition following iron treatment resulted in effective sulfide control, with dissolved sulfide concentrations dropping to 1 mg/L, while sulfate levels increased due to oxidation of iron sulfides and elemental sulfur. This sequential treatment strategy disrupted biofilms, releasing iron and sulfur compounds that contributed to prolonged sulfide removal even after nitrate addition ceased. 4. Conclusions This study underscores the potential of circular economy solutions in wastewater management by demonstrating the dual benefits of resource recovery and operational efficiency. The reuse of DWS, a waste stream from drinking water treatment, exemplifies a sustainable alternative to conventional chemical treatments. Sequential application of DWS and nitrate not only enhances sulfide control but also promotes biofilm disruption, offering long-term benefits for sewer systems. These findings provide a practical pathway for scaling up circular water solutions while fostering climate resilience, economic viability, and ecosystem protection. Engaging stakeholders and integrating these approaches into policy frameworks will be critical for transitioning to sustainable and efficient wastewater management systems. Cost analysis revealed that multi-mineral DWS treatment was the most economical option, while nitrate-only treatment was significantly more expensive. Combined iron and nitrate treatments with recovery periods offered a cost-effective strategy for biofilm destabilization and long-term sulfide control, highlighting the importance of optimizing treatment sequences.

As global food production dominates freshwater consumption and nutrient discharge regulations tighten, there is a need to investigate novel circular water solutions at applied scale. In the Netherlands, the greenhouse horticulture sector is required to achieve (nearly) zero liquid discharge by 2027. This challenge calls for new technologies to produce and reuse irrigation water that meets strict quality standards while reducing environmental impact. We evaluated production of irrigation water and nutrient recovery from greenhouse wastewater using a one-pass capacitive electrodialysis (CED) system at a pilot scale (19.32 m2 membrane area, 1-4 m3/day capacity), employing carbon-based electrodes. Using CED, we produced reclaimed water that meets the target for irrigation water quality (Na+< 0.1 mmol/L). Furthermore, we were able to concentrate nutrients by 42-85% making it possible to reduce emissions while also reducing the need for virgin materials as fertilizer. It was observed that the specific energy consumption (SEC) of CED was 4-fold lower than for reverse osmosis (RO) and conventional electrodialysis (ED) studies, making CED an promising alternative to established water treatment solutions. Operating costs were predominantly driven by energy consumption which accounted for over 80% of total expenses, while ion-exchange membranes contribute approximately 10%, representing potential bottlenecks relative to alternative technologies. Further full-scale demonstrations in collaboration with industry stakeholders are necessary to confirm long-term operational and economic feasibility. Moreover, ongoing research is being done to developing Na⁺/K⁺ selective membrane solutions, optimizing costs, and managing concentrate streams. By addressing both technical challenges and socioeconomic barriers, this work provides critical insights that can guide the scale-up of CED and support policy decisions and for sustainable water management in high-demand agricultural sectors.