Nutrient recovery from wastewater treatment plants (WWTPs) for hydroponic cultivation holds promise for closing the nutrient loop and meeting rising food demands. However, most studies focus on solid products for soil-based agriculture, thus raising questions about their suitability for hydroponics. In this study, we address these questions by performing the first in-depth assessment of the extent to which state-of-the-art nutrient recovery processes can generate useful products for hydroponic application. Our results indicate that less than 11.5% of the required nutrients for crops grown hydroponically can currently be recovered. Potassium nitrate (KNO₃), calcium nitrate (Ca(NO₃)₂), and magnesium sulfate (MgSO₄), constituting over 75% of the total nutrient demand for hydroponics, cannot be recovered in appropriate form due to their high solubility, hindering their separated recovery from wastewater. To overcome this challenge, we outline a novel nutrient recovery approach that emphasizes the generation of multi-nutrient concentrates specifically designed to meet the requirements of hydroponic cultivation. Based on a theoretical assessment of nutrient and contaminant flows in a typical municipal WWTP, utilizing a steady-state model, we estimated that this novel approach could potentially supply up to 56% of the nutrient requirements of hydroponic systems. Finally, we outline fundamental design requirements for nutrient recovery systems based on this new approach. Achieving these nutrient recovery potentials could be technically feasible through a combination of activated sludge processes for nitrification, membrane-based desalination processes, and selective removal of interfering NaCl. However, given the limited investigation into such treatment trains, further research is essential to explore viable system designs for effective nutrient recovery for hydroponics.

Within this paper, the authors explain their transdisciplinary vision of nutrient recovery for sustainable urban plant cultivation in Germany from different but complementary perspectives (SUSKULT vision). Nowadays, the demand for fresh, healthy, locally and sustainably produced food in German urban areas is constantly increasing. At the same time, current agricultural systems contribute significantly to exceeding the planetary boundaries. The disruption of the phosphorus and nitrogen cycles in particular stands out from the manifold effects of modern food production on the Earth system. One central issue that will have to be faced in the future is how increased yields in agriculture will be achieved with high-energy requirements in fertilizer production and pollution of water and soil by phosphorus and reactive nitrogen. City region food systems (CRFS) can be a solution to overcome these issues. Nevertheless, to ensure sustainable CRFS, innovative technologies and methods need to be developed, including nutrient and energy recovery and adapted horticultural cultivation methods that fit complex urban dynamics. Such new strategies need to be integrated in long-term social and political transformation processes to enhance acceptance of food produced by recyclates. The joint contribution of experts from the wastewater, horticultural, and political sciences, together with industrial and societal sector actors, is critical to reach these objectives. The overarching goal of SUSKULT’s vision is the establishment of the field of urban circular agricultural production as an innovative sector of the bio-based economy in Germany.

To meet the requirements of a sustainable agricultural economy such as quality, resource conservation, and efficiency, the interaction between the cultivation parameters of plants and the resulting plant ingredients are becoming more and more interesting, especially regarding secondary metabolites. Therefore, the cultivation of lovage under the influence of light-emitting diode illumination and controlled environment conditions was studied and data on the rutin concentrations obtained are presented. Different extraction agents and processes were tested for the treatment of the leaves and the rutin was analyzed using high performance liquid chromatography (HPLC) and ultraviolet-visible spectroscopy (UV-Vis spectroscopy). UV-Vis spectroscopy was found to provide a simple and rapid method of predicting the rutin concentration. The significant parameter regarding the rutin concentration obtained was light intensity and overall rutin concentrations in the range of 17,005 mg to 34,759 mg of rutin per kg dry leaves were found.

The accurate evaluation of crop quality is vital for sustainable agriculture and optimized production. Raman spectroscopy, renowned for its insensitivity to water interference and its ability to deliver molecular-specific information, presents significant potential as a remote sensing technology. This study explores the feasibility of adapting advanced Raman spectroscopy as a remote crop quality sensor for the precise assessment of carotenoids. Carotenoids were chosen due to their dual role as key stress indicators in crops and their well-established antioxidant benefits for human health.To explore carotenoid variability, Arabidopsis thaliana and Spinacia oleracea were analyzed. Raman spectroscopy measurements were performed on two leaves per plant using a 785 nm laser. For the carotenoid quantification, Linear Discriminant Analysis (LDA) was adapted. The spectra were processed through smoothing, background removal, and normalization, followed by modification with an amplifying factor. This study evaluated the impact of these processing methods, particularly the application of the amplifying factor, on the accuracy of the model. High-Performance Liquid Chromatography (HPLC) was employed as the reference method for validation. Three-quarters of the samples were used to construct the model, while the remaining one-quarter was reserved for validation. As a result, the model utilizing spectra modified with the amplifying factor in most cases achieved higher validation accuracy compared to models based on unmodified spectra.This study introduces a novel Raman spectroscopy-based remote sensing approach for crop quality assessment, establishing an enhanced model for interpreting spectral data. By enabling precise detection of stress-induced changes in plant chemical composition, including carotenoids, this technique paves the way for scalable, real-time monitoring through Raman-equipped machinery or drones, advancing sustainable agriculture practices.