Every year, huge amounts of bottom sediments are extracted worldwide, which need to be disposed. The recycling of bottom sediments for soil fertilization is in line with the long-promoted circular economy policy and enables the use of micro and macronutrients accumulated in sediments for soil fertilization. When considering potential agricultural reuse of the dredge sediments, the first necessary step should be to analyze whether the heavy metal content meets the obligatory criteria. Then, the contents of valuable elements required for plant growth and their ratios should be assessed. In this study, the content of nitrogen, organic carbon, phosphorus, and potassium was tested and iron, sulfur, calcium, and magnesium were also analyzed along vertical profiles of sediments extracted from four urban retention tanks in Gdańsk (Poland). The sediments were indicated to have a low content of nutrients (Ntot 0.01–0.52%, Corg 0.1–8.4%, P₂O₅ 0.00–0.65%, K 0.0–1.0%), while being quite rich in Fe and S (0.2–3.3%, 0.0–2.5%, respectively). The C/N ratio changed in the range of 17.4–28.4, which proved good nitrogen availability for plants. The mean values of the Fe/P ratio were above 2.0, which confirms that phosphorus in the sediments would be available to the plants in the form of iron phosphate. To summarize, the bottom sediments from municipal retention reservoirs are not a perfect material for soil fertilization, but they are a free waste material which, when enriched with little cost, can be a good fertilizer. Future research should focus on cultivation experiments with the use of sediments enriched with N, P, Corg.

Exponential increases in energy consumption and wastewater have often irreversible environmental impacts. As a result, bio-electrochemical devices like microbial fuel cells (MFCs), which convert chemical energy in organic matter to electricity using exoelectrogenic bacteria, have gained interest. However, operational factors affecting efficiency and energy output need further study. This research investigated bioenergy production and COD, TN, and TP removal in mesoscale floating treatment wetlands (FTW-MFC) using Phragmites australis, Iris pseudacorus, and a mix of both. The Iris FTW-MFC achieved a high voltage peak of 2100 mV. The maximum power densities of 484 mW/m², 1196 mW/m², and 441 mW/m² were observed for Phragmites, Iris, and mixed FTW-MFCs, respectively. Despite promising bioenergy yields, pollutant removal was unsatisfactory. A low area/height ratio (0.38 m²/0.8 m) and high loading rate (18.1 g/m²·d COD) boosted bioenergy output but hindered treatment performance and stressed plants, causing root decay. No significant pollutant removal differences were found between FTW-MFC and FTW. Higher relative plant growth rates occurred in the FTW-MFC. Microbial analysis shown that representatives of Pseudomonas and Clostridium species were consistently found across all samples, involved in both organic compound transformation and electricity generation, contributed to successful microscale results. A supporting microscale MFC experiment showed wastewater composition's impact on bioenergy yield and pollutant removal. Pre-inoculated reactors improved organic matter transformation and electricity generation, while aeration increased voltage and treatment performance. The role of plants requires further verification in future experiments.

Graphical abstract showing how oxygen availability affects pollutant removal and bioelectricity generation in LM, LM MFC, MFC, and AC MFC reactors. Forced aeration gives the best overall treatment and electrochemical performance. . This study investigated pollutant removal and bioelectricity generation under different oxygen availabilities, created by forced aeration and dense plant cover. Four 150 L working-volume reactors treating synthetic wastewater were operated as floating treatment wetlands (FTW), microbial fuel cells (MFCs), MFC-assisted FTWs (LM MFCs), and an aerated cathode MFC (AC MFC). The FTW-based configurations were planted with naturally developed Lemna minor (LM). All reactors were carried in batch mode using a well-established system, implemented as a late-season experiment. Regular monitoring included pollutant concentrations, redox potential, and voltage output. The AC MFC achieved the highest nitrogen removal among all configurations, reaching up to 100% NH4-N removal and 86% total nitrogen (TN) removal. Integrating the MFC with LM improved TN removal compared with the LM and MFC reactors (by 10%). COD removal was highest in the MFC (88%) and LM MFC (83%). Total phosphorus (TP) removal was enhanced by forced aeration, reaching 75%. The maximum voltage output was observed in the AC MFC (>200 mV), although voltage generation was unstable and appeared sensitive to temperature and solar irradiance. Overall, the results highlight oxygen availability as a key driver shaping both treatment performance and electrochemical output in FTW-MFC systems.

Sustainable production of lignocellulosic biomass on marginal lands requires strategies that enhance yield while minimizing nutrient losses and supporting circular resource use. In this study, a two‐year (2023–2024) greenhouse meso‐scale experiment was conducted using Miscanthus × giganteus cultivated on nutrient‐poor soil amended with wood‐ or straw‐derived biochar (450°C) and fertilized with either mineral fertilizer (NPK) or spent coffee grounds (Cof). Biomass production and allocation, nutrient mobility in leachates, elemental composition of plant biomass and resulting phyto‐ashes, root anatomy, and plant physiological status were evaluated. Total biomass ranged from 250 to 491 g d.w. m ⁻² in the first growing season and reached 1495 g d.w. m ⁻² after two growing seasons. Biomass allocation was dominated by belowground fractions (58%–89% of total biomass), particularly in Cof‐amended plots. The highest biomass production was observed in the plot amended with straw biochar and Cof, indicating potential complementarity between biochar amendment and organic fertilization under marginal soil conditions. Some biochar‐amended plots (wood biochar + Cof) showed lower and more stable event‐based nitrogen loads in leachates, consistent with reduced nitrogen mobility. Cof‐amended plots exhibited higher chlorophyll‐related indices, while the highest TKN concentration, 9726 mg kg ⁻¹ d.w., was recorded after the second growing season, indicating differences in nitrogen availability and allocation among amendment scenarios. Root anatomical organization also varied among plots. Endpoint Fv/fm values ranged from 0.72 to 0.77 and were below the range commonly reported for non‐stressed plants, while Fm/Fo and Y(II) indicated that PSII photochemical activity was maintained. Here, we demonstrate that biochar combined with organic residues (Cof) modifies biomass partitioning and nutrient dynamics in Miscanthus × giganteus cultivated on marginal soil. In addition, the resulting phyto‐ashes were characterized by elevated K and P concentrations and low levels of potentially toxic elements, supporting their potential relevance for circular nutrient management.

Recycled nutrient fertilizers (RNFs) derived from organic and industrial waste streams offer a promising approach to nutrient recovery and sustainable agricultural production. However, their agronomic performance and the potential benefits of enrichment with biologically active, waste-derived materials remain insufficiently understood. This study evaluated two multi-component RNFs, four-ingredient pellets, first with biochar (BADSS) and second with bovine shavings (SADSS), with and without enrichment using chitosan-containing seafood waste, in a four-month greenhouse experiment with ryegrass across nitrogen application rates ranging from 20 to 370 kg N ha⁻¹. Biomass production, nitrogen uptake, agronomic effectiveness (AE), apparent nitrogen recovery (ANR), soil chemical properties, and photosystem II efficiency were assessed. The results demonstrated that fertilizer performance depended strongly on matrix composition and nitrogen application rate. BADSS induced a stronger increase in residual soil pH, whereas SADSS maintained more balanced soil conditions. Chitosan enrichment enhanced long-term nitrogen uptake and biomass production when combined with SADSS, while its effects in the BADSS matrix were less consistent, particularly at excessive nitrogen inputs. Correcting fertilizer performance for additional nitrogen introduced with the chitosan-containing amendment substantially reduced apparent AE and ANR, highlighting the importance of complete nutrient accounting when assessing enriched fertilizers. Overall, the findings indicate that seafood-waste-derived chitosan can improve the agronomic performance of recycled nutrient fertilizers, although its effectiveness depends on the composition of the fertilizer matrix and the applied nitrogen rate. Integrating seafood-processing residues into waste-derived fertilizer systems offers a promising strategy for valorizing underutilized resources, improving nutrient management, and supporting circular bioeconomy approaches to sustainable agriculture.