Application of fourier transform infrared photoacoustic spectroscopy for quantification of nutrient contents and their plant availability in manure and digestate.

In this study, we assess the feasibility of using Fourier Transform Infrared Photoacoustic Spectroscopy (FTIR-PAS) to predict macro- and micro-nutrients in a diverse set of manures and digestates. Furthermore, the prediction capabilities of FTIR-PAS were assessed using a novel error tolerance-based interval method in view of the accuracy required for application in agricultural practices. Partial Least-Squares Regression (PLSR) was used to correlate the FTIR-PAS spectra with nutrient contents. The prediction results were then assessed with conventional assessment methods (root mean square error (RMSE), coefficient of determination R2, and the ratio of prediction to deviation (RPD)). The results show the potential of FTIR-PAS to be used as a rapid analysis technique, with promising prediction results (R2 > 0.91 and RPD >2.5) for all elements except for bicarbonate-extractable P, K, and NH4+-N (0.8 < R2 < 0.9 and 2 < RPD <2.5). The results for nitrogen and phosphorus were further evaluated using the proposed error tolerance-based interval method. The probability of prediction for nitrogen within the allowed limit is calculated to be 94.6 % and for phosphorus 83.8 %. The proposed error tolerance-based interval method provides a better measure to decide if the FTIR-PAS in its current state could be used to meet the required accuracy in agriculture for the quantification of nutrient content in manure and digestate.

From grass to gas and beyond: Anaerobic digestion as a key enabling technology for a residual grass biorefinery.

Roadside grass clippings hold potential as a sustainable source of bioenergy as they do not compete with crops for land use, and are only partially utilized for low-value applications. In this study, we proposed using roadside grass as a sole feedstock for anaerobic digestion (AD) in three different settings, and assessed the potential of producing biomaterials and fertilizers from grass-based digestate. Wet continuous digestion at pilot scale and dry batch digestion at pilot and large scales resulted in biogas yields up to 700 Nm3.t-1 DOM with a methane content of 49-55 %. Despite promising results, wet AD had operational problems such as clogging and poor mixing; once upscaled, the dry digestion initially also presented an operational problem with acidification, which was overcome by the second trial. Digested grass fibers from the pilot dry AD were processed into biomaterials and performed similarly or better than the undigested fibers, while around 20 % performance reduction was observed when compared to reference wood fibers. A mass balance indicated reduced fiber recovery when higher biogas production was obtained. The liquid fraction from the pilot dry AD was characterized for its nutrient content and used as a biofertilizer in another study. In contrast, the leachate collected from the large-scale dry AD had a low nitrogen content and high chloride content that could hinder its further use. Finally, a regional market analysis was conducted showing that the biocomposites produced with the available grass fibers could substitute at least half of the current European market based on our results.

Large reductions in nutrient losses needed to avoid future coastal eutrophication across Europe.

Rapid technological development in agriculture and fast urbanization have increased nutrient losses in Europe. High nutrient export to seas causes coastal eutrophication and harmful algal blooms. This study aims to assess the river exports of nitrogen (N) and phosphorus (P), and identify required reductions to avoid coastal eutrophication in Europe under global change. We modelled nutrient export by 594 rivers in 2050 for a baseline scenario using the new MARINA-Nutrients model for Europe. Nutrient export to European seas is expected to increase by 13-28% under global change. Manure and fertilizers together contribute to river export of N by 35% in 2050. Sewage systems are responsible for 70% of future P export by rivers. By 2050, the top ten polluted rivers for N and P host 42% of the European population. Avoiding future coastal eutrophication requires over 47% less N and up to 77% less P exports by these polluted rivers.

Enhancing swine manure treatment: A full-scale techno-economic assessment of nitrogen recovery, pure oxygen aeration and effluent polishing.

In regions with intensive livestock production, managing the environmental impact of manure is a critical challenge. This study, set in Flanders (Belgium), evaluates the effectiveness of integrating process intensification measures into the treatment of piggery manure to mitigate nitrogen (N) surplus issues. The research investigates the techno-economic benefits of implementing three key interventions: pure oxygen (PO) aeration, ammonia (NH3) stripping-scrubbing (SS) pretreatment, and tertiary treatment using constructed wetlands (CW), within the conventional nitrification-denitrification (NDN) process. Conducted at a full-scale pig manure treatment facility, our analysis employs steady-state mass balances for N and phosphorus (P) to assess the impact of these process intensification strategies. Findings indicate that the incorporation of advanced treatment steps significantly enhances the efficiency and cost-effectiveness of the manure management system. Specifically, the application of PO aeration is shown to reduce overall treatment costs by nearly 4%, while the addition of an NH3 SS unit further decreases expenses by 1-2%, depending on the counter acid utilized. Moreover, the implementation of a CW contributes an additional 4% in cost savings. Collectively, these measures offer substantial improvements in processing capacity, reduction of by-product disposal costs, and generation of additional revenue from high-quality fertilising products. The study highlights the potential of advanced treatment technologies to provide economically viable and environmentally sustainable solutions for manure management in livestock-dense regions, emphasizing the cumulative economic benefit of a holistic approach to process intensification (10%).

Influence of biochar addition and plant management (cutting and time) on ryegrass growth and migration of As and Pb during phytostabilization.

Phytostabilization of metal-contaminated soils can be enabled or improved by biochar application. However, biochar-aided effects vary on biochar types, and little attention has been paid to plant management (time and cutting) to enhance phytostabilization efficiency in synergy with biochar. Therefore, biochars derived from pig manure (PM), Japanese knotweed (JK), and a mixture of both (P1J1) were applied to Pb and As mining soil with ryegrass cultivation to assess the biochar-induced effects on plant growth, dissolved organic matter (DOM), As and Pb mobility, and bioaccumulation within a phytostabilization strategy. Additional treatments involving the combined biochar (P1J1) and ryegrass were conducted to explore the influence of sequential cutting and growing time on facilitating phytostabilization efficacy. Biochar applications promoted plant growth, progressively increasing over time, but were not enhanced by cutting. Short and long-wavelength humic-like DOM substances identified in the soil pore water after biochar application varied depending on the biochar types used, providing evidence for the correlation among DOM changes, biochar origin, and metal immobilization. Biochar-treated soils exhibited reduced Pb availability and enhanced As mobility, with P1J1 stabilizing Pb significantly similar to PM while causing less As mobilization as JK did. The mobilized As did not result in increased plant As uptake; instead, all biochar-added plants showed a significant decrease in As and Pb concentrations compared to those without biochar. Soil available As decreased while available Pb increased with time, and cutting did not influence soil As behavior but did reduce soil Pb release. Nevertheless, plant As and Pb concentrations decreased over time, whereas those in multiple-cut plants were generally higher than those without cuts. Biochar, especially P1J1, along with growth time, holds promise in promoting plant biomass, reducing plant Pb and As concentrations, and minimizing the migration of PbAs within the soil.

Properties of Poultry-Manure-Derived Biochar for Peat Substitution in Growing Media.

Peat is considered a contentious input in horticulture. Therefore, there is a search for suitable alternatives with similar properties that can be used for partial or complete peat substitution in growing media. Poultry-manure-derived biochar (PMB) is considered such an alternative. This study aimed at determining the properties of PMBs obtained through pyrolysis at selected temperatures and assessing their potentials to substitute peat in growing media based on the selected properties. The scope included the laboratory-scale pyrolysis of poultry manure at the temperatures of 425-725 °C; the determination of selected physico-chemical and physical properties of the obtained biochars, including the contaminants; and the assessment of the potentials of produced biochars to be used as peat substitutes. PMBs contained less than 36% of total organic carbon (TOC). The contents of P and K were about 2.03-3.91% and 2.74-5.13%, respectively. PMBs did not retain N. They can be safely used as the concentrations of heavy metals, polycyclic aromatic hydrocarbons (PAHs), polychlorinatd biphenyls (PCBs), dioxins, and furans are within the permissible values (except for Cr). Due to high pH (9.24-12.35), they can have a liming effect. High water holding capacity (WHC) in the range of 158-232% w/w could allow for the maintenance of moisture in the growing media. PMBs obtained at 525 °C, 625 °C, and 725 °C showed required stability (H/Corg < 0.7).

Impact of soil treatment with Nitrilo Triacetic Acid (NTA) on Cd fractionation and microbial biomass in cultivated and uncultivated calcareous soil.

Purpose: The aim of this study was to evaluate the effectiveness of nitrilotriacetic acid (NTA) on cadmium (Cd) fractions and microbial biomass in a calcareous soil spiked with Cd under cultivated (Zea mays L.) and uncultivated regime subject to soil leaching condition. Expanding investigations related to soil-plant interactions on metal-contaminated soils with insights on microbial activity and associated soil toxicity perspective provides novel perspectives on using metal-chelating agents for soil remediation. Methods: The experimental factors were three levels of Cd contamination (0, 25, and 50 mg kg-1 soil) and three levels of NTA (0, 15, and 30 mmol L-1) in loamy soil under maize-cultured and non-cultured conditions. During the experiment, the adding NTA and leaching processes were performed three times. Results: The results showed that the amount of leached Cd decreased in cultivated soil compared to uncultivated soil due to partial uptake of soluble Cd by plant roots and changes in Cd fractions in soil, so that Cd leached in Cd50NTA30 was 9.2 and 6.1 mg L-1, respectively, in uncultivated and cultivated soils. Also, Cd leached in Cd25NTA30 was 5.7 and 3.1 mg L-1 respectively, in uncultivated and cultivated soils. The best treatment in terms of chemical and microbial characteristics of the soil with the high percentage of Cd removed from the soil was Cd25NTA30 in cultivated soil. In Cd25NTA30 compared to Cd25NTA0 in cultivated soil, pH (0.25 unit), microbial biomass carbon (MBC, 65.0 mg kg-1), and soil respiration (27.5 mg C-CO2 kg-1 24 h-1) decreased, while metabolic quotient (qCO2, 0.05) and dissolved organic carbon (DOC, 20.0 mg L-1) increased. Moreover, the changes of Cd fractions in Cd25NTA30 in cultivated soil compared to uncultivated soil were as follows; the exchangeable Cd (F1, 0.27 mg kg-1) and Fe/Mn-oxide-bounded Cd (F4, 0.15 mg kg-1) fractions increased, in contrast, carbonate-Cd (F2, 2.67 mg kg-1) and, organically bounded Cd (F3, 0.06 mg kg-1) fractions decreased. NTA had no significant effect on the residual fraction (F5). Conclusion: The use of NTA, especially in calcareous soils, where most of the Cd is bound to calcium carbonate, was able to successfully convert insoluble fractions of Cd into soluble forms and increase the removal efficiency of Cd in the phytoremediation method. NTA is a non-toxic chelating agent to improve the accumulation of Cd in maize.

Nutrient recovery and recycling from fishery waste and by-products.

The circular bio-based economy offers great untapped potential for the food industry as possible valuable products and energy can be recovered from food waste. This can promote more sustainable and resilient food systems in Europe in follow-up of the European Commission's Farm to Fork strategy and support the global transition to more sustainable agri-food systems with the common agricultural and fisheries policies. With its high nutrient content, waste and by-products originating from fish and seafood industry (including aquaculture) are one of the most promising candidates to produce alternative fertilising products which can play a crucial role to replace synthetic mineral fertilisers. Whereas several studies highlighted the opportunities to recover valuable compounds from fishery waste, study towards their potential for the production of fertilising products is still scarce. This study presents an extensive overview of the characteristics of fishery waste and by-products (i.e., fish processing waste, fish sludge, seafood waste/by-products), the state-of-the-art nutrient recovery technologies and recovered nutrients as fertilising products from these waste streams. The European Commission has already adopted a revised Fertilising Products Regulation (EU) 2019/1009 providing opportunities for fertilising products from various bio-based origins. In frame of this opportunity, we address the quality and safety aspects of the fishery waste-derived fertilising products under these criteria and highlight possible obstacles on their way to the market in the future. Considering its high nutrient content and vast abundance, fish sludge has a great potential but should be treated/refined before being applied to soil. In addition to the parameters currently regulated, it is crucial to consider the salinity levels of such fertilising products as well as the possible presence of other micropollutants especially microplastics to warrant their safe use in agriculture. The agronomic performance of fishery waste-derived fertilisers is also compiled and reported in the last section of this review paper, which in most cases perform equally to that of conventional synthetic fertilisers.

The Influence of Poultry Manure-Derived Biochar and Compost on Soil Properties and Plant Biomass Growth.

Promising methods for managing poultry manure (PM) include converting poultry manure through pyrolysis to biochar, which can be used for soil applications. The overall goal of this study was to determine the effects of poultry manure-derived biochar and compost on the soil and growth of cherry tomatoes. The biochar obtained at 475 °C was characterized by a relatively high organic matter content of 39.47% and nitrogen content of 3.73%, while it had the lowest C/N ratio of 8.18. According to the recommendations of the EBC, the biochar obtained at 475 °C demonstrated the most beneficial effects in terms of fertilizing potential. The composting of poultry manure with the straw was successful, and the limit of 60 °C was exceeded, which allowed for the hygienization of the compost. The produced compost and biochar are sanitary safe and do not exceed the limits of heavy metal content. The lowest plant biomass was obtained from growing medium A with 3.6 g wet weight (0.24 g dry weight). The measurements of the height of cherry tomatoes showed that growing media D, E, and F allowed the plants to obtain from 602 to 654 mm in height.

Root radial apoplastic transport contributes to shoot cadmium accumulation in a high cadmium-accumulating rice line.

Radial transport of cadmium (Cd) in roots governs the amount of Cd loaded into xylem vessels, where Cd ions are translocated upward into shoots, while the mechanism of differential Cd radial transport between the high Cd-accumulating rice line Lu527-8 and the normal rice line Lu527-4 remains ambiguous. A higher Cd distribution in cross sections and root apoplast and higher bypass flow of Cd were found in Lu527-8, explaining a greater Cd translocation through the apoplastic pathway. The lower relative area of the epidermis and the constant relative area of the cortex in Lu527-8 opened-up root radial transport for Cd. Deposition of apoplastic barriers (Casparian strips and suberin lamellae) was stimulated by Cd, which effectively prevented Cd from entering the stele through the apoplastic pathway. In Lu527-8, apoplastic barriers were further from the root apex with lower expression of genes responsible for biosynthesis of Casparian strips and suberin lamellae, enhancing radial transport of Cd. Our data revealed that the higher radial apoplastic transport of Cd played an integral role in Cd translocation, contributed to a better understanding of the mechanism involved in high Cd accumulation in Lu527-8 and helped achieve the practical application of phytoextraction.

Exploring the environmental consequences of roadside grass as a biogas feedstock in Northwest Europe.

The Russo-Ukrainian war has highlighted concerns regarding the European Union's (EU) energy security, given its heavy dependence on Russian natural gas for electricity and heating. The RePowerEU initiative addresses this challenge by targeting a significant increase in biomethane production (up to 35 billion m3 by 2030) to replace natural gas, aligning with the EU methane strategy's emission reduction and air quality improvement goals. However, the use of energy crops as biogas feedstock has raised land-use concerns, necessitating a policy shift towards alternative sources such as agro-residues, livestock manure, and sewage sludge. This study investigates the environmental impacts of using roadside grass clippings (RG) as an alternative feedstock for biogas production, focusing on selected regions in Northwest Europe (Belgium, Netherlands). The aim is to evaluate the environmental performance of RG as a mono- or co-substrate for biogas production, comparing it to the current practice of composting. Additionally, the study assesses the environmental impacts associated with biogas end-use in these regions. The results indicate that co-digestion of RG with pig manure offers a more environmentally friendly alternative compared to mono-digestion of RG or the existing composting practice. This finding is primarily attributed to the avoided emissions resulting from conventional pig manure management. Furthermore, in terms of climate change impacts concerning biogas end-use, the study identifies that combined heat and power (CHP) systems are preferable to biomethane recovery in regions with a natural gas-based electricity mix. However, for reducing fossil resource use, biomethane recovery emerges as the preferred option. By providing insights into the environmental performance of RG as a biogas feedstock and evaluating the impacts of different biogas end-use options, this study offers insights to policymakers for the development of sustainable energy strategies in Northwest Europe.

Metal behavior and soil quality changes induced by the application of tailor-made combined biochar: An investigation at pore water scale.

The remediation performance of biochar varies based on the biomass used for its production. Further innovation involves developing tailor-made biochar by combining different raw materials to compensate for the limitations of pure biochar. Therefore, tailor-made combined biochar produced from the co-pyrolysis of pig manure and invasive Japanese knotweed (P1J1), as well as biochars produced from these feedstocks separately, i.e., pure pig manure (PM) and pure Japanese knotweed (JK), were applied to Pb and As contaminated soil to evaluate the biochar-induced changes on soil properties, microbial activity, DOM, and metal and metalloids solubility at the soil pore water scale. Biochar application reduced soluble Pb, whereas enhanced the As mobility; the increased soil pH after biochar addition played a fundamental role in reducing the Pb solubility, as revealed by their significant negative correlation (r = -0.990, p < 0.01). In contrast, the release of dissolved P strongly influenced As mobilization (r = 0.949, p < 0.01), especially in P-rich PM and P1J1 treatments, while JK showed a marginal effect in mobilizing As. Soils treated with PM, P1J1, and JK mainly increased Gram-negative bacteria by 56 %, 52 %, and 50 %, respectively, compared to the control. Fluorescence excitation-emission matrix spectroscopy combined with parallel factor analysis identified three components in pore water DOM, C1 (long wavelength humic-like), C2 (short wavelength humic-like), and C3 (protein-like), which were dominant respectively in the P1J1, JK, and PM-added soil. A principal component analysis (PCA) confirmed that the PM and P1J1 had similar performance and were more associated with releasing P and Mg and specific DOM components (C1 and C3). Meanwhile, P1J1 supplemented soil OM/OC and K, similar to JK. The results of this study suggest that combined biochar P1J1 can comprehensively enhance soil quality, embodying the advantages of pure PM and JK biochar while overcoming their shortcomings.

Development of conversion factors to estimate the concentrations of heavy metals in manure-derived digestates.

During biogas production, a residual by-product rich in organic matter, nutrients, and trace elements - called digestate - is generated. Due to the nature of the anaerobic digestion process (i.e., conversion of organic matter into biogas) and the non-digestibility of trace elements, metal concentrations are higher in digestate than initially in the treated feedstock, resulting in a detrimental effect on the environment when directly applied as fertiliser on the soil. This study aims to predict the concentration of heavy metals in digestate through four different process parameters (Biogas yield - M1, Biodegradable fraction - M2, Dry matter - M3 and Power generation - M4) in full-scale biogas plants. For the validation of the process parameters, the predictions were compared against laboratory analyses of feedstocks and digestates samples from mono- and co-digestion processes. The convergence between the conversion factors based on laboratory data and process parameters (CLD and CFA, respectively) ranged in the following order: M3 > M2 > M1 > M4. Based on laboratory analyses, better predictions were obtained for Al, Cr, Cu, Fe, Mn, and Zn employing M3. Moreover, a robust convergence was achieved between the CLD and CFA conversion factors for the mono-digestion process. Further assessment of a diverse range of feedstocks is needed to increase the convergence between the conversion factors based on process parameters and laboratory data, specifically for the co-digestion process M3. The concentrations of Cd, Co, Ni, and Pb elements were below the detection limits, whereas Cr, Cu, and Zn did not exceed the legal threshold limits of the legislations.

Green Biorefinery systems for the production of climate-smart sustainable products from grasses, legumes and green crop residues.

Grasses, legumes and green plant wastes represent a ubiquitous feedstock for developing a bioeconomy in regions across Europe. These feedstocks are often an important source of ruminant feed, although much remains unused or underutilised. In addition to proteins, these materials are rich in fibres, sugars, minerals and other components that could also be used as inputs for bio-based product development. Green Biorefinery processes and initiatives are being developed to better capitalise on the potential of these feedstocks to produce sustainable food, feed, materials and energy in an integrated way. Such systems may support a more sustainable primary production sector, enable the valorisation of green waste streams, and provide new business models for farmers. This review presents the current developments in Green Biorefining, focusing on a broad feedstock and product base to include different models of Green Biorefinery. It demonstrates the potential and wide applicability of Green Biorefinery systems, the range of bio-based product opportunities and highlights the way forward for their broader implementation. While the potential for new products is extensive, quality control approval will be required prior to market entry.

Constructed wetlands and duckweed ponds as a treatment step in liquid manure handling - A life cycle assessment.

Life cycle assessment (LCA) was applied to evaluate duckweed ponds and constructed wetlands as polishing steps in pig manure liquid fraction treatment. Using nitrification-denitrification (NDN) of the liquid fraction as the starting point, the LCA compared direct land application of the NDN effluent with different combinations of duckweed ponds, constructed wetlands and discharge into natural waterbodies. Duckweed ponds and constructed wetlands are viewed as a viable tertiary treatment option and potential remedy for nutrient imbalances in areas of intense livestock farming, such as in Belgium. As the effluent stays in the duckweed pond, settling and microbial degradation reduce the remaining phosphorous and nitrogen concentrations. Combined with duckweed and/or wetland plants that take up nutrients in their plant body, this approach can reduce over-fertilisation and prevent excessive nitrogen losses to aquatic environments. In addition, duckweed could serve as an alternative livestock feed and replace imports of protein destined for animal consumption. The environmental performance of the overall treatment systems studied was found to depend greatly on assumptions about the possible avoidance of potassium fertiliser production through the field application of effluents. If it is assumed that the potassium contained in the effluent replaces mineral fertiliser, direct field application of the NDN effluent performed best. If the application of NDN effluent does not lead to mineral fertiliser savings or if the replaced K fertiliser is of low grade, duckweed ponds seem to be a viable additional step in the manure treatment chain. Consequently, whenever background concentrations of N and/or P in fields allow for effluent application and potassium fertiliser substitution, direct application should be favoured over further treatment. If direct land application of the NDN effluent is not an option, the focus should be on long residence times in duckweed ponds to allow for maximum nutrient uptake and feed production.

Pig Slurry Management Producing N Mineral Concentrates: A Full-Scale Case Study.

Manure treatment to recover nutrients presents a great challenge to delocalize nutrients from overloaded areas to those needing such nutrients. To do this, approaches for the treatment of manure have been proposed, and currently, they are mostly under investigation before being upgraded to full scale. There are very few fully operating plants recovering nutrients and, therefore, very few data on which to base environmental and economic studies. In this work, a treatment plant carrying out full-scale membrane technology to treat manure to reduce its total volume and produce a nutrient-rich fraction, i.e., the concentrate, was studied. The concentrate fraction allowed the recovery of 46% of total N and 43% of total P. The high mineral N content, i.e., N-NH4/total-N > 91%, allowed matching the REcovered Nitrogen from manURE (RENURE) criteria proposed by the European Commission to allow the potential substitution of synthetic chemical fertilizers in vulnerable areas characterized by nutrient overloading. Life cycle assessment (LCA) performed by using full-scale data indicated that nutrient recovery by the process studied, when compared with the production of synthetic mineral fertilizers, had a lower impact for the 12 categories studied. LCA also suggested precautions which might reduce environmental impacts even more, i.e., covering the slurry to reduce NH3, N2O, and CH4 emissions and reducing energy consumption by promoting renewable production. The system studied presented a total cost of 4.3 € tons-1 of slurry treated, which is relatively low compared to other similar technologies.

PULSE process: recovery of phosphorus from dried sewage sludge and removal of metals by solvent extraction.

Phosphorus (P) is an indispensable nutrient for agriculture. Recovery and recycling of phosphorus from waste streams is necessary to ensure a circular P economy and reduce dependence on disproportionately distributed mineral P resources. In this study, a new process called 'PULSE' is presented for the recovery of P from sewage sludge, which can handle high metal contents. The process involves drying of sludge prior to acidic leaching to overcome the challenge of solid-liquid separation at low pH and to reduce the overall material flows. Another key point of the process is the removal of metals using reactive extraction to obtain a high-quality product with good plant availability. Laboratory experiments were conducted to evaluate and select the best process options. A chemical equilibrium tool was developed to simulate the unit operations of the process for optimization. Dissolution of P from sludge depends on leaching pH and the fraction of inorganic P in the sludge. The maximum P leaching efficiency for the sludge used in the study was between 65 and 70%. Under the tested conditions, Fe, Cd, Cu, Hg, Pb, and Zn were successfully removed from the sludge leach liquor by reactive extraction. The recovered product has a nutrient mass fraction of about 51% that includes Ca, PO43-, Mg, and K. Pot trials confirmed that the agronomical efficiency of the product is comparable to that of triple superphosphate.

Nitrogen dynamics in soils fertilized with digestate and mineral fertilizers: A full field approach.

Highly stabilized digestate from sewage sludge and digestate-derived ammonium sulphate (RFs), were used in a comparison with synthetic mineral fertilizers (SF) to crop maize in a three-year plot trial in open fields. RFs and SF were dosed to ensure the same amount of mineral N (ammonia-N). In doing so, plots fertilized with digestate received much more N (+185 kg ha-1 of organic N) because digestate also contained organic N. The fate of nitrogen was studied by measuring mineral and organic N in soil at different depths, ammonia and N2O emissions, and N uptake in crops. Soil analyses indicated that at one-meter depth there was no significant difference in nitrate content between RF, SF and Unfertilized plots during crop season indicating that more N dosed with digestate did not lead to extra nitrate leaching. Ammonia emissions and N content in plants and grains measured were also similar for both RF and SF. Measuring denitrification activity by using gene makers resulted in a higher denitrification activity for RF than SF. Nevertheless, N2O measurements showed that SF emitted more N2O than RF (although it was not statistically different) (7.59 ± 3.2 kgN ha-1 for RF and 10.3 ± 6.8 kgN ha-1 for SF), suggesting that probably the addition of organic matter with digestate to RF, increased the denitrification efficiency so that N2 production was favoured. Soil analyses, although were not able detecting N differences between SF and Rf after three years of cropping, revealed a statistical increasing of total carbon, suggesting that dosing digestate lead to carbon (and maybe N) accumulation in soil. Data seem to suggest that N2O/N2 emission and organic N accumulation in soil can explain the fate of the extra N dosed (organic-N) in RF plots.

Industrial hemp (Cannabis sativa L.) field cultivation in a phytoattenuation strategy and valorization potential of the fibers for textile production.

This paper evaluates the valorization potential of industrial hemp (Cannabis sativa L.) fibers produced on HM-contaminated soil as a safe feedstock for the textile industry. The chosen strategy was phytoattenuation, which combines the progressive soil quality improvement of contaminated land using phytoremediation techniques with the production of safe non-food biomass. A field experiment was set up with two hemp cultivars on a site contaminated with Cd, Pb, and Zn and on a nearby site containing clean soil as a control. Stem height and diameter were analyzed, as well as stem and fiber yield and the HM concentrations in the fibers, which were compared to legal safety standards and toxicity thresholds used in the textile industry. The hemp cultivar Carmagnola Selected (CS) had a significantly higher stem and bigger stem diameter compared to cultivar USO 31 on both sites. Stem yields showed a decrease of 30% and 50%, respectively, for both hemp cultivars grown on the contaminated site. However, the stem yield of CS growing on the contaminated site was similar to the stem yield of USO 31 growing on the control site, indicating that hemp cultivation on contaminated soil can be economically viable. Total and extractable Cd, Pb, and Zn fiber concentrations were far below the toxicity standards for textile production purposes. These results are promising in terms of the potential valorization of contaminated land with hemp cultivation and the development of a non-food value chain within a phytoattenuation strategy.

Field evaluation of industrial non-food crops for phytomanaging a metal-contaminated dredged sediment.

Phytomanagement is a concept fit for a bio-based circular economy that combines phytotechnologies and biomass production for non-food purposes. Here, ten annual and perennial industrial non-food crops (Sorghum Biomass 133, Sorghum Santa Fe red, Linum usitatissimum L., Eucalyptus sp., Salix Inger, Salix Tordis, Beta vulgaris L., Phacelia tanacetifolia Benth., Malva sylvestris L., and Chenopodium album L.) were studied under field conditions for phytomanaging a metal (Cd, Cu, Pb, and Zn)-contaminated dredged sediment in the North of France. The crops were selected according to their relevance to pedoclimatic and future climatic conditions, and one or more non-food end-products were proposed for each plant part collected, such as biogas, bioethanol, compost, natural dye, ecocatalyst, and fiber. Based on the soil-plant transfer of metals, eight out of the crops cultivated on field plots exhibited an excluder behavior (bioconcentration factor, BCF < 1), a trait suitable for phytostabilization. However, these crops did not change the metal mobilities in the dredged sediment. The BCF < 1 was not sufficient to characterize the excluder behavior of crops as this factor depended on the total dredged-sediment contaminant. Therefore, a BCF group ranking method was proposed accounting for metal phytotoxicity levels or yield decrease as a complemental way to discuss the crop behavior. The feasibility of the biomass-processing chains was discussed based on these results and according to a survey of available legislation in standard and scientific literature.