Characterisation of sludge produced by the agri-food industry and recycling options for its agricultural uses in a typical Mediterranean area, the Segura River basin (Spain)

Magnetic iron oxide nanoparticle enhanced microwave pretreatment for anaerobic digestion of meat industry sludge

Our study investigates the effects of iron oxide (Fe3O4) nanoparticles combined microwave pretreatment on the anaerobic digestibility and soluble chemical oxygen demand (SCOD) of meat industry sludge. One of our main objectives was to see whether the different microwave-based pretreatment procedures can enhance biogas production by improving the biological availability of organic compounds. Results demonstrated that combining microwave irradiation with magnetic iron oxide nanoparticles considerably increased SCOD (enhancement ratio was above 1.5), the rate of specific biogas production, and the total cumulative specific biogas volume (more than a threefold increment), while having no negative effect on the biomethane content. Furthermore, the assessment of the sludge samples' dielectric properties (dielectric constant and loss factor measured at the frequency of 500 MHz) showed a strong correlation with SCOD changes (r = 0.9942, R2 = 0.99), offering a novel method to evaluate pretreatment efficiency.

Implications of the use of organic fertilizers for antibiotic resistance gene distribution in agricultural soils and fresh food products. A plot-scale study

The spread of antibiotic resistance genes (ARG) into agricultural soils, products, and foods severely limits the use of organic fertilizers in agriculture. In order to help designing agricultural practices that minimize the spread of ARG, we fertilized, sown, and harvested lettuces and radish plants in experimental land plots for two consecutive agricultural cycles using four types of fertilizers: mineral fertilization, sewage sludge, pig slurry, or composted organic fraction of municipal solid waste. The analysis of the relative abundances of more than 200,000 ASV (Amplicon Sequence Variants) identified a small, but significant overlap (<10%) between soil's and fertilizer microbiomes. Clinically relevant ARG were found in higher loads (up to 100 fold) in fertilized soils than in the initial soil, particularly in those treated with organic fertilizers, and their loads grossly correlated to the amount of antibiotic residues found in the corresponding fertilizer. Similarly, low, but measurable ARG loads were found in lettuce (tetM, sul1) and radish (sul1), corresponding the lowest values to samples collected from minerally fertilized fields. Comparison of soil samples collected along the total period of the experiment indicated a relatively year-round stability of soil microbiomes in amended soils, whereas ARG loads appeared as unstable and transient. The results indicate that ARG loads in soils and foodstuffs were likely linked to the contribution of bacteria from organic fertilizer to the soil microbiomes, suggesting that an adequate waste management and good pharmacological and veterinarian practices may significantly reduce the presence of these ARGs in agricultural soils and plant products.

Industrial-Scale Hydrothermal Carbonization of Agro-Industrial Digested Sludge: Filterability Enhancement and Phosphorus Recovery

Hydrothermal carbonization (HTC) provides an attractive alternative method for the treatment of high-moisture waste and, in particular, digested sludge. HTC could reduce the costs and environmental risks associated with sludge handling and management. Although it is recognized that the dewaterability of hydrochars produced from digested sludge, even at mild temperatures (180–190 °C), is highly improved with respect to the starting material, the filterability of HTC slurries for the recovery of the solid material (hydrochar) still represents a challenge. This study presents the results of an investigation into the filterability of agro-industrial digested sludge HTC slurries produced by a C-700 CarboremTM HTC industrial-scale plant. The filterability of HTC slurries, produced at 190 °C for 1 h, with the use of acid solutions of hydrochloric acid, sulfuric acid or citric acids, was investigated by using a semi-industrial filter press. The use of sulfuric acid or citric acid solutions, in particular, significantly improved the filterability of HTC slurries, reducing the time of filtration and residual moisture content. The acid treatment also promoted the migration of heavy metals and phosphorus (P) in the HTC filtrate solution. This study demonstrates that P can be recovered via the precipitation of struvite in high yields, recovering up to 85 wt% by mass of its initial P content.

Agri-Food Contexts in Mediterranean Regions: Contributions to Better Resources Management

The agri-food frameworks have specific characteristics (production units with small dimensions and in great number with implications in the respective markets) that call for adjusted approaches, even more so when they are considered in Mediterranean contexts (where global warming will have relevant impacts). In fact, the Mediterranean regions and countries have particular specificities (due to their climate conditions) that distinguish them from their neighbours. This is particularly true in Europe, for example, where the southern countries present socioeconomic dynamics (associated with the respective public debt) that are different from those identified in the northern regions. From this perspective, it seems pertinent to analyse the several dimensions of the agri-food systems in the Mediterranean area. To achieve these objectives, a search was carried out on 26 December 2020 on the scientific databases Web of Science Core Collection (WoS) and Scopus for the topics “agr*-food” and “Mediterranean”. These keywords were selected after a previous literature survey and to capture the agri-food contexts in Mediterranean regions. The keyword “agr*-food” was considered in this way to allow for a wider search (including “agri-food”, “agro-food”, etc.). Considering only articles (excluding proceeding papers, book chapters, and books, because in some cases it is difficult to access the entire content of the document), 100 and 117 documents were obtained from the WoS and Scopus, respectively. After removing the duplicated studies and taking into account the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) approach, 137 documents were surveyed through a literature review. As main insights, several dimensions embedded in the concept of agri-food were highlighted, from those related to heritage subjects to natural assets. On the other hand, the following subtopics were identified: agri-food dynamics and sustainability, agriculture and agri-food systems, agri-chains and food consumption, and food production and composition impact on agri-chains. Stressing the gaps in the scientific literature, related to the topics here addressed, there are possibilities to better explore the several dimensions and solutions offered by the new developments associated with smart agriculture and agriculture 4.0, specifically for the Mediterranean contexts and their challenges. Finally, to complement the PRISMA methodologies, an MB2MBA2 (Methodology Based on Benchmarking of Metadata, from scientific databases, and Bibliometric Assessment and Analysis) approach is suggested to carry out systematic literature reviews, based on bibliometric analysis.

The role of Serendipita indica and Lactobacilli mixtures on mitigating mycotoxins and heavy metals' risks of contaminated sewage sludge and its composts

Accumulation of the Municipal Sewage Sludge (MSS) is considered as one of the most harmful renewable ecological and human health problems. MSS is a renewable resource that could be used as a soil organic amendment. This study aims to reduce the Heavy Metals (HMs) from the sludge content and sludge compost. Furthermore, this study is considered the first to assess the mycotoxins content in sludge and sludge compost via a new biological treatment using the fungus Serendipita indica or a mixture of lactic acid bacteria, thus providing safer nutrients for the soil amendment for a longer time and preserving human health. The HMs and mycotoxins were determined. The results exhibited that the biotic remediation of bio-solid waste and sewage sludge compost succeeded; a new bio-treated compost with a very low content of heavy metals and almost mycotoxins-free contents was availed. Also, the results indicated that the Lactobacilli mixture realized the best results in reducing heavy metals contents and mycotoxins. Afterward, S. indica. biotic remediation of bio-solid waste and sewage sludge compost minimized the health risk hazards affecting the human food chain, allowing for the different uses of sludge to be safer for the environment.

The effect of application of digestate and agro-food industry sludges on Dystric Cambisol porosity

The spatial arrangement and pore size distribution play an important role in accumulation and protection of exogenous organic matter (EOM) in the soil, but how different organic materials contribute to modify pore structure is poorly understood. We aimed at exploring possible changes in the complexity of the soil phase during fertilization with different doses of digestate and sludges sourced from the agro-food industry. For this purpose, the short-term effects—one year, of soil fertilization, were investigated in several sampling periods and within two depths (0–25 cm and 25–40 cm). Changes in the specific surface area (SSA), total pore volume (V_MIP), total pore area (S_MIP), average pore radius (R_MIP) and pore size distribution (PSD) were monitored using N₂ adsorption/desorption (NAD) and mercury porosimetry (MIP) methods. Our results showed that the intensity of observed changes depended on the type and dose of organic material, soil depth and sampling date. Accumulation of EOM increased with soil depth, masking a large proportion of SSA. Deeper soil layer was more susceptible to changes in the pore size distributions due to the formation of new elongated pores. We concluded that this specific structural porosity was related to the decomposition of organic matter during the formation of soil aggregates.

The Analysis of the Economic Effects on the Greening and Recovery of the Sludge Waste Resulting from the Biogas Production Activity

Starting from identifying an upward trend in waste disposal costs at the municipal landfill, the research aims to analyze the viability of investment to integrate a compost platform, which transforms the sludge resulting from the biogas production process into a soil improver for agricultural land. The economic entity analyzed activates agri-food and uses a biogas plant as a management tool for the waste from slaughtering chickens, to obtain biogas, heat, and electricity. The study is carried out through the multi-criteria analysis based on the following variants: The operation of the biogas plant with sludge disposal as waste (V1), the operation with recovery of waste as soil improver (V2), the closure of the biogas plant (V3). The economic effects regarding the greening and capitalization of the sludge waste are quantified from a monetary point of view and based on the analysis the optimal variant, V2, is established. It has been proven that the investment generates: Positive results increased by 70.52%, a positive and upward opportunity cost by 37.96%, and marginal profit growth of 53.17%. The study emphasizes that efficient waste management turns an environmental problem and cost into an economic and ecological advantage for the economic entities.