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The tomato industry is a relevant socio-economic activity in the European Union, while it generates a large variety of residues. Tomatoes unfit for consumption, tomato peels, seeds, industrial pomace, and plants are examples of residues of this industry. Commonly, some of the residues can be left in the field, composted, used for animal feeding, or valorized through anaerobic digestion. However, more economic value can be attributed to these residues if a biorefinery approach is applied. Indeed, many value-added compounds can be obtained by the integration of different processes while closing the carbon and nutrient loops. The extraction of bioactive compounds followed by anaerobic digestion and composting seems to be a viable proposal for a biorefinery approach. Thus, this study aims to review the biorefinery strategies for valorizing tomato residues, highlighting the main processes proposed. The recovery of lycopene, β-carotene, and phenolic compounds has been widely studied at the lab scale, while energy recovery has already been applied at the industrial scale. Although techno-economic analysis is scarce for tomato residue valorization processes, positive net present values (NPV) and low payback times (PBT) have been reported in the literature. Thus, more work comparing multiple extraction technologies and biorefinery strategies coupled with economic and environmental assessment should be performed to select the most promising management route for tomato residues.

Sewage sludge (SS) from urban wastewater treatment is still an environmental, economic, and social problem. Current SS management is not consensual, and more alternatives are required to recover some valuable compounds, such as nutrients and organic matter. This study investigates the use of green liquor dregs from the pulp and paper industry—GLDs—as an adjuvant of drying, to develop a product for agronomic applications, focusing on the rheological behavior. The rheological properties were assessed for anaerobically digested sludge (ADS). The limit viscosity of raw ADS was about 0.005 Pa·s in the case of 5% TSs (total solids) increasing to 0.51 Pa·s for 20% TSs. From the oscillatory tests, the ideal viscous flow below 10% TSs was observed, whereas a viscoelastic–solid behavior was detected for a higher concentration of TSs. The addition of GLDs to the ADS reduced the consistency index, reducing the shear resistance of the material. Rheological assays showed that GLDs may facilitate sludge handling (e.g., extrusion) from the dewatering unit to the dryer. Overall, the addition of GLDs to ADS showed to be a viable option for drying and subsequent soil application. Reusing both residues promote the transition from a linear to a circular economy in the wastewater treatment sector.

The optimization of extraction by using solvents of phenolic compounds (TPh) of grape pomace (GP) based on a central composite design was investigated. The GP was characterized, and preliminary assays were conducted with five different solvents (water, ethanol, acetone, methanol, and butanol) and the aqueous mixtures thereof. Ethanol and acetone were revealed to be the best solvents for TPh extraction. The main extraction parameters (temperature—T, time—t, solvent concentration, and liquid–solid ratio—L/S) were optimized by using a central composite design. The optimized conditions for the ethanol extraction (T = 60 °C, t = 1.5 h, L/S = 25 mL/gdryGP) and for acetone (T = 50 °C, t = 1.5 h, L/S = 25 mL/gdryGP) were determined. Single-stage extraction revealed a TPh of 45.18 ± 9.51 mgGAE/gdryGP for acetone and a TPh of 38.70 ± 3.64 mgGAE/gdryGP for ethanol. The characterization of the extracts revealed the presence of gallic acid, caffeic acid, syringic acid, vanillic acid, chlorogenic acid, and p-coumaric acid, where the concentration of the first three compounds stands out in all extracts. A three-stage extraction increased the yield of ethanol to 63.3 mg GAE/gdryGP and the yield of acetone to 59.2 mg GAE/gdryGP. Overall, both solvents allow the extraction of phenolic compounds of grape pomace, but ethanol is commonly considered a greener solvent for this purpose.

The wine industry is one of the most relevant socio-economic activities in Europe. However, this industry represents a growing problem with negative effects on the environment since it produces large quantities of residues that need appropriate valorization or management. From the perspective of biorefinery and circular economy, the winery residues show high potential to be used for the formulation of new products. Due to the substantial quantities of phenolic compounds, flavonoids, and anthocyanins with high antioxidant potential in their matrix, these residues can be exploited by extracting bioactive compounds before using the remaining biomass for energy purposes or for producing fertilizers. Currently, there is an emphasis on the use of new and greener technologies in order to recover bioactive molecules from solid and liquid winery residues. Once the bio compounds are recovered, the remaining residues can be used for the production of energy through bioprocesses (biogas, bioethanol, bio-oil), thermal processes (pyrolysis, gasification combustion), or biofertilizers (compost), according to the biorefinery concept. This review mainly focuses on the discussion of the feasibility of the application of the biorefinery concept for winery residues. The transition from the lab-scale to the industrial-scale of the different technologies is still lacking and urgent in this sector.

Sustainable agriculture practices within the guidelines of nutrient recycling and the circular economy must be increasingly promoted. This work aims to evaluate the performance of dried sewage sludge (DSS), green liquor dregs mixed with sewage sludge (DSSA), raw sewage sludge, and commercial organic fertilizer control, using a short-term agronomic assessment with lettuce crop (Lactuca sativa) in greenhouse conditions. Different application rates based on the nitrogen content were tested for each soil amendment: 0, 85, 170, and 225 kg N/ha (treatments T0, T1, T2, and T3, respectively). DSS and DSSA resulted in fresh lettuce productivities 1.3 and 3.2 times higher in T3 than in T0, respectively. The ideal N content in lettuce leaves was reached for all materials and treatments, with the highest values obtained for DSS (2.88–3.33% from T1 to T3). Lettuce produced in soils amended with DSS and DSSA showed also ideal levels of Ca. Overall, the performance of sludge-based products was similar to commercial fertilizer, without impairing the nutritional balance of the crop and the soil.

Incineration bottom ashes (IBA) are the main waste from municipal solid waste (MSW) incineration. In the Iberian countries (Portugal and Spain), MSW incineration with energy recovery (WtE) plays an important role in MSW management. IBA is highly produced and managed differently both between and within countries. This paper aims to provide a comprehensive overview of the management model of IBA using the Iberian Peninsula as a case study, addressing its properties, current management, incentives and difficulties in valorizing, and prospects. For this purpose, incineration plants of both countries were approached, and a broad literature review was conducted to gather information. About 10% and 41% of IBA have been landfilled in Portugal and Spain, respectively. Metals (mostly ferrous) from Portuguese (6% of IBA) and Spanish (9% of IBA) WtE plants are recycled. In Portugal, the remaining IBA (84%) has been temporarily stored (11%), applied to landfills as a substitute for soil in intermediate and final covers, construction of paths, accesses, and platforms (41%), or used in civil engineering work and road construction (48%). In Spain, the remaining IBA (50%) has been reused mainly as a secondary raw material in the construction and civil engineering fields (77%), while the rest has been temporarily stored (11%), applied in the conditioning of landfills (4%), alsoa secondary aggregate replacing natural materials. Both countries regulate IBA reuse outside landfills but consider different requirements and criteria. Nevertheless, there are both drivers and barriers to valorization. In the future, different IBA applications will likely continue to be developed, with the concern of protecting the environment. Growing confidence in IBA reuse following the publication of proper studies is expected. Globally, uniform legal frameworks among EU members with the same standards would likely lead to better IBA valorization.

The agro-industry of tomato generates three types of residues: ripe rotten tomato (unfit for consumption) (RT), green (unripe) tomato (GT), and tomato branches including leaves and stems (TB). These materials are commonly wasted or used as feed for livestock. Energy production through anaerobic digestion is an alternative way to manage and simultaneously valorise these materials. Initially, the operating conditions of mono anaerobic digestion were investigated using RT. Thus, a design of experiments based on a two-level fractional factorial design with resolution V was performed to determine the factors that affect biochemical methane potential (BMP). The substrate to inoculum ratio (SIR), total volatile solids concentration (VSt), working volume (WV), presence of nutrients (Nu), and the pre-incubation of the inoculum (Inc) were investigated. The results showed that SIR is the most important factor. The maximum BMP for RT was 297 NmLCH4/gVS with SIR = 0.5; tVS = 20 g/L; WV = 20%; no pre-incubation and the presence of nutrients. Using these optimum operating conditions, co-digestion was investigated through a mixture design approach. The substrates RT and GT presented similar BMP values, whereas TB led to a significantly lower BMP. Indeed, when high concentrations of TB were used, a significant decrease in methane production was observed. Nonetheless, the highest BMP was achieved with a mixture of 63% RT + 20% GT + 17% TB, with a production of 324 NmLCH4/gVS, corresponding to a synergetic co-digestion performance index of about 1.20. In general, although the substrate RT generates the highest BMP, the mixture with GT did not impair the methane yield. Overall, the co-digestion of tomato residues must be conducted with SIR close to 0.5 and the content of tomato branches in the reaction mixture should be kept low (up to 20%).

The application of TiO2 as a slurry catalyst for the degradation of contaminants of emerging concern (CEC) in liquid effluents has some drawbacks due to the difficulties in the catalyst reutilization. Thus, sophisticated and expensive separation methods are required after the reaction step. Alternatively, several types of materials have been used to support powder catalysts, so that fixed or fluidized bed reactors may be used. In this context, the objective of this work is to systematize and analyze the results of research inherent to the application of ceramic materials as support of TiO2 in the photocatalytic CEC removal from liquid effluents. Firstly, an overview is given about the treatment processes able to degrade CEC. In particular, the photocatalysts supported in ceramic materials are analyzed, namely the immobilization techniques applied to support TiO2 in these materials. Finally, a critical review of the literature dedicated to photocatalysis with supported TiO2 is presented, where the performance of the catalyst is considered as well as the main drivers and barriers for implementing this process. A focal point in the future is to investigate the possibility of depurating effluents and promote water reuse in safe conditions, and the supported TiO2 in ceramic materials may play a role in this scope.

This work aims to evaluate the microbiological contamination of sewage sludge (SS) collected in urban wastewater treatment plants (WWTP) from Portugal. Two types of SS were considered: urban mixed (UM) and from anaerobic digestion (AD). The two types of samples were characterized in relation to the main physical and chemical parameters, as well as the microbiological contamination (Escherichia coli and Salmonella spp). Then, sanitation tests were conducted through thermal drying and chemical treatments. Towards a circular economy, industrial alkaline wastes (green liquor dregs - GLD, lime mud, coal fly ash, eggshell) were tested as alternatives to lime. Only six out of nineteen samples complied with the legal limits for both microorganisms. However, drying at 130 °C sanitized selected samples below the E. coli limit, regardless of the initial moisture or contamination. Additionally, CaO (obtained from eggshell) led to the complete elimination of E. coli at any dosage studied (0.05−0.15 g/g SSwet basis). GLD evidenced the ability to reduce E. coli contamination at room temperature, but not enough to comply with the legal limit. In general, this work highlights the need to sanitize the SS before its application to the soil, and the positive role of some wastes on this goal.

Kraft pulp mills produce the main raw material for paper, while several waste products are generated in large quantities in the process. This review study addresses four of the main inorganic wastes formed by this industry, namely green liquor dregs (GLD), slaker grits (SG), lime mud (LM) and boiler fly ash (BFA), which are still mostly discarded in landfills. A brief overview of a typical industrial process was included to outline the waste generation points. The main chemical and physical properties are indicated for highlighting the most relevant characteristics to determine which applications may be considered in each case. An in-depth literature review allowed the identification of the main applications that have been tested mainly at the laboratory scale and some at an industrial scale. The applications are grouped into construction materials, geotechnical, environmental, agricultural and others. This assessment shows that the circular economy and the sustainable development goals of the UN are important issues for organizations in general, and the pulp mill in particular. In fact, this industry has managed to close the chemicals loops, recover energy and reduce water consumption in the process. However, the current situation of inorganic waste can still be improved if industrial applications are developed to avoid landfill.