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Recycling
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Biomass Revival: Rethinking Waste Recycling for a Greener Future
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Biomass Revival: Rethinking Waste Recycling for a Greener Future

A special issue of Recycling (ISSN 2313-4321).

Deadline for manuscript submissions: 1 October 2025 | Viewed by 3459

Special Issue Editor

Dr. Salustiano Mato De La Iglesia

E-Mail Website
Guest Editor
Environmental Biology Group, Universidade de Vigo, 36310 Vigo, Spain
Interests: waste management; biodiversity; emergent contaminant; waste valorization; ecotoxicology
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

It is increasingly important in today’s world to optimize the use of our precious resources. We live on a planet with limited resources and an ever-increasing population, so it is essential to ensure the future of the upcoming generations by developing our production processes around the concept of a circular economy. A fundamental aspect of this is to give new life to residual biomass. Therefore, rethinking the recycling of such waste is the main idea behind this Special Issue. We invite you to make original scientific contributions that address new paths for the recycling of organic waste derived from all types of industrial, agricultural, livestock, and forestry activities. By considering the conversion of this waste into new products or by-products and it management to obtain final metabolites, we can give it a second life in a sustainable and environmentally responsible way. Of special interest are studies and reviews that link the processes that will allow us to establish a complete cycle of production waste management with the goal of a zero-waste future.

Dr. Salustiano Mato De La Iglesia
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Recycling is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • biomass
  • recycling
  • waste
  • circular economy

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Published Papers (7 papers)

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Research

18 pages, 1340 KiB  
Article
Efficiency Determination of Water Lily (Eichhornia crassipes) Fiber Delignification by Electrohydrolysis Using Different Electrolytes
by R. Sanchez-Torres, E. Onofre Bustamante, T. Pérez López and A. C. Espindola-Flores
Recycling 2025, 10(4), 130; https://doi.org/10.3390/recycling10040130 (registering DOI) - 1 Jul 2025
Abstract
Nowadays, biomass use has increased due to it being the most abundant raw material on the planet, and treating it is a difficult task, as a result of the number of existing methods and the applications’ diversification. This research work shows the results [...] Read more.
Nowadays, biomass use has increased due to it being the most abundant raw material on the planet, and treating it is a difficult task, as a result of the number of existing methods and the applications’ diversification. This research work shows the results obtained using different delignification methods (physical and chemical) on water lily ((Eichhornia crassipes) fiber lignocellulosic biomass including a seldom exploited method, known as “electrohydrolysis” in order to determinate the removal efficiency of lignin and hemicellulose. The characterization of the physicochemical and morphological properties of the water lily (Eichhornia crassipes) fiber before and after the pretreatments were applied were by means of Fourier Transform Infrared (FT-IR), X-ray diffraction (XRD) and optical microscopy (OM). The results of FT-IR show a significant decrease in the bands associated with lignin and hemicellulose. By XRD, it was determined that the crystallinity of the cellulose increased by 60% for the treated samples with respect to the reference, and an increase in the surface roughness of the samples was observed by OM. In conclusion, it was determined that electrochemistry delignification is an efficient, environmentally friendly methodology to remove the soluble sugars, opening the possibility to use the water lily (Eichhornia crassipes) fiber to produce a green concrete. Full article
(This article belongs to the Special Issue Biomass Revival: Rethinking Waste Recycling for a Greener Future)
15 pages, 1564 KiB  
Article
Organic Waste and Wastewater Sludge to Volatile Fatty Acids and Biomethane: A Semi-Continuous Biorefinery Approach
by Paolo S. Calabrò, Domenica Pangallo, Mariastella Ferreri, Altea Pedullà and Demetrio A. Zema
Recycling 2025, 10(4), 125; https://doi.org/10.3390/recycling10040125 - 21 Jun 2025
Viewed by 270
Abstract
Volatile fatty acids (VFA) are valuable intermediates with growing demand in chemical, pharmaceutical, and environmental applications. Their sustainable production from organic waste is increasingly explored in the context of circular economy and biorefinery models. This study investigates the co-fermentation of waste-activated sludge (WAS) [...] Read more.
Volatile fatty acids (VFA) are valuable intermediates with growing demand in chemical, pharmaceutical, and environmental applications. Their sustainable production from organic waste is increasingly explored in the context of circular economy and biorefinery models. This study investigates the co-fermentation of waste-activated sludge (WAS) and the organic fraction of municipal solid waste (OFMSW) as a strategy for integrated VFA and biogas production. Semi-continuous experiments were carried out to assess the effect of the substrates ratio (WAS:OFMSW = 90:10 and 30:70), hydraulic retention time (HRT), and pH control (5, 9, no control) on VFA yield and composition. Results showed that higher OFMSW content and alkaline conditions favoured VFA production, with a maximum yield of 144.9 mgHAc·gVS−1 at pH 9 and 70:30 ratio. Acetate dominated, while butyrate production peaked at 114.1 mgHBu·gVS−1 under high sludge conditions. However, the addition of alkali required for pH control may lead to excessive accumulation of alkaline-earth metal ions, which can disrupt biological processes due to their potential toxicity. Anaerobic digestion of fermentation residues enhanced biomethane yields significantly (0.27 NL·gVS−1 vs. 0.05 NL·gVS−1 from raw sludge). The proposed process demonstrates potential for converting wastewater treatment plants into biorefineries, maximising resource recovery while reducing environmental impact. Full article
(This article belongs to the Special Issue Biomass Revival: Rethinking Waste Recycling for a Greener Future)
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17 pages, 1472 KiB  
Article
Valorization of Underused Biomass of Acacia dealbata and Acacia melanoxylon Through Vermicomposting as an Alternative Substrate for Cucumber Production
by Maria C. Morais, Elisabete Nascimento-Gonçalves, Tiago Azevedo, Henda Lopes, Helena Ferreira, Ana M. Coimbra, Berta Gonçalves, João R. Sousa, Marta Roboredo and Paula A. Oliveira
Recycling 2025, 10(3), 120; https://doi.org/10.3390/recycling10030120 - 17 Jun 2025
Viewed by 221
Abstract
Invasive alien species are one of the main threats to global biodiversity, and pose significant management challenges in several areas outside their natural range. In southern Mediterranean Europe, the invasion of Acacia species is particularly severe and its control requires costly and often [...] Read more.
Invasive alien species are one of the main threats to global biodiversity, and pose significant management challenges in several areas outside their natural range. In southern Mediterranean Europe, the invasion of Acacia species is particularly severe and its control requires costly and often ineffective actions. The use of vermicompost derived from these species to replace peat-based substrates in horticulture offers a promising alternative to mitigate their economic and environmental impacts while enhancing the sustainability of their control. This study explored the potential of vermicompost produced from the fresh aboveground waste biomass (leaves + stems + flowers) of Acacia dealbata and Acacia melanoxylon (75:25 w/w), two of the most aggressive Acacia species in the Mediterranean, using Eisenia fetida over twelve weeks. In essence, this study aimed to evaluate the quality of the produced vermicompost and its suitability as a partial substitute for potting substrate in the production of cucumber (Cucumis sativus) seedlings for transplant. Four substrate mixtures containing 0%, 10%, 30%, and 50% of Acacia vermicompost (w/w), combined with commercial peat-based potting substrate and perlite (20%) were tested in polystyrene seedling trays. Seedling emergence, growth, and leaf biochemical parameters (photosynthetic pigments, phenolics, soluble sugars and starch, and total thiobarbituric acid-reactive substances—TBARSs) were evaluated. The results showed that the addition of Acacia vermicompost to the commercial substrate did not affect its germination but significantly enhanced seedling growth, particularly in mixtures containing 30% and 50% Acacia vermicompost. In addition, the absence of accumulation of TBARSs also reflected the superiority of these two treatments. These findings suggest that vermicompost derived from A. dealbata and A. melanoxylon biomass can be a viable peat-based substrate alternative for horticultural production, with the dual benefit of promoting sustainable agricultural practices and contributing to invasive species management. Full article
(This article belongs to the Special Issue Biomass Revival: Rethinking Waste Recycling for a Greener Future)
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15 pages, 4184 KiB  
Article
Characterization of Cellulose and Starch Degradation by Extracellular Enzymes in Frankia Strains
by Medhat Rehan and Ahmed Alzoheiry
Recycling 2025, 10(3), 114; https://doi.org/10.3390/recycling10030114 - 7 Jun 2025
Viewed by 933
Abstract
Annually, a considerable amount of agricultural waste is produced leading to serious environmental pollution if not managed effectively. A wide range of bio-decomposers, including fungi, bacteria, and actinomycetes may break down the complex agro-residues in an eco-friendly way through secreting many cellulolytic and [...] Read more.
Annually, a considerable amount of agricultural waste is produced leading to serious environmental pollution if not managed effectively. A wide range of bio-decomposers, including fungi, bacteria, and actinomycetes may break down the complex agro-residues in an eco-friendly way through secreting many cellulolytic and amylolytic enzymes. The present study aimed at exploring the ability of Frankia to degrade cellulose and starch and identifying the cellulase and α-amylase genes in Frankia genomes for potential agricultural waste degradation. Frankia alni ACN14a and Frankia casuarinae CcI3 produced clear zones around growing hyphae on carboxymethyl cellulose (CMC) and starch substrates. The hydrolytic index (HI) ranged from 1 to 2.14 reflecting variation in their degradation efficacy. Quantification of CMCase (carboxymethyl cellulase) production in strain ACN14a presented the maximum activity (0.504 U/mL) under 1% CMC after 16 days whereas strain CcI3 produced a weak activity after 6 days from incubation. Besides, amylase activity in strain ACN14a reached the highest value (3.215 U/mL) after 4 days of growing with 1% starch, while strain CcI3 had the superior production (3.04 U/mL) after 12 days from 1% starch condition. Data mining and genome blasting led to the identification of multiple genes related to cellulose and starch degradation. Two endoglucanases (celA1, FRAAL4955 and celA2, FRAAL4956), two glycosyl hydrolase family 16 (FRAAL6120 and FRAAL2663), and one glycosyl hydrolase family 16 (Francci3_3843) were predicted in the two genomes. Likewise, the α-amylase genes (FRAAL5900) from Frankia alni ACN14a and (Francci3_3679) from strain CcI3 were identified. The gene expression of endo-1, 4-beta-glucanase (celA2, FRAAL4956) revealed the maximum increment in its mRNA abundance under 0.25% CMC exposure and showed a 3.3-fold increase. Frankia capability to degrade cellulose and starch represents a critical process in nutrient cycling and environment protection. Full article
(This article belongs to the Special Issue Biomass Revival: Rethinking Waste Recycling for a Greener Future)
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18 pages, 4764 KiB  
Article
Hydrothermal Carbonization of Biomass Waste for Solid Biofuel Production: Hydrochar Characterization and Its Application in Blast Furnace Injection
by Guangwei Wang, Junyi Wu, Haibo Li, Andrey Karasev, Xiaojun Ning and Chuan Wang
Recycling 2025, 10(3), 89; https://doi.org/10.3390/recycling10030089 - 4 May 2025
Viewed by 634
Abstract
Hydrothermal carbonization (HTC) technology converts biomass into a carbon-rich, oxygen-containing solid fuel. Most studies have focused on hydrochar produced under laboratory conditions, leaving a gap in understanding the performance of industrially produced hydrochar. This study comprehensively analyzes three types of industrially produced hydrochar [...] Read more.
Hydrothermal carbonization (HTC) technology converts biomass into a carbon-rich, oxygen-containing solid fuel. Most studies have focused on hydrochar produced under laboratory conditions, leaving a gap in understanding the performance of industrially produced hydrochar. This study comprehensively analyzes three types of industrially produced hydrochar for blast furnace (BF) injection. The results indicate that hydrochar has a higher volatile and lower fixed carbon content. It has a lower high heating value (HHV) than coal and contains more alkali matter. Nevertheless, hydrochar exhibits a better grindability and combustion performance than coal. Blending hydrochar with anthracite significantly enhances the combustion reactivity of the mixture. The theoretical conversion rate calculations reveal a synergistic effect between hydrochar and anthracite during co-combustion. Environmental benefit calculations show that replacing 40% of bituminous coal with hydrochar can reduce CO2 emissions by approximately 145 kg/tHM, which is equivalent to an annual reduction of 528 kton of CO2 and 208 kton of coal in BF operations. While industrially produced hydrochar meets BF injection requirements, its low ignition point and high explosivity necessitate the careful control of the blending ratio. Full article
(This article belongs to the Special Issue Biomass Revival: Rethinking Waste Recycling for a Greener Future)
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17 pages, 5103 KiB  
Article
Bioeconomy in Textile Industry: Industrial Residues Valorization Toward Textile Functionalization
by Ana M. Fernandes, Ana Isabel Pinheiro, Catarina Rodrigues and Carla J. Silva
Recycling 2025, 10(2), 78; https://doi.org/10.3390/recycling10020078 - 16 Apr 2025
Viewed by 611
Abstract
Industrial residues are sources of functional biopolymers with interesting properties for textile applications. This study aims to evaluate the impact of enzymatic pre-treatment on oil yield and phenolic compounds’ content in an aqueous extraction process, as well as the functional properties incorporated into [...] Read more.
Industrial residues are sources of functional biopolymers with interesting properties for textile applications. This study aims to evaluate the impact of enzymatic pre-treatment on oil yield and phenolic compounds’ content in an aqueous extraction process, as well as the functional properties incorporated into textiles. This research investigated the influence of residue granulometry, biomass percentage, and the application of enzymatic pre-treatment with different enzymes (cellulase, pectinase, xylanase) individually or in combination. Chestnut hedgehog (CH), tobacco plant stems (TPSs), vine shoot trimmings (VSTs), and beer spent grain (BSG) were explored. For textile functionalization, the extracted oils were incorporated into a bio-based formulation and applied on cotton fabric through pad-dry-cure. For CH, the pre-treatment with cellulase and xylanase achieved an oil yield of 149 and 148 mg oil/mL extract, respectively. With the combination of both enzymes, the richest oil in phenolic compounds was extracted: 1967.73 ± 16.86 mg GAE/g biomass. CH and TPS oils presented an antioxidant activity above 60%, and the functionalized textiles also showed the highest antioxidant potential and a UPF of 30. The textiles presented water repellence and washing fastness. This study demonstrates a sustainable oil extraction method and its potential application in the development of functional textiles. Full article
(This article belongs to the Special Issue Biomass Revival: Rethinking Waste Recycling for a Greener Future)
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16 pages, 11180 KiB  
Article
Packed-Bed Pyrolysis of Alkali Lignin for Value-Added Products
by Carmen Branca and Colomba Di Blasi
Recycling 2025, 10(2), 66; https://doi.org/10.3390/recycling10020066 - 9 Apr 2025
Viewed by 415
Abstract
Lignin is the largest renewable source of aromatic biopolymers on Earth, and it is commercially available as by-product of biorefineries and pulp/paper industries. It is mainly burned for heat and power, but pyrolysis can provide high-value-added products. In this study, the pyrolysis characteristics [...] Read more.
Lignin is the largest renewable source of aromatic biopolymers on Earth, and it is commercially available as by-product of biorefineries and pulp/paper industries. It is mainly burned for heat and power, but pyrolysis can provide high-value-added products. In this study, the pyrolysis characteristics of alkali lignin pellets are investigated using a packed-bed reactor at a laboratory scale for heating temperatures of 800–900 K. Conversion dynamics are analyzed by means of the thermal field and the rates of gaseous species release, which is a very innovative aspect of the study. The yields of the lumped product classes do not vary significantly in the range of heating temperatures examined (biochar yields around 58–63 wt%, together with gas and liquid yields around 9–12 and 28–30 wt%, respectively). Carbon dioxide is the most abundant gaseous product, followed by methane and carbon monoxide (smaller amounts of C2 hydrocarbons and hydrogen), while bio-oil is rich in phenolic compounds, especially guaiacols, cresols, and phenol. A comparison with the conversion dynamics of fir, beech, and straw reveals that, mainly as a consequence of softening and melting, the lignin heat- and mass-transfer rates as well as actual reaction temperatures are profoundly different. In fact, the characteristic process size becomes the diameter of the reactor rather than that of the pellets. Full article
(This article belongs to the Special Issue Biomass Revival: Rethinking Waste Recycling for a Greener Future)
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