End-of-life tyre conversion to energy: A review on pyrolysis and activated carbon production processes and their challenges

A comprehensive evaluation of the environmental and health risks associated with the potential utilization of chars produced from tires, electro-waste plastics and biomass

A variety of waste materials are currently being processed using pyrolysis with the objective of valorization, transformation, and conversion into valuable raw materials that can be further utilized. In this work, three different types of char produced from pine sawdust, waste tires and waste from the flat panel display fraction of electrical and electronic equipment were studied. For selection of suitable application, it is necessary to characterize them. The majority of studies focus only on the analysis of the composition and properties of the resulting chars. Nevertheless, the most prevalent utilization of char is in the environment as a soil amendment or adsorbent for the removal of pollutants from water, soil, and air. For this reason, this work incorporated a comprehensive characterization, including an ecotoxicological assessment of the environmental impacts and health risks during their handling/storage. Based on the obtained results and the legislation, a suitable and safe application of the chars was recommended. As presumed, the tested char samples varied in their composition and properties. Biochar from pine sawdust possessed suitable surface properties to be used as a potentially effective adsorbent for water treatment. However, it demonstrated increased ecotoxicity against aquatic organisms, prompting its recommendation for soil application. Waste tires char can be safely used only as an absorbent for air purification due to its high ecotoxicity for aquatic organisms and high PAHs concentration, which disables its soil application. It is inadvisable to utilize char produced from electro-waste plastics in the environment due to its toxic composition, high volatile organic compounds and PAHs content and ecotoxicity. This study confirmed the importance and necessity of using multiple ecotoxicological tests involving different groups of organisms in the characterization of chars (also biochar) to exclude potential negative impacts of their further application.

High-Performance Concrete from Rubber and Shell Waste Materials: Experimental and Computational Analysis

Waste and its environmental impact have driven the search for sustainable solutions across various industries, including construction. This study explores the incorporation of solid waste in the production of eco-friendly structural concrete, aiming to reduce pollution and promote ecological and sustainable construction practices. In this context, two types of eco-friendly concrete were produced using marine shells and recycled rubber as waste materials and compared with conventional concrete through experimental and computational approaches. The results demonstrated that the concrete with marine shells achieved a compressive strength of 32.4 MPa, 26.5% higher than conventional concrete, and a 1% reduction in weight. In contrast, the recycled rubber concrete exhibited a compressive strength of 22.5 MPa, with a 2 MPa decrease compared to conventional concrete, but a 4.3% reduction in density. Computational analysis revealed that porosity affects Young's modulus, directly resulting in a reduction in the maximum achievable strength. This work demonstrates that it is feasible to produce eco-friendly structural concrete through the proper integration of industrial waste, contributing to decarbonization and waste valorization.

Synthesis of Solketal Catalyzed by Acid-Modified Pyrolytic Carbon Black from Waste Tires

Solketal, a widely used glycerol-derived solvent, can be efficiently synthesized through heterogeneous catalysis, thus avoiding the significant product losses typically encountered with aqueous work-up in homogeneous catalysis. This study explores the catalytic synthesis of solketal using solid acid catalysts derived from recovered carbon blacks (rCBs), which are obtained through the pyrolysis of end-of-life tires. This was further converted into solid acid catalysts through the introduction of acidic functional groups using concentrated H2SO4 or 4-benzenediazonium sulfonate (BDS) as sulfonating agents. Additionally, post-pyrolytic rCB treated with glucose and subsequently sulfonated with sulfuric acid was also prepared. Comprehensive characterization of the initial and modified rCBs was performed using techniques such as elemental analysis, powder X-ray diffraction, thermogravimetric analysis, a back titration method, and both scanning and transmission electron microscopy, along with X-ray photoelectron spectroscopy. The catalytic performance of these samples was evaluated through the batch mode glycerol acetalization to produce solketal. The modified rCBs exhibited substantial catalytic activity, achieving high glycerol conversions (approximately 90%) and high solketal selectivity (around 95%) within 30 min at 40 °C. This notable activity was attributed to the presence of -SO3H groups on the surface of the functionalized rCBs. Reusability tests indicated that only rCBs modified with glucose demonstrated acceptable catalytic stability in subsequent acetalization cycles. The findings underscore the potential of utilizing end-of-life tires to produce effective acid catalysts for glycerol valorization processes.

KOH-treated tire pyrolyzed carbon as green and easily available adsorbent for Bisphenol A and Methylene blue adsorption

The occurrence of micropollutants and dyes in water sources has sparked alarm due to their significant impacts on aquatic ecosystems and human health. This study aims to utilize the tire pyrolyzed carbon (TPC) as a source of the adsorbent for removing Bisphenol A (BPA) and Methylene Blue (MB). The adsorbent was synthesized by chemical activation of TPC with KOH at 750 °C. The activated TPC was characterized for different physical and chemical characterization techniques such as XRD, FTIR, SEM, BET, XPS, and TPD and exhibits a higher adsorption capacity of 49.2 and 72.1 mg/g respectively for BPA and MB. The effect of initial concentration, dosage of adsorbent, and initial pH are evaluated for BPA and MB. The adsorption is mainly driven by hydrophobic, electrostatic, π-π interactions, and hydrogen bonding. The removal process follows the second order and Langmuir isotherms. The adsorbent shows excellent recyclability which makes it a potential source of removal of different water-borne pollutants. The production of activated carbon from tire waste is advocated for its economic and environmental benefits.

Municipal solid waste management challenges in developing regions: A comprehensive review and future perspectives for Asia and Africa

The rapid urbanization witnessed in developing countries in Asia and Africa has led to a substantial increase in municipal solid waste (MSW) generation. However, the corresponding disposal strategies, along with constraints in land resources and finances, compounded by unorganized public behaviour, have resulted in ineffective policy implementation and monitoring. This lack of systematic and targeted orientation, combined with blind mapping, has led to inefficient development in many areas. This review examines the key challenges of MSW management in developing countries in Asia and Africa from 2013 to 2023, drawing insights from 170 academic papers. Rather than solely focusing on recycling, the study proposes waste sorting at the source, optimization of landfill practices, thermal treatment measures, and strategies to capitalize on the value of waste as more pertinent solutions aligned with local realities. Barriers to optimizing management systems arise from socio-economic factors, infrastructural limitations, and cultural considerations. The review emphasizes the importance of integrating the study area into the circular economy framework, with a focus on enhancing citizen participation in solid waste reduction and promoting recycling initiatives, along with seeking economic assistance from international organizations.

Waste rubber - Black pollution reframed as a global issue: Ecological challenges and sustainability initiatives

In contrast to "white pollution" originating from waste plastics, waste rubber is often referred to as "black pollution." The quantity and variety of waste rubber are increasing at an alarming rate, with a considerable fraction entering the global ecosystem via various pathways. This study presents the first critical review of waste rubber research with a focus on the risks associated with toxicant discharge and existing problems in waste rubber disposal, management, and recycling practices. We aim to obtain a comprehensive understanding of current research, particularly regarding the ecological impacts of these wastes, highlight major gaps, and propose the most significant research directions. A total of 192 studies published in journals were critically analysed. The importance of conducting long-term and large-scale experiments and developing efficient waste rubber recycling systems is also emphasised. This study highlights the need to address the challenges posed by waste rubber pollution and offers insights and references for undertaking ecological risk assessments and understanding the mechanisms underlying toxicant behaviour. Suggestions and countermeasures are proposed with ecosystem sustainability as the ultimate goal. Further long-term, comprehensive, and systematic research in this area is required.

Adsorption performance of mineral-carbon adsorbents derived from coal gasification fine ash: Prepared via low-temperature alkali fusion method

To address the solid waste challenges associated with coal gasification fine ash, this study conducted a low-temperature alkali fusion de-ashing treatment to transform coal gasification fine ash into mineral-carbon adsorbent. The preparation process was simplified without grinding, carbonization and high-temperature (500-800 °C) activation treatment. The results demonstrate a positive linear correlation between the ash removal rate of the samples (measured during the preparation process, i.e., low-temperature alkaline fusion treatment of coal gasification fine ash) and their maximum equilibrium adsorption capacity for methylene blue. For the samples with an ash removal rate of 95.71 %, which exhibit a maximum adsorption capacity of 161.36 mg/g for methylene blue. The adsorption behavior of methylene blue on mineral-carbon adsorbent was a monolayer adsorption on the surface of homogeneous medium, involving both physical and chemical adsorption. The main adsorb rate-controlling steps for the samples with ash removal rates of 27.91-59.33 % and 95.71 % were the intra particle diffusion process and the liquid film diffusion process, respectively. The adsorption mechanism of methylene blue on the surface of mineral-carbon adsorbent involved electrostatic attraction and hydrogen bonding. The aforementioned results demonstrated the potential of coal gasification fine ash as an adsorbent material, providing new options for promoting the resource utilization and high-value applications of coal gasification fine ash.