Waste

Lignocellulosic biomass, including agricultural, forestry, and energy crop waste, is one of Earth’s most abundant renewable resources, accounting for approximately 50% of global renewable resources. It contains cellulose, hemicellulose, and lignin, making it crucial for biofuels and bio-based chemicals. Due to its complex structure, single-pretreatment methods are inefficient, leading to the development of combined pretreatment technologies. These methods enhance cellulose accessibility and conversion efficiency. This paper analyzes the principles, advantages, and disadvantages of various combined pretreatment methods and their practical benefits. It highlights recent research achievements and applications in biofuel, biochemical production, and feed. By integrating multiple pretreatment methods, biomass degradation efficiency can be significantly improved, energy consumption reduced, and chemical reagent use minimized. Future advancements in combined physical, chemical, and biological pretreatment technologies will further enhance biomass utilization efficiency, reduce energy consumption, and protect the environment, providing robust support for sustainable renewable energy development and ecological protection. Full article

This study examines recovery efforts at Gran Tarajal Harbor following a significant oil spill, employing a combination of innovative technologies tailored to enhance oil spill remediation. Cleanup operations incorporated advanced absorbent sponges with high reusability, absorbent granulates for targeted hydrocarbon capture, bioremediation techniques using allochthonous microorganisms to accelerate natural degradation processes, and the integration of newly designed oil containment barriers coupled with sponges. These technologies were instrumental in effectively mitigating environmental damage, as evidenced by a reduction in hydrocarbon concentrations in sediments from nearly 60,000 mg/kg to under 1600 mg/kg within seven months. Notably, advanced absorbent sponges demonstrated superior capacity for repeated use, optimizing the cleanup process and contributing to the sustainability of the response efforts. The most important finding of this research is the demonstrated efficacy of integrated approach in not only reducing hydrocarbon contamination but also in promoting ecological recovery. Heavy metal analyses revealed that lead and copper concentrations were primarily associated with routine port activities, while mercury levels, attributed to the spill, decreased significantly over time. Tissue analysis of local organisms showed minimal contamination, and assessments of biological communities indicated signs of ecological recovery. This work highlights the necessity of introduce new disruptive technologies in contingency plans. Full article

An investigation has been carried out to understand the solution chemistry of the Cu-NH⁻-SO₄⁻² system, focusing on the effect of pH on the solubility of copper in the solution and maximizing the Cu(I):Cu(II) ratio. A Pourbaix diagram for the Cu-N-S system has also been created using the HSC Chemistry software for a wide range of Cu-NH₃ species, unlike most other studies that focused only on Cu(NH₃)₄²⁺ and Cu(NH₃)₅²⁺ (Cu(II)) as the dominant species. The Pourbaix diagram demonstrated that the Cu(I) exists as Cu(NH₃)₂⁺, while the Cu(II) species are present in the system as Cu(NH₃)₄²⁺ and Cu(NH₃)₅²⁺, depending upon the Eh and pH of the solution. Copper precipitation was observed in the electrolyte at pH values less than 8.0, and the precipitation behavior increased as the pH became acidic. The highest Cu(I):Cu(II) ratio was observed at higher pH values of 10.05 due to the higher solubility of copper at higher alkaline pH. The maximum Cu(II) concentration can be achieved at 4.0 M NH₄OH and 0.76 M (NH₄)₂SO₄. In the case of low pH, the highest Cu(I):Cu(II) ratio obtained was 0.91 against the 4.0 M and 0.25 M concentrations of NH₄OH and (NH₄)₂SO₄, respectively. Meanwhile, at high pH, the maximum Cu(I):Cu(II) ratio was 15.11 against the 0.25 M (NH₄)₂SO₄ and 4.0 M NH₄OH. Furthermore, the low pH experiments showed the equilibrium constant (K) K < 1, and the high pH experiments demonstrated K > 1, which justified the lower and higher copper concentrations in the solution, respectively. Full article

Pyrus communis (P. communis) is the most cultivated and consumed species of pear within the European continent. This fruit has been a staple in Greece since ancient times, hence the name “Gift of the Gods”. Given the extensive utilization of this fruit in the industrial sector and the focus on the exploitation of by-products to create new food and beverage products, the present research aimed to enhance the antioxidant activity of the P. communis peel through the implementation of a multifactor extraction system. Increased total polyphenols and ascorbic acid concentration, and enhanced antioxidant activity through radical scavenging and Fe³⁺ to Fe²⁺ reduction, all assist in boosting the health benefits of the extracts. The results indicated that the best conditions for compound yields were a 75% v/v hydroethanolic concentration, an extraction temperature of 80 °C, and 30 min of extraction time. Under the optimal conditions, the total polyphenol content was up to 4.98 mg of gallic acid equivalents (GAE)/g dried weight (dw). The radical scavenging activity by the 2,2-diphenyl-1-picrylhydrazyl (DPPH^•) method was expressed as 18.36 μmol ascorbic acid equivalents (AAE)/g dw, while by the ferric-reducing antioxidant power (FRAP) method, it was 35.09 μmol AAE/g dw. Finally, the amount of ascorbic acid was measured at 20.16 mg/100 g dw. In this regard, this study has been conducted to assess and enhance the level of these bioactive compounds in the extract of the P. communis peel, leading to an extract with several applications in different food and beverage industries. Full article

Electrolytic Manganese Residue (EMR) is a secondary material generated during the process of manganese production, poses significant environmental challenges, including land consumption and contamination threats to soil and water bodies due to its heavy metal content, soluble manganese, ammonia nitrogen, and disposal issues. This review thoroughly examines EMR, emphasizing its metallurgical principles, environmental impacts, and sustainable treatment methods. We critically analyze various approaches for EMR management, including resource recovery, utilization of construction materials, and advanced treatment techniques to mitigate its environmental challenges. Through an extensive review of recent EMR-related literature and case studies, we highlight innovative strategies for EMR valorization, such as the extraction of valuable metals, conversion into supplementary cementitious materials, and its application in environmental remediation. Our findings suggest that integrating metallurgical principles with environmental engineering practices can unlock EMR’s potential as a resource, contributing to the circular economy and reducing the environmental hazards associated with its disposal. This study aims to deepen the understanding of EMR’s comprehensive utilization, offering insights into future research directions and practical applications for achieving sustainable management of electrolytic manganese waste. Finally, we propose some recommendations to address the issue of EMR, intending to offer guidance for the proper disposal and effective exploitation of EMR. Full article

This study investigates the potential for recycling fishing rope waste from the Magdalen Islands, Canada, into sustainable wall cladding panels, addressing both environmental concerns and waste management challenges. A comprehensive characterization of the fishing ropes was conducted using various analytical techniques to assess their suitability for recycling. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) identified polyethylene (PE) and isotactic polypropylene (iPP) as the main polymers present in the ropes, with a composition of approximately 25% PE and 75% PP. The effects of photodegradation were evaluated through carbonyl index analysis, differential scanning calorimetry (DSC), tensile testing, and gel permeation chromatography (GPC). The results showed reduced crystallinity, a 20% decrease in tensile strength, and lower molecular weights due to environmental exposure in comparison with unused ropes. However, melt flow rate (MFR) measurements aligned with virgin HDPE and PP values used in rope manufacturing, indicating suitable processability for recycling. Panels produced from recycled fishing ropes exhibited lower flexural and impact properties compared to commercial alternatives due to the presence of mineral contaminants and voids in the panels as revealed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). This comprehensive investigation provides valuable insights into the potential repurposing of fishing rope waste, contributing to the development of sustainable waste management strategies for coastal communities. Full article

The development of efficient recovery methods for waste printed circuit boards (WPCBs) not only tackles the environmental risks of disposal but also promotes the conservation of resources within the electronics industry. This study proposes a two-step leaching approach for recovering metals from WPCBs. Initially, transition metals are leached using nitric acid, followed by the recovery of precious metals with thiourea in the second stage. In the first stage, dissolution rates exceeding 90 wt% were achieved for transition metals, including Cu, Fe, Ni, Pb, and Sn. In this stage, the dissolution of precious metals (i.e., Au and Pd) was insignificant. In the second stage, the effect of four parameters was investigated, including the impact of temperature, concentrations of ferric ions, sulfuric media, and thiourea on the recovery of Au and Pd. Precise control over sulfate concentration played a vital role in achieving maximum Au recovery. The optimal acid concentration was 0.2 M, resulting in a recovery rate of ~50 wt%. Ferric ion concentration positively affects Au recovery, whereas, in extracting Pd, optimal conditions imposed the absence of ferric ions. Thiourea concentration positively impacted Au and Pd recovery rates, peaking at 49 wt% for Au at 1 M and 44 wt% for Pd at 1.5 M. Prolonged leaching resulted in declining Au recovery rates, indicating a decrease in reagent concentration. Temperature variation yielded similar outcomes, with 50 °C resulting in peak recovery rates of 53 wt% for Au and 54 wt% for Pd. Metal dissolution kinetics during leaching were analyzed using pseudo-first-order and pseudo-second-order models. The second-order model proved suitable for transition metals in the first stage, while only for Au and Pd in the second stage (with R² = 0.99). Full article

Indigenous knowledge systems related to solid waste management in economically marginalized communities have been largely overlooked in the scientific literature, even though the indigenous communities of developing nations struggling to manage solid waste rely on these practices. It is startling that indigenous solid waste management practices are scarcely documented in the scientific literature despite their position as potential alternative disposal methods. This gap persists amid limited municipal budgets, inadequate waste collection services, and poor infrastructure in economically marginalized indigenous rural communities in developing nations. Subsequently, in the discipline of solid waste management, this obstacle impedes the recognition and inclusion of indigenous waste management practices into integrated waste management plans. As a result, this causes a delay in their progress or elevation to the same level of credibility as mainstream scientific knowledge. In the process, this relegates the waste management practices of indigenous communities to the background. Against this background, the current study sought to investigate the indigenous solid waste management practices of rural communities in Bushbuckridge Local Municipality. As such, ten cases that captured the spatial cultural diversity of indigenous communities’ practices across Bushbuckridge Local Municipality (BLM) were selected for sampling. Data were collected using ethnographic research methods. Data analysis was carried out using the thematic analysis approach. Inductive logic was used in the interpretation of the current study results. The results of the current study indicate that indigenous communities of Bushbuckridge Local Municipality, in the absence of formal waste management services from the local authority, resort to an indigenous knowledge system to manage solid waste. Waste burning (100%), open-air dumping (100%), and backyard pits (90%) are some of the indigenous waste management practices espoused by the rural communities of BLM. The similarity in practices was corroborated by statistical inferences that revealed that between BLM communities, the amount of indigenous waste management practices is not significant (p > 0.05). However, there are concerns that despite the sustainability aspect associated with recycling (<25%) practices, these disposal methods are not common in the rural communities of BLM. This is a setback for an indigenous knowledge system that is supposed to advance environmental sustainability practices. Full article

(1) The enactment of Sub-Decree No. 113/2015 on Solid Waste Management marked a significant policy shift towards the decentralisation of waste management in Cambodia and some progress has been observed in Phnom Penh and some other large cities and tourist destinations. However, information in rural areas is lacking. Rapid and simple waste assessment methodologies are needed in rural areas where waste data is scarce and different waste management measures are required compared to urban areas. This study aimed to fill the information gap on the status and fate of municipal solid waste management in rural areas by focusing on three underrepresented cities in different geographical areas through empirical studies. (2) Rapid waste assessments, including waste composition analysis, truck scaling, waste recovery surveys, waste flow analysis, and waste hotspot surveys, were conducted. (3) The per capita waste generation averaged 0.44 kg/day, which is lower than the national average, but did not show significant differences between income levels. The waste composition was similar to that of urban areas, with plastics making up more than 20% of the waste. There were major contrasts in the waste collection rates, with one city having a high rate (85.9%) while the other two cities were as low as 22.6% and 24.2%, respectively. This suggests that rural cities in Cambodia are at different stages of transition in establishing their waste management systems after the decentralisation of waste management to municipalities. The main cause of the low waste collection rate was that private waste collectors were finding it difficult to collect service fees. In the absence of waste collection services, a total of 370 waste hotspots were identified outside of the waste collection areas, where littering and open burning of waste were common. (4) Addressing these challenges requires urgent development of sustainable financing mechanisms, enhanced institutional capacities, and implementation of targeted awareness-raising programmes. These measures are essential for providing basic waste collection and disposal services, as well as for curbing littering and open burning of waste in rural cities in Cambodia. Full article

This review aims to streamline the approach to assessing the most used valorization methods for fruit and vegetable waste (FVW) that are eco-friendly, cost-effective, and sustainable within a circular economy framework. Green processing technologies for the extraction of bioactive compounds from FVW, their applications, and the technico-economical assessment of FVW’ biorefinery to support circular economy are highlighted. Important value-added products generated by FVW include bioactive compounds, pectin, protein isolates, such as soy, natural pigments such as anthocyanins, quinones, carotenoids, betalains, and chlorophyll. At this time, the prospects of using FVW have increased in the food supplements, bioactive and edible food packaging, agriculture, energy, and water purification fields. The findings report that proper management of FVW not only minimizes their addition to landfills in the absence of composting, but also promotes the efficient utilization of resources for the development of innovative materials with a wide range of beneficial applications. Implementing the possible solutions described in this paper would not only reduce environmental impact, but also open up new economic opportunities through the valorization of FVW. Full article

Cyclones are employed in many waste treatment industries for the dust collection or abatement purposes. The prediction of the dust collection efficiency is crucial for the design and optimization of the cyclone. However, this is a difficult task because of the complex physical phenomena that influence the removal of particles. Aim of the paper is to present two new meta-models for the prediction of the collection efficiency curve of cyclone separators. A Backpropagation Neural Network (BPNN) and Support Vector Regression (SVR) models were developed using Python environment. These were trained with a set of experimental data taken from the literature. The prediction capabilities of the models were first assessed by comparing the estimated collection efficiency for several cyclones against the corresponding experimental data. Second, by comparing the collection efficiency curves predicted by the models and those obtained from classic models available in the literature for the cyclones included in the validation dataset. The BPNN demonstrated better predictive capability than the SVR, with an overall mean squared error of 0.007 compared to 0.015, respectively. Most important, a 40% to 90% accuracy improvement of the literature models predictions was achieved. Full article

The production of heterogeneous solid waste, such as municipal solid waste (MSW), construction and demolition waste (CDW), and industrial solid waste (ISW), has increased dramatically in recent decades, and its management is one of today’s biggest concerns. Using waste as a resource to produce value-added materials such as char is one of the most promising strategies for successful and sustainable waste management. Virtually any type of waste, through various thermochemical technologies, including torrefaction, pyrolysis, hydrothermal carbonization, and gasification, can produce char with potential material and energy applications. Pyrolysis is the most widespread technology, and there are more studies on producing and applying waste-derived char using this technology. The properties of waste-derived char seem to be influenced by the conversion technology and conditions, as well as by the composition of the source waste. A literature search indicated that the properties of waste-derived char are highly variable with the composition of the raw material, with carbon content in the range 8–77%, a higher heating value of 2.5–28.4 MJ/kg and a specific surface area of 0.7–12 m²/g. Depending on the properties of char derived from waste, there are greater or minor difficulties in applying it, with ash content, heavy metals, and polycyclic aromatic hydrocarbon (PAH) concentrations being some of its limiting properties. Therefore, this review attempts to compile relevant knowledge on the production of waste-derived char, focusing on heterogeneous solid waste, applied technologies, and practical application routes in the real world to create a supply chain, marketing, and use of waste-derived char. Some challenges and prospects for waste-derived char are also highlighted in this study. Full article

Recycled Concrete Aggregate (RCA) of the chemical and biological effects must be understood to avoid potential adverse impacts to the bay’s aquatic ecosystem. RCA application as a base material for oyster reefs did not adversely affect oyster spat growth and survival, or the surrounding environment. Evaluated RCA leaching for petroleum byproducts showed that RCA as a base material for oyster reefs did not leach any hydrocarbon chemicals, and no water extractable SVOC were detected. The research found potential RCA application to the Chesapeake Bay watershed as a bottom conditioning material for oyster aquaculture. Overall, the findings support the use of RCA for oyster aquaculture. Full article

This study concerns the optimization of an industrial recycling line; in other terms, this paper aims to find the optimal processing parameters that allow for a decrease in the loss of stress crack resistance (SCR) using a notched crack ligament stress (NCLS) test and an increase in the gain of the elongation at break, flexural modulus, and Izod impact strength of a polyethylene (PE) blend before and after recycling. The recycling line is composed mainly of a mono- and twin-screw extruder and a filtration system. Hence, the research question is as follows: How can we optimize the recycling process, without compromising the mechanical properties of recycled polyethylene (PE) blends? To answer the research question, Taguchi’s design of experiment and grey relational analysis (GRA) for multiobjective optimization was applied. Experiments were performed according to $L_{16}$ standard orthogonal array based on five process parameters: mono-screw design, screw speed of the mono- and twin-screw extruder, melt pump pressure, and filter mesh size. Based on grey relational analysis (GRA), the optimal setting of process parameters was identified, and a barrier screw and a higher screw speed for both extruders were allowed to have optimal mechanical properties. Furthermore, the analysis of variance (ANOVA) indicated that the mono-screw design and screw speed of the mono- and twin-screw extruder significantly impact the mechanical properties of recycled polyethylene (PE) blends. Full article

Statistics reveal that egg production has increased in recent decades. This growth suggests there is a global rise in available eggshell biomass due to the current underutilization of this bio-waste material. A number of different applications for waste eggshells (WEGs) are known, that include their use as an additive in human/animal food, soil amendment, cosmetics, catalyst, sorbent, and filler in polymer composites. In this article, worldwide egg production and leading countries are examined, in addition to a discussion of the various applications of eggshell biomass. Eggshells are a rich supplement of calcium carbonate; therefore, they can be added as a particulate filler to polymer composites. In turn, the addition of a lower-cost filler, such as eggshell or calcium carbonate, can reduce overall material fabrication costs. Polylactic acid (PLA) is currently a high-demand biopolymer, where the fabrication of PLA composites has gained increasing attention due to its eco-friendly properties. In this review, PLA composites that contain calcium carbonate or eggshells are emphasized, and the mechanical properties of the composites (e.g., tensile strength, flexural strength, tensile elastic modulus, flexural modulus, and elongation (%) at break) are investigated. The results from this review reveal that the addition of eggshell/calcium carbonate to PLA reduces the tensile and flexural strength of PLA composites, whereas an increase in the tensile and flexural modulus, and elongation (%) at break of composites are described herein. Full article

Printed circuit boards (PCBs) are the main components of e-waste. In order to reduce the negative impact of waste PCBs on human health and the environment, they must be properly disposed of. A new method is demonstrated for recycling waste PCBs. It is referred to as the high-temperature thermo-mechano-chemical gasification (TMCG) of PCBs by the detonation-born gasification agent (GA), which is a blend of H₂O and CO₂ heated to a temperature above 2000 °C. The GA is produced in a pulsed detonation gun (PDG) operating on a near-stoichiometric methane–oxygen mixture. The PDG operates in a pulsed mode producing pulsed supersonic jets of GA and pulsed shock waves possessing a huge destructive power. When the PDG is attached to a compact flow reactor filled with waste PCBs, the PCBs are subject to the intense thermo-mechano-chemical action of both strong shock waves and high-temperature supersonic jets of GA in powerful vortical structures established in the flow reactor. The shock waves grind waste PCBs into fine particles, which undergo repeated involvement and gasification in the high-temperature vortical structures of the GA. Demonstration experiments show full (above 98%) gasification of the 1 kg batch of organic matter in a setup operation time of less than 350 s. The gaseous products of PCB gasification are mainly composed of CO₂, CO, H₂, N₂, and CH₄, with the share of flammable gas components reaching about 45 vol%. The solid residues appear in the form of fine powder with visible metal inclusions of different sizes. All particles in the powder freed from the visible metal inclusions possess a size less than 300–400 μm, including a large fraction of sizes less than 100 μm. The powder contains Sn, Pb, Cu, Ni, Fe, In, Cd, Zn, Ca, Si, Al, Ti, Ni, and Cl. Among these substances, Sn (10–20 wt%), Pb (5–10 wt%), and Cu (up to 1.5 wt%) are detected in the maximum amounts. In the powder submitted for analysis, precious elements Ag, Au, and Pt are not detected. Some solid mass (about 20 wt% of the processed PCBs) is removed from the flow reactor with the escaping gas and is partly (about 10 wt%) trapped by the cyclones in the exhaust cleaning system. Metal inclusions of all visible sizes accumulate only in the flow reactor and are not detected in powder samples extracted from the cyclones. The gasification degree of the solid residues extracted from the cyclones ranges from 76 to 91 wt%, i.e., they are gasified only partly. This problem will be eliminated in future work. Full article

Concrete waste recycling processes involve multiple stages, equipment, and procedures which produce Fine Recycled Concrete Aggregates (FRCA) for use in construction. This research aims at performing a comprehensive overview of the recycling technologies, recycling processes, and normative requirements to produce high-quality FRCA and to investigate the influence of these processes on their physical properties. The properties investigated were the particle size distribution (PSD), water absorption, oven-dry density, and adhered paste. The correlations between these properties were also investigated. The results indicate that the recycling processes with the highest potential for producing high-quality aggregates demand jaw crusher and impact crusher combinations. These processes are better suited for achieving FRCA with the desired particle size distribution and oven-dry density. However, water absorption and adhered paste, which are critical factors for obtaining high-quality FRCA, seem to be more dependent on the original material than on the recycling process. Full article

Sugarcane bagasse (SCB) is a waste product from Mexico’s sugar industry that is generally burned or discarded. It contains around 48% cellulose, representing a significant source of this component from industrial waste. Eugenol is found in clove oil; it has been used for its medicinal and antimicrobial benefits in the food and pharmaceutical industries. This study aims to develop a filtering material using sugarcane bagasse (SCB) and encapsulated eugenol as an antimicrobial agent. The study involves extracting cellulose from SCB using alkaline hydrolysis with ultrasound, followed by forming composite materials encapsulated in alginate with eugenol concentrations from 0 to 1% v/v. These materials were characterized and tested for antimicrobial efficacy. The findings indicate that the cellulose–eugenol–alginate composite displays high eugenol encapsulation efficiency and effective short-term release. In well-diffusion assays, the material showed inhibition halos up to 20.47 mm against S. aureus, suggesting its potential as an eco-friendly alternative to traditional antimicrobial agents in filter materials. Full article

One of the largest issues facing countries, particularly emerging nations with high population, production, and consumption growth, is an inadequate waste management system (WMS). This paper analyzes the development of the waste management systems of nine capital cities in the Association of Southeast Asian Nations (ASEAN) region by using a recently developed approach, the Waste Management System–Development Stage Concept. This concept comprises five development stages and various components, including Collection and Transport, Waste Disposal, Energy Recovery, Waste Recycling, and Waste Prevention and Reuse. The findings indicate that in terms of waste collection, waste disposal, and energy recovery, Singapore is at a higher development stage (Stage 5) and is more advanced than other ASEAN cities. For most of the components, Bangkok, Jakarta, Kuala Lumpur, and Manila fall into stages 2 to 4, whereas the early development stages 1 to 3 are present in Bandar Seri Begawan, Hanoi, Phnom Penh, and Vientiane. The results will be used to determine the next steps in developing the WMSs, including the introduction of separate collection for recycling or the installation of a waste-to-energy plant. The environmental impact of each measure will be later assessed using the LCA approach, and the most effective measures shall be identified in future studies. Full article