ABSTRACT The growing concern over greenhouse gas emissions and climate change has led to substantial advancements in carbon capture and utilization (CCU) technology. Carbon nanofiber (CNF)-based materials are effective solutions due to their high thermal stability, large surface area, adjustable porosity, and modifiable surface chemistry. This review critically examines recent innovations in CNF-based materials for CO₂ capture, with an emphasis on two key dimensions: (i) synthesis and functionalization strategies that govern adsorption performance and (ii) the scalability, energy footprint, and techno-economic feasibility of their practical deployment. Fabrication approaches, such as electrospinning and chemical vapor deposition (CVD), are examined for their role in tailoring CNF structures to enhance adsorption efficiency. They are evaluated both for their structural tuning capabilities, production scalability, energy footprint, and cost-effectiveness Functionalization strategies – including nitrogen doping, amine modifications, and integration with metal-organic frameworks (MOFs) – are analyzed concerning their influence on binding affinity, selectivity, and reversibility, thereby improving CO₂ adsorption capacity, selectivity, and regeneration potential.Different CNF-based materials, such as K₂CO₃-CNF, nitrogen-doped CNF, amine-functionalized CNF, and hydrazine-modified CNF, are discussed, each exhibiting unique adsorption properties. The role of pore size distribution, particularly the interplay between microporous and mesoporous structures, is analyzed for its effect on CO₂ diffusion kinetics and adsorption capacity. Polyacrylonitrile-derived CNF depicted the highest CO₂ adsorption capacity of 58 mmol/g, attributed to its large surface area, porosity, and functional groups. Beyond laboratory performance, this review highlights challenges in industrial translation – including material regeneration, mechanical integrity, and cost-effectiveness – while outlining opportunities for integrating CNF-based systems into sustainable CCU technologies.

ABSTRACT The mixing of ferrate (IV) with ferrate (VI) rapidly produced ferrate (V), Ferrate (V) react at much higher rates than the ferrate(VI), leading to the rapid abatement of organic pollutants. In this reported study researched a new method of water treatment. The oxidation efficiencies of ferrate(IV), ferrate(VI), and mixtures of ferrate(IV) + ferrate(VI) for the oxidation of wastewater containing Acid Red 88 were investigated. The rates of oxidation of the Acid Red 88 were as follows: ferrate (IV) + ferrate (VI) > ferrate (VI) > ferrate (IV), and the highest oxidation rate of the dye was achieved when the molar ratio of ferrate (IV) to ferrate (VI) was approximately 1:1 are only valid under acidic conditions. Ferrate (IV) mixed 1:1 with ferrate (VI) appeared to produce a black–gray substance that disappeared from the solution after approximately 1 min. It was demonstrated that this material was Fe(V) through the phosphate experiment. It had a characteristic UV absorption at 546 nm and an IR absorption at 1112 cm−1. UV spectroscopy revealed that the oxidation mechanisms of ferrate(IV) + ferrate(VI), ferrate(VI), and ferrate(IV) were essentially the same. A mixture of ferrate (IV) and ferrate (VI) is used to degrade organic matter so that the reaction rate can be improved without increasing the cost.

ABSTRACT Due to their continuous usage, thousands of tonnes of dyes are annually released into water bodies, resulting in water pollution. Neutral red (NR) dye is widely used in research and as a tracer in the textile industry. Unfortunately, NR dye is toxic and carcinogenic. Thus, it is necessary to treat wastewater polluted by NR dye before discharge. Among the decontamination strategies available, adsorption is considered facile with low cost. The present review article explores the elimination of NR dye using various adsorbents, with a maximum adsorption capacity of 3866 mg/g achieved at pH 7 using carbon nano-onions. The effects of various operational parameters have been discussed. In addition, isotherms, kinetics, thermodynamics, mechanism, regeneration, and reusability have also been discussed. The uptake of NR dye usually fits either Langmuir or Freundlich’s isotherm model along with the pseudo-second-order kinetic model. ΔG° values for the adsorption of NR dye are usually below zero while ΔS° values are usually greater than zero. In addition, ΔH° values are of any thermic nature (endothermic/exothermic). The few studies reporting the desorption of NR dye from various adsorbents revealed high efficiency using ethanol-based desorbing agents. Such findings will guide researchers on the opportunities and challenges of various adsorbents towards remediating wastewater polluted by NR dye via adsorption. Furthermore, future prospects have been provided to aid towards filling the research gaps of novel adsorbent development, competitive studies, and continuous/column studies, including the employment of AI tools such as neural networks, fuzzy inference systems, etc. in adsorption works involving NR dye.

ABSTRACT Bioremediation is traditionally performed using free bacterial cells; however, immobilised bacterial cells have gained attention recently as a promising technique due to the numerous benefits presented. Removing dyes by biological processes is gaining apparent interest because it is profitable and environmentally friendly. Azo dyes, released into the environment, have dangerous effects on aquatic and human life, and their persistence and discharge into the environment are becoming a global concern. Considering the importance of the aspects involved in the bioremediation of azo dyes by immobilised microbial cells and the growing number of publications on the subject, this review aimed to survey state-of-the-art and make a bibliometric mapping of these studies in the period from 2013 to 2023. The analysis of articles was selected from the Science Direct database. The bibliometric mapping provided relevant data to understand the evolution of research in the area and the main bottlenecks that must be overcome for future advances to be achieved.

ABSTRACT Globally, bioenergy development depends on the efficacy and affordability of conversion technologies and the availability of renewable biomass sources. As a tropical country, Indonesia has a wide range of biomass sources, either from land or marine biomass (i.e. macroalgae). The current estimation of macroalgae potential in Indonesia is estimated at approximately 9.96 million tonnes or about 26.86% share of world production in 2021. Specifically, marine macroalgae (wild or cultivated) have received attention for their potential as renewable resources for the sustainable bioenergy production, supporting a move towards a circular economy. However, as a developing country, Indonesia still needs to evolve and further advances its technology and skill capacity to address research, development, and innovation challenges in this area. Thus, this paper examines the potential biorefinery approach for application and commercialisation in Indonesia. It discusses cultivation practices and the future direction of the most sustainable and feasible routes for bioenergy production from macroalgae, exploring recent developments, opportunities, and challenges towards circular processes. The study proposed that the biorefining of macroalgae into bioethanol, biogas, compost, and solid fuels, either as mono – or co-production, are potential. Therefore, this paper may offer to narrowing the literature’s gap and adding a new perspective on the adoption of macroalgae-based bioenergy with integrated biorefinery and closed-loop systems approaches.

ABSTRACT Plastic waste (PW) poses risks to human health and the environment, but it is now being viewed as a potential energy resource through waste-to-energy conversion, particularly using the efficient gasification technology. This technology can replace traditional fossil fuels by generating power. However, gasifying only plastic faces challenges like agglomeration and the production of toxic components. Co-gasification is a solution that provides benefits such as improved yield, cold gas efficiency, consistent feedstock supply, and cost-effective production. To expedite technology adoption, an efficient and cost-effective system with optimal parametric performance is required. Because, different types of feed stock, gasification technology, and operation condition significantly trades off the quality of producer gas. So far, several studies have been performed into gasification of individual PW, but few reports on co-gasification of PW with coal-biomass. Therefore, it must be reviewed the pros and cons of co-gasification in order to use producer gas as a fuel with very promising solution of waste to energy conversion. Hence, this review aims to attend PW co-gasification with coal and biomass and the consequence of these feedstock proportions on gasification performance. Specially, this review summarizes the effects of several operating parameters: gasifying agents, feed material like PW, coal, biomass, and their blending fraction on the producer gas composition. Moreover, it explores the impact on co-gasification performance, like carbon conversion, cold gas efficiency, gas yield, tar content, and calorific value. Thus, this review will provide altogether co-gasification parametric study as a prerequisite for further technology improvement.

ABSTRACT In light of resource depletion, energy scarcity, and toxic waste management, gasification is regarded as a viable waste-to-energy conversion method. Moreover, the Gasifier-Engine-Genest combo provides a suitable alternative for distributed electric power, waste conversion, and alleviating electricity scarcity. Despite an abundance of research report, it is not usually acknowledged as a viable alternative to traditional energy sources. Thus, to promote Gasification, efficient technology is required to maximize the yield of syngas with clean and improved calorific value. Furthermore, there is a void in the prior study that summarises the various types of biomasses and their pre-treatment, as well as the progression of conventional gasification to advanced gasification for the improvement of syngas quality and respective critical applications. Moreover, this is necessary in order to organise the conditions and biomass for gasification, which are many and frequently scattered in the literature. Hence, this study summarises the detailed review of recent novel concepts development over conventional techniques of biomass gasification. Recent reports on feed material properties of diverse biomass, as well as pre-treatment employing biomass torrefaction for gasification, are presented in this paper in order to evaluate their potential. In addition, a literature review of the various categories of gasification, the gasification processes, and the impact of technology on the quality of syngas, power generation and distribution were reported. In conclusion, it is proposed that enhanced gasification technology be employed to implement sustainable development in order to reduce the existing reliance on non-renewable energy sources.

ABSTRACT The presence of toxic heavy metals in water bodies is a subject of international concern due to the deleterious effects caused by these contaminants on both humans and the ecosystem. Adsorption is among the most successfully used methods for the abatement of heavy metals from water and low-cost adsorbents are sought after. Coffee waste is generated in ton volumes and its inherent chemical structural groups have elicited interest from researchers to investigate it for developing low-cost adsorbents for heavy metal removal. Functional groups of interest are the dominant carboxyl and hydroxyl groups which have been explored for metal ion binding. In this review, we attempt to correlate the treatment methods (physical (pyrolysis) and chemical) of charred and uncharred adsorbents with adsorption efficiency. The adsorption efficiencies of the different classes of modifications are not clearly distinguishable, which then dwarfs the purpose of surface modification. There have been some studies where excellent adsorption performances were reported, with adsorption capacity reaching 302 mg/g for chromium six but these are very few. The comprehensive comparison data provided in this review shows that more work still needs to be done in extending the adsorption to other metal ions and improving the surface modification reactions to include grafting, crosslinking, and the fabrication of composite materials incorporating nanoparticles other than magnetite to improve the adsorption efficiency as well as analyzing the cost-effectiveness of coffee waste adsorbents. HIGHLIGHTS Valorization of coffee wastes for applications in water treatment is reviewed Carboxyl and hydroxyl surface functional groups improve metal adsorption Adsorption capacity as high as 302 mg/g for Cr(VI) has been reported Gaps and recommendations are provided for future research

ABSTRACT It has long been known that the textile industry generates a massive amount of synthetic waste across the globe. Dye-containing wastewater is carcinogenic, mutagenic, recalcitrant, and xenobiotic. Several techniques have been developed for textile wastewater treatment. Most often, especially for dye-containing synthetic waste, bioremediation has now become one of the emerging techniques. Bioreactor, a common apparatus, whenever possible, may operate either continuously or in batches; has been extensively used for carrying out the hardest-to-meet biological reactions. The objective of this review is to emphasize a brief description of different bioreactors’ performance, their features, and shortcoming. Special emphasis has been laid out on Membrane Bioreactor, Fluidized Bed Bioreactor, Moving Bed Bioreactor, Packed Bed Bioreactor, Airlift Bioreactor, Stirred Tank Bioreactor, Fixed Bed Bioreactor, and Rotating Biological Contactor. The key findings of each bioreactor’s dye degradation performance have been reviewed. A brief discussion about recent trends in dye wastewater treatment has been depicted and based on the above facts future outlook is critically highlighted. A techno-economic assessment of bioremediation technology emphasizes its applicability for industrial scale. The review is expected to be beneficial to readers who are dealing with bioprocess, hybrid bioreactors, and designing bioreactors at a laboratory, pilot plant, and even on an industrial scale for the treatment of real textile waste. However, the selection criterion of a suitable bioreactor has relied on bioprocess engineering and economics. New technological advancements in the bioreactor have been discussed and Microbioreactor seems as a future outlook toward dye degradation.

ABSTRACT The anammox process is considered a sustainable, low-cost, and promising alternative for the treatment of effluents with high concentrations of nitrogen (N) and low concentrations of chemical oxygen demand (COD). Mature landfill leachates are rich in nitrogen and a potential source of water and soil contamination, potentially causing eutrophication of surface water bodies. In developing countries, leachates have been treated together with municipal effluents in WWTP. However, there are few reports on nitrogen removal in these systems. This review evaluated studies using anammox-based processes, including partial nitrification and anammox (PN/A), focusing on mature leachates and their co-treatment with municipal wastewater. We aimed to identify anammox-based treatment strategies leading to high N and COD removal efficiencies. For PN/A, sequential batch reactors have been successfully used to treat different effluents such as leachates. Recirculation and leachate dilution in anammox-based processes were strategies successfully adopted to achieve high nitrogen removal. Temperatures above 30°C and pH values from 7.8–8.5 had positive effects on the performance of co-treatment processes. The best performances in the co-treatment processes using PN/A were achieved for dilution rates between 2 and 11.5 parts of municipal wastewater to 1 part of mature leachate, reaching N and COD removal efficiencies above 90% and 86%, respectively. Inhibition of nitrite-oxidizing bacteria, acclimatization of anammox bacteria for long periods, as well as extracellular polymeric substances production by anammox bacteria are important factors in the performance of PN/A systems for the co-treatment of mature leachate and domestic wastewater.