Continuous environmental degradation, volatility in the oil market, and unimpressive functioning of fossil-based (FB) fuels in compression ignition engines have expanded the tempo of the search for alternative fuels. Due to the astronomical rise in global population, improved agricultural, commercial, and manufacturing activities, enhanced farming and other food production and utilization ventures, agricultural waste generation, renewable fuel consumption, and emission of toxic gases. The need for cost-effective, readily available, and environmentally benign agricultural waste to biofuels has never been more crucial. Biofuels are renewable, biodegradable, low-cost, and eco-friendly fuels that are produced by microorganisms from waste lignocellulosic biomass. Conversion of agricultural wastes to biofuel does not exacerbate food security, contributes to waste management, prevents environmental degradation, and ensures energy security. This study reviews the conversion of agricultural wastes into biofuels with special emphasis on bioethanol, biohydrogen, biobutanol, biomethane, biomethanol, and biodiesel for various applications. It is safe to conclude that wastes generated from agricultural activities and processes are useful and can be harnessed to meet the affordable and accessible global renewable energy target. The result of this investigation will improve the body of knowledge and provide novel strategies and pathways for the utilization of agricultural wastes. Going forward, more collaborative and interdisciplinary studies are required to evolve state-of-the-art, ecofriendly, and cost-effective conversion pathways for agricultural wastes to promote the utilization of the generated renewable fuels. More human, financial, and infrastructural investments are desirable to motivate the conversion of agricultural waste into biofuels to ensure environmental sanitation and sustainability, promote renewable fuel utilization, and avert the raging implosion of our planet.

Biofuel, a cost-effective, safe, and environmentally benign fuel produced from renewable sources, has been accepted as a sustainable replacement and a panacea for the damaging effects of the exploration for and consumption of fossil-based fuels. The current work examines the classification, generation, and utilization of biofuels, particularly in internal combustion engine (ICE) applications. Biofuels are classified according to their physical state, technology maturity, the generation of feedstock, and the generation of products. The methods of production and the advantages of the application of biogas, bioalcohol, and hydrogen in spark ignition engines, as well as biodiesel, Fischer–Tropsch fuel, and dimethyl ether in compression ignition engines, in terms of engine performance and emission are highlighted. The generation of biofuels from waste helps in waste minimization, proper waste disposal, and sanitation. The utilization of biofuels in ICEs improves engine performance and mitigates the emission of poisonous gases. There is a need for appropriate policy frameworks to promote commercial production and seamless deployment of these biofuels for transportation applications with a view to guaranteeing energy security.

Research shows that monolithic Al alloy has very attractive properties required in the production of aerospace, automotive, electrical and electronic, sports and recreational components/equipment. However, its low strength and low wear resistance have challenged its applications in some other critical industrial utilities. Nonetheless, the invention of metal composites has removed such barriers. The addition of one or more reinforcements to Al has helped in the creation of aluminium matrix composites (AMCs), which has not only increased the global utilization of Al alloy, but has been a major source of global revenue and job. This review was, therefore, aimed at studying recent works on AMCs with the aim of ascertaining the recent innovations in the development of advanced Al composites, which can replace steel components in most industrial applications at a cheaper rate. It was observed from the study that AMCs can be developed via solid and liquid fabrication techniques. Powder metallurgy was reported as the most effective method of producing hybrid Al nanocomposites, with spark plasma sintering as the best technique. In the liquid process, stir casting was reported as the most cost effective, but was challenged by agglomeration. It was recommended that agglomeration be ameliorated by cryogenic ball milling and an in situ fabrication technique. It was also recommended that more cost effective agro-waste nanoparticles should be developed to replace more costly conventional reinforcements. In summary, it was recommended that more research on the exploration of Al alloy at a cheaper rate should be carried out.

The management of the huge amounts of waste generated from domestic and industrial activities has continued to be a source of concern for humanity globally because of its impact on the ecosystem and human health. Millions of tons of such used materials, substances, and products are therefore discarded, rejected, and abandoned, because they have no further usefulness or application. Additionally, owing to the dearth of affordable materials for various applications, the environmental impact of waste, and the high cost of procuring virgin materials, there have been intensive efforts directed towards achieving the reduction, minimization, and eradication of waste in human activities. The current review investigates zero-waste (ZW) manufacturing and the various techniques for achieving zero waste by means of resource recycling. The benefits and challenges of applying innovative technologies and waste recycling techniques in order to achieve ZW are investigated. Techniques for the conversion of waste glass, paper, metals, textiles, plastic, tire, and wastewater into various products are highlighted, along with their applications. Although waste conversion and recycling have several drawbacks, the benefits of ZW to the economy, community, and environment are numerous and cannot be overlooked. More investigations are desirable in order to unravel more innovative manufacturing techniques and innovative technologies for attaining ZW with the aim of pollution mitigation, waste reduction, cost-effective resource recovery, energy security, and environmental sustainability.

High modulus of about 1 TPa, high thermal conductivity of over 3000 W/mK, very low coefficient of thermal expansion (CTE), high electrical conductivity, self-lubricating characteristics and low density have made CNTs one of the best reinforcing materials of nano composites for advanced structural, industrial, high strength and wear-prone applications. This is so because it has the capacity of improving the mechanical, tribological, electrical, thermal and physical properties of nanocomposites. So, this study is aimed at providing the latest discoveries on the tribological behavior of CNTs-reinforced composites. The composites reviewed included metal matrix composites (MMCs), polymer matrix composites (PMCs) and ceramic matrix composites (CMCs) reinforced with CNTs. Their tribological characteristics, uses, production challenges, conclusion and recommendations are presented. The work presented the best technique to disperse CNTs on matrices to avoid its agglomeration, since agglomeration is one of the major challenges in reinforcing with CNTs. It was discovered that ball milling destroys the outer walls of CNTs but recommended that ultrasonication and functionalization before ball milling eliminate this adverse effect of ball milling. In addition, it was discovered that addition of CNTs to composite matrices improved the wear resistance, reduced the wear volume, decreased the coefficient of friction (COF) and provided self-lubricating effect on MMCs, PMCs and CMCs.