The USA, China and India are the top three producers of municipal solid waste. The composition of solid wastes varies with income: low-to-middle-income population generates mainly organic wastes, whereas high-income population produces more waste paper, metals and glasses. Management of municipal solid waste includes recycling, incineration, waste-to-energy conversion, composting or landfilling. Landfilling for solid waste disposal is preferred in many municipalities globally. Landfill sites act as ecological reactors where wastes undergo physical, chemical and biological transformations. Hence, critical factors for sustainable landfilling are landfill liners, the thickness of the soil cover, leachate collection, landfill gas recovery and flaring facilities. Here, we review the impact of landfill conditions such as construction, geometry, weather, temperature, moisture, pH, biodegradable matter and hydrogeological parameters on the generation of landfill gases and leachate. Bioreactor landfills appear as the next-generation sanitary landfills, because they augment solid waste stabilization in a time-efficient manner, as a result of controlled recirculation of leachate and gases. We discuss volume reduction, resource recovery, valorization of dumped wastes, environmental protection and site reclamation toward urban development. We present the classifications and engineered iterations of landfills, operations, mechanisms and mining.

Municipal solid waste management and landfilling technologies: a review

A state-of-the-art review on thermochemical conversion of biomass for biofuel production: A TG-FTIR approach

A review of China’s municipal solid waste (MSW) and comparison with international regions: Management and technologies in treatment and resource utilization

Review and comparison of various hydrogen production methods based on costs and life cycle impact assessment indicators

This paper critically reviews the current status of utilization of municipal solid waste and biomass blends for energy and resources recovery together with identifying the opportunities for future development in technological equipment and physicochemical waste compositions involved in such complex processes. Among numerous thermochemical conversion techniques, gasification of municipal solid waste with different biomass blends has unveiled as an auspicious technology to develop a sustainable waste management system that would substantially reduce pollution and maximize energy and materials recovery. Municipal solid wastes and biomass have different properties and elemental compositions and are abundantly available. These materials have the potential to produce various types of value-added products in terms of energy and chemicals through the gasification process. Recently, hybrid systems have been introduced with simple gasification technologies in terms of fuel oxidation system, plasma torch, or some biochemical conversion systems to enhance the process efficiency, energy, economics, quality, the yield of syngas, and to alter the composition of gaseous products. Consequently, gasification of biomass and waste would be the most suitable option to reduce toxic elements and harmful gases for the surroundings. For instant, ecological influence is not the real issue for limitation of biomass and waste gasification development, while a feasible economic return could appeal to investors and initiate its commercialization. Energy and resource recovery is assessed as an integrated approach to overcoming limitations. Also, techno-economic and environmental impact, life cycle assessment, and their implications are discussed in detail. Key bottlenecks that need urgent attention to facilitate global recognition of hybrid technology are highlighted.

Gasification of municipal solid waste blends with biomass for energy production and resources recovery: Current status, hybrid technologies and innovative prospects

Plasma gasification can be a viable technology for converting municipal solid waste (MSW) into value for the circular economy. However, in its current state, plasma gasification is mostly limited to lab or pilot scales as there are various challenges associated with it; there exist knowledge gaps which need attention and research for its successful future commercialisation. The present study critically reviewed the current status of plasma gasification for waste-to-value processing. Various traditional techniques for MSW disposal and processing available in the literature were discussed and were compared with plasma gasification in terms of cost, service life, energy comparison, and environmental impact comparison. After the review, knowledge gaps were identified, challenges associated with the plasma gasification technology were discussed, and a possible roadmap for the successful future commercialisation of plasma gasification for waste-to-value processing was suggested. Furthermore, various strategies to cope with challenges associated with plasma gasification were discussed. The successful commercialisation of plasma gasification can be achieved by reducing its costs by generating revenue or value in the form of synthesis gas or fuels from MSW, energy can be saved or reused using insulation, process integration, and process intensification, the technology and community readiness levels can be improved with better communication between relevant stakeholders and adding extra layers of safety, and process understanding can be improved by conducting extensive fundamental studies, as well as plasma gasification technology being standardised by establishing standards and standards organisations.

Plasma gasification of municipal solid waste for waste-to-value processing

Plasma electrolytic oxidation (PEO) is a surface-treatment process extensively used to protect the surfaces of light metals such as Mg, Al, and Ti. Here, we report an environmentally friendly PEO process that uses nitrogen-containing electrolytes and low voltages (120 V) to form ~ 12 micron thick, uniform, adherent and porous oxide coatings on T1 titanium alloy surfaces. We evaluated the influence of nitrogenation by comparing the coatings to alloys treated in PEO baths without nitrogen-containing compounds. Both sets of samples exhibited basalt-like morphologies with distinct variation in the pore structures. The composition analyses showed that the coatings were primarily composites of titanium oxides and silicates. The T1 Ti alloys treated with nitrogen-containing electrolytes also contained TiC and TiN. This is the first ever report of producing TixOy, Ti-Si-O, TiC, and TiN composite coatings using a single PEO bath without carbide/nitride nanoparticles. The bandgaps of the coatings suggested visible light functionality. The use of nitrogen-based compounds in the PEO baths improved the hardness of the oxide layers but introduced stress-induced cracking which are potentially responsible for the reduction in corrosion resistance of the nitride and carbide containing coatings. 

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Low voltage environmentally friendly plasma electrolytic oxidation process for titanium alloys

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Low-density metals such as Mg and Al (and their alloys) are of high interest for lightweight engineering applications in various industries. Moisture sensitivity, poor tribology, and corrosion susceptibility limit the direct application of these light metals. Plasma electrolytic oxidation (PEO) is extensively used to passivate light metals against corrosion and enhance their mechanical properties. PEO processes in current use are often energy-intensive and use toxic electrolytes. Incorporating composite characteristics to PEO-treated surfaces typically requires modification of electrolytes with nanoparticle addition. Some applications also need post-treatment of oxidized coatings to ensure functionality. We report a versatile, environmentally friendly PEO process that uses organo-silicate electrolytes enriched with nitrogen-containing solutions. The single-step process produces ∼6 μm thick, uniform, adherent, and porous oxide coatings on AZ80 and Al6061 surfaces in 15 min. We evaluated the influence and effectiveness of in situ nitridation by comparing the coating properties with those on alloys treated in PEO electrolytes without nitrogen-containing chemicals. The two sets of coatings were porous with multilayered basalt-like topographies and were composed of metal oxides and metal silicates. Alloys treated in nitrogen-containing electrolytes exhibited the presence of oxynitrides. The use of nitrogen-containing PEO electrolytes resulted in coatings with enhanced mechanical behavior. We found that the corrosion resistance of coatings prepared using low voltages in this study was comparable to the traditional PEO-treated coatings reported in the literature. Nitridation of the coatings, however, appears to have a slightly negative influence on the coatings’ corrosion resistance. Our future work will focus on improving the corrosion resistance of the mechanically resilient, nitride-containing PEO-treated coatings.

I. Mardon

Papers

Plasma gasification of municipal solid waste for waste-to-value processing

Low voltage environmentally friendly plasma electrolytic oxidation process for titanium alloys

Low voltage environmentally friendly plasma electrolytic oxidation process for titanium alloys

Protecting Light Metal Alloys Using a Sustainable Plasma Electrolytic Oxidation Process