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Plastic production has been rapidly growing across the world and, at the end of their use, many of the plastic products become waste disposed of in landfills or dispersed, causing serious environmental and health issues. From a sustainability point of view, the conversion of plastic waste to fuels or, better yet, to individual monomers, leads to a much greener waste management compared to landfill disposal. In this paper, we systematically review the potential of pyrolysis as an effective thermochemical conversion method for the valorization of plastic waste. Different pyrolysis types, along with the influence of operating conditions, e.g., catalyst types, temperature, vapor residence time, and plastic waste types, on yields, quality, and applications of the cracking plastic products are discussed. The quality of pyrolysis plastic oil, before and after upgrading, is compared to conventional diesel fuel. Plastic oil yields as high as 95 wt.% can be achieved through slow pyrolysis. Plastic oil has a heating value approximately equivalent to that of diesel fuel, i.e., 45 MJ/kg, no sulfur, a very low water and ash content, and an almost neutral pH, making it a promising alternative to conventional petroleum-based fuels. This oil, as-is or after minor modifications, can be readily used in conventional diesel engines. Fast pyrolysis mainly produces wax rather than oil. However, in the presence of a suitable catalyst, waxy products further crack into oil. Wax is an intermediate feedstock and can be used in fluid catalytic cracking (FCC) units to produce fuel or other valuable petrochemical products. Flash pyrolysis of plastic waste, performed at high temperatures, i.e., near 1000 °C, and with very short vapor residence times, i.e., less than 250 ms, can recover up to 50 wt.% ethylene monomers from polyethylene waste. Alternatively, pyrolytic conversion of plastic waste to olefins can be performed in two stages, with the conversion of plastic waste to plastic oil, followed by thermal cracking of oil to monomers in a second stage. The conversion of plastic waste to carbon nanotubes, representing a higher-value product than fuel, is also discussed in detail. The results indicate that up to 25 wt.% of waste plastic can be converted into carbon nanotubes.

There is an enormous body of the literature, proving that soil amendments enhance plant growth/yield and prevent the impact of pathogens/toxins. To the best of our knowledge, there is no comprehensive assessment focused on the synergistic effects of microorganisms and soil amendments with biochar or compost for upgrading the current fertilizers towards a more sustainable agriculture. The main objective of the present work is to discuss the most current information needed for developing advanced soil amendments using microorganisms along with safe, sustainable and low-cost waste sourced materials. The first step in designing the biofertilizer is the selection of a microorganism from among a variety of bacterial/fungi strains that have been identified as plant growth promoting (PGP) in the literature. This study classifies the effective types of soil microorganisms with respect to their functionality to facilitate the choice of the best compatible microbial strain(s) in order to satisfy the host environment requirements. The second part is dedicated to various inorganic and organic carriers, such as perlite, peat, fly ash and compost, for delivering of microorganism into the soils. The role of carriers in the survival and the functional contribution of the microbes to soilplant systems are investigated. Lastly, biochar is evaluated as a promising microbial carrier together with its influence on the soil biota including microorganisms and plants. The superior features of biochar, for example high surface area, porosity, customizable structure, high stability, carbon sequestration and synergy, with other fertilizers are also discussed.

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In this study, biochar was thermally and chemically (thermo-chemically) modified and compared to the unmodified parent char in carbon dioxide adsorption. The biochars were sourced from sawmill residues and produced via fast pyrolysis in an auger reactor. The biochar was chemically functionalized using two novel methods of amine functionalization: (i) nitration, followed by reduction, and (ii) condensation of aminopropyl triethoxysilane on the surface. The obtained outcomes indicated functionalization resulted in a reduction in the pore volume and surface area of the biochar. The biochars (unmodified and chemically modified) were thermally activated via air diluted with nitrogen at moderate 560 °C to determine if the adsorption properties could be enhanced. The thermally treated functionalized chars had a lower H:C ratio, higher surface area, micropore volume, and sufficient amount of nitrogen compared to the unmodified char. The thermally treated aminopropyl triethoxysilane char had the highest adsorption capacity of 3.7 mmol/g with 0.24 wt % nitrogen. Biochars sourced from residues demonstrated high efficiency of carbon dioxide removal, comparable to some synthesized adsorbents reported in the literature.