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Globally there are over 20millionha of land contaminated by the heavy metal(loid)s As, Cd, Cr, Hg, Pb, Co, Cu, Ni, Zn, and Se, with the present soil concentrations higher than the geo-baseline or regulatory levels. In-situ and ex-situ remediation techniques have been developed to rectify the heavy metal-contaminated sites, including surface capping, encapsulation, landfilling, soil flushing, soil washing, electrokinetic extraction, stabilization, solidification, vitrification, phytoremediation, and bioremediation. These remediation techniques employ containment, extraction/removal, and immobilization mechanisms to reduce the contamination effects through physical, chemical, biological, electrical, and thermal remedy processes. These techniques demonstrate specific advantages, disadvantages, and applicability. In general, in-situ soil remediation is more cost-effective than ex-situ treatment, and contaminant removal/extraction is more favorable than immobilization and containment. Among the available soil remediation techniques, electrokinetic extraction, chemical stabilization, and phytoremediation are at the development stage, while the others have been practiced at full, field scales. Comprehensive assessment indicates that chemical stabilization serves as a temporary soil remediation technique, phytoremediation needs improvement in efficiency, surface capping and landfilling are applicable to small, serious-contamination sites, while solidification and vitrification are the last remediation option. The cost and duration of soil remediation are technique-dependent and site-specific, up to $500ton soil (or $1500m soil or $100m land) and 15years. Treatability studies are crucial to selecting feasible techniques for a soil remediation project, with considerations of the type and degree of contamination, remediation goals, site characteristics, cost effectiveness, implementation time, and public acceptability.

a b s t r a c tMartensite decay in bearing steels manifested as dark etching regions (DERs) under rolling contact fatigue (RCF) is modelled. The proposed model is established based on a dislocation-assisted carbon migration mechanism. The proposed model is capable of predicting the progress of DER formation and the corresponding mechanical property evolution with increasing number of cycles, in good agreement with the experimental data reported throughout seventy years. The effects of RCF testing conditions on DER formation are studied and a useful tool, DER% maps, is developed for illustrating the temperature, contact pressure and number of cycles for DER occurrence. Moreover, an atom probe tomography study is carried out, revealing the nature of DER ferrite and obtaining strong evidence supporting the postulated DER formation mechanism. The successful application of the dislocation assisted carbon migration mechanism to DER formation provides a plausible explanation to the phenomenon of martensite decay under rolling contact fatigue.

Recent research suggests that biochar amendment is a promising approach to mitigate soil contamination via immobilizing heavy metals and organic pollutants. Through intensive literature review, this paper was aimed to better understand the processes, mechanisms, and effectiveness of biochar in immobilizing chemical contaminants in soil. The quality characteristics of biochar as a soil amendment varied greatly with the feedstock materials and the pyrolysis conditions. Biochar products from different sources demonstrated remarkably diversified capacities and efficiencies for stabilizing soil contaminants. Soil-incorporated biochar was able to stabilize Cd, Cu, Ni, Pb, and Zn and reduce their bioavailability through enhanced sorption (based on electrostatic attraction, ion exchange, and surface complexation) and chemical precipitation (incurred from soil pH elevation and ash addition of carbonates and phosphates). The stabilization efficacy was largely determined by cation exchange capacity, pH, and ash content of the biochar. Biochar amendment increased the mobility of anionic toxic elements [e.g., CrO 2− 4 , AsO − 3 , and Sb(OH) − 6 ] in soil. Soil-incorporated biochar was also able to adsorb non-polar organic compounds (through pore filling, partition, and hydrophobic effect) and polar organic compounds (via H-bonding, electrostatic attraction, specific interaction, and surface precipitation). The adsorption efficiency was controlled by the biochar surface properties specific surface area, microporosity, and hydrophobicity. Biochar may facilitate the mineralization of organic pollutants by enhancing soil microbial activities. The effectiveness of biochar-facilitated soil remediation was case specific, changing with the biochar source, amendment rate, placement, soil type, and pollutant species. More field studies are needed to evaluate the long-term effectiveness of biochar-facilitated soil remediation under practical circumstances.

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Bioeconomy refers to economic activities using renewable biological resources to produce energy and domestic consumables. The U.S. bioeconomy emerged in the early 2000s as a result of the societal pursuit of energy independence and security, greenhouse gas emission mitigation and sustainable development. Founded on biotechnologies and stimulated by federal policies, the U.S. bioeconomy has been growing rapidly over the past decade. Intensive research and development endeavors have been carried out to explore advanced technologies for efficient biomass production, conversion, and valorization, through which numerous biotechnological innovations have been achieved to realize the commercial, cost-effective production of diverse transportation biofuels and high-value domestic bioproducts from various biomass feedstocks. The bioenergy products currently commercialized in the U.S. include bioethanol, biodiesel, biogas, bioheat and biopower; the commercialized bioproducts extend to biopolymers, biochemicals, biopharmaceuticals and bioadhesives. In 2017, more than 65.4 billion liters of biofuels and 2500 certified bioproducts were produced, creating 4 million job opportunities and sharing 2.5% of the U.S. economy. Commercial production of cellulosic ethanol, renewable diesel, green jet fuel and other advanced biofuels remains at the demonstration stage and needs further improvement in cost-competitiveness. Envisioning a Billion-Ton-Bioeconomy by 2030, the U.S. federal government has been implementing strategic activities to realize the goal. High costs of delivered biomass feedstock, immature biomass refinery technologies, lack of cost-comparative bioproducts, and low fossil fuel prices have been identified as the major constraints to a strong U.S. bioeconomy. To improve the bioeconomic viability, further biotechnological advances and integrated biorefinery processes are warranted.

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