423 research outputs found
COVID-19: resource recovery from plastic waste against plastic pollution
To combat with the challenge of plastic pollution, a sustainable, systematic, and hierarchical plastic management roadmap that clearly defines the
relative roles and socioeconomic and environmental impacts of these measures is
needed. It requires plastic waste type-specific and country demand-specific action
plans as well as greater support from policymakers and the more general public.
Finally, disaster resilience needs to be considered in consistent with the Sendai
Framework for Disaster Risk Reduction 2015–2030
Selective removal of arsenic in water: A critical review
Selective removal of arsenic (As) is the key challenge for any of As removal mechanisms as this not only increases the efficiency of removal of the main As species (neutral As(III) and As(V) hydroxyl-anions) but also allows for a significant reduction of waste as it does not co-remove other solutes. Selective removal has a number of benefits: it increases the capacity and lifetime of units while lowering the cost of the process. Therefore, a sustainable selective mitigation method should be considered concerning the economic resources available, the ability of infrastructure to sustain water treatment, and the options for reuse and/or safe disposal of treatment residuals. Several methods of selective As removal have been developed, such as precipitation, adsorption and modified iron and ligand exchange. The biggest challenge in selective removal of As is the presence of phosphate in water which is chemically comparable with As(V). There are two types of mechanisms involved with As removal: Coulombic or ion exchange; and Lewis acid-base interaction. Solution pH is one of the major controlling factors limiting removal efficiency since most of the above-mentioned methods depend on complexation through electrostatic effects. The different features of two different As species make the selective removal process more difficult, especially under natural conditions. Most of the selective As removal methods involve hydrated Fe(III) oxides through Lewis acid-base interaction. Microbiological methods have been studied recently for selective removal of As, and although there have been only a small number of studies, the method shows remarkable results and indicates positive prospects for the future
Mercury speciation, transformation, and transportation in soils, atmospheric flux, and implications for risk management : a critical review
Mercury (Hg) is a potentially harmful trace element in the environment and one of the World Health Organization's foremost chemicals of concern. The threat posed by Hg contaminated soils to humans is pervasive, with an estimated 86 Gg of anthropogenic Hg pollution accumulated in surface soils worldwide. This review critically examines both recent advances and remaining knowledge gaps with respect to cycling of mercury in the soil environment, to aid the assessment and management of risks caused by Hg contamination. Included in this review are factors affecting Hg release from soil to the atmosphere, including how rainfall events drive gaseous elemental mercury (GEM) flux from soils of low Hg content, and how ambient conditions such as atmospheric O3 concentration play a significant role. Mercury contaminated soils constitute complex systems where many interdependent factors, including the amount and composition of soil organic matter and clays, oxidized minerals (e.g. Fe oxides), reduced elements (e.g. S2−), as well as soil pH and redox conditions affect Hg forms and transformation. Speciation influences the extent and rate of Hg subsurface transportation, which has often been assumed insignificant. Nano-sized Hg particles as well as soluble Hg complexes play important roles in soil Hg mobility, availability, and methylation. Finally, implications for human health and suggested research directions are put forward, where there is significant potential to improve remedial actions by accounting for Hg speciation and transportation factors
A critical review on sustainable biochar system through gasification: energy and environmental applications
This review lays great emphasis on production and characteristics of biochar through gasification. Specifically, the physicochemical properties and yield of biochar through the diverse gasification conditions associated with various types of biomass were extensively evaluated. In addition, potential application scenarios of biochar through gasification were explored and their environmental implications were discussed. To qualitatively evaluate biochar sustainability through the gasification process, all gasification products (i.e., syngas and biochar) were evaluated via life cycle assessment (LCA). A concept of balancing syngas and biochar production for an economically and environmentally feasible gasification system was proposed and relevant challenges and solutions were suggested in this review
Towards practical application of gasification: a critical review from syngas and biochar perspectives
Syngas and biochar production are mainly influenced by temperature,
feedstock properties, gasifying agent, pressure, and
the mass ratio between gasifying agent and feedstock with
temperature being the most significant factor. Increasing temperature
generally promotes syngas production while suppressing
biochar production. The selection of gasifiers (fixed
bed, fluidized bed, and entrained flow) is highly dependent
on scale requirement (e.g., volume of feedstock and energy
demand), feedstock characteristics (e.g., moisture and ash content),
and the quality of syngas and biochar. Updraft fixed
bed gasifiers are suitable for the feedstocks with a moisture
content up to 50 wt.%. High ash feedstocks such as Indian
coal, dried sewage sludge, and municipal solid waste that are
not suitable for fixed bed gasifiers, have been successfully
gasified in bubbling fluidized bed reactors. Woody biomass is
not suitable for entrained flow gasifiers unless specialized
feeding methods are employed such as wood torrefaction and
grinding followed by the existing feeding methods for pulverized
coals, biomass-oil biochar slurry preparation followed by
pumping, wood or torrefied wood slurry preparation followed
by pumping, etc. Syngas and biochar can potentially be contaminated
by NH3, H2S, and tar, which can be removed using
catalysts (e.g., Ni-based), metal oxides-based sorbents, and
thermal and catalytic cracking methods. Existing syngas and
biochar upgrading methods suffered from various problems
such as economic infeasibility, limited productivity, and fouling,
and future syngas and biochar upgrading methods should
be aimed to have the features of reliability, security, affordability,
and sustainability, towards the practical, large-scale production
of syngas- and biochar-based products. One potential
solution is to develop integrated systems by combining biochar
upgrading and application with syngas upgrading, which
warrants an integrated perspective based on both life cycle
assessment and economic analysis
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