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

Biochar as a tool for the improvement of soil and environment

Biochar is a versatile and sustainable tool for agricultural and environmental remediation due to its unique physicochemical properties in terms of soil fertility, nutrient retention, and water holding capacity. As a stable carbon-rich material, biochar promotes plant growth and increases crop yields by enhancing microbial activity. It can also be used as a sorbent for removing pollutants such as heavy metals, organic contaminants, and nutrients from soil and water systems. However, the utility of biochar in soil and its ecological impact can be affected by the combined effects of many variables. This paper discusses the effects of biochar application on soil properties and its potential to mitigate various environmental challenges by enhancing soil composition, augmenting water accessibility, and removing pollutants as part of efforts to promote sustainable agriculture based on recent findings. These findings are expected to improve the utility of biochar in farming while contributing to the mitigation of climate change in diverse routes (e.g., by sequestering atmospheric carbon, improving soil quality, and reducing greenhouse gas emissions). This paper offers a promising opportunity to help harness the power of biochar and to pave the way for a more sustainable and resilient future

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

Effect of biochars pyrolyzed in N2 and CO2, and feedstock on microbial community in metal(loid)s contaminated soils

Little is known about the effects of applying amendments on soil for immobilizing metal(loid)s on the soil microbial community. Alterations in the microbial community were examined after incubation of treated contaminated soils. One soil was contaminated with Pb and As, a second soil with Cd and Zn. Red pepper stalk (RPS) and biochars produced from RPS in either N2 atmosphere (RPSN) or CO2 atmosphere (RPSC) were applied at a rate of 2.5% to the two soils and incubated for 30 days. Bacterial communities of control and treated soils were characterized by sequencing 16S rRNA genes using the Illumina MiSeq sequencing. In both soils, bacterial richness increased in the amended soils, though somewhat differently between the treatments. Evenness values decreased significantly, and the final overall diversities were reduced. The neutralization of pH, reduced available concentrations of Pb or Cd, and supplementation of available carbon and surface area could be possible factors affecting the community changes. Biochar amendments caused the soil bacterial communities to become more similar than those in the not amended soils. The bacterial community structures at the phylum and genus levels showed that amendment addition might restore the normal bacterial community of soils, and cause soil bacterial communities in contaminated soils to normalize and stabilize

Biorefining Waste Sludge From Water and Sewage Treatment Plants Into Eco-Construction Material

This study aims to investigate the feasibility of using different waste sludge and coal combustion residuals in eco-concrete block production. The compressive strength of the eco-concrete blocks produced by waterworks sludge, bottom and fly ashes were 36 MPa, which comply with the standard specifications for paving blocks in Hong Kong. The optimal mixing proportion (by weight) of different materials in the blocks, such as aggregates, cementitious materials, water, and fly ash was 1.1:1.0:0.5:0.22, respectively. The environmental and toxicological impacts of the final products were then evaluated according to the toxicity characteristic leaching procedure (TCLP). While several heavy metals (i.e., Hg, Cu, and Pb) have been identified in the specimens, the levels of these contaminants complied with Standards (US 40 CFR 268.48). Waste materials generated from water and sewage treatment processes and power plants are feasible to be used as ingredients for paving concrete block production. These products are environmentally acceptable and mechanically suitable for resource recovery of waste materials

Slow pyrolyzed biochars from crop residues for soil metal(loid) immobilization and microbial community abundance in contaminated agricultural soils

This study evaluated the feasibility of using biochars produced from three types of crop residues for immobilizing Pb and As and their effects on the abundance of microbial community in contaminated lowland paddy (P-soil) and upland (U-soil) agricultural soils. Biochars were produced from umbrella tree [Maesopsis eminii] wood bark [WB], cocopeat [CP], and palm kernel shell [PKS] at 500\ua0°C by slow pyrolysis at a heating rate of 10\ua0°C min-1. Soils were incubated with 5% (w\ua0w-1) biochars at 25\ua0°C and 70% water holding capacity for 45\ua0d. The biochar effects on metal immobilization were evaluated by sequential extraction of the treated soil, and the microbial community was determined by microbial fatty acid profiles and dehydrogenase activity. The addition of WB caused the largest decrease in Pb in the exchangeable fraction (P-soil: 77.7%, U-soil: 91.5%), followed by CP (P-soil: 67.1%, U-soil: 81.1%) and PKS (P-soil: 9.1%, U-soil: 20.0%) compared to that by the control. In contrast, the additions of WB and CP increased the exchangeable As in U-soil by 84.6% and 14.8%, respectively. Alkalinity and high phosphorous content of biochars might be attributed to the Pb immobilization and As mobilization, respectively. The silicon content in biochars is also an influencing factor in increasing the As mobility. However, no considerable effects of biochars on the microbial community abundance and dehydrogenase activity were found in both soils

Quantitative analysis of polystyrene microplastic and styrene monomer released from plastic food containers

Since the COVID-19 outbreak, the use of disposable plastics has rapidly increased along with the amount of plastic waste. During fragmentation, microplastics and other chemical substances contained in plastics are released. These then enter humans through food which could be problematic considering their hazardous potential. Polystyrene (PS), which is widely used in disposable containers, releases large amounts of microplastics (MPs), but no studies have investigated the release mechanisms of PS-MPs and simultaneously exposed contaminants. Therefore, in this study, the effects of pH (3, 5, 7, and 9), temperature (20, 50, 80, and 100 °C), and exposure time (2, 4, 6, and 8 h) on MPs release were systematically examined. A quantitative/qualitative study of MPs and styrene monomers was performed using microscopy-equipped Fourier-transformed infrared spectroscopy and gas chromatography-mass spectrometry. The release of PS-MPs (36 items/container) and simultaneously exposed pollutants (SEP), such as ethylene glycol monooleate (EGM), was highest at pH 9, 100 °C, and 6 h, which was proportional to the test temperature and time. Under the same conditions, 2.58 μg/L of styrene monomer migrated to the liquid food simulants. The fragmentation was proceeded by oxidation/hydrolysis and accelerated by increased temperature and exposure time. The strong positive correlation between PS-MPs and SEPs releases at pH and temperature indicates that PS-MPs and SEPs follow the same release process. However, a strongly negative correlation between PS-MPs and styrene monomers at the exposed time shows that styrene migration does not follow the same release process, but does its partition coefficient

Renewable routes to monomeric precursors of nylon 66 and nylon 6 from food waste

Renewable chemicals, which could potentially replace crude oil-derived chemicals, have been receiving increased interest due to their environment-friendliness (i.e., carbon neutrality). Nylon 66 and nylon 6 are synthetic polymers that are widely used in daily life, synthesized by polycondensation of adipic acid and hexamethylenediamine (HMDA) and by ring-opening polymerization of ε-caprolactam, respectively. This review assesses catalytic productions of these three monomers from food waste. The food waste-based routes to the target compounds are analyzed separately and compared to conventional petroleum-based routes. Even though no commercially available methods to directly convert food waste into the target molecules exist, we have suggested emerging and promising catalytic routes via combined processes. The proposed pathways for the renewable production of adipic acid, HMDA, and ε-caprolactam are not yet fully competitive with petrochemical pathways due to higher costs and lower process efficiencies. However, considering that the renewable food waste-based routes are still being developed, their commercialization should happen soon

Carbon dioxide-cofeeding pyrolysis of pine sawdust over nickle-based catalyst for hydrogen production

This study aimed to determine the synergistic effects of CO2 on the catalytic pyrolysis of pine sawdust over a Ni-based catalyst (Ni/SiO2) to establish a sustainable platform for H2 production. To elucidate the reaction mechanism, the CO2-cofeeding pyrolysis of pine sawdust was performed. The CO2-cofeeding pyrolysis of pine sawdust proved that the gas-phase reaction between CO2 and pyrolysates led to the increase in the amount of generated CO. The CO2 enhanced thermal cracking and dehydrogenation. These mechanistic features of CO2 were catalytically enhanced when Ni/SiO2 was employed as heterogeneous catalyst, which led to an increase in the amounts of generated H2 and CO. Hence, the CO that was additionally generated during the gas-phase reaction of CO2 and pyrolysates could be further converted into H2. In addition, CO2 could be looped in the CO2-cofeeding pyrolysis of pine sawdust. Furthermore, exploiting CO2 as raw material or reactive gas medium in the catalytic pyrolysis process also offered a strategic means for preventing coke formation

Air Pollution and Its Association with the Greenland Ice Sheet Melt

The Greenland Ice Sheet (GrIS) has been a topic of extensive scientific research over the past several decades due to the exponential increase in its melting. The relationship between air pollution and GrIS melting was reviewed based on local emission of air pollutants, atmospheric circulation, natural and anthropogenic forcing, and ground/satellite-based measurements. Among multiple factors responsible for accelerated ice melting, greenhouse gases have long been thought to be the main reason. However, it is suggested that air pollution is another piece of the puzzle for this phenomenon. In particular, black carbon (BC) and other aerosols emitted anthropogenically interact with clouds and ice in the Arctic hemisphere to shorten the cloud lifespan and to change the surface albedo through alteration of the radiative balance. The presence of pollution plumes lowers the extent of super cooling required for cloud freezing by about 4 °C, while shortening the lifespan of clouds (e.g., by altering their free-energy barrier to prompt precipitation). Since the low-level clouds in the Arctic are 2–8 times more sensitive to air pollution (in terms of the radiative/microphysical properties) than other regions in the world, the melting of the GrIS can be stimulated by the reduction in cloud stability induced by air pollution. In this study, we reviewed the possible impact of air pollution on the melting of the GrIS in relation to meteorological processes and emission of light-absorbing impurities. Long-term variation of ground-based AERONET aerosol optical depth in Greenland supports the potential significance of local emission and long-range transport of air pollutants from Arctic circle and continents in the northern hemisphere in rapid GrIS melting trend