Recognizing that bioenergy with carbon capture and storage (BECCS) may still take years to mature, this study focuses on another photosynthesis-based, negative-carbon technology that is readier to ...implement in China: biomass intermediate pyrolysis poly-generation (BIPP). Here we find that a BIPP system can be profitable without subsidies, while its national deployment could contribute to a 61% reduction of carbon emissions per unit of gross domestic product in 2030 compared to 2005 and result additionally in a reduction in air pollutant emissions. With 73% of national crop residues used between 2020 and 2030, the cumulative greenhouse gas (GHG) reduction could reach up to 8620 Mt CO
-eq by 2050, contributing 13-31% of the global GHG emission reduction goal for BECCS, and nearly 4555 Mt more than that projected for BECCS alone in China. Thus, China's BIPP deployment could have an important influence on achieving both national and global GHG emissions reduction targets.
•Feedstock and temperature influence specific biochar properties to a different extent.•Heterogeneity depended on feedstock and temperature were compared quantitatively.•Carbon sequestration, fixed C ...and minerals were determined by feedstock.•Biochar pH, specific surface area and recalcitrance were dominated by temperature.•Alkyl-C, aliphatic-C and aromatic-C were more highly related to temperature.
The aim of this study was to quantify the influence of the two main categories of factors determining the yield and properties of biochar, i.e., feedstock properties and production conditions, here represented by the highest treatment temperature (HTT). To achieve this, a wide range of production temperatures (200–650°C) and an extensive set of diverse feedstock (n=12) were used to calculate the sensitivity. The quantitative evaluation was based on statistical analysis of coefficients of variation, and thus derived indices representing the extent of influence of the two factors, i.e., a feedstock-depended heterogeneity (HF) and a temperature-depended heterogeneity (HT). The results showed that both feedstock properties and production conditions are important for determining the yield and properties of biochar, but their respective influence changes with the property or set of properties of interest. The biochar parameters most affected by feedstock properties were e.g., total organic carbon, fixed carbon, and mineral elements of biochar. On the other hand, biochar surface area and pH was mainly influenced by highest treatment temperature. Biochar recalcitrance was mainly determined by production temperature, while the potential total C sequestration (product of recalcitrance and pyrolysis carbon yield) depended more on feedstock. Overall, the work sheds some light on the relative importance of different biochar production process parameters on the final biochar product, which is an important step towards “designed” biochar.
•Chemical components and characteristics of microalgae and macroalgae are discussed.•Algal biochar uses in soil, wastewater treatment, and supercapacitors are discussed.•Overview of bio-oil ...production by conventional and advanced pyrolysis is provided.
Algae, as a feedstock with minimum land footprint, is considered a promising biomass for sustainable fuels, chemicals, and materials. Unlike lignocellulosic biomass, algae consist mainly of lipids, carbohydrates, and proteins. This review focusses on the bio-oil and biochar co-products of algae-pyrolysis and presents the current state-of-the-art in the pyrolysis technologies and key applications of algal biochar. Algal biochar holds potential to be a cost-effective fertilizer, as it has high P, N and other nutrient contents. Beyond soil applications, algae-derived biochar has many other applications, such as wastewater-treatment, due to its porous structure and strong ion-exchange capacity. High specific capacitance and stability also make algal biochar a potential supercapacitor material. Furthermore, algal biochar can be great catalysts (or catalyst supports). This review sheds light on a wide range of algae-pyrolysis related topics, including advanced-pyrolysis techniques and the potential biochar applications in soil amendment, energy storage, catalysts, chemical industries, and wastewater-treatment plants.
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•Fe doping using iron rich waste increases the pyrolysis gas energy content.•Goethite is thermally reduced to magnetite/maghemite during pyrolysis.•Fe doped activated biochars show ...excellent magnetic properties.•Magnetic biochars display increased adsorption capacity for emerging contaminants.
Magnetic carbons can significantly lower the costs of wastewater treatment due to easy separation of the adsorbent. However, current production techniques often involve the use of chlorinated or sulfonated Fe precursors with an inherent potential for secondary pollution. In this study, ochre, an iron-rich waste stream was investigated as a sustainable Fe source to produce magnetic activated biochar from two agricultural feedstocks, softwood and wheat straw. Fe doping resulted in significant shifts in pyrolysis yield distribution with increased gas yields (+50%) and gas energy content (+40%) lowering the energy costs for production. Physical activation transformed ochre to magnetite/maghemite resulting in activated magnetic biochars and led to a 4-fold increase in the adsorption capacities for two common micropollutants – caffeine and fluconazole. The results show that Fe doping not only benefits the adsorbent properties but also the production process, leading the way to sustainable carbon adsorbents.
Biochar can be contaminated during pyrolysis by re-condensation of pyrolysis vapours. In this study two biochar samples contaminated by pyrolysis liquids and gases to a high degree, resulting in high ...volatile organic compound (high-VOC) content, were investigated and compared to a biochar with low volatile organic compound (low-VOC) content. All biochar samples were produced from the same feedstock (softwood pellets) under the same conditions (550 °C, 20 min mean residence time). In experiments where only gaseous compounds could access germinating cress seeds (Lepidium sativum), application amounts ranging from 1 to 30 g of high-VOC biochar led to total inhibition of cress seed germination, while exposure to less than 1 g resulted in only partial reduction. Furthermore, leachates from biochar/sand mixtures (1, 2, 5 wt.% of biochar) induced heavy toxicity to germination and showed that percolating water could dissolve toxic compounds easily. Low-VOC biochar didn't exhibit any toxic effects in either germination test. Toxicity mitigation via blending of a high-VOC biochar with a low-VOC biochar increased germination rate significantly. These results indicate re-condensation of VOCs during pyrolysis can result in biochar containing highly mobile, phytotoxic compounds. However, it remains unclear, which specific compounds are responsible for this toxicity and how significant re-condensation in different pyrolysis units might be.
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•Re-condensation of vapours during pyrolysis can produce VOC-rich biochars.•Vapours and leachates from VOC-rich biochars inhibited cress seed germination.•Reduction of biochar toxicity through storage and blending was partly successful.•Re-condensed compounds from pyrolysis are mobile and phytotoxic.
► Effect of pyrolysis conditions on biochar properties, particularly its stability. ► Relative stability of biochar increased with pyrolysis temperature. ► Yield of stable carbon showed only minor ...dependence on the pyrolysis temperature. ► Labile carbon presents only minor fraction of biochar.
Biochar, a solid product of biomass pyrolysis, is a promising concept for climate change mitigation and adaptation, as it can sequester atmospheric CO2 while improving quality of soil where it is stored. However, for this potential to be realised, it is necessary for biochar to have high environmental stability, i.e., resist various decomposition processes over long time. The main objective of this work has been to relate biochar production conditions to the yield, and properties of biochar, particularly its long-term stability. We used our lab-scale pyrolysis facilities to produce biochar at three temperatures between 350°C and 550°C, from selected feedstock (pine, mixed larch and spruce chips, softwood pellets). We measured the yield of biochar and then used an accelerated ageing assay to obtain information on the stability of biochar. Such information is very important for the assessment of the climate change mitigation potential of biochar, as it has not yet been clearly defined what proportion of biochar actually remains “permanently” sequestered and how much is released back to the atmosphere in the short to medium term. The results of this work showed that despite increase in the stability of biochar with increasing pyrolysis temperature, the yield of stable biochar fraction is nearly independent of the temperature. These findings are essential for the optimisation of pyrolysis conditions for production of biochar with selected properties, as well as for modelling biochar systems and their climate change mitigation potential as compared to other uses of biomass, such as bioenergy, biofuels and/or chemicals.
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•H2, CH4, C2H6 and CO increased with temperature resulted in a higher gas HHV.•The lower energy limit was surpassed by all pyrolysis at ⩾450°C.•The upper energy limit was only reached ...during pyrolysis at 650°C.•Solid and liquid by-products utilised for high value products rather than as a fuel.
This work aimed to investigate the impact of highest treatment temperature (HTT), heating rate, carrier gas flow rate and feedstock on the composition and energy content of pyrolysis gas to assess whether a self-sustained system could be achieved through the combustion of the gas fraction alone, leaving other co-products available for alternative high-value uses. Calculations based on gas composition showed that the pyrolysis process could be sustained by the energy contained within the pyrolysis gases alone. The lower energy limit (6% biomass higher heating value (HHV)) was surpassed by pyrolysis at ⩾450°C while only a HTT of 650°C consistently met the upper energy limit (15% biomass HHV). These findings fill an important gap in literature related to the energy balance of the pyrolysis systems for biochar production, and show that, at least from an energy balance perspective; self-sustained slow pyrolysis for co-production of biochar and liquid products is feasible.
The physical properties of biochar have been shown to dramatically influence its performance as a soil amendment. This study assessed the role of biochar particle size and hydrophobicity in ...controlling soil water movement and retention. Softwood pellet biochar in five particle size ranges (>2 mm, 2–0.5 mm, 0.5–0.25 mm, 0.25–0.063 mm and <0.063 mm) was used for the experiment. These particle sizes were tested on two soil types (sandy loam and loamy sand) at four different application rates (1, 2, 4 and 8%) in the laboratory. Soil water suction at wet range and dry range were measured using the Hyprop and WP4‐T, respectively. From this, the moisture content at field capacity (θfc), permanent wilting point (θpwp) and plant available water (θawc), were determined. Saturated hydraulic conductivity (Ksat) was measured using the KSAT device and biochar hydrophobicity was determined using the ethanol drop test method. Our results showed that biochar hydrophobicity increased with decreasing biochar particle size, leading to a reduction in its water retention capacity. The highest θfc (0.087 cm−3 cm−3) and θawc (0.064 cm−3 cm−3) were observed for soils amended with >2 mm biochar. The soil hydraulic conductivity increased with decreasing biochar particle sizes, with the exception of <0.063 mm biochar, which showed a significant (p ≤ 0.05) decrease in soil hydraulic conductivity compared to the larger particle sizes. The results clearly showed that both biochar intraporosity (pores inside biochar particles) and interporosity (pore spaces between biochar and soil particles) are important factors affecting amended soil hydraulic properties. Biochar interpores affected mainly hydraulic conductivity; both interpores and intrapores controlled soil water retention properties. Our results suggest that for a more effective increase in soil water retention of coarse soils, the use of hydrophilic biochar with high intraporosity is recommended.
Highlights
Biochar increases soil water retention and reduces hydraulic conductivity.
Hydrophobicity of biochar increased with decreasing particle size.
Coarse biochar particles increased soil water retention due to hydrophilic surfaces and increased intraporosity.
Fine biochar particles decreased hydraulic conductivity due to reduced macropores.
•Multi-modified clay composites show better performance than single-modified clays.•Clay composites with various modifications exhibit different absorption mechanisms.•Clay-biochar composites ...represent an environmentally superior alternative.
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Adsorption techniques offer unique advantages owing to the use of synthetic (e.g., nanosized metal oxides and polymer-functionalized nanocomposites) and natural (e.g., clay and biochar) materials for pollutant removal. Although the most widely used adsorbent is activated carbon, extensive studies have highlighted the promising potential of modified clay minerals and biochar for removing heavy metal and organic pollutants from industrial, drinking, and eutrophic wastewater, due to their low cost and easy accessibility. However, clay modification using acids, calcination, polymers, or surfactants exhibits relatively low absorption/regeneration ability towards antibiotics, aromatics, and various dyes. The coexistence of numerous contaminants in industrial wastewater inhibited the performance of adsorbents, which accelerated the development of novel modified clay composites such as clay-biochar, organo-bentonite/sodium alginate beads, and enhanced biochar. This review summarizes recent studies and absorption mechanisms concerning clay composites based on various modification methods and component materials. The comparison of clay composites used for the removal of organic and inorganic contaminants provides valuable insight into real wastewater treatment. Knowledge gaps, uncertainties, and future challenges involved in the fabrication and regeneration of modified clay composites are also identified.
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