Exploring the carbon capture and sequestration performance of biochar-artificial aggregate using a new method

Interaction of reed litter and biochar presences on performances of constructed wetlands

Constructed wetlands (CWs) are frequently used for effective biological treatment of nitrogen-rich wastewater with external carbon source addition; however, these approaches often neglect the interaction between plant litter and biochar in biochar-amended CW environments. To address this, we conducted a comprehensive study to assess the impacts of single or combined addition of common reed litter and reed biochar (pyrolyzed at 300 and 500 °C) on nitrogen removal, greenhouse gas emission, dissolved organic matter (DOM) dynamics, and microbial activity. The results showed that combined addition of reed litter and biochar to CWs significantly improved nitrate and total nitrogen removal compared with biochar addition alone. Compared to those without reed litter addition, CWs with reed litter addition had more low-molecular-weight and less aromatic DOM and more protein-like fluorescent DOM, which favored the enrichment of bacteria associated with denitrification. The improved nitrogen removal could be attributed to increases in denitrifying microbes and the relative abundance of functional denitrification genes with litter addition. Moreover, the combined addition of reed litter and 300 °C-heated biochar significantly decreased nitrous oxide (30.7 %) and methane (43.9 %) compared to reed litter addition alone, while the combined addition of reed litter and 500 °C-heated biochar did not. This study demonstrated that the presences of reed litter and biochar in CWs could achieve both high microbial nitrogen removal and relatively low greenhouse gas emissions.

Using the Conditional Process Analysis Model to Characterize the Evolution of Carbon Structure in Taxodium ascendens Biochar with Varied Pyrolysis Temperature and Holding Time

Temperature determines biochar structure during pyrolysis. However, differences in holding time and feedstock types may affect this relationship. The conditional process analysis model was used in this paper to investigate the potential to affect this mechanism. The branch and leaf parts of Taxodium ascendens were separately pyrolyzed at 350, 450, 650, and 750 °C, and kept for 0.5, 1, and 2 h at each target temperature. We measured the fixed carbon and ash contents and the elemental composition (C, H, O and N) of the raw materials and their char samples. After plotting a Van Krevelen (VK) diagram to determine the aromatization of chars, the changes in the functional groups were analyzed using Fourier transform infrared (FTIR), Raman, and X-ray photoelectron spectroscopy (XPS). The results revealed that pyrolysis at temperatures between 450 and 750 °C accounted for the aromatization of biochar because the atomic H/C ratio of branch-based chars (BC) decreased from 0.53-0.59 to 0.15-0.18, and the ratio of leaf-based chars (LC) decreased from 0.56-0.68 to 0.20-0.22; the atomic O/C ratio of BC decreased from 0.22-0.27 to 0.08-0.11, while that of LC decreased from 0.26-0.28 to 0.18-0.21. Moreover, the average contents of N (1.89%) and ash (13%) in LC were evidently greater than that in BC (N:0.62%; Ash: 4%). Therefore, BC was superior to LC in terms of the stability of biochar. In addition, the increasing ID/IG and ID/I(DR+GL) ratios in BC and LC indicated an increasing amount of the amorphous aromatic carbon structure with medium-sized (2~6 rings) fused benzene rings. According to the CPA analysis, an extension of the holding time significantly enhanced the increase in aromatic structures of LC with temperature. But this extension slightly reduced the growth in aromatic structures of BC. All indicate that holding time and feedstock types (branch or leaf feedstock) could significantly affect the variation in biochar aromatic structure with respect to temperature.

CO2 utilization and sequestration in ready-mix concrete-A review

CO2 utilization and sequestration in concrete have been gaining increased attention in recent years. CO2 can be injected into ready-mix concrete, which is defined as carbonation ready-mix concrete (CRC) showing a huge CO2 sequestration potential. CRC technology was comprehensively reviewed in this paper. Firstly, the methods of CRC technology in lab and industrial production were summarized. Then, special attentions were paid to the hydration reaction combined with the carbonation reaction in CRC. The factors affecting the capacity of CO2 sequestration in CRC were also discussed. Furthermore, the workability, mechanical property, and durability of CRC were evaluated. Finally, based on life cycle assessment (LCA), the CO2 footprint and carbon index of CRC were analyzed.

The influence of biomass type on hydrothermal carbonization: Role of calcium oxalate in enhancing carbon sequestration of hydrochar

Addressing climate change through effective carbon sequestration strategies is critical. This study presents an investigation into the hydrothermal carbonization (HTC) and co-hydrothermal carbonization (Co-HTC) of invasive plants (IPs) to produce hydrochars to unveil the significant impact of biomass type and unique mineral on the stability of hydrochars. Nine hydrochars were produced from six IPs, utilizing both single and mixed biomass. A key finding is the observable that calcium oxalate forms as a surface mineral during HTC through different characterization techniques, the presence of which notably influenced the stability of hydrochars, resulting in enhanced thermal (highest R50 = 0.81) and chemical (lowest carbon loss rate = 4.02%) stability of hydrochars, possibly acting as a protective layer. Besides, a positive correlation was established between the yield of hydrochars and the lignin content of the original biomass. It is also observed that Co-HTC of plant materials rich in Ca2+ can enhance the formation of calcium oxalate minerals. This is likely due to their synergistic role in the HTC process, promoting the release of more C2O42- and Ca2+. Our results signify the crucial role of biomass composition in the HTC process and spotlight the potential of calcium oxalate in augmenting hydrochar stability. This study offers valuable insights that bolster the theoretical framework for employing hydrochar derived from IPs as a potent material for carbon sequestration.

Biomass Pyrolysis-Derived Biochar: A Versatile Precursor for Graphene Synthesis

Graphene, a two-dimensional carbon allotrope with a honeycomb structure, has emerged as a material of immense interest in diverse scientific and technical domains. It is mainly produced from graphite by mechanical, chemical and electrochemical exfoliation. As renewable energy and source utilization increase, including bioenergy from forest and woody residues, processed, among other methods, by pyrolysis treatment, it can be expected that biochar production will increase too. Thus, its useful applications, particularly in obtaining high-added-value products, need to be fully explored. This study aims at presenting a comprehensive analysis derived from experimental data, offering insights into the potential of biomass pyrolysis-derived biochar as a versatile precursor for the controlled synthesis of graphene and its derivatives. This approach comprehended the highest energy output and lowest negative environmental footprint, including the minimization of both toxic gas emissions during processing and heavy metals' presence in the feedstock, toward obtaining biochar suitable to be modified, employing the Hummers and intercalation with persulfate salts methods, aiming at deriving graphene-like materials. Material characterization has revealed that besides morphology and structural features of the original wooden biomass, graphitized structures are present as well, which is proven clearly by Raman and XPS analyses. Electrochemical tests revealed higher conductivity in modified samples, implying their graphene-like nature.

Carbonation of steel slag at low CO2 concentrations: Novel biochar cold-bonded steel slag artificial aggregates

Carbonation technology resolves the volume expansion of steel slag by combining CO2 with f-CaO, but the previous stringent carbonation conditions (99%vol) significantly limit the application prospect of steel slag. To achieve the carbonation of steel slag at lower CO2 concentrations, a novel cold-bonded artificial aggregates (CASSAs) based on steel slag and biochar is produced in this paper. The carbon capture capacities of CASSAs with different biochar contents (5 wt%, 10 wt%, and 15 wt%) are investigated in a low-CO2 concentration environment (10.79 % vol) and natural environment using the porosity and CO2 adsorption capacity of biochar. The changes in the performance of CASSAs before and after carbonation are investigated at different curing ages (7 d and 28 d). The results reveal that biochar increases the pores of the CASSAs. At 7 d, B15 achieves complete carbonation at low concentrations and can uptake 6.5 wt% of CO2. CO2 adsorption capacity by biochar in the natural environment facilitates the diffusion of CO2 in CASSAs. Regarding mechanical properties, the addition of biochar makes B15 at 7 d half as strong as B0, but B15 exhibits long-term strength development. B15 at 7 d has a strength of 8.49 MPa after carbonation, which is almost the same as B0. In addition, B15 achieves a net CO2 emission of -39.9 kg/ton. This study combines biochar with CASSAs to provide a potential method to carbonate steel slag at low CO2 concentrations. A new methodology was also used to quantitatively assess the ability of biochar CASSAs to solidify CO2 under low concentration conditions and natural environments from a macroscopic perspective. Biochar CASSAs have great potential to realize resource utilization and carbon capture from steel slag.