Microwave-assisted combustion to produce benzene polycarboxylic acids as molecular markers for biochar identification and quantification

Biochar is a promising carbon dioxide removal (CDR) technology for climate change mitigation. Current procedures for its determination are lengthy, labor-intensive, and difficult to conduct. Benzene polycarboxylic acids (BPCA) are the most promising molecular markers for identification and quantification of biochar and its quality as they specifically represent the stable polyaromatic backbone of biochar. Therefore, using the BPCA method, its stability and, thus, its C sequestration potential could be used for CDR accounting. The current BPCA method relies on a specific high-pressure digestion apparatus, which is not available around the world. Therefore, the aims of the present work were (i) to compare the conventional high-pressure nitric acid oxidation with a microwave-assisted digestion technique and optimize the oxidation conditions in such a way that previous results are comparable with future ones, and (ii) to significantly reduce the digestion time of soil samples of 8 h and to develop a suitable routine method that produces comparable and reproducible results. For this purpose, soil and control sample series were prepared for different temperature–time-program. Obtained results were compared with the values of the conventional method both for individual samples and for the whole dataset separately. To ensure the representativeness of the results, in addition to various soil samples with different properties, we included two reference materials into our data set, one without biochar (wheat flour) and a biochar sample. Our results showed that conventional nitric acid oxidation in the BPCA determination at 170 °C and 8 h can be substituted by digestion in a microwave reaction system (CEM Mars6) at 190 °C and 1 h. Our results further showed that this condition needs to be strictly matched, because, otherwise, over- or underestimation of biochar quantity and/or quality will be the consequence. The goal of a less time-consuming BPCA extraction from soil samples was achieved by reducing the extraction time from 8 to 1 h using the microwave-assisted method. However, one disadvantage of the new method is that five times more sample material and chemicals are needed for further BPCA analysis, compared to the original method.

Biochar alleviates metal toxicity and improves microbial community functions in a soil co-contaminated with cadmium and lead

Soil amendment with biochar alleviates the toxic effects of heavy metals on microbial functions in single-metal contaminated soils. Yet, it is unclear how biochar application would improve microbial activity and enzymatic activity in soils co-polluted with toxic metals. The present research aimed at determining the response of microbial and biochemical attributes to addition of sugarcane bagasse biochar (SCB) in cadmium (Cd)-lead (Pb) co-contaminated soils. SCBs (400 and 600 °C) decreased the available concentrations of Cd and Pb, increased organic carbon (OC) and dissolved organic carbon (DOC) contents in soil. The decrease of metal availability was greater with 600 °C SCB than with 400 °C SCB, and metal immobilization was greater for Cd (16%) than for Pb (12%) in co-spiked soils amended with low-temperature SCB. Biochar application improved microbial activity and biomass, and enzymatic activity in the soils co-spiked with metals, but these positive impacts of SCB were less pronounced in the co-spiked soils than in the single-spiked soils. SCB decreased the adverse impacts of heavy metals on soil properties largely through the enhanced labile C for microbial assimilation and partly through the immobilization of metals. Redundancy analysis further confirmed that soil OC was overwhelmingly the dominant driver of changes in the properties and quality of contaminated soils amended with SCB. The promotion of soil microbial quality by the low-temperature SCB was greater than by high-temperature SCB, due to its higher labile C fraction. Our findings showed that SCB at lower temperatures could be applied to metal co-polluted soils to mitigate the combined effects of metal stresses on microbial and biochemical functions.

Environmental life cycle assessment of supercapacitor electrode production using algae derived biochar aerogel

Porous carbon aerogel material has gained an increasing attraction for developing supercapacitor electrodes due to its cost-effective synthesis process and relatively high electrochemical performance. However, the environmental performances of supercapacitor electrodes produced from different carbon aerogel materials are never comparatively studied, hindering our knowledge of supercapacitor electrode production in a sustainable pattern. In this study, nitrogen-doped biochar aerogel-based electrode (BA-electrode) produced from Entermorpha prolifera was simulated to investigate the environmental performance by using life cycle assessment method. For comparison, the assessment of graphene oxide aerogel-based electrode (GOA-electrode) was also carried out. It can be observed that the life cycle global warming potential for the BA-electrode was lower than that of GOA-electrode with a reduction of 53.1‒68.1%. In comparison with GOA-electrode, the BA-electrodes endowed smaller impacts on environment in majority of impact categories. Moreover, in comparison with GOA-electrode, the environmental damages of BA-electrode were greatly decreased by 35.8‒56.4% (human health), 44.9‒62.6% (ecosystems), and 87.0‒91.2% (resources), respectively. The production stages of GOA and graphene oxide and stages of nitrogen-doped biochar aerogel production and Entermorpha prolifera drying were identified as the hotspots of environmental impact/damage for the GOA-electrode and BA-electrode, respectively. Overall, this finding highlights the efficient utilization of algae feedstock to construct a green and sustainable technical route of supercapacitor electrode production.

Post-processing of biochars to enhance plant growth responses: a review and meta-analysis

A number of processes for post-production treatment of “raw” biochars, including leaching, aeration, grinding or sieving to reduce particle size, and chemical or steam activation, have been suggested as means to enhance biochar effectiveness in agriculture, forestry, and environmental restoration. Here, I review studies on post-production processing methods and their effects on biochar physio-chemical properties and present a meta-analysis of plant growth and yield responses to post-processed vs. “raw” biochars. Data from 23 studies provide a total of 112 comparisons of responses to processed vs. unprocessed biochars, and 103 comparisons allowing assessment of effects relative to biochar particle size; additional 8 published studies involving 32 comparisons provide data on effects of biochar leachates. Overall, post-processed biochars resulted in significantly increased average plant growth responses 14% above those observed with unprocessed biochar. This overall effect was driven by plant growth responses to reduced biochar particle size, and heating/aeration treatments. The assessment of biochar effects by particle size indicates a peak at a particle size of 0.5–1.0 mm. Biochar leachate treatments showed very high heterogeneity among studies and no average growth benefit. I conclude that physiochemical post-processing of biochar offers substantial additional agronomic benefits compared to the use of unprocessed biochar. Further research on post-production treatments effects will be important for biochar utilization to maximize benefits to carbon sequestration and system productivity in agriculture, forestry, and environmental restoration.