Life cycle assessment of greenhouse gas emissions for various feedstocks-based biochars as soil amendment

Anaerobic fermentation integrated with pyrolysis for carbon resource recovery from food waste and biogas sludge: Effects of inoculation ratio and pyrolysis temperature

In view of the food waste (FW) as well as its digestate are both the organic sources of municipal solid waste, this study explored the anaerobic fermentation (AF) and following pyrolysis carbonization to co-disposal the two wastes for carbon resource recovery, including short chain organic acid (SCOAs), pyrolysis gas and biochar. Results indicated that both the rate and yield of SCOAs production both increase with the rising ratio of biogas sludge (BS) to FW, enhancing the soluble carbon recovery. The highest SCOAs production of 474.33 mg/g-VS was achieved at the ratio of 2:1 in 72 h. To further utilize the carbon source, the solids from the fermented residue (FR) was pyrolyzed at 400, 600 and 800 °C, respectively. Findings showed that the carbon content in biochar decreases with the increasing pyrolysis temperature, while the carbon in pyrolysis gas exhibits the opposite trend. Integrating the AF and pyrolysis contributed to a carbon recovery about 56.39% when the FW and BS were co-fermented at a 2:1 ratio, followed by its FR was pyrolyzed at 600 °C. Additionally, the biochar prepared under these conditions displayed a specific surface area (SSA) of 313.10 m2/g, along with abundant pore structures and functional groups, indicating its potential applications as pollutant adsorbents and soil amendments. This research offers a new perspective on efficiently recovering high-value carbon sources through the co-treatment of FW and its digestate via AF integrated with pyrolysis.

Sustainable removal of gaseous Hg0 using sulfur functionalized biochar: Adsorption experiment and life cycle assessment

Maximizing the sorption capacity of gaseous Hg0 by sulfur-functionalized biochar can lead to increased energy consumption and the production of secondary environmental pollutants such as greenhouse gases. This study evaluates the environmental impact of producing sulfurized biochar through a life cycle assessment (LCA), weighing these impacts against the benefits of enhanced Hg removal efficiencies. The biochar's Hg0 adsorption capacity, which ranges between 3 and 22 μg-Hg0/g-biochar, is influenced by several factors: it increases with higher sulfur loading (0-15 %), higher O2 levels (0-21 %), and longer pyrolysis times (1-5 h). However, it also decreases with increased pyrolysis temperature (100-500 °C). XPS and FT-IR analysis confirm that the sulfur in the biochar primarily exists as elemental sulfur, but each sulfurization condition also resulted in the formation of sulfate, organic sulfur, and sulfone. LCA results indicate that using biochar as a sorbent for Hg0 is carbon-negative when the biochar is disposed of in landfills. Sensitivity analysis showed that increasing mercury adsorption capacity through excessive investment in energy and resources does not necessarily reduce the overall environmental impact. Consequently, when selecting an adsorbent for mercury removal, it is crucial to consider both sorption capacity and environmental impact.

Greenhouse gas removal in agricultural peatland via raised water levels and soil amendment

Peatlands are an important natural store of carbon (C). Drainage of lowland peatlands for agriculture and the subsequent loss of anaerobic conditions had turned these C stores into major emitters of greenhouse gases (GHGs). Practical management strategies are needed to reduce these emissions, and ideally to reverse them to achieve net GHG removal (GGR). Here we show that a combination of enhanced C input as recalcitrant organic matter, CH4 suppression by addition of terminal electron acceptors, and suppression of decomposition by raising water levels has the potential to achieve GGR in agricultural peat. We measured GHG (CO2, N2O, and CH4) fluxes for 1 year with intensive sampling (6 times within the first 56 days) followed by monthly sampling in outdoor mesocosms with high (0 cm) and low (- 40 cm) water table treatments and five contrasting organic amendments (Miscanthus-derived biochar, Miscanthus chip, paper waste, biosolids, and barley straw) were applied to high water table cores, with and without iron sulphate (FeSO4). Biochar produced the strongest net soil C gain, suppressing both peat decomposition and CH4 emissions. No other organic amendment generated similar GGR, due to higher decomposition and CH4 production. FeSO4 application further suppressed CO2 and CH4 release following biochar addition. While we did not account for life-cycle emissions of biochar production, or its longer-term stability, our results suggest that biochar addition to re-wetted peatlands could be an effective climate mitigation strategy.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42773-024-00422-2.

Biochar for sustainable agriculture: Improved soil carbon storage and reduced emissions on cropland

Climate change, driven by excessive greenhouse gas (GHG) emissions from agricultural land, poses a serious threat to ecological security. It is now understood that significant differences exist in the responses of soil GHG emissions and soil carbon (C) sequestration to the application of different C-based materials (i.e., straw, organic manure (OM), and biochar). Therefore, elucidating the mechanisms by which differences in the properties of these materials affect soil GHG emissions is essential to comprehensively investigate the mechanisms through which variations in material properties influence soil GHG emissions. Herein, we conducted a field experiment to evaluate the responses of soil GHG emissions to cropland application of different C-based materials and employed molecular modeling calculations to explore the mechanisms by which differences in the properties of these materials affect soil GHG emissions. The results showed that biochar demonstrated superior resistance to biochemical decomposition and soil GHG adsorption capacity, leading to a significant reduction in soil GHG emissions due to its excellent physicochemical properties. The active surface properties of straw and OM enhanced their interaction with decomposing enzymes and accelerated their biochemical decomposition. Wheat-maize rotation with biochar application reduced CO2 emissions by 1089.8 kg CO2eq ha-1 and increased soil organic carbon by 141.8% compared to the control after one year. Collectively, these results contribute to the optimization of cropland application strategies for crop residues to balance soil C sequestration and soil GHG emissions, and to ensure sustainable agriculture and ecological security.

The effect of combined application of biochar and phosphate fertilizers on phosphorus transformation in saline-alkali soil and its microbiological mechanism

This study investigated the effects of combining Phragmites australis-based biochar, prepared at 400 °C, with various types of phosphate fertilizers-soluble, insoluble, and organic-on the content and transformation of phosphorus fractions in saline-alkali soil. Additionally, we explored microbiological mechanisms driving these transformations. The results showed that this combination significantly increased the concentrations of dicalcium phosphate (Ca2P), octacalcium phosphate (Ca8P), aluminum phosphate (AlP), moderately labile organic phosphorus (MLOP), and resistant organic phosphorus (MROP) in soil. Conversely, the levels of hydroxyapatite (Ca10P) and highly resistant organic phosphorus (HROP) decreased. The increase in labile organic phosphorus (LOP) content or decrease in iron phosphate (FeP) was found to effectively enhance the availability of Olsen phosphorus (Olsen-P) in soil. Furthermore, the study revealed that biochar mixed with organic phosphate fertilizers increased the activity of soil acid phosphatase (ACP) and neutral phosphatase (NEP), while reducing alkaline phosphatase (ALP) activity. In contrast, biochar combined with soluble and insoluble phosphate fertilizers decreased the activity of ACP (22.59 % and 28.57 %, respectively) and NEP (62.50 % and 11.11 %, respectively), with the combination with insoluble fertilizers also reducing ALP activity by 55.84 %, whereas the soluble combination increased it by 190.34 %. Additionally, the co-application of biochar and phosphate fertilizers altered the composition and abundance of the gene phoD-harboring microbial community, enhancing the abundance of Proteobacteria and reducing that of Actinobacteria. Correlation analysis between phoD-functional microbial species and various phosphorus fractions showed that Rhodopseudomonas was significantly associated with several phosphorus components, exhibiting a positive correlation with Ca2P, Ca8P, AlP, LOP, MLOP, and MROP, but a negative relationship with Ca10P. These findings suggest that the combined application of biochar and phosphate fertilizers could change the abundance of Rhodopseudomonas, potentially influencing phosphorus cycling in the soil. This research provides a strong scientific foundation for the efficient combined use of biochar and phosphate fertilizers in managing saline-alkali soil.

Maize straw increases while its biochar decreases native organic carbon mineralization in a subtropical forest soil

Organic soil amendments have been widely adopted to enhance soil organic carbon (SOC) stocks in agroforestry ecosystems. However, the contrasting impacts of pyrogenic and fresh organic matter on native SOC mineralization and the underlying mechanisms mediating those processes remain poorly understood. Here, an 80-day experiment was conducted to compare the effects of maize straw and its derived biochar on native SOC mineralization within a Moso bamboo (Phyllostachys edulis) forest soil. The quantity and quality of SOC, the expression of microbial functional genes concerning soil C cycling, and the activity of associated enzymes were determined. Maize straw enhanced while its biochar decreased the emissions of native SOC-derived CO2. The addition of maize straw (cf. control) enhanced the O-alkyl C proportion, activities of β-glucosidase (BG), cellobiohydrolase (CBH) and dehydrogenase (DH), and abundances of GH48 and cbhI genes, while lowered aromatic C proportion, RubisCO enzyme activity, and cbbL abundance; the application of biochar induced the opposite effects. In all treatments, the cumulative native SOC-derived CO2 efflux increased with enhanced O-alkyl C proportion, activities of BG, CBH, and DH, and abundances of GH48 and cbhI genes, and with decreases in aromatic C, RubisCO enzyme activity and cbbL gene abundance. The enhanced emissions of native SOC-derived CO2 by the maize straw were associated with a higher O-alkyl C proportion, activities of BG and CBH, and abundance of GH48 and cbhI genes, as well as a lower aromatic C proportion and cbbL gene abundance, while biochar induced the opposite effects. We concluded that maize straw induced positive priming, while its biochar induced negative priming within a subtropical forest soil, due to the contrasting microbial responses resulted from changes in SOC speciation and compositions. Our findings highlight that biochar application is an effective approach for enhancing soil C stocks in subtropical forests.

Influencing factors and spatiotemporal heterogeneity of livestock greenhouse gas emission: Evidence from the Yellow River Basin of China

Livestock is one of major sources of greenhouse gas (GHG) emissions in China. Clarifying spatiotemporal characteristics of GHG emissions from livestock and exploring influencing factors can provide reference for grasping regional changes of GHG emission and formulate strategies of carbon reduction for livestock industry. However, existing literatures considered both spatial and temporal impacts and dynamic evolution trend of these factors seldomly. This paper used the life cycle assessment (LCA) method to estimate GHG emissions of livestock in 114 cities of the YRB from 2000 to 2021. On this basis, spatiotemporal heterogeneity of influencing factors was analyzed by using geographically and temporally weighted regression (GTWR) model. Finally, future evolution trend of GHG emissions from livestock was predicted by combining traditional and spatial Markov chain. Four main results were listed as follows. Firstly, GHG emission in the life cycle of livestock industry increased from 57.202 million tons (Mt) carbon dioxide equivalent (CO2e) in 2000 to 77.568 Mt CO2e in 2021. Secondly, structure of livestock industry, labor flow and mechanization were vital factors that led to increase of GHG emissions from livestock. Positive effects of labor flow and mechanization were increasing year by year, while negative effect of urbanization and positive effect of economic development were decreasing year by year. Markov chain analysis shown that probability of keeping high level of GHG emissions of livestock in the YRB unchanged were 96% (T = 1) and 90% (T = 5), and there also existed a Matthew effect. In addition, probability of level transfer of GHG emission in urban livestock was spatially dependent. Government should formulate strategies for livestock development and optimize low-carbon transformation of energy structure for livestock and poultry husbandry based on local conditions and key driving factors in the future. Meanwhile, boundaries of administrative divisions should be broken to promote reduction of GHG emissions in livestock comprehensively.