Production and characterization of biochar produced from co-pyrolysis of lignocellulosic biomass and plastic mulching sheets

Agricultural biomass waste contaminated with agricultural plastics is a prominent waste stream in intense agricultural areas and complete separation of the plastic residues from the biomass is not always straightforward There is a high possibility to use agricultural biomass and agricultural plastic wastes together in a single stream to produce valuable products via pyrolysis. However, effect of small scale plastic material presence on pyrolysis product yield is still unknown. Hence, the effect of low levels of agricultural plastics in the biomass on the mass balance and product composition of pyrolysis products were examined during this study. Co-pyrolysis of mixed soft wood and low-density polyethylene (black color agricultural plastic used for mulching) was carried out at 500 ºC in a mini pyrolysis reactor set up. The produced char was characterized using proximate, elemental analysis, thermogravimetric analysis and analytical pyrolysis at 750 ºC using PyGC/MS. Five types of char were produced during this study. Namely soft wood only (0%AgPlC) and mixtures of 1%, 5%, 10%, and 25% agricultural plastic material and soft wood (mass basis), referred to as 1%AgPlC, 5%AgPlC, 10%AgPlC and 25%AgPlC respectively. According to the mass balances experimentally obtained, the char yield was not significantly altered after incorporation of the plastic material into the feedstock. However increased plastic mass fraction increased the yield in tar/oil and decreased the gas yield. Moreover, the fixed C content and total C content were reduced and volatile matter content, total H content and H/C molar ratio were increased in the char material with increased levels of plastic in the feedstock. This indicates the lower stability of char produced with higher plastic levels. According to the analytical pyrolysis results of the char, molecular compounds composition was varying after plastic material incorporation. Phenol, toluene and xylene peak area percentage were higher in plastic incorporated char materials. These results can be used to understand the biomass and plastic interaction during pyrolysis. Further studies are recommended to identify the contaminants in the products of copyrolysis of agricultural biomass feedstocks contaminated with plastics

Distinct spatial dependency of carbon distribution between soil pools in grassland SOIL

Grassland soils play a key role in climate change and food security, and carbon (C) and nitrogen (N) mineralization is central to this. Although there are a number of mathematical models available to estimate C and N mineralization, they do not encompass the variability of the process and there is uncertainty in their predictions. The input parameters of the SOMA model (Soil Organic Matter “A”) have been conceptualized and validated to predict mineralization in arable soils. The objective of this research was to measure the spatial dependence of the input parameters in order to further ob - tain spatial predictions of mineralisation in a grassland system. A nested design was applied using sampling intervals of 30 m, 10 m, 1 m, and 0.12 m as sources of variation. From each sampling point a soil sample was taken (0-23 cm) and physical sequential fractionation was applied to obtain the free light fraction (FLF) and intra-aggregate light fraction (IALF). The C and N contents in the fractions were measured by mass spectrometry, and the results analysed by residual maximum likelihood (REML) to obtain components of variance at each stage, and then accumulated to plot the approach to a variogram. Both fractions showed spatial dependence at the finest scales measured, and the general pattern was different from that in an arable site. The recommended soil sampling interval where C and N mineralization predictions would be spatially distributed according to the correlation of input light fractions parameters of SOMA is 0.5m

How to trace back an unknown production temperature of biochar from chemical characterization methods in a feedstock independent way

Besides the feedstock composition, the highest treatment temperature (HTT) in pyrolysis is one of the key production parameters. The latter determines the feedstock’s carbonization extent, which influences physicochemical properties of the resulting biochar, and in consequence its performance in industrial and agricultural applications. The actual HTT of biomass is difficult to measure in a reliable manner in many large-scale pyrolysis units (e.g., rotary kilns). Therefore, producers and end-users often rely on unreliable or biased information regarding this key production parameter that affects biochar quality. Data from indirect chemical assessment methods of biochar’s carbonization extent correlate well with the highest treatment temperature. Therefore, this study demonstrates that the HTT can be accurately assessed posteriori and feedstock-independently via a simple-to-use model based on biochar characteristics related to the carbonization extent. For that purpose, 24 contrasting biochars from 12 different feedstocks produced in the most common production temperature range of 350-700 °C were analysed using 5 different established biochar chemical characterization methods. Then, experimental data was used to establish a multilinear regression model capable of correlating the HTT, which was successfully validated for external datasets. The correlation accuracy for biochars of various origin (lignocellulosic, manure) was satisfactorily high (R2adj. = 0.853, RSME =47 °C). The obtained correlation proved that the HTT can be predicted feedstock independently with the use of basic input data. It also provides a quick, simple, and reliable tool to verify the HTT of a given biochar

Passive CO₂ removal in urban soils:evidence from brownfield sites

Management of urban brownfield land can contribute to significant removal of atmospheric CO2 through the development of soil carbonate minerals. However, the potential magnitude and stability of this carbon sink is poorly quantified as previous studies address a limited range of conditions and short durations. Furthermore, the suitability of carbonate-sequestering soils for construction has not been investigated. To address these issues we measured total inorganic carbon, permeability and ground strength in the top 20 cm of soil at 20 brownfield sites in northern England, between 2015 and 2017. Across all sites accumulation occurred at a rate of 1–16 t C ha−1 yr−1, as calcite (CaCO3), corresponding to removal of approximately 4–59 t CO2 ha−1 yr−1, with the highest rate in the first 15 years after demolition. C and O stable isotope analysis of calcite confirms the atmospheric origin of the measured inorganic carbon. Statistical modelling found that pH and the content of fine materials (combined silt and clay content) were the best predictors of the total inorganic carbon content of the samples. Measurement of permeability shows that sites with carbonated soils possess a similar risk of run-off or flooding to sandy soils. Soil strength, measured as in-situ bearing capacity, increased with carbonation. These results demonstrate that the management of urban brownfield land to retain fine material derived from concrete crushing on site following demolition will promote calcite precipitation in soils, and so offers an additional CO2 removal mechanism, with no detrimental effect on drainage and possible improvements in strength. Given the large area of brownfield land that is available for development, the contribution of this process to CO2 removal by urban soils needs to be recognised in CO2 mitigation policies

Practical assessment of biochar stability indicators: Sensitivity to feedstock type and production conditions

Addition of biochar to soil, among other beneficial abilities has the potential of the carbon sequestration, improvement of soil fertility, and remediation of contaminated land (e.g., heavy metals immobilization). In a long-term perspective, these positive properties depend on the resistance against decomposition (stability) of the biochar in the soil matrix. The stability is influenced by the biochar production process parameters (i.e., pyrolysis), feedstock\u27s origin, and the (a)biotic environmental conditions [1]. Due to numerous factors impacting on the stability, its objective assessment is a complex task, and one assessment method can be not sufficient. In literature has been reported several biochar stability indicators, but each of them rather covers the influence of the specific factor, than give complete information of biochar\u27s stability. Therefore is legitimate to ask the question, are the stability predictors show any similarities between each other? An investigation of possible correlations among results from different stability assessment methods can lead to the improvement of the understanding of the biochars stability, and development of one, objective assessment\u27s method. [2]. In this study, were analyzed 24 biochar samples produced from a variety of the feedstock: algal biomass, agricultural residues and wastes, woody biomass, and industrial wastes. Highest treatment temperature (HTT) during pyrolysis ranged from 300 °C to 750 °C with a residence time of the materials from 10 to 90 minutes and the heating rate from 5 to 25 °C/min. For the indicators similarity assessment, the stability indicators were derived, among others: H/C ratio, recalcitrance index (R50), stability according to the Edinburgh stability tool (EST) [2], compounds ratios from analytical pyrolysis measurement (e.g., benzene/toluene ratio). The Principal Component Analysis (PCA) was performed to grasp possible trends in this high-dimensional data. Two main principal components (i.e., dimensions) of PCA retained ca. 70% of the original variance in the data, which is satisfactory value, especially for such inhomogeneous data matrix. Results arrangement indicated that the first principal component (PC1) could be strongly linked with the biochar’s stability, and the second component (PC2) can be related to the biochar\u27s feedstock origin. The H/C ratio, VM content (d.b.), benzene/toluene ratio, the EST and the R50 shown the highest impact on the first component and were assumed as the feedstock-independent biochar’s stability indicators. The FC and ash content (d.b.), O/C ratio, phenol/benzene ratio were shown the highest impact on PC2. Therefore, they were assumed as the feedstock-dependent parameters. Since the feedstock properties are usually treated as unchangeable parameters, the correlations between the feedstock-independent, so production-dependent predictors were investigated. The H/C ratio shown a good Pearson correlation with benzene/toluene ratio (-0.76) and a bit weaker with EST (-0.61). The benzene/toluene ratio was shown correlation with R50 index (0.56) and EST (0.67). In conclusion, successful division of the stability indicators on the feedstock-dependable and -independent was achieved. It allowed observing a correlation between pairs of stability indicators. Therefore the existence of the similarities between certain parameters was proven. Future analysis of the data should focus on the ruling out possible multicollinearity in the stability indicators dataset. It will allow minimizing and clear the dataset for the objective stability assessment. That can open the route for establishing one, multipart stability parameter, which can be beneficial in biochar stability improvement studies and allow for broader application of the biochar in the future. References: [1] J. Wang, Z. Xiong, Y. Kuzyakov, Biochar stability in soil: Meta-analysis of decomposition and priming effects, GCB Bioenergy. 8 (2016) 512–523. DOI:10.1111/gcbb.12266. [2] A. Cross, S.P. Sohi, A method for screening the relative long-term stability of biochar, GCB Bioenergy. 5 (2013) 215–220. DOI:10.1111/gcbb.12035