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

Chemical stabilization of Cd contaminated soil using fresh and aged wheat straw biochar

Soil pollution can adversely affect the ecosystem services provided by the soil. Polluted soils reduce land productivity by reducing crop yields and polluting groundwater. Also, both crops and water in polluted lands may unsafe for the consumption by animals or humans. Release of chemicals or toxic substance can happen through industrial and agricultural activities. Metal mining and smelting to separate minerals is one such of activity which can introduce large quantities of heavy metals into the environment which persist in the soil for long periods even after those activities are ended. The Campine area on the border of Belgium and the Netherlands contains Cd contaminated sites due to historic metal smelting activities. A soil collected in that region containing 11±0.5 ppm Cd exceeding soil remediation standards was taken in consideration for this soil remediation study. Biochar is increasingly getting attention as a remediation tool to immobilizing heavy metals in contaminated soils. However, long-term provisioning of such service is mainly depends on the biochar carbon stability. Biochar carbon stability is mainly depending on the biochar production conditions, nature of the feedstock material and the biotic and abiotic environmental conditions that biochar is being used. Also, the heavy metal immobilization process heavily depends on the soil and biochar pH and the nature of the functional groups present on biochar surfaces such as carbonates and phosphates. Within this context, three types of wheat straw biochar were produced using a screw reactor at 400 °C, 500 °C, and 600 °C. To age the biochar samples, biochar samples were subjected to accelerated aging using a method suggested by Cross and Sohi, 2013 [1]. This method can be used as proxy for environmental aging of biochar approximately 100 years under temperate conditions. Then these six biochar samples (BC400F, BC500F, BC600F, BC400A, BC500A, BC600A) were characterized for elemental analysis, ash content, volatile matter content and fixed carbon content, pH, EC, phosphate and carbonate content and FT-IR analysis. The soil used in this study was characterized for the soil texture, elemental contents, organic matter content, pH and EC. Six months of laboratory incubation study was conducted with contaminated soil amended with each type of biochar at 2 % rate (w/w). Rhizon extractions were collected at the end of each month to quantify the Cd concentration, pH and total organic carbon content in the soil pore water. At the end of the six months of incubation time, Cd concentration in the pore water ranged from 100.36 ppb in BC600A to 249.85 ppb BC400A. The Cd concentration in each treatment was BC600A\u3c BC400F\u3c BC600F\u3c BC500F\u3c Soil only (control) \u3c BC500A\u3c BC400A. According to the FT-IR analysis of the six biochar samples, more carboxylic-C and carbonate- C functional groups were present in aged biochar samples compared to the freshly produced wheat straw biochar samples. Also, biochar produced at lower temperatures were characterized by lower pH and a lower amount of stable C compounds compared to the biochar produced freshly and in higher production temperatures. These results suggest that the stability of biochar carbon and pH of both biochar and soil have a significant impact on the stabilization of heavy metals in the soil environment. Therefore, the selection of biochar with desired qualities thus choosing of suitable biochar production conditions is essential in decision-making processes to keeping the biochar services in the long run. References: [1]. Cross, A., & Sohi, S. P. (2013). A method for screening the relative long‐term stability of biochar. Gcb Bioenergy, 5(2), 215-220

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

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

Biochar from sawmill residues: Characterization and evaluation for its potential use in the horticultural growing media

Peat remains the primary constituent of horticultural growing media in professional use. However, use of peat in horticultural growing media results in greenhouse gas emissions and biodiversity loss due to excavation of natural peatlands. Biochar is gaining attention as a sustainable alternative to peat use in horticulture. This study examined the potential of biochar produced from a particular type of sawmill residue, as a partial replacement for peat in horticultural growing media. Five treatments including peat only, biochar only, biochar and peat in 1:1, 1:3, and 3:1 (V/V) ratios were assessed. The addition of biochar into growing media increased the pH and EC of the medium. However, physical properties (air-filled porosity and water holding capacity) were negatively affected with the increase in biochar content in the medium. According to the germination test results, biochar significantly improved germination and the shoot and root length of germinated seeds of cress, lettuce and tomato when compared to peat-only and biochar-only treatments. The inclusion of biochar in 25–50% volume ratio improved plant growth parameters compared to peat-only and biochar-only media. Results obtained from this study suggest that sawmill residue offers great potential as a feedstock for biochar production and inclusion of biochar has positive effects on seed germination and plant growth that might compete with modified pea

Investigation of biomass and agricultural plastic co-pyrolysis: Effect on biochar yield and properties

Complete separation of mixed plastic and biomass waste is a technically difficult, laborious, expensive and time-consuming process. Hence, co-pyrolysis of these agricultural waste streams with low levels of plastic contamination presents a novel approach for the management of these plastic containing wastes, producing stable forms of carbon with potential use in environmental, agricultural and industrial applications. In this study, spent growing medium along with plastic growing bags, and bean crop residues along with mulching sheets were selected to assess how the presence of plastics would affect the characteristics of the biochars produced. These feedstocks were combined in mass ratios (of plastic in the biomass-plastic mixture) of 0, 0.25, 2.5, 5 and 10%. The resulting feedstock underwent slow pyrolysis in a fixed bed pyrolysis reactor at a temperature of 550 °C to ensure complete conversion of the plastic components of the feedstock. From the results obtained from pyrolysis, low ratios of plastic were found to have a positive impact on biochar yield, while high plastic ratios were found to have negative effect. Higher level of plastic in the feedstock have resulted peculiar functional groups in the biochar, including carboxylate anions, amides and aromatic groups. Biochars produced from spent growing medium along with plastic grow bags (GM biochars) showed no phytotoxic effect, irrespective of the concentration of plastic contamination in the feedstock. Biochars produced from bean crop residues along with mulching sheets (BM biochars) on the other hand showed high level of phytotoxicity (zero germination), irrespective of level of plastic contamination. After washing all BM biochar, very low phytotoxicity levels with no statistically significant effect of plastic contamination were observed, with the exception of 10BM that showed somewhat a reduced germination rate (93%). The results of this study will be beneficial for determining the tolerable level of plastic contamination in managing mixed agricultural waste biomass and to produce biochars suitable for environmental, agricultural and/or industrial applications

Chemical stabilization of Cd-contaminated soil using fresh and aged wheat straw biochar

Metal mining and smelting activities can introduce a substantial amount of potentially toxic elements (PTE) into the environment that can persist for an extended period. That can limit the productivity of the land and creates dangerous effects on ecosystem services. The effectiveness of wheat straw biochar to immobilize Cd in contaminated soil due to metal smelting activities was investigated in this study. The biochar carbon stability and long-term provisioning of services depend on the biochar production conditions, nature of the feedstock, and the biotic and abiotic environmental conditions in which the biochar is being used. Within this context, three types of wheat straw biochar were produced using a screw reactor at 400 °C, 500 °C, and 600 °C and tested in a laboratory incubation study. Soil was amended with 2 wt% of biochar. Both fresh and aged forms of biochar were used. Biochars produced at lower temperatures were characterized by lower pH, a lower amount of stable C, and higher amounts of acidic surface functional groups than the freshly produced biochars at higher production temperatures. At the end of the 6 months of incubation time, compared to the soil only treatment, fresh and aged forms of wheat straw biochar produced at 600 °C reduced the Cd concentration in soil pore water by 22% and 15%, respectively. Our results showed that the aged forms of biochar produced at higher production temperatures (500 °C and 600 °C) immobilized Cd more efficiently than the aged forms of lower temperature biochar (400 °C). The findings of this study provide insights to choose the production parameters in wheat straw biochar production while considering their aging effect to achieve successful stabilization of Cd in contaminated soils