European Biochar Certificate Research Articles

Biochar Production From Plastic‐Contaminated Biomass

ABSTRACTAnaerobic digestion and composting of biowastes are vital pathways to recycle carbon and nutrients for agriculture. However, plastic contamination of soil amendments and fertilizers made from biowastes is a relevant source of (micro‐) plastics in (agricultural) ecosystems. To avoid this contamination, plastic containing biowastes could be pyrolyzed to eliminate the plastic, recycle most of the nutrients, and create carbon sinks when the resulting biochar is applied to soil. Literature suggests plastic elimination mainly by devolatilization at co‐pyrolysis temperatures of > 520°C. However, it is uncertain if the presence of plastic during biomass pyrolysis induces the formation of organic contaminants or has any other adverse effects on biochar properties. Here, we produced biochar from wood residues (WR) obtained from sieving of biowaste derived digestate. The plastic content was artificially enriched to 10%, and this mixture was pyrolyzed at 450°C and 600°C. Beech wood (BW) chips and the purified, that is, (macro‐) plastic‐free WR served as controls. All biochars produced were below limit values of the European Biochar Certificate (EBC) regarding trace element content and organic contaminants. Under study conditions, pyrolysis of biowaste, even when contaminated with plastic, can produce a biochar suitable for agricultural use. However, thermogravimetric and nuclear magnetic resonance spectroscopic analysis of the WR + 10% plastics biochar suggested the presence of plastic residues at pyrolysis temperatures of 450°C. More research is needed to define minimum requirements for the pyrolysis of plastic containing biowaste and to cope with the automated identification and determination of plastic types in biowaste at large scales.

Post-Extractivism and Bioeconomy: An Experimental Analysis of Combustion and Pyrolysis Processes as Alternatives to Add Value to Agro-Residues (Coffee Husks) Generated in Farmer Cooperatives of the Ecuadorian Amazon

A post-extractivist development model for communities in the Amazon that is not based on non-renewable resource extraction demands the study and demonstration, in the field, of alternative economic activities that add value to currently generated residual biomass. Following the principles of bioeconomy, this study presents an experimental analysis of a retort burner and a pilot-scale auger-type pyrolysis reactor used to convert coffee husks generated in a collection and post-harvesting center of a farmer’s cooperative into thermal energy and biochar, respectively. This study shows that coffee husks, whether used as feedstock for combustion or pyrolysis processes, can supply the thermal energy required by the post-harvesting processes. The combustion or pyrolysis of coffee husks avoids its accumulation and decomposition while replacing fossil fuels used in post-harvesting operations, reducing costs and making farmers independent of fossil fuel subsidies. Unlike combustion (11,029.4 mg/Nm3), the CO concentration in the flue gas during the pyrolysis process was 458.3 mg/Nm3, which is below the eco-design standard of 500 mg/Nm3. According to the European Biochar Certificate, carbon content (67.4 wt%) and H/Corg, O/Corg (0.6 and 0.1, respectively) are within the typical values of biochars used for soil amendment and carbon sequestration. Nonetheless, the concentration of polycyclic aromatic hydrocarbons must be assessed to fully regard this material as biochar. Finally, further studies are required to assess the ability of cooperatives to generate and trade carbon credits linked with the application of biochar in their cropping systems.

Biochars from chlorine-rich feedstock are low in polychlorinated dioxins, furans and biphenyls

Chlorinated aromatic hydrocarbons like polychlorinated dibenzo-p-dioxins and -furans (PCDD/F) and polychlorinated biphenyls (PCB) are omnipresent in the environment due to historic production, use, and (unintended) release. Nowadays, their emission and maximum concentration in environmental compartments is strictly regulated. During biochar production, PCDD/F and PCB may be formed and retained on the solid pyrolysis product. Industrial biochars certified, e.g., under the European Biochar Certificate (EBC), exhibit concentrations that were always well below threshold values for soil application and even animal feed. However, this has not been sufficiently tested for chlorine (Cl) rich organic material such as marine biomass or polyvinyl chloride (PVC) contaminated feedstock. Here, we analyzed PCDD/F and PCB contamination in biochars produced at different temperatures from different biomasses with comparatively high Cl contents in the range from 0.2 % to 3.8 % (w/w, seagrass, two types of saltwater macroalgae, tobacco stalks, and PVC contaminated wood). All of the biochars produced showed PCDD/F and PCB contents well below the applicable threshold values given by the EBC (< 20 ng TEQ kg−1 for PCDD/F and < 2×105 ng kg−1 for PCB). The EBC thresholds were undershot by a minimum of factor 1.5 for PCDD/F (mostly factor 20) and by a minimum of factor 90 for PCB. Between 1 and 27 ppb of feedstock Cl were transformed to Cl bound in PCDD/F and PCB in the biochars. No consistent correlation between biomass Cl contents and contents of PCDD/F and PCB were found but higher Cl contents in the feedstock led to a more diverse PCDD/F congener pattern in the biochars. Pyrolysis of PVC-amended wood resulted in consistently higher contamination of PCDD/F and PCB in the biochars compared to pyrolysis of the other biomasses, potentially due to differences in Cl speciation in the feedstocks i.e., Cl in PVC is already covalently bound to an organic carbon backbone. A high contamination in PCDD/F and PCB in biochar was intentionally triggered by separation of pyrogas and biochar in the reactor at < 300 °C to promote condensation of contaminants on the solid product. Between 20 % and 80 % of feedstock Cl was released via the pyrogas, i.e., neutralization of HCl in burnt pyrogas might be necessary when pyrolyzing Cl-rich feedstock in industrial biochar production. Our results indicate that biochars produced from Cl-rich feedstocks with proper biochar production process control are conform with European certification guidelines for PCDD/F and PCB contamination. The results open the opportunity to exploit and valorize so far non-used marine or otherwise Cl enriched biomasses for the production of biochar and carbon sinks.

Ensuring safety standards in sewage sludge-derived biochar: Impact of pyrolysis process temperature and carrier gas on micropollutant removal

The application of sewage sludge to agricultural land is facing increasing restrictions due to concerns about various micropollutants, including polycyclic aromatic hydrocarbons (PAHs), dioxins and furans (PCDD/Fs), polychlorinated biphenyls (PCBs), per- and poly-fluoroalkyl substances (PFAS), and heavy metals (HMs). As an alternative approach to manage this residue, the use of pyrolysis, a process that transforms sludge into biochar, a carbon-rich solid material, is being explored. Despite the potential benefits of pyrolysis, there is limited data on its effectiveness in removing micropollutants and the potential presence of harmful elements in the resulting biochar. This study aims to evaluate the impact of the temperature and the use of a carrier gas (N2) during a two-stage pyrolysis and cooling on micropollutant removal. Pilot-scale tests showed that a higher temperature (650 °C) and the use of a carrier gas (0.4 L/min N2) during the pyrolysis and the cooling process led to a reduction of PAHs, PCDD/Fs, PCBs and PFAS below their detection limits. As such, the generated biochar aligns with the guidelines set by the International Biochar Initiative (IBI) and the European Biochar Certificate (EBC) for all micropollutants, except for zinc and copper. Additional investigation is required to determine whether the micropollutants undergo destruction or transition into other pyrolysis end-products, such as the gas or liquid phase.

Micropollutants in biochar produced from sewage sludge: A systematic review on the impact of pyrolysis operating conditions

Biochar obtained from sewage sludge serves as a valuable soil amendment in agriculture, enhancing soil properties by increasing the nutrient content, cation exchange capacity, water retention, and oxygen transmission. However, its utilisation is hampered by the presence of micropollutants such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs), and volatile organic compounds (VOCs). Previous studies indicate that the type and amount of micropollutants can be significantly adjusted by selecting the right process parameters. This literature review provides an overview of how (1) pyrolysis temperature, (2) carrier gas flow and type, (3) heating rate, and (4) residence time affect the concentration of micropollutants in biochar produced from sewage sludge. The micropollutants targeted are those listed by the European Biochar Certificate (EBC) and by the International Biochar Institution (IBI), including PAHs, PCDD/Fs, PCBs and VOCs. In addition, per- and poly-fluoroalkyl substances (PFAS) are also considered due to their presence in sewage sludge.The findings suggest that higher pyrolysis temperatures reduce micropollutant levels. Moreover, the injection of a carrier gas (N2 or CO2) during the pyrolysis and cooling processes effectively lowers PAHs and PCDD/Fs, by reducing the contact of biochar with oxygen, which is crucial in mitigating micropollutants. Nevertheless, limited available data impedes an assessment of the impact of these parameters on PFAS in biochar. In addition, further research is essential to understand the effects of carrier gas type, heating rate, and residence time in order to determine the optimal pyrolysis process parameters for generating clean biochar.

Biochar production from the pyrolysis of food waste: Characterization and implications for its use

Food waste (FW) represents a large group of wastes that impose several issues on their management, especially in terms of microbiological and leaching pollution, and greenhouse gas emissions. According to the EU circular economy vision, finding a new way for FW valorisation to obtain reusable materials or compounds represents a priority. Thermal treatment represents one of the suitable ways for FW processing, and pyrolysis in particular presents many advantages in producing solid carbonaceous biochar, reusable oil and gas. This paper analyses biochar that was produced via thermal pyrolysis of FW. The influence of an organic additive (wooden sawdust) and a catalyst (zeolite) on the pyrolytic process at 600 °C was investigated. The results highlight how the initial composition of the feedstock (FS) influenced the characteristics of the obtained biochar. The addition of organic additives and catalyst did not change significantly the Brunauer–Emmett–Teller surface area and the calorific value. For all the analysed parameters, all tested FS respected the guidelines proposed by International Biochar Initiative (IBI) and the European Biochar Certificate (EBC) for possible reuse in agriculture and urban areas. The results suggest that biochar from FW could be potentially used in agriculture and urban green infrastructure, but the authors suggest further studies, especially on the effect of high electrical conductivity due to the typical high concentration of salts in FW.

Comparative Analysis of Pigeonpea Stalk Biochar Characteristics and Energy Use under Different Biochar Production Methods

The disposal of crop residues from agricultural fields is often seen as a burden due to the difficulties involved. However, this study aims to turn pigeonpea stalks into biochar, which can serve as a fuel substitute and soil amendment to sequester carbon. Different pyrolysis methods were employed to investigate the variations in yield, physicochemical characteristics, and higher heating value (HHV) of biochar produced from pigeonpea stalks. The biochar produced using a muffle furnace exhibited higher fixed carbon and ash content. These characteristics make it beneficial for restoring degraded agricultural soils by enhancing carbon sequestration. In addition, the muffle furnace biochar demonstrated a total potential carbon ranging from 262.8 to 264.3 g of carbon per kilogram of biochar, along with a CO2 reduction potential ranging from 77.17 to 79.68 CO2 eq per kg. Both the European Biochar Certificate and the International Biochar Initiative confirmed the agronomic abilities of the biochar and its compliance with the highest quality standards for soil carbon sequestration, with 0.11 H/C and 0.7 O/C ratios. Furthermore, biochar produced by muffle furnace from pigeonpea stalks exhibited superior fixed carbon recovery efficiency (181.66 to 184.62%), densification (5.86 to 6.83%), energy density (1.77 to 2.06%), energy retention efficiency (54.80 to 56.64%), fuel ratio (18.95 to 22.38%), and HHV (30.66 to 32.56 MJ kg−1). Additionally, it had lower H/C and O/C ratios, suggesting its potential as an alternative solid fuel. The results of the characterization of biochar with scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) revealed that the biochar samples prepared with both the methods had carbonyl (C=O), C=C, and aromatic C-H functional groups; however, the biochar prepared in the muffle furnace had more porosity. In summary, this study highlights the potential of using pigeonpea stalks to produce biochar, which can be utilized as a renewable fuel substitute and soil amendment to sequester carbon. The biochar derived from the muffle furnace exhibited desirable physicochemical characteristics, high carbon content, and excellent energy properties, making it a promising option for various applications.

The importance of biochar quality and pyrolysis yield for soil carbon sequestration in practice

AbstractBiochar is a carbon (C)‐rich material produced from biomass by anoxic or oxygen‐limited thermal treatment known as pyrolysis. Despite substantial gaseous losses of C during pyrolysis, incorporating biochar in soil has been suggested as an effective long‐term option to sequester CO2 for climate change mitigation, due to the intrinsic stability of biochar C. However, no universally applicable approach that combines biochar quality and pyrolysis yield into an overall metric of C sequestration efficiency has been suggested yet. To ensure safe environmental use of biochar in agricultural soils, the International Biochar Initiative and the European Biochar Certificate have developed guidelines on biochar quality. In both guidelines, the hydrogen‐to‐organic C (H/Corg) ratio is an important quality criterion widely used as a proxy of biochar stability, which has been recognized also in the new EU regulation 2021/2088. Here, we evaluate the biochar C sequestration efficiency from published data that comply with the biochar quality criteria in the above guidelines, which may regulate future large‐scale field application in practice. The sequestration efficiency is calculated from the fraction of biochar C remaining in soil after 100 years (Fperm) and the C‐yield of various feedstocks pyrolyzed at different temperatures. Both parameters are expressed as a function of H/Corg. Combining these two metrics is relevant for assessing the mitigation potential of the biochar economy. We find that the C sequestration efficiency for stable biochar is in the range of 25%–50% of feedstock C. It depends on the type of feedstock and is in general a non‐linear function of H/Corg. We suggest that for plant‐based feedstock, biochar production that achieves H/Corg of 0.38–0.44, corresponding to pyrolysis temperatures of 500–550°C, is the most efficient in terms of soil carbon sequestration. Such biochars reveal an average sequestration efficiency of 41.4% (±4.5%) over 100 years.

Influence of Thermochemical Conversion Technologies on Biochar Characteristics from Extensive Grassland for Safe Soil Application

Grass and other herbaceous biomass are abundant, but often under- or not utilized as a renewable resource. Here, the production of biochar from extensive late-harvest grass via multiple thermochemical conversion technologies was investigated at lab and farm scale for use in soil applications. While biochar is a product with highly diverse potential applications, it has a multitude of benefits for agricultural usage as a soil amendment, if the quality adheres to certain limit values of potentially toxic constituents. The results show that the biochar can adhere to all limit values of the European Biochar Certificate (EBC) for utilization in agriculture. Generally, the contents of heavy metals were well below the proposed EBC limits and very low PAH concentrations in the biochar were achieved. The high ash content in the grass of 7.71 wt%db resulted in high nutrient concentrations in the biochar, of benefit in soil applications, but the ash also contains chlorine, nitrogen and sulphur, which presents a challenge for the operation of the thermochemical processes themselves due to corrosion and emission limits. In the farm-scale processes, ash retention ranged from 53.7 wt%db for an autothermal batch process, reaching up to 93.7 wt%db for a batch allothermal process. The release of Cl, N and S was found to differ substantially between processes. Retention ranged from 41.7%, 22.9% and 27.6%, respectively, in a continuous allothermal farm-scale pyrolysis process, to 71.7%, 49.7% and 73.9%, with controlled lab-scale pyrolysis at 450 °C, demonstrating that process optimization may be possible.

Conversion of quinoa and lupin agro-residues into biochar in the Andes: An experimental study in a pilot-scale auger-type reactor.

In the last decades, the cultivation of quinoa and lupin became an important source of income for Andean farmers due to the demand for high nutrient-density foods from the Global North. The increase in the cultivation intensity caused by this exogenous demand led to the overexploitation of local ecosystems and a decrease in soil fertility. As an alternative to recover and improve soil quality, this work uses a pilot-scale auger pyrolysis reactor, implemented in the Andes, to assess the conversion of the agro residues generated in the post-harvesting processes of quinoa and lupin into biochar for soil amendment. Following the European Biochar Certificate guidelines, the pyrolyzed quinoa stems can be classified as biochar while the pyrolyzed quinoa husks can be classified as pyrogenic carbonaceous material. Both can be used for soil amendment considering their molar ratios (H/Corg, O/Corg) and carbon content. It was not possible to carbonize lupin stems and seedcases. Despite the altitude (2,632m.a.s.l), the CO concentration during the carbonization of quinoa stems and husks were 1,024.4 and 559 mg/Nm3, this last, near the European eco-design standard of 500 mg/Nm3. A subsequent SWOT analysis showed the need to explore low-cost and low-complexity pyrolysis reactors that allow the decentralized conversion of agro residues at the farm-scale. The development of local standards to regulate the production and use of biochar is also essential to grant the safety of the processes, the quality of the products, and mobilize funds that allow implementation at relevant scales.

Influence of indirectly heated steam-blown gasification process conditions on biochar physico-chemical properties

Our work provides a thorough characterization of different biochars produced by a novel 50 kWth Indirectly Heated Bubbling Fluidized Bed Steam Reformer. This study investigates the effect of temperature and gasification agent on the physico-chemical properties of biochars. We combined macro, micro and nano characterization techniques to provide a clear picture of the biochar characteristics, surface functionality and its “inert” nature toward potential applications. Our results demonstrate that indirect gasification is capable of producing carbon-rich biochars (> 92%) with increased porosity (89–198 cm3.g−1), high heating value (28–31 MJ.kg−1 a.r.) and aromaticity compared to the parent biomass. All biochars have lower O/C (0.02–0.04) and H/C atomic ratios (0.09–0.19), similar to anthracite. For the range of tested gasification conditions, air/steam gasification at an equivalence ratio of 0.20 and steam-to-biomass ratio of 1.2 provides the highest biochar yield (7.3%), while maintaining syngas composition optimal. On the other hand, air gasification produces biochars with relatively high content of inorganic elements. Indirectly heated biochars are compliant with the European Biochar Certificate regarding the carbon content, O/C ratio, H/C ratio. Our biochars may provide an improvement in agricultural yield and CO2 adsorption, especially those produced under air/steam gasification conditions. Our novel indirect design not only constitutes a promising development in the field of biomass allothermal gasification but also can help improving gasification circularity through the production of high quality biochar.

Quality and suitability of fecal biochar in structurally stable urban tree substrates

This study examines the effects of pyrolyzed materials (biochar) from horse manure, plant residues and human feces on the growth of 1-year old birch seedlings cultivated in a novel, structurally stable tree substrate. For this purpose, the composition of the produced biochar, the leachate from the substrates and the health and growth rate of the birch seedlings were observed over a period of 322 days. The results show that each of these biochars complies with the European Biochar Certificate (EBC) guidelines. No toxic heavy metals were detected. Furthermore, the presence of the biochar in the substrates enhanced the survival rate of the birch trees.

Characterization of Biochar Derived from Crop Residues for Soil Amendment, Carbon Sequestration and Energy Use

The crop residues generated in agricultural fields are mostly considered a burden due to their disposal issues. This study attempts to effectively use pigeon pea stalk (PPS) for biochar production, a promising source as a soil amendment for carbon sequestration and alternative fuel source. PPS was pyrolyzed at different loads and reaction times to optimize the kiln temperature (350–400 °C and 450–500 °C) and changes in physicochemical properties, higher heating value (HHV) and yield were assessed. The results indicated that biochar yield, volatile matter, bulk density, O/C and H/C atomic ratios decreased, whereas fixed carbon, ash content and total porosity increased with increasing kiln temperature across all loads. Biochar produced at 450–500 °C (18 kg load kiln−1) had higher total carbon, nitrogen, phosphorous, recovered total carbon and total nitrogen, total potential carbon and CO2 reduction potential. Biochar produced at 350–400 °C had the maximum cation exchange capability (43.0 cmol kg−1). Biochar has estimated O/C and H/C atomic ratios of 0.07–0.15 and 0.35–0.50, respectively. Biochar exhibited good agronomic characteristics and fulfilled key quality criteria of H/C &lt; 0.7 and O/C &lt; 0.4 for soil carbon sequestration, as described by the European Biochar Certificate and the International Biochar Initiative. The estimated mean residence time and the mass fraction of carbon that would remain after 100 years were consistently greater than 1000 years and 80%, respectively. The biochar produced at 450–500 °C (at 18.0 kg kiln−1) from PPS had higher fixed carbon (65.3%), energy density (1.51), energetic retention efficiency (53%), fuel ratio (4.88), and HHV (25.01 MJ kg−1), as well as lower H/C and O/C ratios, implying that it is suitable for use as an alternative solid fuel.

A comprehensive assessment on bioavailability, leaching characteristics and potential risk of polycyclic aromatic hydrocarbons in biochars produced by a continuous pyrolysis system

Biochar application as a soil amendment has attracted worldwide attention. Nevertheless, polycyclic aromatic hydrocarbons (PAHs) formed during biochar production might enter into ecosystems and threaten human health after application to soil. Continuous pyrolysis systems tend to cause an accumulation of PAHs in biochar owing to short residence time and rapid cooling. This study conducted a comprehensive assessment regarding potential risk of PAHs in biochars produced by a continuous pyrolysis system based on bioavailability, leaching behavior, toxic equivalent quantity, health risk and phytotoxicity of PAHs. Results showed that the concentrations of total PAHs in biochars were in the range of 93.40–172.40 mg/kg, exceeding the European Biochar Certificate standard. 3-rings PAHs were the predominant groups. The percentages of total freely dissolved and leachable PAHs were lower than 1%. RH contained the least bioavailable and leachable PAHs concentration and phytotoxicity compared with CS and PS, which might attribute to the characteristic of three biochars. CS and PS were acidic and exhibited high levels of DOC and VFAs, while RH was strongly alkaline and presented greater aromaticity and higher surface area, which might have resulted in high adsorptive capacity and decreased bioavailability of PAHs. When the biochar application rate was higher than 0.6 t/ha, the incremental lifetime cancer risk value for human exposure to biochar-borne PAHs through the biochar-amended soil was over 10−6, suggesting carcinogenic risks. Germination index values of biochars ranged from 25.66 to 88.95%. Phytotoxicity mainly was caused by bioavailable PAHs and dissolved organic compounds. Overall, these findings highlighted that although the percentage of bioavailable PAHs was low, the potential health risk and phytotoxicity of PAHs in biochars produced by a continuous pyrolysis system was of a great concern. High biochar application rates should be avoided without processing both for soil safety and human health.

Exploratory study of polycyclic aromatic hydrocarbons occurrence and distribution in manure pyrolysis products

The occurrence and distribution of polycyclic aromatic hydrocarbons (PAH) have been investigated in the products derived from the pyrolysis of pig manure at low temperatures (<550 °C) in a fixed bed reactor. The focus was on the sixteen PAH identified as priority pollutants by the US Environment Protection Agency (EPA). The pyrolysis does not generate a significant additional amount of EPA-PAH to that existing in the original pig manure, under the operational conditions studied (<550 °C). While the total EPA-PAH yield does not indicate a notable dependence on the pyrolysis temperature, the EPA-PAH distribution among the three pig manure pyrolysis products as well as the speciation changed significantly with the temperature. The proportion of heavy PAH species increased as the temperature increased. The initial EPA-PAH in the manure samples plays a significant role in both their concentration and speciation in the biochar. The relationship of the EPA-PAH concentration and speciation in the biochar with those of the raw material was corroborated with a cow manure sample and the biochars obtained from its pyrolysis. For this reason, feedstocks with low EPA-PAH concentrations are recommended in order to obtain biochars with concentrations below the maximum allowed threshold established for their use as a soil enhancer by the International Biochar Initiative (IBI) and in the European Biochar Certificate.

Production and Characterization of Crop Residues Derived Biochars for Soil Amendment and Carbon Sequestration

This study focused on the production and characterization of biochars from three types of crop residues comprising cotton stems, corn cobs and sorghum stems. The reactor used was a local cone kiln made from a 200-liter drum. The production parameters measured included the duration of pyrolysis, the amount of biochar produced and the production yield. The chemical characteristics of the biochars were determined using the usual analytical methods used for organic amendment analyses. According to the study, pyrolysis time, biochar quantities and production yields depended on the type of crop residues. The three types of biochar obtained showed high C/N values indicating that their use as soil amendment must be combined with mineral fertilizers to ensure good plant development and crop yield. The heavy metal contents of the three biochar types complied with the international standards recommended for biochars by the International Biochar Initiative (IBI) and by the European Biochar Certificate (EBC). The production and the use of Biochar from crop residues is an interesting alternative for sustainable soil fertility management in the Sahelian countries.

Alkaline modified biochar derived from spent coffee ground for removal of tetracycline from aqueous solutions

The feasibility of applying alkaline modified-biochar prepared through pyrolysis of spent coffee ground (NaOH-SCG) in the elimination of tetracycline (TC) from different aqueous solutions was investigated through this study. The physico-chemical characterization of NaOH-SCG was scrutinized by distinct techniques. The PAHs concentration of NaOH-SCG (500 °C) was 693 μg kg−1, which do not exceed the international acceptable threshold of PAHs in biochar as reported by International Biochar Initiative (6–20 mg kg−1) and European Biochar Certificate (4 mg kg−1 for premium class, 6 mg kg−1 for basic class). From the experimental results, the adsorption capacity (qmax) of NaOH-SCG biochar (113.64 mg g−1) exhibited 2.9 times higher than that of the non-modified SCG (39.22 mg g−1). Furthermore, environmental factors, namely, pH and ions, affecting the interaction between biochar and TC was investigated. Alkaline modified-biochar exhibited high tetracycline adsorption capacity and therefore has a great prospect as an environmentally effective adsorbent in separation of hazardous chemicals from different aqueous solutions.

The effect of biochar application on soil properties and growth of the model plant Zea mays

The classic way of land cultivation means the use of inorganic fertilizers that are salts that dissolve rapidly in a short time and improve soil fertility. This process negatively affects soil salinity and the life of microorganisms. The use of biochar as a soil conditioner is a promising solution. The aim of the work is to enrich the properties of less fertile soils and to enhance the growth of the model plant Zea mays (corn) by biochar application. We used four different soil types commonly spread in the Czech Republic – regosol, chernozem, cambisol and fluvisol representing a broad range of organic matter content. Also, we applied two different EBC (The European Biochar Certificate) certified biochars for use in agriculture. Corn seeds were germinated and cultivated for 3 months in repeated plant life cycles. Soils and biochar samples were characterized before and after cultivation by TGA, EA, BET, SEM, extraction of organic matter. The effect of biochar application was observed continuously through the measurement of plant height, the number of leaves and cobs. After the finalization of cultivation experiments, the dry mass of individual plants was measured, and root image analysis of every plant was performed. Fluvisol and cambisol have much higher organic matter content than regosol and chernozem. The application of biochar had the most significant impact on regosol regardless of the application dose; these results are in good agreement with the root image analysis. Furthermore, plants in soils treated with biochar had more corn cobs. The analysis on biochar samples showed the continual leaching of both organic and inorganic molecules from biochar to surrounding soil, which is crucial for its possible use as a soil conditioner and confirms the long-timescale positive effect on soil properties.

A comprehensive assessment of potential hazard caused by organic compounds in biochar for agricultural use

Great attention has been paid to using biochar as soil conditioner and bio-accumulator. Nevertheless, biochar application in agriculture might cause a potential hazard to ecosystems, considering that toxic organic pollutants present in biochar may enter the environment. European Biochar Certificate (EBC) set certain criteria for biochar production. Achieving the EBC established values of the molar ratio of H/Corg <0.7 and O/Corg <0.4, does not ensure that biochar will not cause phytotoxicity. The results of root growth inhibition of Sinapis alba were in the range of 9% (eucalyptus wood biochar) to 82% (maize biochar). Phytotoxicity of biochar was possibly caused by the presence of water-soluble organic compounds. In total, 62 organic compounds were identified in the leachate from noncertified biochar and 35 organic compounds in the leachate from certified biochar. Biochar safety, in terms of the presence of organic compounds, can be recognised by the evaluation of the ratio of organic carbon (OC) and elemental carbon (EC). Biochar with the highest phytotoxicity showed the ratio between OC/EC > 0.1, inhibition of Sinapis alba <30% was observed with OC/EC < 0.02. To achieve Sinapis alba inhibition <20%, these parameters should be met: volatile matter (VM) <30%; concentration of OC < 4%; aromaticity ratio AL/AR < 0.35.

Balancing Waste and Nutrient Flows Between Urban Agglomerations and Rural Ecosystems: Biochar for Improving Crop Growth and Urban Air Quality in The Mediterranean Region

Mediterranean ecosystems are threatened by water and nutrient scarcity and continuous loss of soil organic carbon. Urban agglomerations and rural ecosystems in the Mediterranean region and globally are interlinked through the flows of resources/nutrients and wastes. Contributing to balancing these cycles, the present study advocates standardized biochar as a soil amendment, produced from Mediterranean suitable biowaste, for closing the nutrient loop in agriculture, with parallel greenhouse gas reduction, enhancing air quality in urban agglomerations, mitigating climate change. The study’s scope is the contextualization of pyrolytic conditions and biowaste type effects on the yield and properties of biochar and to shed light on biochar’s role in soil fertility and climate change mitigation. Mediterranean-type suitable feedstocks (biowaste) to produce biochar, in accordance with biomass feedstocks approved for use in producing biochar by the European Biochar Certificate, are screened. Data form large-scale and long-period field experiments are considered. The findings advocate the following: (a) pyrolytic biochar application in soils contributes to the retention of important nutrients for agricultural production, thereby reducing the use of fertilizers; (b) pyrolysis does not release carbon dioxide to the atmosphere, contributing positively to the balance of carbon dioxide emissions to the atmosphere, with carbon uptake by plant photosynthesis; (c) biochar stores carbon in soils, counterbalancing the effect of climate change by sequestering carbon; (d) there is an imperative need to identify the suitable feedstock for the production of sustainable and safe biochar from a range of biowaste, according to the European Biochar Certificate, for safe crop production.