A critical review on sustainable biochar system through gasification: Energy and environmental applications

Possibility Routes for Textile Recycling Technology

The fashion industry contributes to a significant environmental issue due to the increasing production and needs of the industry. The proactive efforts toward developing a more sustainable process via textile recycling has become the preferable solution. This urgent and important need to develop cheap and efficient recycling methods for textile waste has led to the research community's development of various recycling methods. The textile waste recycling process can be categorized into chemical and mechanical recycling methods. This paper provides an overview of the state of the art regarding different types of textile recycling technologies along with their current challenges and limitations. The critical parameters determining recycling performance are summarized and discussed and focus on the current challenges in mechanical and chemical recycling (pyrolysis, enzymatic hydrolysis, hydrothermal, ammonolysis, and glycolysis). Textile waste has been demonstrated to be re-spun into yarn (re-woven or knitted) by spinning carded yarn and mixed shoddy through mechanical recycling. On the other hand, it is difficult to recycle some textiles by means of enzymatic hydrolysis; high product yield has been shown under mild temperatures. Furthermore, the emergence of existing technology such as the internet of things (IoT) being implemented to enable efficient textile waste sorting and identification is also discussed. Moreover, we provide an outlook as to upcoming technological developments that will contribute to facilitating the circular economy, allowing for a more sustainable textile recycling process.

Mechanistic insights into the (im)mobilization of arsenic, cadmium, lead, and zinc in a multi-contaminated soil treated with different biochars

The effect and mechanistic evidence of biochar on the (im)mobilization of potentially toxic elements (PTEs) in multi-contaminated soils, with respect to the role of surface-functional groups and organic/inorganic compounds of biochar, are poorly understood. Herein, biochars produced from grass residues, rice straw, and wood were applied to a mining-soil contaminated with As, Cd, Pb, and Zn for 473-d. Biochars did not reduce the mobilization of Cd and Zn, whereas they simultaneously exhibited disparate effects on As and Pb mobilization. The phenolic hydroxyl and carboxylic groups on the wood biochar's surfaces promoted the conversion of Pb²⁺ into PbCO₃/Pb(OH)₂ and/or PbO, minimally by the rice and grass biochars. Rice and grass biochars led to the dissolution of scorodite and the formation of less stable forms of Fe-oxide-bound As (i.e., goethite and ferrihydrite); furthermore, it resulted in the reduction of As(V) to As(III). The PTEs mobilization and phytoavailability was mainly governed by the release of dissolved aliphatic- and aromatic-carbon, chloride, sulfur chemistry, phosphate competition, and the electrostatic repulsion in biochar-treated soils. In conclusion, pristine-biochar has a limited impact on the remediation of multi-contaminated soils, and the use of modified-biochar, possessing higher surface areas and functionality and active exchange sites, are preferred under such conditions.

A life cycle assessment of hard carbon anodes for sodium-ion batteries

Waste management is one of the biggest environmental challenges worldwide. Biomass-derived hard carbons, which can be applied to rechargeable batteries, can contribute to mitigating environmental changes by enabling the use of renewable energy. This study has carried out a comparative environmental assessment of sustainable hard carbons, produced from System A (hydrothermal carbonization (HTC) followed by pyrolysis) and System B (direct pyrolysis) with different carbon yields, as anodes in sodium-ion batteries (SIBs). We have also analysed different scenarios to save energy in our processes and compared the biomass-derived hard carbons with commercial graphite used in lithium-ion batteries. The life cycle assessment results show that the two systems display significant savings in terms of their global warming potential impact (A1: -30%; B1: -21%), followed by human toxicity potential, photochemical oxidants creation potential, acidification potential and eutrophication potential (both over -90%). Possessing the best electrochemical performance for SIBs among our prepared hard carbons, the HTC-based method is more stable in both environmental and electrochemical aspects than the direct pyrolysis method. Such results help a comprehensive understanding of sustainable hard carbons used in SIBs and show an environmental potential to the practical technologies. This article is part of the theme issue 'Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 2)'.

Propensity and appraisal of biochar performance in removal of oil spills: A comprehensive review

Recently, the adsorption-based environmental remediation techniques have gained a considerable attention, due to their economic viability and simplicity over other methods. Hence, detailed presentation and analysis were herein focused on describing the role of biochar in oil spill removal. Oil removal by utilizing biochar is assumed as a green-oriented concept. Biochar is a carbon-rich low-cost material with high porosity and specific surface chemistry, with a tremendous potentiality for oil removal from aqueous solutions. Oil sorption properties of biochar mainly depend on the biochar production/synthesis method, and the biomass feedstock type. In order to preserve the stability of functional groups in the structure, biochar needs to be produced/activated at low temperatures (<700 ᵒC). In general, biochar derived from biomass containing high lignin content via slow pyrolysis is more favorable for oil removal. Exceptional characteristics of biochar which intensify the oil removal capability such as hydrophobicity, oleophilicity or/and specific contaminant-surface interaction of biochar can be enhanced and be tuned by chemical and physical activation methods. Considering all the presented results, future perspectives such as the examination of biochar efficacy on oil removal efficiency in multi-element contaminated aqueous solutions to identify the best biomass feedstocks, the production protocols and large-scale field trials, are also discussed.

Review on upgrading organic waste to value-added carbon materials for energy and environmental applications

Value-added materials such as biochar and activated carbon that are produced using thermo-chemical conversion of organic waste have gained an emerging interest for the application in the fields of energy and environment because of their low cost and unique physico-chemical properties. Organic waste-derived materials have multifunctional abilities in the field of environment for capturing greenhouse gases and remediation of contaminated soil and water as well as in the field of energy storage and conversion. This review critically evaluates and discusses the current thermo-chemical approaches for upgrading organic waste to value-added carbon materials, performance enhancement of these materials via activation and/or surface modification, and recent research findings related to energy and environmental applications. Moreover, this review provides detailed guidelines for preparing high-performance organic waste-derived materials and insights for their potential applications. Key challenges associated with the sustainable management of organic waste for ecological and socio-economic benefits and potential solutions are also discussed.

Soils and Beyond: Optimizing Sustainability Opportunities for Biochar

Biochar is most commonly considered for its use as a soil amendment, where it has gained attention for its potential to improve agricultural production and soil health. Twenty years of near exponential growth in investigation has demonstrated that biochar does not consistently deliver these benefits, due to variables in biochar, soil, climate, and cropping systems. While biochar can provide agronomic improvements in marginal soils, it is less likely to do so in temperate climates and fertile soils. Here, biochar and its coproducts may be better utilized for contaminant remediation or the substitution of nonrenewable or mining-intensive materials. The carbon sequestration function of biochar, via conversion of biomass to stable forms of carbon, does not depend on its incorporation into soil. To aid in the sustainable production and use of biochar, we offer two conceptual decision trees, and ask: What do we currently know about biochar? What are the critical gaps in knowledge? How should the scientific community move forward? Thoughtful answers to these questions can push biochar research towards more critical, mechanistic investigations, and guide the public in the smart, efficient use of biochar which extracts maximized benefits for variable uses, and optimizes its potential to enhance agricultural and environmental sustainability.

Impact of coffee biochar on carbon, microbial biomass and enzyme activities of a sandy soil cultivated with bean

Biochar has been used to reuse the agro-industrial wastes and improve soil quality. Several studies have been carried out to show the impact of biochar on physical and chemical soil attributes. However, there are still gaps regarding the effects on as microbial biomass and enzymatic activities that are important to determine sensitive indicators to evaluate changes in management practices. The objective of this study was to assess the effect of two biochars on the chemical, microbial biomass carbon, and the enzymatic activities in an Entisol cultivated with bean. We evaluate two types of coffee biochar: ground and husks, four doses (4, 8, 12, and 16 Mg ha-1) and control. All treatments received organic fertilization with cow manure. Husks biochar increase the soil pH, Ca, and K, also contributing to the reduction of toxic aluminum contents and raising the concentrations of P labile. The treatments that received ground biochar showed higher soil organic carbon, microbial biomass, β-glucosidase, and fluorescein diacetate. Biochar produced from coffee residues increased sandy soil quality. We showed the first report on the beneficial impact of coffee biochar on enzymatic and microbiological quality of sandy soil cultivated with the bean.

Gasification biochar from horticultural waste: An exemplar of the circular economy in Singapore

Organic waste, the predominant component of global solid waste, has never been higher, resulting in increased landfilling, incineration, and open dumping that releases greenhouse gases and toxins that contribute to global warming and environmental pollution. The need to create and adopt sustainable closed-loop systems for waste reduction and valorization is critical. Using organic waste as a feedstock, gasification and pyrolysis systems can produce biooil, syngas, and thermal energy, while reducing waste mass by as much as 85-95% through conversion into biochar, a valuable byproduct with myriad uses from soil conditioning to bioremediation and carbon sequestration. Here, we present a novel case study detailing the circular economy of gasification biochar in Singapore's Gardens by the Bay. Biochar produced from horticultural waste within the Gardens was tested as a partial peat moss substitute in growing lettuce, pak choi, and pansy, and found to be a viable substitute for peat moss. At low percentages of 20-30% gasification biochar, fresh weight yields for lettuce and pak choi were comparable to or exceeded those of plants grown in pure peat moss. The biochar was also analyzed as a potential additive to concrete, with a 2% biochar mortar compound found to be of suitable strength for non-structural functions, such as sidewalks, ditches, and other civil applications. These results demonstrate the global potential of circular economies based on local biochar creation and on-site use through the valorization of horticultural waste via gasification, generating clean, renewable heat or electricity, and producing a carbon-neutral to -negative byproduct in the form of biochar. They also indicate the potential of scaled-up pyrolysis or gasification systems for a circular economy in waste management.

Adsorption of neutral red dye by chitosan and activated carbon composite films

Research indicates the use of adsorbent materials to remove pollutants from wastewater and effluents, which can be obtained from renewable materials such as biomass, biopolymers (chitosan) or composites. Thus, the objective of this work was to produce and evaluate activated carbon (AC) and chitosan composite films as adsorbents of neutral red dye. AC films were produced using CO₂ and water vapor. The variables of the activation process were time (1 and 2 h) and temperature (600 and 750 °C). Five films were produced, with one pure chitosan (T1) film and four activated carbon with chitosan films (T2, T3, T4 and T5). The T2 film refers to activated carbon produced at 600 °C for 1 h + chitosan, T3 to activated carbon produced at 600 °C for 2 h + chitosan, T4 to activated carbon produced at 750 °C for 1 h + chitosan and T5 to activated carbon produced at 750 °C for 2 h + chitosan. The T5 film increased its adsorption capacity by approximately 87% and its removal efficiency of neutral red dye by 43% compared to T1. The presence of activated carbon in the films provided an increase in the adsorption capacity of the neutral red dye.

Potential of Microalgae in Bioremediation of Wastewater

The increase in global pollution, industrialization and fast economic progress are considered to inflict serious consequences to the quality and availability of water throughout the world. Wastewater is generated from three major sources, i.e. industrial, agricultural, and municipal which contain pollutants, such as: xenobiotics, microplastics, heavy metals and augmented by high amount of carbon, phosphorus, and nitrogen compounds. Wastewater treatment is one of the most pressing issues since it cannot be achieved by any specific technology because of the varying nature and concentrations of pollutants and efficiency of the treatment technologies. The degradation capacity of these conventional treatment technologies is limited, especially regarding heavy metals, nutrients, and xenobiotics, steering the researchers to bioremediation using microalgae (Phycoremediation). Bioremediation can be defined as use of microalgae  for removal or biotransformation of pollutants and CO2 from wastewater with concomitant biomass production. However, the usage of wastewaters for the bulk cultivation of microalgae is advantageous for reducing carbon, nutrients cost, minimizing the consumption of freshwater, nitrogen, phosphorus recovery, and removal of other pollutants from wastewater and producing sufficient biomass for value addition for either biofuels or other value-added compounds. Several types of microalgae like Chlorella and Dunaliella have proved their applicability in the treatment of wastewaters. The bottlenecks concerning the microalgal wastewater bioremediation need to be identified and elucidated to proceed in bioremediation using microalgae. This objective of this paper is to provide an insight about the treatment of different wastewaters using microalgae and microalgal potential in the treatment of wastewaters containing heavy metals and emerging contaminants, with the specialized cultivation systems. This review also summarizes the end use applications of microalgal biomass which makes the bioremediation aspect more environmentally sustainable. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Enhancement of methanogenic performance by gasification biochar on anaerobic digestion

This work evaluates the performance of different biochar-amended anaerobic digestion systems. The Fourier Transform Infrared analysis showed that more ordered aromatic groups formed and the aromatization degree increased with the rise of gasification temperature. The biochar produced at 900 °C still showed an excellent ability to maintain the stability of anaerobic digestion performance, where the specific methane yield content steadily reached 742 mL CH₄/g ethanol. Besides, the enzymatic activity test indicated an improved performance with the addition of biochar obtained at gasification temperature. The relationship between the microbial community and metabolism pathways result are signified due to the direct interspecies electron transfer among Pseudomonas or Candidatus cloacimonas and Methanosaeta via biochar. These links have promoted the methane metabolism pathway of acetate decarboxylation. Therefore, the current study helps better understand the influence of surface functional groups of biochar at different temperatures on anaerobic digestion performance.

The Role of Biochar in Regulating the Carbon, Phosphorus, and Nitrogen Cycles Exemplified by Soil Systems

Biochar is a carbon-rich material prepared from the pyrolysis of biomass under various conditions. Recently, biochar drew great attention due to its promising potential in climate change mitigation, soil amendment, and environmental control. Obviously, biochar can be a beneficial soil amendment in several ways including preventing nutrients loss due to leaching, increasing N and P mineralization, and enabling the microbial mediation of N2O and CO2 emissions. However, there are also conflicting reports on biochar effects, such as water logging and weathering induced change of surface properties that ultimately affects microbial growth and soil fertility. Despite the voluminous reports on soil and biochar properties, few studies have systematically addressed the effects of biochar on the sequestration of carbon, nitrogen, and phosphorus in soils. Information on microbially-mediated transformation of carbon (C), nitrogen (N), and phosphorus (P) species in the soil environment remains relatively uncertain. A systematic documentation of how biochar influences the fate and transport of carbon, phosphorus, and nitrogen in soil is crucial to promoting biochar applications toward environmental sustainability. This report first provides an overview on the adsorption of carbon, phosphorus, and nitrogen species on biochar, particularly in soil systems. Then, the biochar-mediated transformation of organic species, and the transport of carbon, nitrogen, and phosphorus in soil systems are discussed. This review also reports on the weathering process of biochar and implications in the soil environment. Lastly, the current knowledge gaps and priority research directions for the biochar-amended systems in the future are assessed. This review focuses on literatures published in the past decade (2009–2021) on the adsorption, degradation, transport, weathering, and transformation of C, N, and P species in soil systems with respect to biochar applications.

Assessing the diverse environmental effects of biochar systems: An evaluation framework

Biochar has been recognised as a carbon dioxide removal (CDR) technology. Unlike other CDR technologies, biochar is expected to deliver various valuable effects in e.g. agriculture, animal husbandry, industrial processes, remediation activities and waste management. The diversity of biochar side effects to CDR makes the systematic environmental assessment of biochar projects challenging, and to date, there is no common framework for evaluating them. Our aim is to bridge the methodology gap for evaluating biochar systems from a life-cycle perspective. Using life cycle theory, actual biochar projects, and reviews of biochar research, we propose a general description of biochar systems, an overview of biochar effects, and an evaluation framework for biochar effects. The evaluation framework was applied to a case study, the Stockholm Biochar Project. In the framework, biochar effects are classified according to life cycle stage and life cycle effect type; and the biochar's end-of-life and the reference situations are made explicit. Three types of effects are easily included in life cycle theory: changes in biosphere exchanges, technosphere inputs, and technosphere outputs. For other effects, analysing the cause-effect chain may be helpful. Several biochar effects in agroecosystems can be modelled as future productivity increases against a reference situation. In practice, the complexity of agroecosystems can be bypassed by using empirical models. Existing biochar life cycle studies are often limited to carbon footprint calculations and quantify a limited amount of biochar effects, mainly carbon sequestration, energy displacements and fertiliser-related emissions. The methodological development in this study can be of benefit to the biochar and CDR research communities, as well as decision-makers in biochar practice and policy.

Purification of Wastewater from Biomass-Derived Syngas Scrubber Using Biochar and Activated Carbons

Phenol is a major component in the scrubber wastewater used for syngas purification in biomass-based gasification plants. Adsorption is a common strategy for wastewater purification, and carbon materials, such as activated carbons and biochar, may be used for its remediation. In this work, we compare the adsorption behavior towards phenol of two biochar samples, produced by pyrolysis and gasification of lignocellulose biomass, with two commercial activated carbons. Obtained data were also used to assess the effect of textural properties (i.e., surface area) on phenol removal. Continuous tests in lab-scale columns were also carried out and the obtained data were processed with literature models in order to obtain design parameters for scale-up. Results clearly indicate the superiority of activated carbons due to the higher pore volume, although biomass-derived char may be more suitable from an economic and environmental point of view. The phenol adsorption capacity increases from about 65 m/g for gasification biochar to about 270 mg/g for the commercial activated carbon. Correspondingly, service time of commercial activated carbons was found to be about six times higher than that of gasification biochar. Finally, results indicate that phenol may be used as a model for characterizing the adsorption capacity of the investigated carbon materials, but in the case of real waste water the carbon usage rate should be considered at least 1.5 times higher than that calculated for phenol.

Analysis and Characterization of Metallic Nodules on Biochar from Single-Stage Downdraft Gasification

Biochar, which is a byproduct of gasification, is used in a wide range of fields such as water filtration, agriculture, and electronics, to name a few. The metals in the biomass were thought to end up either in the ash or distributed throughout the biochar. In this study, the goal was a more thorough characterization of biochar resulting from a single-stage downdraft gasifier. One of the first observations was that some metals actually localize into small (~25 micron diameter) metallic nodules on the biochar surface. Further analysis included ultimate and proximate analysis, Brunauer–Emmert–Teller (BET) analysis, and scanning electron microscopy X-ray spectroscopy (SEM-EDS). Biomass fuel included corn grains, soybeans, and wood pellets, with wood biochar showing the highest fixed carbon content, at 91%, and the highest surface area, at 92.4 m2/g. The SEM analysis showed that certain minerals, including potassium, phosphorus, calcium, iron, nickel, silicon, and copper, formed nodules with over 50% metal mass next to pores in the carbon substrate. Aluminum, chlorine, magnesium, and silicon (in certain cases) were mostly uniformly distributed on the biochar carbon substrate. Corn biochar showed a high concentration in the nodules of 9–21% phosphorus and up to 67% potassium. Soybean biochar showed a similar trend with traces of iron and nickel of 2% and 4.1%, respectively, while wood biochar had a significant amount of potassium, up to 35%, along with 44% calcium, 3% iron, and up to 4.2% nickel concentrations. A morphology analysis was also carried out.

Comparative study on carbon dioxide-cofed catalytic pyrolysis of grass and woody biomass

This study investigated the mechanistic functions of CO₂ on the pyrolysis of two different biomasses to elucidate the effect of CO₂ on syngas formations during pyrolysis. To this end, CO₂-assisted pyrolysis of cellulosic biomass (barnyard grass, Echinochloa) and lignin-rich woody biomass (retinispora, Chamaecyparis obtusa) were compared. The confirmed mechanistic effectiveness of CO₂ on pyrolysis of biomass was gas phase reactions between CO₂ and volatile matters from biomass pyrolysis. Lignin-rich biomass had more CO₂ susceptibility, resulting in more enhanced CO formation via the gas phase reactions. To expedite the slow reaction rate of the gas phase reactions during biomass pyrolysis, earth-abundant catalysts (Co/SiO₂ and Ni/SiO₂) were employed for pyrolysis of two biomass substrates. With Co and Ni catalysts, the syngas formations were 2 and 3 times higher comparing to the pyrolysis of without catalyst. The cumulative formations of syngas from lignin-rich biomass was nearly doubled than that from cellulosic biomass.

Technical and Benefit Evaluation of Fruit-Wood Waste Gasification Heating Coproduction of an Activated Carbon System

Biomass gasification polygeneration technology can well address both the economic and environmental issues that impeded the development of biomass gasification technology. To further improve the utilization efficiency of biomass, preactivation of gasified carbon is realized in the gasification reactor. The aim of this study is to adopt a new gasification reactor and an environmental protection combustion chamber to obtain high value-added activated carbon with clean heating. In this paper, an experimental study on the fruit-wood waste gasification heating coproduction of an activated carbon system was carried out. The results show that the yield of gasified carbon is 20.22%, the specific surface area of gasified carbon reaches 590 m²/g, the yield of activated carbon is 10.37%, and the gas yield is 1.9 Nm³/kg. The gasification efficiency of the system is 57.83%, the energy that is transferred to the activated carbon is 18.72%, and the percentage of fixed carbon is 24.3%. Compared with the biomass particle, coal, and natural gas heating projects, the environmental protection benefits of the project are significant, and the negative emission of CO₂ is realized. Compared with the heating benefit of coal and natural gas, the economic benefit of this project is more significant.

Techno-Economic Assessment of a Gasification Plant for Distributed Cogeneration in the Agrifood Sector

This research work presents a techno-economic analysis of a biomass gasification plant fueled with residues from the olive oil and almond industries for combined heat and power generation in the agrifood sector. The experimental plant consists of a downdraft fixed bed gasifier, a producer gas cleaning and cooling system and a spark-ignition engine–generator set as a power generation unit, which generates about 10–12 kW of rated electric power. With an average consumption between 13–14 kg/h of exhausted olive pomace pellets as feedstock, the producer gas volumetric flow rate was 31 Nm3/h (vol. %: 19.2 H2, 12.9 CO, 1.9 CH4, 19.2 CO2, 46.7 N2). The average cold gas efficiency was nearly 63%. This work also addresses the characterization and potential application of the carbonaceous solid residue (biochar), discharged from the gasifier at 1.7 kg/h. Finally, an economic feasibility analysis was developed, wherein the payback period ranges between 5–9 years.

The addition of biochar as a sustainable strategy for the remediation of PAH-contaminated sediments

The contamination of sediments by polycyclic aromatic hydrocarbons (PAHs) has been widely spread for years due to human activities, imposing the research and development of effective remediation technologies for achieving efficient treatment and reuse of sediments. In this context, the amendment of biochar in PAH-contaminated sediments has been lately proposed as an innovative and sustainable technology. This review provides detailed information about the mechanisms and impacts associated with the supplementation of biochar to sediments polluted by PAHs. The properties of biochar employed in these applications have been thoroughly examined. Sorption onto biochar is the main mechanism involved in PAH removal from sediments. Sorption efficiency can be significantly improved even in the presence of a low remediation time (i.e. 30 d) when a multi-PAH system is used and biochar is provided with a high dosage (i.e. by 5% in a mass ratio with the sediment) and a specific surface area of approximately 360 m² g^-1. The use of biochar results in a decrease (i.e. up to 20%) of the PAH degradation during bioaugmentation and phytoremediation of sediments, as a consequence of the reduction of PAH bioavailability and an increase of water and nutrient retention. In contrast, PAH degradation has been reported to increase up to 54% when nitrate is used as electron acceptor in low-temperature biochar-amended sediments. Finally, biochar is effective in co-application with Fe²⁺ for the persulfate degradation of PAHs (i.e. up to 80%), mainly when a high catalyst dose and an acidic pH are used.

Valorization of synthetic textile waste using CO2 as a raw material in the catalytic pyrolysis process

Since an invention of synthetic fibers (textiles), our life quality has been improved. However, the cumulative production and disposal of them have perceived as significant since they are not biodegradable and hard to be upcycled/recycled. From washing textiles, microplastics are released into the environment, which are regarded as emerging contaminants. As a means for source reduction of microplastics, this study proposed a rapid disposal platform for waste textiles (WTs), converting them into value-added products. To this end, catalytic pyrolysis of WT was studied. To offer more environmentally sound process, CO₂ was used as a raw material for WT pyrolysis. Thermal cracking of WT led to the production of syngas and CH₄ under the CO₂ environment. CO₂ resulted in additional CO production via gas phase reaction with volatile compounds evolved from pyrolysis of WT. To expedite the reaction kinetics for syngas formation, catalytic pyrolysis was done over Co-based catalyst. Comparing to non-catalytic pyrolysis, CO₂-assisted catalytic pyrolysis had 3- and 8-times higher production of H₂ and CO, respectively. This process also suppressed catalyst deactivation, converting more than 80 wt% of WT into syngas and CH₄. The more generation of CO from the use of CO₂ as a raw material offers an effective means to minimize the formations of harmful chemical species, such as benzene derivatives and polycyclic aromatic hydrocarbons.

Biodiesel synthesis from swine manure

This study demonstrates that the biodiesel (BD) from swine manure (SM) could be a promising way for large scale generation of biofuel. Also, the economic and environmental benefits of SM derived BD were evaluated. Transesterification of lipid contents extracted from the collected SM had low BD yield (14.2 wt%) using H₂SO₄ catalyst due to high acid value and impurities. However, thermo-chemical non-catalytic transesterification with a porous material showed 94.7 wt% yield of BD from the lipid in SM. Considering the current population of swine, the annual production of BD from SM was estimated. The SM derived BD could cover 19.7 and 46.8 wt% of BD currently produced in both Korea and the USA with the economic benefits of up to $96 million and $2.1 billion, respectively. The proposed approach also can save vast arable lands needed to cultivate oil-bearing feedstocks for BD production.

Roles of the mineral constituents in sludge-derived biochar in persulfate activation for phenol degradation

Biochar as an environmental-friendly and low-cost catalyst has gained increasing attention in the catalytic degradation of organic pollutants. However, the roles of endogenous mineral constituents in biochar in the catalytic degradation are still unclear. In this study, the mineral-rich biochar produced from sewage sludge at 400 °C (SS400) and 700 °C (SS700) and their corresponding demineralized biochar (DSS400 and DSS700) were used to be the persulfate (PS) activator for phenol degradation. Results showed that the mineral-rich biochar + PS system had negligible phenol degradation (≤12.6 %), whereas distinct degradation of phenol were obtained in the demineralized biochar + PS system where DSS400 + PS and DSS700 + PS exhibited 36.3 % and 57.8 % degradation, respectively. Different minerals in mineral-rich biochar exhibited varying functions on phenol degradation. Mg and K in biochar had less effect on the phenol degradation, while Fe-containing minerals favored the phenol degradation. However, Ca-containing minerals more greatly reduced the formation of hydroxyl radical, resulting in more inhibited degradation of phenol. Thus, the overall degradation of phenol was reduced by the mineral-rich biochar. The findings indicated that the inherent minerals in biochar were not favorable for the phenol degradation, which guides us the application of biochar containing different minerals in the remediation of organic pollutants.

Valorization of swine manure biochar as a catalyst for transesterifying waste cooking oil into biodiesel

As demand of proteins from meats has significantly increased with economy growth, the population of livestock proliferates. Thus, heavy amount of livestock byproducts released from livestock industries will become more problematic if they are handled in an unsatisfactory manner. In this study, swine manure (SM) waste was directly valorized to be used as a reaction catalyst for biodiesel production. Pyrolysis was adapted to produce swine manure biochars at 500 (SMB@500) and 650 °C (SMB@650), and the materials were used for conversion of waste cooking oil into biodiesels (i.e., fatty acid methyl esters: FAMEs). The properties of SMBs and resulting pyrolytic gases (i.e., H₂, CO, and C_1-2 hydrocarbons (HCs)) and liquids during pyrolysis were also characterized. SMBs used in this study included a large quantity of metallic contents that significantly contributed to the rapid reaction for biodiesel production. In detail, SMB@500 and SMB@650 showed higher than 96% of FAME yield at 305 and 210 °C of reaction temperature, while non-catalytic reaction using SiO₂ showed similar FAME yield at 330 °C. Thus, this work offers a sustainable way to recycle organic and inorganic materials in livestock manures for energy (biodiesel, pyrolytic oil, H₂, and C_1-2 HCs) production.

Current Status of Energy Production from Solid Biomass in North-West Italy

Data on the thermochemical plants fed by solid biomass in the north-west area of Italy (Liguria, Lombardy, Piedmont and Aosta Valley) have been organised, analysed and discussed. Moreover, the biomass availability and potential has been evaluated. A total of 28,167 plants have been categorised according to their typology and output: thermo-electric power plants for electricity production, thermal plants for heat production, cogeneration plants for combined heat and electricity production and district heating installations for local heating purposes. In general, separate observations for the different provinces may be drawn. Liguria stands out as the most evident case of under-exploited biomass potential, followed by Aosta Valley, which, however, is rich in hydroelectricity. Lombardy and Piedmont are more virtuous and have several plants in their territory. The construction of new plants and the upgrade of existing ones may bring noteworthy benefits, as well as the use of added value sub-products to foster circular economy approaches.

Biochar technology in wastewater treatment: A critical review

Biochar is a promising agent for wastewater treatment, soil remediation, and gas storage and separation. This review summarizes recent research development on biochar production and applications with a focus on the application of biochar technology in wastewater treatment. Different technologies for biochar production, with an emphasis on pre-treatment of feedstock and post treatment, are succinctly summarized. Biochar has been extensively used as an adsorbent to remove toxic metals, organic pollutants, and nutrients from wastewater. Compared to pristine biochar, engineered/designer biochar generally has larger surface area, stronger adsorption capacity, or more abundant surface functional groups (SFG), which represents a new type of carbon material with great application prospects in various wastewater treatments. As the first of its kind, this critical review emphasizes the promising prospects of biochar technology in the treatment of various wastewater including industrial wastewater (dye, battery manufacture, and dairy wastewater), municipal wastewater, agricultural wastewater, and stormwater. Future research on engineered/designer biochar production and its field-scale application is discussed. Based on the review, it can be concluded that biochar technology represents a new, cost effective, and environmentally-friendly solution for the treatment of wastewater.

Assessment of biomass demineralization on gasification: From experimental investigation, mechanism to potential application

Considering the advantages (e.g. agglomeration mitigation) and disadvantages (e.g. inorganic species catalysis removal) of biomass demineralization, it is valuable to investigate its effects on gasification performance, thus assessing its necessity prior to performing gasification. To accomplish this, corn straw (CS) was demineralized to different degrees with H₂O and HCl, respectively. H₂O and HCl demineralization behaved different abilities to inorganic species removal. Cellulose and hemicelluloses content decreased, while lignin content increased, especially with HCl demineralization. The experiments were investigated by using a bench-scale downdraft fixed-bed gasifier at 600-800 °C and were further analyzed via thermogravimetric coupled with Fourier transform infrared spectrometry. Demineralization demonstrated a positive effect on gasification at lower temperatures (600-700 °C) for a dominant effect of lignin content and an insignificant effect of inorganic species removal. However, the catalysis of inorganic species increased as the temperature increased, resulting in the highest H₂ (11.30 vol%) and CO (16.02 vol%) production of raw CS compared to demineralized CS at 800 °C. Inorganic species had a dual positive effect on CO generation, promoting both CO₂ and char generation leading to a higher CO yield following Boundouard reaction, and increasing the formation of active intermediates thus producing more CO. These effects enhanced when the gasification temperature increased. Additionally, inorganic species catalyzed the aromatic rings rearrangement to generate more H₂O, thus driving the endothermic Primary water-gas to produce H₂. This was also positively correlated with gasification temperature. Therefore, raw CS demonstrated higher H₂ and CO production than demineralized CS at a higher gasification temperature. Moreover, the promotion effect of inorganic species on thermal devolatilization of methoxyl groups and Methanation reaction led to the higher CH₄ production of raw CS. This research clarifies the effects of biomass demineralization on its gasification and suggests the potential application.

Efficacies of Carbon-Based Adsorbents for Carbon Dioxide Capture

Carbon dioxide (CO2), a major greenhouse gas, capture has recently become a crucial technological solution to reduce atmospheric emissions from fossil fuel burning. Thereafter, many efforts have been put forwarded to reduce the burden on climate change by capturing and separating CO2, especially from larger power plants and from the air through the utilization of different technologies (e.g., membrane, absorption, microbial, cryogenic, chemical looping, and so on). Those technologies have often suffered from high operating costs and huge energy consumption. On the right side, physical process, such as adsorption, is a cost-effective process, which has been widely used to adsorb different contaminants, including CO2. Henceforth, this review covered the overall efficacies of CO2 adsorption from air at 196 K to 343 K and different pressures by the carbon-based materials (CBMs). Subsequently, we also addressed the associated challenges and future opportunities for CBMs. According to this review, the efficacies of various CBMs for CO2 adsorption have followed the order of carbon nanomaterials (i.e., graphene, graphene oxides, carbon nanotubes, and their composites) < mesoporous -microporous or hierarchical porous carbons < biochar and activated biochar < activated carbons.

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.

Engineering pyrolysis biochar via single-step microwave steam activation for hazardous landfill leachate treatment

Improving the sustainability and cost-effectiveness of biochar production is crucial to meet increased global market demand. Here, we developed a single-step microwave steam activation (STMSA) as a simplified yet efficient method to produce microwave activated biochar (MAB) from waste palm shell (WPS). The STMSA recorded a higher heating rate (70 °C/min) and higher conversion (45 wt%) of WPS into highly microporous MAB (micropore surface area of 679.22 m²/g) in contrast with the conventional heating approach (≤ 12-17 wt%). The MAB was then applied as biosorbent for hazardous landfill leachate (LL) treatment and the adsorption performance was compared with commercial activated carbon under different pH, adsorbent quantity, adsorbate concentrations, and contact times. The MAB demonstrated high adsorption capacity, achieving maximum adsorption efficiency at 595 mg/g and 65 % removal of chemical oxygen demand (COD) with 0.4 g/L of adsorbent amount under optimal acidic conditions (pH ≈ 2-3) after 24 h of contact time. The Freundlich isotherm and pseudo second-order kinetic models were well-fitted to explain the equilibrium adsorption and kinetics. The results indicate the viability of STMSA as a fast and efficient approach to produce activated biochar as a biosorbent for the treatment of hazardous landfill leachate.

Methane yield enhancement of mesophilic and thermophilic anaerobic co-digestion of algal biomass and food waste using algal biochar: Semi-continuous operation and microbial community analysis

The impact of algal biochar addition on mesophilic and thermophilic anaerobic co-digestion of algal biomass and food waste was investigated with a focus on semi-continuous operations and functional microbial communities. Under batch co-digestion, the highest co-digestion synergy was observed for a mixture of 25% food waste and 75% algal biomass. During semi-continuous co-digestion of 25% food waste-75% algal biomass mixture, biochar amended digesters exhibited a 12-54% increase in average methane yield (275.8-394.6 mL/gVS) compared to the controls. Elevated temperature induced narrow distributions of volatile fatty acids (VFAs) by inhibiting the production of branched VFAs. Genus Proteiniphilum was selectively enriched by 3.2 folds in mesophilic digesters with biochar amendment while genus Defluviitoga was selectively enriched in thermophilic digesters due to elevated temperature. Methanogenic communities were significantly different in mesophilic and thermophilic digesters. Biochar amendment contributed to shifts in the predominant methanogens leading to a more balanced state of two methanogenic pathways.

Advances in design strategies for preparation of biochar based catalytic system for production of high value chemicals

The aim of this review is to provide the comprehensive and mechanistic information of biochar based catalytic systems for the production of fuels and fine chemicals with a concept of integrated biorefinery. The review presents an in-depth assessment of relationships between physico-chemical properties and catalytic performances of biochar based catalytic systems during the production of targeted compounds at the molecular/fundamental level. The catalytic performance of the biochar is associated with its unique physico-chemical properties (surface area/surface functionality/pores/mechanical strength/inorganic species) which provide a distinct catalytic route. The review also discusses the preparation methods and significance of the activation process for tuning of physico-chemical properties of biochar.

Synthesis of nickel/biochar composite from pyrolysis of Microcystis aeruginosa and its practical use for syngas production

This study proposes a sustainable waste-to-energy/biochar platform using a toxic microalgal biomass waste. In particular, CO₂-feeding pyrolysis of Microcystis aeruginosa (M. aeruginosa) waste was investigated, focusing on the analysis of gaseous pyrolysates and properties of biochar with a construction of mass balance. Also, the catalytic capability of biochar produced from M. aeruginosa was explored to reinforce the mechanistic impact of CO₂ on the pyrolysis process within the overall process level. Ni impregnated biochar composite was further synthesized and used as a catalyst to promote syngas formation in the CO₂-feeding pyrolysis process of M. aeruginosa.

Biochar facilitated bioprocessing and biorefinery for productions of biofuel and chemicals: A review

Biochar is traditionally used to improve soil properties in arable land and as adsorbent or precursor of activated carbon in wastewater treatment. Recent advances have shown biochar potentials in enhancing productions of biofuels and chemicals such as bio-ethanol, butanol, methane, hydrogen, bio-diesel, hydrocarbons and carboxylic acids. The properties of biochar such as high levels of porosity, functional groups, cation exchange capacity, pH buffering capacity, electron conductivity, and macro-/micro- nutrients (Na, K, Ca, Mg, P, S, Fe, etc.) provide appropriate conditions to relieve physicochemical stresses on microorganisms through pH buffering, detoxification, nutrients supply, serving as electron carrier and supportive microbial habitats. This paper critically reviewed biochar production and characteristics, biochar utilization in anaerobic digestion, composting, microbial fermentation, hydrolysate detoxification, catalysis in biomass refinery and biodiesel synthesis. This review provides novel vision of biochar application, which could guide future research towards cleaner and more economic production of renewable fuels and bio-based chemicals.

A Review on the Feedstocks for the Sustainable Production of Bioactive Compounds in Biorefineries

Since 2015, the sustainable development goals of the United Nations established a route map to achieve a sustainable society, pushing the industry to aim for sustainable processes. Biorefineries have been studied as the technological scheme to process integrally renewable resources. The so-called “bioactive” compounds (BACs) have been of high interest, given their high added value and potential application in pharmaceutics and health, among others. However, there are still elements to be addressed to consider them as economic drivers of sustainable processes. First, BACs can be produced from many sources and it is important to identify feedstocks for this purpose. Second, a sustainable production process should also consider valorizing the remaining components. Finally, feedstock availability plays an important role in affecting the process scale, logistics, and feasibility. This work consists of a review on the feedstocks for the sustainable production of BACs in biorefineries, covering the type of BAC, composition, and availability. Some example biorefineries are proposed using wheat straw, hemp and grapevine shoots. As a main conclusion, multiple raw materials have the potential to obtain BACs that can become economic drivers of biorefineries. This is an interesting outlook, as the integral use of the feedstocks may not only allow obtaining different types of BACs, but also other fiber products and energy for the process self-supply.

Potentials, Limitations, Co-Benefits, and Trade-Offs of Biochar Applications to Soils for Climate Change Mitigation

Biochar is one of the most affordable negative emission technologies (NET) at hand for future large-scale deployment of carbon dioxide removal (CDR), which is typically found essential to stabilizing global temperature rise at relatively low levels. Biochar has also attracted attention as a soil amendment capable of improving yield and soil quality and of reducing soil greenhouse gas (GHG) emissions. In this work, we review the literature on biochar production potential and its effects on climate, food security, ecosystems, and toxicity. We identify three key factors that are largely affecting the environmental performance of biochar application to agricultural soils: (1) production condition during pyrolysis, (2) soil conditions and background climate, and (3) field management of biochar. Biochar production using only forest or crop residues can achieve up to 10% of the required CDR for 1.5 ∘ C pathways and about 25% for 2 ∘ C pathways; the consideration of dedicated crops as biochar feedstocks increases the CDR potential up to 15–35% and 35–50%, respectively. A quantitative review of life-cycle assessment (LCA) studies of biochar systems shows that the total climate change assessment of biochar ranges between a net emission of 0.04 tCO 2 eq and a net reduction of 1.67 tCO 2 eq per tonnes feedstock. The wide range of values is due to different assumptions in the LCA studies, such as type of feedstock, biochar stability in soils, soil emissions, substitution effects, and methodological issues. Potential trade-offs between climate mitigation and other environmental impact categories include particulate matter, acidification, and eutrophication and mostly depend on the background energy system considered and on whether residues or dedicated feedstocks are used for biochar production. Overall, our review finds that biochar in soils presents relatively low risks in terms of negative environmental impacts and can improve soil quality and that decisions regarding feedstock mix and pyrolysis conditions can be optimized to maximize climate benefits and to reduce trade-offs under different soil conditions. However, more knowledge on the fate of biochar in freshwater systems and as black carbon emissions is required, as they represent potential negative consequences for climate and toxicity. Biochar systems also interact with the climate through many complex mechanisms (i.e., surface albedo, black carbon emissions from soils, etc.) or with water bodies through leaching of nutrients. These effects are complex and the lack of simplified metrics and approaches prevents their routine inclusion in environmental assessment studies. Specific emission factors produced from more sophisticated climate and ecosystem models are instrumental to increasing the resolution and accuracy of environmental sustainability analysis of biochar systems and can ultimately improve the characterization of the heterogeneities of varying local conditions and combinations of type feedstock, conversion process, soil conditions, and application practice.

Advances in lignin valorization towards bio-based chemicals and fuels: Lignin biorefinery

Lignin is one of the most promising renewable sources for aromatic hydrocarbons, while effective depolymerization towards its constituent monomers is a particular challenge because of the structural complexity and stability. Intensive research efforts have been directed towards exploiting effective valorization of lignin for the production of bio-based platform chemicals and fuels. The present contribution aims to provide a critical review of key advances in the identification of exact lignin structure subjected to various fractionation technologies and demonstrate the key roles of lignin structures in depolymerization for unique functionalized products. Various technologies (e.g., thermocatalytic approaches, photocatalytic conversion, and mechanochemical depolymerization) are reviewed and evaluated in terms of feasibility and potential for further upgrading. Overall, advances in pristine lignin structure analysis and conversion technologies can facilitate recovery and subsequent utilization of lignin towards tailored commodity chemicals and fungible fuels.

Steam gasification of land, coastal zone and marine biomass by thermal gravimetric analyzer and a free-fall tubular gasifier: Biochars reactivity and hydrogen-rich syngas production

The steam gasification properties and kinetics, products distribution and syngas composition derived from land, coastal zone and marine biomass have been studied by TGA and free-fall tubular gasifier. Volume model, shrinking core model and random pore model were applied to describe the reaction kinetics. The influence of temperature and fuel types on steam gasification in a free-fall tubular gasifier were clarified simultaneously. Results showed that gasification reactivity of reed (Re) and Sargassum horneri (Sh) chars were better than that of corn stalks (Cs) char, which mostly determined by its carbonaceous structure and the varying inorganic contents. RPM model was applied successfully to corresponding to the experimental data. Bench scale reactor test found that the steam gasification of Re gave the largest amount of gaseous product than Sh and Cs, while no liquidus formation in Sh. An increase in the temperature during gasification process boosted produced sharply total gas production yield, more yield of H₂ and CO₂ and less CO and CH₄ from different biomass.

Biochar application and summer temperatures reduce N2O and enhance CH4 emissions in a Mediterranean agroecosystem: Role of biologically-induced anoxic microsites

Biochar applications have been proposed for mitigating some soil greenhouse gas (GHG) emissions. However, results can range from mitigation to no effects. To explain these differences, mechanisms have been proposed but their reliability depends on biochar type, soil and climatic conditions. Furthermore, it is found that the mitigation capacity is dependent on how the biochar is aging under field conditions. The effects on N₂O, CH₄ and CO₂ emission rates of a gasification pine biochar (applied as 0, 5, and 30 t ha^-1) were studied between 8 and 21 months of the application in an alkaline soil cropped to barley under Mediterranean climate. Together with GHG, soil chemical and biological properties were assessed, namely, changes in labile organic matter content and nutrient status, and pH, as well as microbial abundance, activity, and functional composition. During the 2 years of the application, significant changes were observed at the highest rate of biochar application such as higher contents of water, K⁺, Mg²⁺, SO₄^2-, higher basal respiration, and with non-significant changes in microbial community, though with some temporal effects. Regarding GHG, N₂O decreases coupled with CH₄ increases in the summer sampling were measured, although only for the highest application rate scenario. Such effects were unrelated to pH, bioavailable nitrogen status, or bulk soil microbial community shifts. We hypothesized that the key is the porous structure of our wood biochar, which is able to provide more and diversified microbial microhabitats in comparison to bulk soil. At higher temperatures in summer, biologically-induced anoxic conditions in biochar pores acting as microsites may be promoted, where total denitrification to N₂ occurs which leads to N₂O uptake, while CH₄ production is promoted.

Fractionation of alkali lignin by organic solvents for biodegradable microsphere through self-assembly

Here we report a centrifugation-based fractionation methodology that was integrated with three types of organic solvents to fractionate industrial alkali lignin toward the fabrication of lignin microsphere. The Fourier-transform infrared spectroscopy (FT-IR) result showed that the chemical structure of lignin was not changed by solvent fractionation. Soluble lignin in each solvent had lower molecular weight, improved polydispersity index (PDI) and less impurities (S, N), while insoluble lignin had a high bio-char yield and can be utilized as potential carbon source for porous carbon nanosphere materials. In addition, well-shaped lignin microsphere with smooth or anisotropic surface can be prepared by selecting proper lignin fraction without any chemical modification. This work thus provides a new strategy for the derivation of lignin as raw materials for value-added products, which paved a new way to develop a green and sustainable bio-refining industry.

Orange peel valorization by pyrolysis under the carbon dioxide environment

To valorize biomass waste, pyrolysis of orange peel was mainly investigated as a case study. In an effort to establish a more sustainable thermolytic platform for orange peel, this study particularly employed CO₂ as reactive gas medium. Accordingly, this study laid great emphasis on elucidating the mechanistic role of CO₂ in pyrolysis of orange peel. The thermo-gravimetric analysis (TGA) confirmed that no occurrence of the heterogeneous reactions between the solid sample and CO₂. However, the gaseous effluents from pyrolysis of orange peel experimentally proved that CO₂ effectively suppressed dehydrogenation of volatile matters (VMs) evolved from the thermolysis of orange peel by random bond scissions. Moreover, CO₂ reacted VMs, thereby resulting in the formation of CO. Note that the formation of CO was being initiated at temperatures ≥550 °C. The two identified roles of CO₂ led to the compositional modification of pyrolytic oil by means of lowering aromaticity.

A comprehensive review on physical activation of biochar for energy and environmental applications

Biochar is a solid by-product of thermochemical conversion of biomass to bio-oil and syngas. It has a carbonaceous skeleton, a small amount of heteroatom functional groups, mineral matter, and water. Biochar’s unique physicochemical structures lead to many valuable properties of important technological applications, including its sorption capacity. Indeed, biochar’s wide range of applications include carbon sequestration, reduction in greenhouse gas emissions, waste management, renewable energy generation, soil amendment, and environmental remediation. Aside from these applications, new scientific insights and technological concepts have continued to emerge in the last decade. Consequently, a systematic update of current knowledge regarding the complex nature of biochar, the scientific and technological impacts, and operational costs of different activation strategies are highly desirable for transforming biochar applications into industrial scales. This communication presents a comprehensive review of physical activation/modification strategies and their effects on the physicochemical properties of biochar and its applications in environment-related fields. Physical activation applied to the activation of biochar is discussed under three different categories: I) gaseous modification by steam, carbon dioxide, air, or ozone; II) thermal modification by conventional heating and microwave irradiation; and III) recently developed modification methods using ultrasound waves, plasma, and electrochemical methods. The activation results are discussed in terms of different physicochemical properties of biochar, such as surface area; micropore, mesopore, and total pore volume; surface functionality; burn-off; ash content; organic compound content; polarity; and aromaticity index. Due to the rapid increase in the application of biochar as adsorbents, the synergistic and antagonistic effects of activation processes on the desired application are also covered.

Fabrication and environmental applications of multifunctional mixed metal-biochar composites (MMBC) from red mud and lignin wastes

This study fabricated a new and multifunctional mixed metal-biochar composites (MMBC) using the mixture of two abundant industrial wastes, red mud (RM) and lignin, via pyrolysis under N₂ atmosphere, and its ability to treat wastewater containing various contaminants was comprehensively evaluated. A porous structure (BET surface area = 100.8 m² g^-1) was created and metallic Fe was formed in the MMBC owing to reduction of Fe oxides present in RM by lignin decomposition products during pyrolysis at 700 °C, which was closely associated with the transformation of liquid to gaseous pyrogenic products. The potential application of the MMBC was investigated for the removal of heavy metals (Pb(II) and Ni(II)), oxyanions (As(V) and Cr(VI)), dye (methylene blue), and pharmaceutical/personal care products (para-nitrophenol and pCBA). The aluminosilicate mineral, metallic Fe, and porous carbon matrix derived from the incorporation of RM and lignin contributed to the multifunctionality (i.e., adsorption, chemical reduction, and catalytic reaction) of the MMBC. Thus, engineered biochar composites synthesized from selected industrial wastes can be a potential candidate for environmental applications.

Biochar composition-dependent impacts on soil nutrient release, carbon mineralization, and potential environmental risk: A review

Biochar application has multiple benefits for soil fertility improvement and climate change mitigation. Biochar can act as a source of nutrients and sequester carbon (C) in the soil. The nutrient release capacity of biochar once applied to the soil varies with the composition of the biochar, which is a function of the feedstock type and pyrolysis condition used for biochar production. Biochar has a crucial influence on soil C mineralization, including its positive or negative priming of microorganisms involved in soil C cycling. However, in various cases, biochar application to the soil may cause negative effects in the soil and the wider environment. For instance, biochar may suppress soil nutrient availability and crop productivity due to the reduction in plant nutrient uptake or reduction in soil C mineralization. Biochar application may also negatively affect environmental quality and human health because of harmful compounds such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated dibenzodioxins, and dibenzofurans (PCDD/DF). In this review, we discuss the linkage between biochar composition and function, evaluate the role biochar plays in soil fertility improvement and C sequestration, and discuss regulations and concerns regarding biochar's negative environmental impact. We also summarize advancements in biochar production technologies and discuss future challenges and priorities in biochar research.