Carbon Storage with Benefits Sohi, Saran P.
Science (American Association for the Advancement of Science),
11/2012, Letnik:
338, Številka:
6110
Journal Article
Recenzirano
Biochar is the solid, carbon-rich product of heating biomass with the exclusion of air (pyrolysis or "charring"). If added to soil on a large scale, biochar has the potential to both benefit global ...agriculture and mitigate climate change. It could also provide an income stream from carbon abatement for farmers worldwide. However, biochar properties are far from uniform, and biochar production technologies are still maturing. Research is beginning to point the way toward a targeted application of biochar to soils that maximizes its benefits.
Recognition of biochar as a potential tool for long-term carbon sequestration with additional agronomic benefits is growing. However, the functionality of biochar in soil and the response of soils to ...biochar inputs are poorly understood. It has been suggested, for example, that biochar additions to soils could prime for the loss of native organic carbon, undermining its sequestration potential. This work examines the priming potential of biochar in the context of its own labile fraction and procedures for their assessment. A systematic set of biochar samples produced from C4 plant biomass under a range of pyrolysis process conditions were incubated in a C3 soil at three discrete levels of organic matter status (a result of contrasting long-term land management on a single site). The biochar samples were characterised for labile carbon content ex-situ and then added to each soil. Priming potential was determined by a comparison of CO
2 flux rates and its isotopic analysis for attribution of source. The results conclusively showed that while carbon mineralisation was often higher in biochar amended soil, this was due to rapid utilisation of a small labile component of biochar and that biochar did not prime for the loss of native organic soil organic matter. Furthermore, in some cases negative priming occurred, with lower carbon mineralisation in biochar amended soil, probably as a result of the stabilisation of labile soil carbon.
► Development of accurate and sensitive method for screening priming potential of biochar. ► No additional carbon mineralisation from soils with different organic matter status. ► No evidence for short term priming of native soil carbon following biochar application. ► Evidence to suggest stabilisation of native soil carbon following biochar application.
Magnetic biochar was made from peanut hull biomass using iron chloride in a simplified aqueous phase approach and pyrolysis at alternative peak temperatures (450–650 °C). Magnetic biochar showed an ...extreme capacity for adsorption of hexavalent chromium Cr (VI) from aqueous solution, which was 1–2 orders of magnitude higher compared to standard (non-magnetic) biochar from the same feedstock. Adsorption increased with pyrolysis temperature peaking at 77,542 mg kg−1 in the sample pyrolysed at 650 °C. In contrast to magnetic biochar, the low adsorption capacity of standard biochar decreased with increasing pyrolysis temperature. The fine particle size of magnetic biochar and low aqueous pH were also important for adsorption. Surfaces of products from batch adsorption experiments were characterized by scanning electron microscopy, energy-dispersive X-ray analysis, X-ray diffraction, X-ray photoelectron spectroscopy and vibrating sample magnetometer. This revealed that γ-Fe2O3 was crucial to the properties (adsorbance and magnetism) of magnetic biochar. The removal mechanism was the Cr (VI) electrostatic attracted on protonated –OH on γ-Fe2O3 surface and it could be desorbed by alkaline solution. Findings suggest that pyrolysis has potential to create effective, magnetically recoverable adsorbents relevant to environmental application.
Simplified method for creating magnetic biochar from peanut hulls and its effect on Cr (VI) removal from aqueous solution. Display omitted
•Magnetic biochar derived peanut hull was simplified created with higher adsorption for Cr(VI) in aqueous.•γ-Fe2O3 loaded on biochar played a key role in Cr(VI) adsorption.•Higher pyrolysis temperature and smaller particle size of magnetic biochar could result in higher adsorption of Cr(VI).
Biochar has potential to control the bioavailability and migration of potentially toxic heavy metals in soil by adsorption. Natural ageing in the environment may change the physicochemical properties ...and adsorption function of biochar over the long-term. The present study compared the effects of different simulated ageing treatments on Cd adsorption of high and low temperature biochar from straw of corn (Zea mays). Fresh and aged biochars were systematically characterized by elemental analysis, FTIR, XPS, Zeta, SEM-EDS, XRD and the composition of their mineral ash. The adsorption of Cd to fresh and aged biochars was then assessed under the influence of pH. Drawing the results together the effects of ageing on the extent and mode of Cd adsorption could be elucidated. The results showed that the adsorption capacity of fresh biochar produced at 650 °C was higher than of biochar made at 350 °C, and that mineral co-precipitation plays a dominant role in Cd sorption. Leaching removed organic and inorganic ash components from biochars, markedly diminishing the capacity of the high temperature biochar to adsorb Cd. The adsorption performance of the low temperature biochar was dependent on surface complexation. The adsorption capacity of low-temperature biochar was markedly enhanced by oxygen-containing functional groups formed through acidification and oxidation. The long-term benefits of biochar in the management of polluted soil require a rethink, considering the contrasting ageing behavior of different temperature biochar and their response to different ageing environments.
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•Surface complexation controls cadmium adsorption for low-temperature biochar.•Mineral co-precipitation controls cadmium adsorption for high-temperature biochar.•Progressive leaching diminishes adsorption related to both organic and inorganic components of biochar.•Acidification/oxidation both increase the density of oxygen-containing function groups on biochar.•Acidification and oxidation have opposite effects on the inorganic components of biochar.
A capsule of main findings: Our results show that there are significant differences in the physicochemical properties of low/high temperature biochars that explain their differential response to ageing in terms of Cd adsorption.
Addressing food security issues arising from phosphorus (P) scarcity is described as one of the greatest global challenges of the 21st Century. Dependence on inorganic phosphate fertilisers derived ...from limited geological sources of P creates an urgent need to recover P from wastes and treated waters, in safe forms that are also effective agriculturally – the established process of P removal by chemical precipitation using Fe or Al salts, is effective for P removal but leads to residues with limited bioavailability and contamination concerns. One of the greatest opportunities for P recovery is at wastewater treatment plants (WWTPs) where the crystallisation of struvite and Ca-P from enhanced biological P removal (EBPR) sludge is well developed and already shown to be economically and operationally feasible in some WWTPs. However, recovery through this approach can be limited to <25% efficiency unless chemical extraction is applied. Thermochemical treatment of sludge ash produces detoxified residues that are currently utilised by the fertiliser industry; wet chemical extraction can be economically feasible in recovering P and other by-products. The bioavailability of recovered P depends on soil pH as well as the P-rich material in question. Struvite is a superior recovered P product in terms of plant availability, while use of Ca-P and thermochemically treated sewage sludge ash is limited to acidic soils. These technologies, in addition to others less developed, will be commercially pushed forward by revised fertiliser legislation and foreseeable legislative limits for WWTPs to achieve discharges of <1 mg P/L.
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•P recovery is a pressing issue and wastewater provides a substantial opportunity.•Struvite/Ca-P crystallisation can be limited to <25% recovery of influent P load.•Crystallisation, thermo- and wet-chemical processes are being commercially applied.•Revised fertiliser legislation and P limits drives wider adoption of technologies.•All approaches should focus on obtaining agriculturally effective forms of P.
To address inorganic and organic contaminants in the environment, economic new adsorbents are required. Here we test magnetic biochar for efficient capture of the typical pollutants Cr(VI) and ...trichloroethylene (TCE) from solution. We used a simple synthesis using 2M FeCl3 solution and peanut hull biomass to prepare magnetic ZVI biochar at alternate pyrolysis temperatures between 650 and 800 °C. The physicochemical character of the biochars were assessed using X-ray diffraction (XRD) and the Brunauer-Emmett-Teller (BET) method for surface area. The magnetic ZVI biochars were highly effective in the removal of Cr(VI) and TCE. The most effective magnetic biochar produced at 800 °C was further examined using scanning electron microscopy (SEM), revealing a high and even loading of ZVI. After sorption the same magnetic biochar was examined by X-ray photoelectron spectroscopy (XPS) to ascertain the underlying mechanisms. The dependence of Cr(VI) capture on solution pH was also examined. Our interpretation suggests that when pH < pHzpc (2.5) electrostatic attraction and redox reactions dominated the adsorption of Cr(VI). When pH > pHzpc the removal process was controlled mainly by redox reaction and substitution of chromate anions for hydroxyl (OH) groups. Capture of TCE in contrast involved hydrophobic partitioning, pore-filling and reductive degradation. Overall our results suggest that simple synthesis of magnetic ZVI biochar could offer an economic and effective option to address water contamination issues.
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•Magnetic ZVI biochar synthesized at 800 °C using a single step method.•Magnetic ZVI biochar has adsorptive and reductive capability for Cr(VI) and TCE.•Electrostatic interaction and ion exchange dominate in Cr(VI) removal.•Hydrophobic partitioning, pore-filling play a role in TCE removal.
Biomass derived biochar is a stable carbon-rich product with potential for soil amendment. Introduced into the natural environment, biochar will naturally experience ‘ageing’ processes that are ...liable to change its physicochemical properties and the mobility of sorbed pollutants over the longer term. To elucidate the reciprocal effects of biochar ageing and heavy metal adsorption on the affinity of biochar for organic pollutants, we systematically assessed the adsorption of diethyl phthalate (DEP), representative of phthalic acid esters (PAEs), to fresh and aged biochars with and without coexistence of Cd2+. Long-term oxidative ageing was simulated using 5% H2O2 and applied to biochar samples made from corn cob, maize straw and wheat straw made by pyrolysis at both 450 °C and 650 °C. Our results showed that biochar made at lower temperature (450 °C) and from straw exhibited the higher adsorption capacity, owing to their greater polarity and abundance of O-containing functional groups. The adsorption of DEP onto fresh biochars was found to be driven by van der Waals force and H-bonding. Biochar made at the higher temperature (650 °C) displayed higher carbon stability than that produced at lower pyrolysis temperature. Oxidized biochar showed lower adsorption capacity than fresh biochar owing to the formation of three-dimensional water clusters on biochar surface, which blocked accessible sites and decreased the H-bonding effect between DEP and biochars. The coexistence of Cd2+ suppressed the sorption of DEP, via competition for the same electron-rich sites. This indicates that cation/π-π EDA interactions are the primary mechanism for PAE and Cd2+ stabilization on biochar. Our study sheds light on the mechanism of organic pollutant sorption by biochar, as well as the potential susceptibilities of this sorption to ageing effects in the natural environment.
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•The oxidative ageing and coexisting Cd2+ decreased adsorption capacity of DEP on biochars.•Lower temperature straw biochar has high adsorption capacity driven by van der Waals force and H-bonding.•Formation of three dimensional water clusters on oxidized biochar surface suppressed H-bonding adsorption of DEP.•Coexisting Cd2+ suppressed the adsorption of DEP via competition for the same electron-rich sites on biochar surfaces.•Cation/π -π EDA interactions between Cd2+, PAEs and biochars were the primary mechanism of DEP stabilization.
Our results show that ageing increases the affinity of biochar for PAEs but decreases the differences between them. Sorption of PAEs will always be diminished by coexistence and sorption of heavy metals.
Recovery and re-use of phosphorus (P) from wastewater treatment systems as agricultural fertiliser presents an important and viable target for P waste reduction and recycling. In this study novel ...biochar materials for P filtration of wastewater were designed and produced using waste feedstocks, with consideration of the plant accessibility of the P captured by the biochars. The biochars were produced using batch slow pyrolysis at 450 °C and 550 °C from a) AD: anaerobically digested sewage sludge and b) OCAD: a 1:1 mixture of anaerobically digested sewage sludge and ochre, a mineral product from mine drainage treatment. A set of experiments was designed using pH buffering to provide a robust framework for assessing the P recovery capacity and affinity of the biochars compared to other potential P recovery materials (unprocessed ochre, activated carbon and zeolite). After 5 days of repeated exposure to a P solution at a wastewater-relevant concentration (0.02 g P l−1) replenished each 24 h, relatively high masses of P were recovered by ochre (1.73 ± 8.93×10−3 mg P g−1) and the biochars OCAD550 (1.26 ± 4.66×10−3 mg P g−1), OCAD450 (1.24 ± 2.10×10−3 mg P g−1), AD450 (1.06 ± 3.84×10−3 mg P g−1), and AD550 (0.986 ± 9.31×10−3 mg P g−1). The biochar materials had higher removal rates than both activated carbon (0.884 ± 1.69×10−2 mg P g−1) and zeolite (0.130 ± 1.05×10−2 mg P g−1). To assess the extractability of recovered P, P exposure was followed by repeated extraction for 4 days with pH 7-buffered deionised water. The AD biochars retained 55% of the P recovered, OCAD biochars 78% and ochre 100%. Assessment of potentially toxic element concentrations in the biochars against guideline values indicated low risk associated with their use in the environment. Our successful demonstration of biochar materials highlights the potential for further development of P filters for wastewater treatment systems from anaerobic digestate produced and pyrolysed on-site with energy recovery.
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•Biochar from anaerobically digested sewage sludge has strong affinity for aqueous P.•Addition of ochre to sludge increases the rate of biochar P recovery from solution.•Once enriched with P, the biochars have the potential for use as fertiliser.
Biochar is being actively explored as a tool for long‐term soil carbon sequestration. However, in order for this to be effective the long‐term environmental stability of biochar must be assured. ...Here, we define and test an accelerated ageing method that seeks to reflect the oxidative nature of biochar degradation in soil. The method was applied to a systematic set of biochar samples produced from sugarcane bagasse, and a set of biochar samples produced from four different biomass sources. The stability of carbon in these samples was found to range between 41.6% and 76.1%, loosely correlating with biochar O : C ratio (r = 0.73). Increasing intensity of oxidative treatment eliminated more carbon. It also increased surface O : C ratio in a manner reported for naturally aged charcoal samples. The method effectively discriminated biochar produced under contrasting pyrolysis conditions and could be used as a proxy for environmental ageing of approximately 100 years under temperate conditions.
One attraction of using hydrochar (HC) and biochar (BC) in soil is their intrinsic affinity for organic contaminants. Oxidative ageing is likely to induce changes in physicochemical properties and ...functionality. To explore the long-term potential trajectories for corn stalk HC and BC to adsorb organic pollutants, we employed HC and BC exposure in 5% H2O2 to simulate oxidative ageing and get insights into mechanisms of atrazine adsorption on fresh and artificially aged materials. The physicochemical properties of fresh and aged materials were systematically compared using elemental analysis, SSA, FTIR, XPS and SEM-EDS, alongside K2Cr2O7/H2SO4 treatment to assess chemical oxidation stability. Atrazine is a typical herbicide chemical and hydrophobic organic pollutant. Adsorption isotherms of atrazine were used to reveal differences in mechanisms of sorption to BC and HC, by assessment before and ageing. BC freshly produced at 650 °C displayed higher capacity for atrazine sorption than BC produced at 500 °C, with a dominant role for π-π EDA interactions. The sorption capacity of HC freshly produced at 250 °C was higher than for HC produced at 200 °C HC, owing to higher C content and atrazine partitioning into the organic phase. Ageing increased the surface abundance of oxygenated functional groups for BC and HC and diminished bulk aromaticity. After ageing, atrazine sorption by high temperature BC was lower, but for HC it was increased. Such divergent effects must be considered when developing strategies to co-manage contaminants and carbon through the addition of carbonized materials to land.
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•Oxidative ageing increases oxygenated functional groups on biochar and hydrochar.•Oxidative ageing diminishes the aromaticity of biochar and hydrochar.•The π-π EDA interactions play a dominant role in atrazine sorption by biochar.•Partitioning into the organic phase dominates atrazine sorption by hydrochar.•Atrazine sorption on hydrochar increased after ageing, while decreased on biochar.
Our results show clear changes in the dominant mechanism of atrazine sorption by biochar and hydrochar and their surface functionality resulting from ageing.
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