Acceleration of biochar surface oxidation during composting? (original) (raw)
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Biochar (BC) is a carbonaceous product that comes from pyrolysis process of different biomasses, such as lignocellulosic feedstocks. Biomass nature, pyrolysis temperature and speed heating rate affect the physical and chemical characteristics of BC produced. The aim of this work concerned the investigation of recalcitrant aspects of carbonaceous structures in biochar's matrix, which evolved during its long time permanence in soil. Using X-Ray diffraction and Raman Spectroscopy, this study was focalized on the evolution of carbonaceous structures with increasing pyrolysis temperature. Fresh samples, produced in laboratory from larch wood feedstock, were compared with ancient fragments (dated 1859), collected in Oriental Alps soils (PejoValley, Trentino, Italy) and produced in ancient kilns from larch wood as well. From this comparison, we found a significant degradation of aliphatic compounds and low-extended aromatic ring systems as a function of incubation time in soil. It was observed, over degradation on carbonaceous structures, signs coming from the interactions with the environment against the time, such as the adsorption processes of mineral elements and encapsulation of mineral crystalline phases, that increase the stability of the carbonaceous residual fractions of biochar.
PRODUCTION AND CHARACTERIZATION OF BIOCHAR FROM DIFFERENT BIOLOGICAL WASTES
Biochar, a stable form of carbon, is produced from pyrolysis of biological materials. It is attracting growing interest because of its potential to improve soil nutrients status, increase crop yield and sequester carbon (C) in the soil. Biochar serve as a source of reduced carbon compounds (organic molecules adsorbed to the particle's matrix) for any biochar colonizing soil bacteria. Therefore, C entering the soil as charcoal is a significant sink for atmospheric CO2 and may be important for global C sequestration. The biochar proves to be stable and effective carbons sink. The carbon locked in them do not release as CO2 due to the microbial activity. The carbon in the biomass is subjected to easy degradation since they contain low grade carbon. But in biochar, pyrogenic carbon is formed by pyrolysis. Hence they remain in the soil for long periods. Biochars were produced from the pyrolysis of a variety of biological materials viz., paddy straw, maize stalk, coconut shell, groundnut shell, coir waste and prosopis wood, in a specially designed pyrolysis-stove. The Biochars differed much in their characteristics.
Can biochar and hydrochar stability be assessed with chemical methods?
Organic Geochemistry, 2013
Field application of biochar is intended to increase soil carbon (C) storage. The assessment of C storage potential of biochars lacks methods and standard materials. The reactivity of biochars and hydrochars may be one possible means of evaluating their environmental stability. The aim of this study was to evaluate the reactivity of biochar produced by gasification (GS) and hydrochar produced by hydrothermal carbonisation (HTC). The approach included analysis of the two different char types produced from the same three feedstocks. Moreover, we analysed the reactivity of Holocene charcoal (150 and 2000 yr old) to evaluate whether or not their use as standard materials to represent stable biochar is meaningful. We assessed carbon loss following oxidation with acid dichromate as well as hydrolysis with HCl. Our results showed that chemical reactivity is not a straightforward approach for characterising the stability of biochar and hydrochar. Acid hydrolysis showed little difference between HTCs and GSs, despite the contrasting elemental composition. Using acid dichromate oxidation, we determined that GSs contained ca. 70% of oxidation resistant C while the proportion for HTCs was < 10%. The different feedstocks had a slight, but significant, influence on the reactivity of GSs and HTCs. The content of oxidation resistant C decreased in the order 100 yr old charcoal = GSs > 2000 yr old charcoal > HTCs > feedstock and was related to elemental composition. This shows that acid dichromate oxidation may allow differentiation of the reactivity of modern biochars but that there is not necessarily a relationship between reactivity and age of Holocene charcoals. As the chemical reactivity of biochars may change with exposure time in soil, it is poorly suited for assessing their environmental residence time.
Changes in biochar physical and chemical properties: Accelerated biochar aging in an acidic soil
Carbon, 2017
Biochar (BC) is increasingly used as soil amendment; however, its stability and alteration in the soil environment are still unclear. Here, we investigated BC decomposition and changes of BC characteristics during a long-term incubation experiment. 13 C-depleted BCs were incubated for two years in an acidic Planosol and a calcareous Chernozem, respectively. BC decomposition inferred from the C isotope signature of the incubated materials was marginal. Yet, small angle X-ray scattering showed that the surface roughness of the BCs increased over time. Mid-infrared spectra indicated changes in the BCs' molecular characteristics upon aging. There was an overall increase of infrared bands assigned to Hand O-containing functional groups, especially carboxylic groups. Contact angle measurements revealed that the hydrophobic surfaces of freshly produced BCs became more hydrophilic during soil incubation. Our results suggest that BC aging is strongly influenced by soil traits. In the more acidic Planosol, these aging processes were accelerated.
Biochar: carbon sequestration, land remediation and impacts on soil microbiology
2011
Biochar-charcoal used to amend land and sequester carbon-is attracting considerable interest. Its distinctive physical/chemical/biological properties, including high water-holding capacity, large surface area, cation exchange capacity, elemental composition and pore size/volume/distribution, effect its recognised impacts, especially on microbial communities. These are explored in the context of agriculture, composting and land remediation/restoration. Considerable focus is given to mycorrhizal associations, which are central to exploitation in environmental technologies involving biochar. The characteristics of biochar, its availability for nutrient cycling, including the beneficial and potentially negative/inhibitory impacts, and the requisite multidisciplinary analysis (physico-chemical, microbiological and molecular) to study these in detail, are explored. Agricultural benefits arising from biochar are varied and of presently uncertain and probably complex mechanisms. Reviews by Sohi et al. (2010), Atkinson et al. (2010) and Joseph et al. (2010) have detailed the agricultural implications of biochar and its mechanistic aspects. In this review we briefly discuss the production and characterisation of char and outline the benefits that have been reported before moving on to highlight aspects of mechanisms that are mediated by microbial community responses to biochar amendment. In addition, we consider the potential utility of biochar in composting and microbiological remediation of contaminated land. 2. Char physico-chemical characterisation Anaerobic thermal conversion of biomass can be achieved in three different processes: pyrolysis/carbonisation; gasification; and liquefaction. All three give products in three phases, solid, liquid and gas, with the product composition dependent on process conditions. Thus, pyrolysis is characterised by long residence times and moderate temperatures, liquefaction occurs under high heating rates, while gasification is defined by high temperatures, often with additional, though sub-stoichiometric, oxygen. Pyrolysis typically produces a solid, structured, carbonaceous material which, compared to the feedstock, exhibits a high surface area (
NEXAFS and XPS characterisation of carbon functional groups of fresh and aged biochars
Organic Geochemistry, 2014
The oxidation of surface functional groups on biochar increases its reactivity and may contribute to the cation exchange capacity of soil. In this study, two Eucalyptus wood biochars, produced at 450°C (B450) and 550°C (B550), were incubated separately in each of the four contrasting soils for up to 2 years at 20°C, 40°C and 60°C. Carbon functional groups of the light fraction (< 1.8 g/cm 3 ) of the control and biochar amended soils (fresh and aged for 1 and 2 years at 20°C, 40°C and 60°C) were investigated using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and X-ray photoelectron spectroscopy (XPS). The spectra of biochar and light fractions of the control and biochar amended soils showed two distinct peaks at $285.1 eV and 288.5 eV, which were attributed to the C1s-p ⁄ C@C transitions of aromatic C and C1s-p ⁄ C@O transitions of carboxylic C, carboxyamide C and carbonyl C. The proportion of aromatic C was substantially greater in the light fraction of the biochar amended soils than the corresponding light fraction of the control soils. Also, the proportion of aromatic C was much higher in the light fraction of the B550 amended soils than in the corresponding B450 amended soils. Neither NEXAFS nor XPS results show any consistent change in the proportion of aromatic C of biochar amended soils after 1 year ageing. However, XPS analysis of hand-picked biochar samples showed an increase in the proportion of carboxyl groups after ageing for 2 years, with an average value of 8.9% in the 2 year aged samples compared with 3.0% in the original biochar and 6.4% in the control soil. Our data suggest that much longer ageing time will be needed for the development of a significant amount of carboxyl groups on biochar surfaces.
Chemosphere, 2018
Biochar is a beneficial soil amendment but the changes in its surface properties during the aging process, especially the oxygen-containing functional groups and the associated adsorption behaviors, are not well documented. In this paper, the aged wheat straw biochar was simulated by chemical oxidation with HNO-HSO and NaOH-HO systems. Characterization results showed that carbon loss and oxygen incorporation ran throughout the aging process. Surface oxygen-containing functional groups were found to be increased in all treated biochars, especially for carboxyl. Much more developed mesopores were observed in aging biochar, specific surface area was increased by 126% for biochar treated with NaOH-HO, and 226% for biochar treated with 40% of HNO-HSO. Thermogravimetric analysis showed that the increasing oxygen-containing functional groups led to 14% and 30% mass loss by treating biochar with alkali and acid, respectively. The improved biochar surface through the increase of oxygen-conta...