1,721,001 research outputs found
Adsorption and desorption of emerging pollutants with engineered biochar adsorbents
No full textEmerging pollutants and personal care products have raised significant environmental concerns due to their persistence and potential adverse effects. Among these, caffeine, which is widely present in water systems, has become a prominent model compound for studying adsorption and desorption processes.
Adsorption is a widely used method in water treatment due to its simplicity, cost-effectiveness, and adaptability. However, adsorbents can become saturated over time, requiring frequent replacement and generating significant amounts of solid waste. Additionally, adsorption retains pollutants without degradation, posing challenges for managing used adsorbents. Improper disposal of spent adsorbents, such as landfilling, can lead to environmental contamination. Thus, effective regeneration of biochar adsorbents is essential for long-term and environmentally sustainable applications.
There are various regeneration techniques, including thermal, chemical, ultrasonic, microwave, electrochemical, and supercritical regeneration. Supercritical solvent extraction, particularly with supercritical carbon dioxide, is an emerging alternative due to its unique properties. Under supercritical conditions, CO2 exhibits high diffusivity in the adsorbent’s micropores and low surface tension at mild conditions, enabling efficient desorption with minimal impact on the adsorbent structure. After desorption, CO2 and the adsorbate can be rapidly separated through decompression and recovered as pure compounds of potential added value.
In this study, biochar was produced through slow batch pyrolysis of birchwood (woody biomass) and miscanthus (herbaceous biomass) pellets, followed by physical activation to enhance surface properties. Adsorption experiments demonstrated that the physicochemical characteristics of the biochar, including surface area, porosity, and functional groups, significantly influenced its adsorption capacity. The effects of pH were also analyzed to elucidate the interactions between caffeine molecules and the biochar surface. The performances of two regeneration methods, e.g. solvent extraction and supercritical CO2 desorption, were compared featuring the potential of the latter to recover the pure adsorbate without contaminations and the need of expensive downstream separation processes
Production of biochar from the pyrolysis of spent mushroom substrate
No full textMushroom waste substrate is produced in large quantities, up to 5 kg per 1 kg of mushroom. It contains fungal spores, making landfill disposal not allowed; thus, mushroom waste substrate is currently accumulated. The objective of this study was to explore the conversion of mushroom waste substrate into biochar through pyrolysis, with the aim to apply the biochar in the cultivation of mushroom and for carbon sequestration.
The study involved two types of mushroom substrate: fresh (e.g. the medium used to grow mushrooms) and spent (e.g. leftover material enclosing fungal mycelium). While the study is focused on the valorization of spent substrate, the fresh one was evaluated to explore the potential for future feedstock design. The experiments were conducted in a lab-scale horizontal mechanically fluidized bed reactor consisting of a 15L stainless-steel cylindrical chamber heated by an induction system. Pyrolysis batch tests were performed at 350, 450 and 550 C. The obtained biochars were quantified and characterized through proximate and elemental analyses and H/C ratio to evaluate their features and to determine the optimal conditions for further testing.
As expected, biochar yields decreased by increasing temperature, and gas yields displayed an opposite trend. The achieved results were consistent for the spent and fresh substrates. In details, biochar yields were 48% at 350 C, 34% at 450 C and 28% at 550 C for the spent substrate; and 45%, 32% until 28% for the fresh one. Gas yields were 29% at 350 C, 35% at 450 C and 43% at 550 C for the spent substrate; and 27%, 38% until 43% for the fresh substrate. Bio-oil yields were 23% at 350 C, 31% at 450 C and 29% at 550 C for the spent substrate; and 28%, 30% and 29% for the fresh substrate. About the characteristics of biochar, the results are consistent with literature: the fixed Carbon content increased with temperature, from 61% at 350 C, to 74% at 450 C and 77% at 550 C, and correspondingly the volatile Carbon decreased from 31%, to 17% and to 12%; the ash content increased from 8% at 350 C, to 9% at 450 C and to 11% at 550 C. The biochars obtained at the three tested temperatures showed in all cases a H/C ratio below 0.7 (reaching values as low as 0.35) which makes them eligible for carbon offset credits.
In conclusion, this study preliminarily demonstrates that mushroom substrate is a valuable feedstock for producing high-quality biochar via pyrolysis, with promising potential for carbon sequestration and as soil amendment. The results showed that higher temperatures improved biochar quality and stability by increasing the carbon and ash contents and reducing volatile matter. Further research is necessary to investigate how the biochar could be reintegrated into the mushroom cultivation process as a component of the growth substrate, following a circular economy approach that provides a sustainable solution to the significant challenge of mushroom substrate disposal
Analysis of the influence of activated biochar properties on methane production from anaerobic digestion of waste activated sludge
Full text linkThis work describes the impacts of biochar (BC) addition to the anaerobic digestion (AD) of waste activated sludge (WAS). Three BCs, produced by pyrolysis at 550 °C of different waste biomasses (soft wood, sewage sludge and rice husk), then physically activated at 900 °C with CO2, were investigated as additives. AD tests were performed in batch mode at 37 °C, feeding 2% total solids and 10 g L−1 BC. While none of the considered BCs increased biogas yield compared to control digesters, the activated BCs with higher surface area, porosity and hydrophobicity (RH550a from rice husk and SS550a from sewage sludge) boosted methane yield (up to 105% for RH550a). The experimental methane production were: 0.037 Nm3 kgVS−1 for SWP550a, 0.081 Nm3 kgVS−1 for SS550a, 0.142 Nm3 kgVS−1 for RH550a and 0.069 Nm3 kgVS−1 for control reactors. CO2 adsorption (3.14 mmol g−1 for RH550a, 0.97 mmol g−1 SS550a) calculated from experimental data was consistent with literature (0.4–2.3 mmol g−1 BC). The fitting of experimental methane productions through the modified Gompertz equation showed an acceleration of methane production for all BCs, with a reduction of the lag phase compared to control reactors (0.5 days vs 2.6 days). This work, although confirming literature data about CO2 adsorption, brings new insights on the influence of specific physico-chemical properties of BC as additive in AD of WAS. Surface area, porosity, hydrophobicity and alkali and alkaline metals content in ashes were the most important BC properties affecting AD of activated sewage sludge
Semi-continuous anaerobic digestion of mixed wastewater sludge with biochar addition
Full text linkThis work analysed the effects of Biochar (BC) addition to the Anaerobic digestion (AD) of wastewater Mixed sludge (MS) in semi-continuous mode. A 3 L digester was operated at 37 °C for 100 days, feeding MS collected every three weeks in the same wastewater treatment plant, and 10 g L−1 of BC. The average performance of MS digestion (biogas 188 NmL d−1, 68% methane) improved in presence of BC (biogas 244 NmL d−1, 69% methane). According to the results of the multiple linear regression analysis performed on the experimental data, the 79% variation of the soluble COD in the MS was the driving factor for the 38% increase of biogas and methane yields. In conclusion, in the considered experimental conditions, the variability of the substrate's composition was the key factor driving the performances of the AD of MS, independently of the addition of BC
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Techno-economic assessment of the pyrolysis of rubber waste
Full text linkSlow rubber pyrolysis was performed at 300–500 ◦C in a horizontal batch mechanically fluidized reactor with
30–60 min holding time, and the products were characterized. The char (yield = 50%-wt) exhibited a high
heating value (HHV) around 30 MJ/kg, comparable with bituminous coke, and 84%-wt Carbon. The gas products
(yield = 24–31%) had a composition dependent on temperature: 21%-v ethylene, 46%-v propane, and 11%-v
butane at 300 ◦C; over 20%-v hydrogen and methane at 400 ◦C; at 500 ◦C hydrogen ranged 46-69%-v and
methane 21-36%-v. Oil products (yield = 17–22% yield) consisted o
Biochar from residual biomass as a concrete filler for improved thermal and acoustic properties
No full textThe current imbalance of carbon in the atmosphere is stimulating the search for carbon sequestration opportunities and for alternative processes and products with a reduced carbon footprint. Biochar, produced from residual biomass of the bio-ethanol industry (Dry Distillers Grains), was added as filler to a standard concrete, aiming at finding potential solutions for simultaneous carbon sequestration and improved properties and performance of the concrete. The addition of biochar resulted in a linear decrease in concrete density, with a concrete density of 1454 kg/m3 for 15 wt% biochar. The addition of biochar also considerably increased the sound absorption coefficient of concrete across the range of 200–2000 Hz, as it created pore networks within the concrete. The thermal conductivity of the concrete showed the largest reductions with 2 wt% of biochar, reaching lows of 0.192 W/(m·K). Finally, the incorporation of biochar showed a detrimental effect on the compressive strength of the concrete, which would put bio-enhanced concretes in the low-strength concrete classification category
Addition of different biochars as catalysts during the mesophilic anaerobic digestion of mixed wastewater sludge
Full text linkBiochar (BC) recently gained attention as an additive for anaerobic digestion (AD). This work aims at a critical analysis of the effect of six BCs, with different physical and chemical properties, on the AD of mixed wastewater sludge at 37 °C, comparing their influence on methane production and AD kinetics. AD batch tests were performed at the laboratory scale operating 48 reactors (0.25 L working volume) for 28 days with the addition of 10 g L−1 of BC. Most reactors supplemented with BCs exhibited higher (up to 22%) methane yields than the control reactors (0.15 Nm3 kgVS−1). The modified Gompertz model provided maximum methane production rate values, and in all reactors the lag-phase was equal to zero days, indicating a good adaptation of the inoculum to the substrate. The potential correlations between BCs’ properties and AD performance were assessed using principal component analysis (PCA). The PCA results showed a reasonable correlation between methane production and the BCs’ O–C and H–C molar ratios, and volatile matter, and between biogas production and BCs’ pore volume, specific surface area, and fixed and total carbon. In conclusion, the physic-chemical properties of BC (specifically, hydrophobicity and morphology) showed a key role in improving the AD of mixed wastewater sludge
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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