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Despite being a promising biomass source for gasification, the practical use of rice straw in Vietnam is hindered by its low gasification efficiency. This study introduces an innovative approach by integrating the production of syngas and CO 2 adsorbent during the gasification process of rice straw, departing from the conventional focus solely on improving gasification efficiency. Results showed that the gasification of rice straw, conducted in the 20 kWe commercial gasification system (PP20 All Power Lab), attained a thermal conversion efficiency of 58.7%. Syngas produced exhibited consistent composition, with CO and H 2 content ranging from 12.1% to 15%, CO ranging from 16.9% to 22.1%, and CH 4 ranging from 1.9% to 3.9% throughout the operation, demonstrating relative stability. Notably, a considerable amount of residual char, accounting for 22.1 wt% of the initial feedstock, was generated. Characterized by notable traits such as high surface basicity, aromaticity, and a dense concentration of (ultra-)micropores, the residual char demonstrates suitability for applications in CO 2 adsorption. In controlled laboratory conditions (25 °C, 1 atm, without heat-mass transfer limitations), the adsorption capacity reached 1.2 mmol g−1. Transitioning to more practical conditions (40 °C, 1 atm, within a 2-cm adsorbent bed subject to diffusion constraints), the CO 2 adsorption capacity of the residual char ranged between 2% and 4.8% of the adsorbent's weight, while the CO 2 /N 2 selectivity measured between 25.5 and 29.7. These findings underscore the significant potential of integrating syngas and CO 2 adsorbent production through rice straw gasification, indicating a promising avenue for sustainable energy and carbon capture technologies. [Display omitted] • Stable syngas quality obtained throughout rice straw gasificatiom. • Use of residual char after gasification as cost-effective and scalable CO 2 adsorbents. • CO 2 capture capacities reached up to 1.2 mmol g−1 at 25 °C, 1 atm. • Potential for cascading use of rice straw for energy and adsorbent production. [ABSTRACT FROM AUTHOR]

This study investigates carbon stability of biochars produced from wood, herbaceous, and fruit agricultural waste products from southern Vietnam. The biochars were produced by pyrolysis to 500 °C, 700 °C, and 900 °C at a heating rate of 10 °C/min. Organic geochemistry and petrology have well-established measurable parameters that define degree of preservation of organic carbon in the Earth's crust. These parameters are utilized, comparatively, to infer the organic carbon stability in biochars relative to that preserved in the geological carbonaceous rocks. The stability of carbon was assessed by measuring incident-light random reflectance (%R o) to determine the degree of thermally induced aromatization/ordering of the biochar carbon molecules. Additionally, the organic carbon content of the biochars was quantitatively separated into reactive and non-reactive carbon fractions based on thermodynamic stability of C H and C O bonds. The results show increasing carbon stability with increasing pyrolysis temperature and indicate high stability has been achieved at 700 °C and 900 °C where the biochars have the highest total organic carbon (TOC) contents and lowest Hydrogen Index values. Occurrence of a small quantity of readily degradable, labile free hydrocarbons (soluble organic matter; SOM) is due to condensation of the thermally generated hydrocarbons on the surfaces of the biochars. This fraction is minimized in the biochars produced at 700 °C and 900 °C due to volatilization of the free hydrocarbons at higher pyrolysis temperatures. The relatively substantial content of labile hydrocarbons associated with particulate organic matter (POM) in the 500 °C produced biochars is attributed to the incomplete pyrolyzation of the feedstock at this temperature. This fraction declines to near zero at 700 °C and 900 °C as complete carbonization is achieved at these higher temperatures. The overall carbon budget within the biochar shows that irrespective of the biochar type, over 97% of the TOC consists of highly refractory, residual carbon that geochemically is considered to possess long-term stability ("inert"). This is further underpinned by a pronounced increase in biochar mean random reflectance from <2.33% at 500 °C to >4.35% when pyrolyzed at 700 °C, indicating a highly polyaromatized condensed carbon structure. Rice husk is an exception as it yields a mean reflectance of 4.55% at 500 °C suggesting that pyrolysis temperature is not the only factor controlling %R o and hence carbon stability. Furthermore, the biochar compositions show a relationship between feedstock and pyrolysis temperature. The biochar morphotype composition changes significantly with increasing temperature, but the analyzed biochars are all dominated by fusinoid/solid (primarily fusinoid) morphotypes with the highest initial quantity recorded at 500 °C. This quantity decreases with increasing pyrolysis temperature while porous morphotypes (tenuinetwork, crassinetwork, mixed porous, mixed dense) increase. Variations in morphotype composition observed between the biochars is attributed to the structural nature of the feedstocks. [ABSTRACT FROM AUTHOR]

In this work, alginate-modified biochar derived from rice husk waste was synthesized using a simple process. The modified biochar (MBC) and rice husk biochar (RhBC) were investigated for removing Pb (II) ions in wastewater. The BET result displayed significantly improved specific surface area of MBC up to 120 m2/g along with a total pore volume of 0.653 cm3/g. FTIR spectrums presented the higher oxygen-contained functional groups of MBC as compared to RhBC, resulting in increasing adsorption capacity of Pb (II). MBC had higher adsorption capacity (112.3 mg/g) and faster removal rate (0.0081 g mg−1 min−1) than those of RhBC (41.2 mg/g and 0.00025 g mg−1 min−1). Modified RhBC can remove more than 99% of Pb (II) from wastewater and it could be utilized for three cycles with a removal performance of over 90%. In addition, the Pb adsorption mechanism by using MBC was proposed and the practical application of MBC for the treatment of wastewater in Vietnam was discussed. [Display omitted] • Alginate modified rice husk biochar (MBC) was used for Pb (II) removal in wastewater. • MBC had higher adsorption capacity (112.3 mg/g) as compared to others adsorbents. • More than 99% of Pb (II) in wastewater sample was removed by MBC. • MBC still has high efficiency of Pb (over 90%) after 3 times reused. [ABSTRACT FROM AUTHOR]

This study estimated the climate change effects of alternative rice production systems in North Vietnam with different residue management options, using Life Cycle Assessment (LCA). The traditional practice of open burning of residues (System A) was compared with the alternative of converting residues to biochar, which was returned to the same land area from which the residues were obtained (System B). Pyrolytic cook-stoves and drum ovens were assumed to be used by households to produce biochar, and the cook-stoves produced heat energy for cooking. The annual rate of biochar applied was determined by the amount of biochar produced from the straw and husk available. We assumed that agronomic effects of biochar increased with each annual biochar application until reaching maximum benefits at 18 Mg ha −1 , which takes eight years to be produced in pyrolytic cook-stoves and drum ovens. The largest contributor to the carbon footprint of rice at the mill gate, was CH 4 emissions from soil, in both systems. Biochar addition reduced the carbon footprint of spring rice and summer rice by 26% and 14% respectively, compared with System A, in the first year of application. These values substantially increased to 49% and 38% after eight years of biochar addition. The climate effect of System B was most sensitive to the assumed suppression of soil CH 4 emissions due to biochar application. [ABSTRACT FROM AUTHOR]