Rice Straw Carbon Research Articles

Acid treatment for enhancing Hg0 removal efficiency of chlorine-loaded biochar: mechanism and kinetic analysis.

Adsorbents modified solely with chlorine have limited effectiveness in removing mercury at high temperatures. This study aims to investigate the influence of various acid (HNO3, H2SO4, and H2O2) loadings on the removal efficiency of mercury from NH4Cl-modified adsorbents. The objective is to develop rice straw carbon adsorbents that are both more efficient and cost-effective. The experiments were conducted on a fixed bed experimental platform, with SEM and BET to observe the physical property changes of the modified char samples. XPS analysis was employed to analyze the effects of oxygen, chlorine, and sulfur functional groups. Additionally, a kinetic model was used to investigate the interaction mechanism between the adsorbent and mercury. The findings demonstrate that co-modification surpasses the use of NH4Cl alone, with the combination of NH4Cl and HNO3 yielding the best results. Co-modification enhances the development of a more refined and compact pore structure on the char surface, promoting the physical adsorption of mercury. Moreover, an increased presence of chlorine and oxygen functional groups is observed on the char surface, particularly in the NH4Cl and HNO3 co-modified samples, further enhancing the chemical adsorption capacity of the char. The results from the kinetic analysis support this conclusion. Furthermore, the adsorption process of Hg0 relies on both external mass transfer and chemical adsorption, with the chemical adsorption process playing a more significant role as the controlling factor.

The effect of rice residue management on rice paddy Si, Fe, As, and methane biogeochemistry

Rice production results in residues of straw and husk, and the management of these residues has implications for the sustainability of the rice agroecosystem. Rice straw is typically incorporated into soil either as fresh residue or is burned prior to incorporation. Rice husk is not typically returned to rice fields. However, rice husk contains high levels of silicon, which has been shown to decrease rice accumulation of arsenic. In this work, we studied the resulting biogeochemical changes in rice paddy soils when paddies were amended with either straw or burned straw and either no husk, husk, or burned husk over two years. Using a full-factorial design, we observed that the higher lability of rice straw carbon controlled redox-sensitive processes despite the application of husk and straw at similar carbon rates. Amending paddies with straw, rather than burned straw, increased porewater Fe and As, plant As, and methane emissions regardless of husk amendment. Husk addition provided insignificant Si to the plant despite its high concentration of Si, suggesting limited short-term mobility of Si and that long-term additions of husk or higher rates may need to be studied.

Rice straw carbon mineralization is affected by the timing of exogenous glucose addition in flooded paddy soil

Crop straw amendment is a farm management approach for enhancing soil carbon sequestration. Moreover, crop straw residue decomposition rates are affected by irregular exogenous organic carbon secretion or metabolism such as that from root exudates or microbial metabolites. To quantify the mineralization rate of straw residue affected by exogenous organic carbon addition and elucidate the underlying mechanisms, in this study, a total of 0.5 g 13C- labeled dry rice straw was added into pre-incubated soil (equivalent to 200 g dry soil) and incubated for 20 days. Then,1mL of a solution with 50 mg glucose was added only once into the soil on day 21 (G(1a)) or day 35 (G(1b)), twice with 25 mg glucose every 14 days (G(2)) or four times with 12.5 mg glucose every 7 days (G(4)). Soil without glucose addition served as a control. The frequent addition of glucose induced higher soil respiration than that induced by only one addition, and stimulated the mineralization of rice straw carbon compared to that in the control in the following order: G(4) (14.6%) > G(1a) (12.7%) > G(2) (12.3%) > G(1b) (11.2%) = control (11.2%). In general, frequent addition of glucose decreased the soil redox potential (Eh) and fungi to bacteria ratio. Structural equation modeling analysis showed that the rice straw carbon mineralization rate was positively correlated with the 13C-dissolved organic carbon (13C-DOC) content and negatively regulated by Eh. Microbial bioactivity exerted indirect positive effects on rice straw carbon mineralization by influencing the 13C-DOC content. A decrease in the fungi to bacteria ratio induced by frequent addition of glucose improved the microbial bioactivity and enhanced rice straw carbon mineralization. Our results suggested that single exogenous organic carbon additions may underestimate residue or soil organic matter decomposition rates in the field.

Methane production from rice straw carbon in five different methanogenic rice soils: rates, quantities and microbial communities

The input of organic substances (e.g., rice straw) in rice field soils usually stimulates the production and emission of the greenhouse gas methane (CH4). However, the amount of CH4 derived from the applied rice straw, as well as the response of bacterial and archaeal communities during the methanogenic phase, are poorly understood for different rice field soils. In this study, samples of five different rice soils were amended with 13C-labeled rice straw (RS) under methanogenic conditions. Immediately after RS addition, the RS-derived CH4 production rates were higher in soils (Uruguay, Fuyang) that possessed a stronger inherent CH4 production potential compared with other soils with lower inherent potentials (Changsha, the Philippines, Vercelli). However, soils with higher inherent potential did not necessarily produce higher amounts of CH4 from the RS applied, or vice versa. Quantitative PCR showed copy numbers of both bacteria and methanogens increased in straw-amended soils. High-throughput sequencing of 16S rRNA genes showed distinct bacterial communities among the unamended soil samples, which also changed differently in response to RS addition. Nevertheless, RS addition generally resulted in all the rice field soils in a relative increase of primary fermenters belonging to Anaerolineaceae and Ruminococcaceae. Meanwhile, RS addition also generally resulted in a relative increase of Methanosarcinaceae and/or Methanocellaceae. Our results suggest that after RS addition the total amounts of RS-derived CH4 are distinct in different rice field soils under methanogenic conditions. Meanwhile, there are potential core bacterial populations that are often involved in primary fermentation of RS under methanogenic conditions.

Regulation of gene expression involved in the remobilization of rice straw carbon reserves results from moderate soil drying during grain filling.

Carbon reserves in rice straw before flowering contribute greatly to grain filling. Moderate soil drying imposed at the post-anthesis stage significantly promotes carbon reserve remobilization in straws of rice, but the regulation of this process at the proteomic and transcriptomic level remains poorly understood. In this study, we applied moderate soil drying (MD) to rice at the post-anthesis stage, which was followed by dynamic proteomic and transcriptomic studies using SWATH-MS and RNA-seq analysis. MD treatment upregulated the proteins alpha-glucosidase, beta-glucosidase and starch phosphorylase, which are responsible for starch degradation. Furthermore, MD treatment enhanced the expression of proteins involved in the sucrose synthesis pathway, including SPS8 and SPP1. In addition, various monosaccharide transporters (MSTs) and sucrose transporter 2 (SUT2), which are pivotal in carbon reserve remobilization, were also upregulated in straw by MD treatment. Differentially expressed transcription factors, including GRAS, TCP, trihelix, TALE, C3H, and NF-YC, were predicted to interact with other proteins to mediate carbon reserve remobilization in response to MD treatment. Further correlation analysis revealed that the abundances of most of the differentially expressed proteins were not correlated with the corresponding transcript levels, indicating that the carbon reserve remobilization process was probably regulated by posttranscriptional modification. Our results provide insights into the molecular mechanisms underlying the regulation of carbon reserve remobilization from straw to grain in rice under MD conditions.

Physical and Chemical Properties of the Rice Straw Activated Carbon Produced from Carbonization and KOH Activation Processes

In this study, highly porous activated carbon was produced from rice straw by carbonization and followed by activation using potassium hydroxide (KOH). Activated carbon samples were prepared under different activation temperatures, i.e., 650, 750 and 850°C, and their physical and chemical properties were characterized accordingly. The BET surface area of the activated carbon samples was increased from 520 to 1048 m2/g with the increase of activation temperature from 650 to 850°C. These values were much higher than the non-activated rice straw carbon i.e., 1.16 m2/g. The pore sizes of the rice straw activated carbon were found to be mainly in mesopore size range of 2-50 nm. Total carbon content of the AC sample was increased from 8.35% to 31.73% with the increase of activation temperature from 650 to 850°C. XRD and Raman spectroscopy confirmed the graphite properties of the activated carbons produced. SEM images proved high porosity of the AC after KOH activation.

Incorporation of rice straw carbon into dissolved organic matter and microbial biomass along a 100-year paddy soil chronosequence

Dissolved organic matter (DOM) and microbial biomass (MB) are small but reactive pools of soil organic matter (SOM). The incorporation of carbon (C) from rice residue into DOM and MB in paddy soils under aerobic condition when rice straw remains in the field is poorly understood. A one-year incubation experiment was conducted, in which 13C-labelled rice straw was added to a cultivation chronosequence of paddy soils ranging from 0 to 100 years. Rice straw was rapidly decomposed during the first 30 days, after which 73% of the added straw C, on average, was retained in the soil and 46% of the straw C remained in the soil after one year. Throughouttheentireincubation period, 0.2–0.9% of the added straw C was incorporated into DOM, and 2–5% was recovered in MB. The paddy cultivation age strongly affected the straw contribution to the organic C pools. In barren land (0 year), 32–60% of the DOM was derived from straw C, while 13–30% of the DOM was derived from straw C in 5–100-year paddy soils. On average, straw C contributed to 88% of the MB in barren land, 50% in 5-year soil, and 13% in 100-year soil. Consequently, over the duration of paddy cultivation, the contribution of rice straw C to the MB decreased, while the contribution of SOM increased. Our study has indicated that DOM in paddy soils mainly originates from SOM rather than from added plant residues but that plant residues are an important C source for microorganisms.

Exploration of biodegradation mechanisms of black carbon-bound nonylphenol in black carbon-amended sediment

The present study aimed to investigate biodegradation mechanisms of black carbon (BC)-bound contaminants in BC-amended sediment when BC was applied to control organic pollution. The single-point Tenax desorption technique was applied to track the species changes of nonylphenol (NP) during biodegradation process in the rice straw carbon (RC)-amended sediment. And the correlation between the biodegradation and desorption of NP was analyzed. Results showed that microorganisms firstly degraded the rapid-desorbing NP (6 h Tenax desorption) in RC-amended sediment. The biodegradation facilitated the desorption of slow-desorbing NP, which was subsequently degraded as well (192 h Tenax desorption). Notably, the final amount of NP degradation was greater than that of NP desorption, indicating that absorbed NP by RC amendment can be degraded by microorganisms. Finally, the residual NP amount in RC-amended sediment was decided by RC content and its physicochemical property. Moreover, the presence of the biofilm was observed by the confocal laser scanning microscope (CLSM) and scanning electron microscope (SEM) so that microorganisms were able to overcome the mass transfer resistance and directly utilized the absorbed NP. Therefore, single-point Tenax desorption alone may not be an adequate basis for the prediction of the bioaccessibility of contaminants to microorganisms or bioremediation potential in BC-amended sediment.

Comparison of different rice straw based adsorbents for chromium removal from aqueous solutions

Chromium is a well known highly toxic heavy metal and one of the major pollutants in the tannery wastewaters. This research aims at studying the feasibility of using different rice straw-based adsorbents, fine rice straw (FRS), rice straw carbon (RSC), and rice straw activated carbon (RSAC) for removal of chromium from aqueous solution. In batch experiments, effect of operating variables such as contact time, adsorbent dose, pH of solution, and initial chromium concentration have been studied. The best operating conditions were: FRS—equilibrium time 12 h, FRS dose 20 g/l, pH 2; RSC—equilibrium time 8 h, RSC dose 12 g/l, pH 2; RSAC—equilibrium time 4 h, RSAC dose 8 g/l, pH 2. The maximum adsorption achieved at pH 2.0 for all studied adsorbents. The adsorption results for the studied adsorbents were fitted to Langmuir and Freundlich isotherms with correlation coefficient of 0.99, 0.95, respectively, and the maximum adsorption capacity was 7.99, 18.83, and 40.32 mg/g. Desorption of chromium from different rice straw (RS) particles using acid and base treatment exhibited a higher desorption efficiency by more than 85, 95, and 97% for FRS, RSC, and RSAC, respectively. The present study showed that RS could be used as a biosorbent for removal of chromium from aqueous solution with a limited ratio.

Preparation and electrochemical behaviour of biomass based porous carbons as electrodes for supercapacitors — a comparative investigation

We compared the relationship of the behavior and performance of sugarcane baggase and rice straw as supercapacitor electrodes. X-ray diffraction revealed the evolution of crystallites of carbon and silica during activation at higher temperature. The morphology of the carbon samples was determined by SEM. The surface area, pore volume, and pore size distribution of carbon composites were measured. The electrochemical responses were studied by using cyclic voltammetry experiment at 25 °C in a three-electrode configuration. The specific capacitance of the sugarcane bagasse carbon electrodes was in the range 92-340 F/g, whereas for rice straw, it was found to be 56–112 F/g at scan rates of 2-3 mV/s. The sugarcane bagasse carbon exhibited better performance than rice straw carbon using H2SO4 as the electrolyte. However, the results clearly show that lignocellulosic wastes possess a new biomass source of carbonaceous materials for high-performance supercapacitors.

Desorption and distribution of pentachlorophenol (PCP) on aged black carbon containing sediment

Purpose There is a strong affinity between organic compounds and black carbon (BC) in sediments, but the release of adsorbed organic compounds from BC may vary with the duration of contaminant–sediment contact (i.e., aging). The objective of this paper was to evaluate the effect of the application of rice straw carbon (RC) on the control of hydrophobic ionizable organic compounds (HIOCs) pollution and investigate whether aging affects the release of adsorbed pentachlorophenol (PCP) in RC-amended sediment.

Contribution of rice straw carbon to CH4 emission from rice paddies using 13C‐enriched rice straw

It is generally recognized that the application of rice straw (RS) increases CH4 emission from rice paddies. To estimate the contribution of RS carbon to CH4 emission, a pot experiment was conducted using 13C‐enriched RS. The percentage contributions of RS carbon to CH4 emission throughout the rice growth period were 10±1, 32±3, and 43±3% for the treatments with RS applied at the rates of 2, 4, and 6 g kg−1 soil, respectively. The increase in the rate of application of RS increased CH4 emission derived from both RS carbon and other carbon sources. The percentage contribution of RS carbon to CH4 emission was larger in the earlier period (maximum 96%) when the decomposition rate of RS was larger. After RS decomposition had slowed, CH4 emission derived from RS carbon decreased. However, the δ13C values of CH4 emitted from the pots with 13C‐enriched RS applied at rates of 4 and 6 g kg−1 soil were significantly higher than those from the pots with natural RS until the harvesting stage. An increased atom‐13C% of roots of rice plants growing in the pots with 6 g kg−1 of 13C‐enriched RS at around the maximum tiller number stage and a decrease during the following 2 months suggested that rice plants assimilated RS carbon once and then released a portion of it. This supply of RS carbon from roots may be one of the sources of CH4 in the late period of rice growth.

Methane formation and emission from flooded rice soil incorporated with 13C-labeled rice straw

Pot experiments with or without 13C-labeled rice straw and rice plants were made to investigate the contribution of organic sources to the formation and emission of CH 4 from flooded rice soil. The 13C abundance in emitted CH 4 and contained in soil bubbles peaked at 20–40 d after flooding (DAF). After 40 DAF, 13C abundance was higher in unplanted pots than in planted pots. A similar pattern was found in the abundance of 13CCO 2 in the soil bubbles. Using the δ 13C values in the soil bubbles of the pots without straw application as the background values, the percentages of the CH 4 emitted from soil to the atmosphere or contained in the soil bubbles originating from straw were calculated. These percentages were multiplied by the CH 4 flux to estimate the quantities of the emitted CH 4 from rice straw. The most active CH 4 emission from the straw was found during 40–80 DAF, when the first peak of CH 4 emission was observed. The contribution of sources other than added straw to the formation and emission of CH 4 increased sharply only in the planted pots after 80 DAF (heading stage), suggesting this increase was due to the release of organic materials from rice plants. The relative contribution of 13C derived from straw in CH 4 and CO 2 was not significantly different, indicating that methanogens did not have any preference for the straw-derived substrates. After the cropping season, ca. 5% of the rice straw carbon remained in the soil and 1% was incorporated into the rice plants.