Anaerobic Digestion Of Rice Straw Research Articles

Efficient methane production from anaerobic co-digestion of lignin-based feedstock and waste plastic: Digester performance and microbial community structures

Waste plastic (WP) and lignocellulosic biomass (LCB) are both refractory polymers that can provide feedstocks for the production of fuels. Anaerobic digestion (AD) is a widely recognized technology utilized in waste management and renewable energy production. It involves the utilization of microorganisms to decompose organic matter into methane (CH4). Nevertheless, mono-digestion, which refers to AD utilizing a single feedstock, encounters difficulties related to the properties of the feedstock. Therefore, the utilization of co-digestion with multiple feedstocks provides the potential to overcome these limitations. This study might be the first to examine the impact of co-digestion of low-density polyethylene (LDPE) with rice straw (RS) for biogas and CH4 production. The cumulative CH4 production for AD-1, AD-2, AD-3, AD-4, AD-5, and AD-6 was 154.9, 177.4, 52, 81.2, 98.43, and 135.15 NmL/g VS. The methane energy yields varied between 2.29 and 7.64 MJ/m3, while their respective βece values spanned from 17.6 to 58.8 %. Volatile solid removal was enhanced for the treated RS-LDPE mixture, as demonstrated in AD-6, in comparison to the untreated substrate in the AD-2 digester. There is a notable disparity in the composition of bacterial communities within the bioreactors that were constructed prior to and subsequent to the AD process. The proliferating Firmicutes, Bacteroidetes, and Protobacteria were crucial to the AD of RS and LDPE. The three predominant methanogenic genera present in the constructed digesters and inoculum were Methanobacterium, Methanolinea, and Methanosarcina, each with a distinct abundance level. The findings open up the possibility of better understanding the effect of co-digestion of WP and LCB on enhancing methane production, which is critical for developing strategies for bioremediation and waste valorization simultaneously with biofuel production.

Effect of hydrothermal-acid pretreatment on methane yield and microbial community in anaerobic digestion of rice straw

Hydrothermal pretreatment has been proposed to enhance straw methane yield during anaerobic digestion recently. However, the combined effect of hydrothermal and organic acid pretreatment (HTOAP) needs further investigation. This study identified optimal pretreatment at 120 °C with 3 % acetic acid for 24 h by orthogonal design method. The HTOAP increased the reducing sugar content by destroying the lignocellulosic structure. A 79 % increment of methane production after HTOAP was observed compared to the untreated group. Microbial analysis showed that HTOAP enriched the relative abundance of lignocellulose-degraders, such as W5053, Thermanaerovibrio, Caldicoprobacter, as well as the syntrophic acetate oxidizing bacteria Syntrophaceticus. Moreover, Methanobacterium conducted hydrogenotrophic methanogenesis dominantly. Furthermore, the potential function analysis showed that HTOAP stimulated the expression of key enzymes in the hydrogenotrophic pathway, including carbon-monoxide dehydrogenase (EC 1.2.7.4) and coenzyme F420 hydrogenase (EC 1.12.98.1). This investigation illustrated the potential of HTOAP of rice straw to facilitate methane production.

Synergistic effect of two bacterial strains promoting anaerobic digestion of rice straw to produce methane

A large amount of agricultural waste causes global environmental pollution. Biogas production by microbial pretreatment is an important way to utilize agricultural waste resources. In this study, Sporocytophaga CG-1 (A, cellulolytic strain) was co-cultured with Bacillus clausii HP-1 (B, non-cellulolytic strain) to analyze the effect of pretreatment of rice straw on methanogenic capacity of anaerobic digestion (AD). The results showed that weight loss rate of filter paper of co-culture combination is 53.38%, which is 29.37% higher than that of A. The synergistic effect of B on A can promote its degradation of cellulose. The cumulative methane production rate of the co-culture combination was the highest (93.04 mL/g VS substrate), which was significantly higher than that of A, B and the control group (82.38, 67.28 and 67.70 mL/g VS substrate). Auxiliary bacteria can improve cellulose degradation rate by promoting secondary product metabolism. These results provide data support for the application of co-culture strategies in the field of anaerobic digestion practices.

Rice straw anaerobic co-digestion: Comparing various pre-treatment techniques to enhance biogas production

Study investigates rice straw size impact on co-digestion with four pre-treatments: thermal, hydrogen peroxide, combined thermal and hydrogen peroxide, and hydrogen peroxide followed by thermal treatment. Rice straw is divided into four sizes: 3–5 cm, 1–2 cm, 5–10 mm, and 300 μm. Co-substrates, sewage sludge, and chicken manure are used at a 20 % total solids concentration. Pre-treatment effects on rice straw and volatile fatty acid content post-digestion are assessed by quantifying cellulose, hemicellulose, and lignin content. Thermal pre-treatment, particularly on 1–2 cm-sized rice straw, demonstrates the highest efficacy with biogas production of 389 mL/g-VS. Preferred rice straw sizes for adaptability are ranked: 1–2 cm > 5–10 mm > 3–5 cm > 300 μm. However, pre-treatment fails to enhance biogas production compared to the control, attributed to structural deterioration, accelerated hydrolysis, elevated VFA levels, methanogenic inhibition, and increased hemicellulose content. Co-digestion is recommended over pre-treatment for rice straw anaerobic digestion.

Effects of inocula on methane production and the microbial community in a rice straw anaerobic digestion system

Field experiments have shown that the mixed anaerobic digestion of straw with livestock and poultry manure can improve the efficiency of biogas production. We hypothesize that inoculation with livestock and poultry manure increase the efficiency of methane production by improving the diversity and structure of microbial community in the field anaerobic digestion system. In this study, an experimental system was established to simulate the microbial community of the mixed anaerobic digestion system in the field. The methane production and taxonomic composition of bacterial and archaeal communities in the rice straw anaerobic digestion systems were determined. We aim to reveal the effects of the inocula on the diversity and composition of bacterial and archaeal communities and the mechanism underlying the impact on biogas production in the field. The following results were obtained. (1) Inoculation significantly improved the efficiency of methane production in anaerobic digestion, and the best performance was achieved with treatment A (cleared biogas slurry), which obtained methane production that were 39.59 %, 106.85 %, and 123.00 % higher than in treatment B (pig manure extract), C (cleared biogas slurry + pig manure extract), and the control, respectively. (2) The inocula increased the abundance and diversity of bacterial communities in the early and middle stages and archaeal communities in the early stage. (3) The inocula also had a significant impact on bacterial and archaeal community composition in the early and middle stages. The inocula increased the relative abundance of Aquamicrobium_A, Proteiniphilum, and Cryptobacteroides but reduced the relative abundance of Macellibacteroides, Acinetobacter, and Phocaeicola. The dominant genus of archaeal community was altered from Methanosarcina to Methanocorpusculum. (4) It is concluded that inoculation significantly increase methane production as the inocula improve the abundance and diversity of bacteria and archaea of anaerobic digestion systems in the early and middle stages of digestion, as well as improve the structure and metabolic pathway of archaeal communities.

Adaptability and diversity of core microbiome in evaluating the effect of digested versus raw manure in anaerobic digestion of rice straw

The application of anaerobic digestion (AD) for the management of rice straw (RS) provides a way to generate bioenergy to tackle greenhouse gas emissions caused by conventional burning and tilling of straw back into the fields. The existing research often neglects inoculum selectivity and microbial community roles in AD. This study demonstrates the superiority of the microbial community from digested manure (ADS) over raw manure (CD) in producing biogas from rice straw. Notably, the microbial community of digested manure progressively resembled that of raw cow dung after 45 days of anaerobic digestion showing 116 common bacterial genera in comparison to just 9 at the beginning of the experiment. The dominant bacterial genus observed was Clostridiales, with its abundance rising from 9.86% to 38.40% in ADS and declining from 38.16% to 7.53% in CD from day 0 and day 45. This was succeeded by a rise in Prevotella and a reduction in Pseudomonas as the days advanced. Methanobrevibacter was the dominant genus of hydrogenotrophic archaea whose abundance increased from 8.20% to 64.25% in ADS and decreased from 61.41% to 8.98% in CD. Reactors inoculated with ADS outperformed those inoculated with raw CD by producing 7.07 times higher biogas. Additionally, the study highlights the influence of microbial dynamics on volatile fatty acid accumulation, and buffering capacity of the AD system. The significance of this research lies in enhanced microbial activity and digestion rate, reduced start-up time, and adaptation to feedstock resulting in higher biogas production.

Ruminal content biochar supplementation for enhanced biomethanation of rice straw: Focusing on biochar characterization and dose optimization

Anaerobic digestion (AD) of agricultural wastes is a promising approach for energy recovery and crop residue management. However, its recalcitrant chemical structure hinders microbial hydrolysis and reduces biomethane production under AD. Biochar supplementation has been proven to promote the digestibility and biomethanation of lignocellulosic substrates. Therefore, this study investigated the influence of different pyrolysis temperatures (450 °C, 550 °C, and 650 °C) on the physicochemical properties of biochar. Furthermore, the impact of ruminal content biochar supplementation (1 %, 2 %, and 3 %) on the AD of rice straw with rumen fluid as inoculum has been investigated. The ruminal content biochar (RUCB) supplemented reactors showed an increment in biomethane yield and the highest cumulative biomethane yield 243.11 mL/g volatile solids (VS)) was recorded at 2 % RUCB supplementation, followed by 227.12 mL/g VS at 1 % RUCB supplementation and 162.86 mL/g VS at 3 % RUCB supplementation (P > 0.05). Compared to the control reactors (128.68 mL/g VS), RUCB supplemented reactors exhibited 1.88-fold, 1.76-fold, and 1.26-fold increments in biomethane yield due to pH stabilization and facilitation of microbial biofilm formation on the biochar. The correlation analysis showed that biomethane production is positively correlated with VS reduction (R2 = 0.9852). This study proposed a potential strategy to utilize ruminal content waste as a feedstock for biochar production and its application in AD for accelerating the biomethanation of rice straw.

Effect of fungal pretreatment by Pycnoporus sanguineus and Trichoderma longibrachiatum on the anaerobic digestion of rice straw

Rice straw is composed of complex lignocellulosic biomass, representing a major obstacle in its conversion to bioenergy. The objective of this study was to evaluate the usefulness of less explored fungal strains Trichoderma longibrachiatum (TL) and Pycnoporus sanguineus (PS) in improving hydrolysis and bioavailability of rice straw in anaerobic digestion (AD). The fungal treatment of rice straw for 10 days by PS and TL increased biogas production by 20.79% and 17.85% and reduced soluble chemical oxygen demand (sCOD) by 71.43% and 64.70%, respectively. The AD samples containing fungal-treated rice straw showed higher lignocellulolytic enzyme activities contributing to better process performance. The taxonomic profile of microbial communities in treated samples showed increased diversity that could sustain consistent system performance and exhibit enhanced resilience against pH fluctuations. Metagenomic analysis revealed 60.82% increase in Proteobacteria in PS and 11.58% increase in Bacteroidetes in TL-treated rice straw samples resulting in improved hydrolysis.

A Mass Balance-Based Method for the Anaerobic Digestion of Rice Straw

Current rice straw disposal practices have serious repercussions on the environment and, in addition, do not consider its energy potential. On the contrary, the anaerobic digestion of rice straw makes it possible to produce renewable energy and to reintroduce into the soil the nutrients present in the digestate, at the same time, reducing greenhouse gas emissions from paddies. For rice straw of different geographical origin, by applying a mass balance method to the digester, the minimum requirements in terms of conditioners (nitrogen, phosphorus and potassium) and water, which allow obtaining the maximum production of methane, were calculated. The results obtained show that after the first 30 days (hydraulic retention time) for each ton of rice straw digested, the daily water consumption varies considerably from one country to another, from a minimum value of 1.5 m3/d to a maximum of 4.3 m3/d. After the same time, the addition of nitrogen and phosphorus is only required for the optimal anaerobic digestion of Indian rice straw. The low presence of these elements in Indian straw requires an addition of 3 kg/d of urea and 1.5 kg/d of superphosphate to compensate for the lack of nitrogen and phosphorus, respectively. In all the examined cases, the concentration of potassium, even if higher than the optimal value, does not reach levels that can significantly affect the methane production.

Enhancement of anaerobic digestion of rice straw by amino acid-derived ionic liquid

This study proposes a novel method to enhance methane production from anaerobic digestion using an amino acid-derived ionic liquid, glycine hydrochloride, ([Gly][Cl]), as an exogenous additive. After 40 days of digestion with 5% [Gly][Cl], the cumulative methane production was 115.56 mL/g VS, which was 73% higher than that of the control group (without additive). Specifically, the peak activities of cellulase, xylanase, and lignin peroxidase were significantly higher than those of the control group. The addition of [Gly][Cl] increased bacterial diversity and reduced archaeal diversity. Synergistota represented by Syner-01, Fibrobacterota represented by BBMC-4, Bacteroides, and unclassified_f__Lachnospiraceae significantly increased in relative abundance. It suggested that [Gly][Cl] stimulated the activities of protein-hydrolyzing and acid-producing bacteria. [Gly][Cl] also increased the abundance of methanogens and archaea, converting more lignocellulose to methane. Methanobacterium, that metabolizes H2 and CO2 to CH4, was more abundant. Therefore, [Gly][Cl] can improve methane yield as an anaerobic digestion additive.

Two-step anaerobic digestion of rice straw with nanobubble water

Lignocellulose usually requires pretreatment to improve biogas production. To enhance lignocellulose biodegradability and improve anaerobic digestion (AD) efficiency, different types (N2, CO2, and O2) of nanobubble water (NW) were applied in this study as soaking agent and AD accelerant to increase the biogas yield of rice straw. The results showed that the cumulative methane yields of treating with NW in two-step AD increased by 11.0%–21.4% compared with untreated straw. The maximum cumulative methane yield was 313.9±1.7 mL/gVS in straw treated with CO2-NW as soaking agent and AD accelerant (PCO2-MCO2). The application of CO2-NW and O2-NW as AD accelerants increased bacterial diversity and relative abundance of Methanosaeta. This study suggested that using NW could enhance soaking pretreatment and methane production of rice straw in two-step AD; however, combined treatment with inoculum and NW or microbubble water in the pretreatment needs to compare in future.

Comparison of GHG emissions from open field burning and anaerobic digestion of rice straw

ABSTRACT Rice straw (RS) has been burned in open fields in many countries, which is a growing environmental concern. Anaerobic digestion (AD) of RS is one of the sustainable alternatives to open burning of RS for converting the biomass into methane, carbon dioxide, and digestate for use as agricultural manure. The present study evaluates the RS generation, use patterns, and greenhouse gas emissions from open field burning and the AD of RS. Results indicate the AD of RS offers greater environmental benefits than that by RS open field burning. As a result of the open burning of RS in India emitted 592032.52 kg of CO2 equivalents/kg per year, whereas AD of RS contributes 122.86 kg of CO2 equivalents/kg per year. If RS were burned in an open field, its Global Warming Potential would be 493,873 times greater than that of AD. By minimizing GHG emissions and creating sustainable energy from waste, sustainable development, and circular economies are achieved.

Maximizing the energy recovery from rice straw through two-step conversion using eggshell-catalytic pyrolysis followed by enhanced anaerobic digestion using calcium-rich biochar

Anaerobic digestion of lignocelluloses for biogas production is greatly restricted by the poor biomass degradability. Herein, a novel approach is suggested to enhance the energy recovery from rice straw through a two-step conversion using eggshell-based catalytic pyrolysis followed by biochar-based anaerobic co-digestion. Pyrolysis with eggshell significantly enhanced the crude bio-oil yield by 4.6 %. Anaerobic digestion of rice straw using 4 g L−1 of rice straw biochar (RB) showed the highest recorded biogas yield of 503.7 L kg−1 VS, with 268.6 L kg−1 VS biomethane yield. However, 4 g L−1 of calcium-enriched eggshell rice straw biochar (ERB) enhanced the biomethane yield to 281.8 L kg−1 VS, which represented 95.6 % higher than the control. It was attributed to enhancement of biomethanation, which resulted in 74.5 % maximum recorded biomethane content at the 7th day of anaerobic digestion. Microbial analysis confirmed that Methanosarciniales was the most dominant Archael group in the control (14.84 %), which increased sharply to 73.91 % and 91.66 % after addition of 4 g L−1 RB and ERB, respectively. The suggested route enhanced the energy recovery in the form of bio-oil and biomethane by 41.6 %.

Effect of time and temperature of pretreatment and anaerobic co-digestion of rice straw and swine wastewater by domesticated paddy soil microbes

Rice straw and swine wastewater are abundant, easy to obtain, and inexpensive biomass materials. Anaerobic digestion of rice straw and swine wastewater effectively regulates the carbon-to-nitrogen ratio and also improves methane production efficiency. The dense lignocellulosic structure, unsuitable carbon-to-nitrogen ratio, and light texture of rice straw hinder its application in anaerobic digestion. Effective pretreatment technologies can improve degradation efficiency and methane production. Our study is the first to apply domesticated paddy soil microbes to enhance the efficiency of hydrolytic acidification of rice straw and swine wastewater at varying temperatures and times. The results show that the highest total organic carbon (1757.2 mg/L), soluble chemical oxygen demand (5341.7 mg/L), and organic acid concentration (4134.6 mg/L) appeared in the hydrolysate after five days of hydrolytic acidification at 37 °C. Moreover, the use of hydrolysate produced 13% more gas and reduced the anaerobic digestion period by ten days compared to the untreated control. This suggests that using domesticated paddy soil microbes as a pretreatment might be a sustainable and cost-effective strategy for improving the degradation efficacy and methane production from lignocellulosic materials.

Improving the biodegradability of rice straw by electrochemical pretreatment

The efficacy of NaOH, alkaline hydrogen peroxide (NaOH-H2O2), electrochemically produced NaOH-H2O2 (eNaOH-H2O2) and electrohydrolysis (EH) pretreatments was investigated for anaerobic digestion of rice straw. The cumulative biogas production was enhanced by 8%, 22% and 14% in the NaOH-H2O2, eNaOH-H2O2 and EH relative to conventional NaOH pretreatment. The chemical and electrochemical pretreatments decreased the crystallinity of cellulose and created a porous surface vein. Electrochemical NaOH-H2O2 pretreatment is efficient to promote microbial degradation of lignocellulose for biogas production while the risks associated with the transportation and storage of H2O2 are avoided. EH reduces the pretreatment time significantly and is a promising approach for utilizing rice straw biomass to produce renewable energy.

Solid-state anaerobic digestion of rice straw pretreated with swine manure digested effluent

Solid-state anaerobic digestion (SSAD) is a key technology for utilization of agricultural waste due to higher volumetric methane productivity, having a high load of organics, and nearly no effluent produced. The swine manure digested effluent (SMDE) containing high concentrations of ammonia nitrogen (1000, 1500, and 2000 mg L−1, respectively) were innovatively used to pretreat rice straw replacing alkaline chemicals at 30 °C for 2d, 4d, 6d, 8d, and downstream processed in SSAD loaded with solid digestate of swine manure (SDSM). After pretreatment, the surface structure of rice straw was obviously destroyed, and the removal rates of lignin, cellulose and hemicellulose were 1.3–20.4%, 1.3–26.3% and 13.9–28.4%, respectively. The concentrations of ammonia nitrogen in the pretreatment system were reduced by 16.75–75.47%. In the subsequent SSAD process, the accumulative methane yields in the digester loaded with pretreated rice straw increased by 93.25–261.08%, and the technical digestion time to achieve 80% of the maximum cumulative methane yield (T80) occurred 10–14 days earlier. The highest daily methane yield and accumulative methane yield of 7.37 mL/(g·VSadded·d) and 105.27 mL/(g·VSadded), respectively, were noted in the digester loaded with 2000 mg/L ammonia pretreated rice straw. Overall, SMDE pretreatment could significantly improve the biodegradability and anaerobic digestibility of rice straw, and improve the production efficiency of SSAD. The novel integrated approach to reutilization of SMDE, rice straw and SDSM not only reduced the environmental pollution, but also stimulated the sustainable development of swine farms, and promoted the carbon neutrality and economic development via effective bioenergy production as well. A large-scale trial and wide application of this approach could be expected in future.

Dry Anaerobic Digestion of Rice Straw Pretreated with Pig Manure Biogas Slurry: Properties and Microbial Characteristics When Mixed with Biogas Residue

Dry Anaerobic Digestion of Rice Straw Pretreated with Pig Manure Biogas Slurry: Properties and Microbial Characteristics When Mixed with Biogas Residue

Understanding the substrate mediated microbial community shift within the anaerobic ecosystems via 16S metagenomic studies

Microorganisms are smart enough to evolve within the anaerobic ecosystems with tiny alteration in the process of fermentation as per the system dynamics. This study tries to elucidate the change in community structure of the consortia in anaerobic digestion of rice straw, bagasse, press mud, and vegetable waste with respect to its complexity. With the aid of metagenomic studies, it is found that Bacteroidetes and Firmicutes dominated the metabolic pathway for generation of precursors for methane production. The highest methane yield of 0.38 L CH4/(g VSadded) was obtained for rice straw followed by bagasse, press mud and vegetable waste. However, maximum VS reduction of 70% was observed for vegetable waste followed by rice straw (67%), baggase (60%) and press mud (60%). Acetoclastic methanogenesis is the dominating methane metabolic pathway with Methanosaeta dominating archaea in all the reactors.

Applying EEM- PARAFAC Analysis With Quantitative Real-Time PCR to Monitor Methanogenic Activity of High-Solid Anaerobic Digestion of Rice Straw.

The methanogenic activity is an important indicator to assess the efficiency of high-solid anaerobic digestion. However, it is not yet elucidated clearly how to detect the parameter rapidly and reliably in the rice straw feeding reactor. Co-inoculated with ruminal digesta and anaerobic sludge, the digestion performance was studied at three different organic loading rates (OLRs). The excitation emission matrix–parallel factor analysis (EEM–PARAFAC) was used to detect dynamic changes in the characteristic of fluorescence components. Our results revealed that CH4 productivity reached 280.90 mL/g volatile solid (VS) with a 54.39% CH4 content under the OLR of 2.26 g/(L⋅d), which amount to 80.29% of its theoretical value. At the OLR of 2.47 g/(L⋅d), the average accumulated NH4+ concentration was 1082.63 mg/L, which resulted in the hydrogenotrophic Methanobacteriales decreasing from 1.70 × 109 to 1.04 × 106 copies/g in the solid residues, whereas the acetotrophic Methanosarcinales increased from 7.89 × 106 to 9.44 × 106 copies/g. The dynamics of the methanogenic community consequently influenced the bioconversion efficiency of rice straw, and CH4 productivity was reduced to 256.54 mL/g VS. The three fluorescent components, at the excitation/emission wavelength of 420 nm/470 nm, 340 nm/430 nm, and 280 nm/340 nm, were decomposed by PARAFAC model in the digestate. Fluorescence intensities of coenzyme F420 and NADH reflected the dynamic changes of CH4-producing activity and anaerobic digestion efficiency, respectively. The coenzyme F420, unique to hydrogenotrophic methanogens, was correlated with methane yield, suggesting they played a dominant role in the anaerobic reactor. This study demonstrates that the EEM–PARAFAC combined with Q-PCR can be used to characterize methanogenic activity variation during the high-solid anaerobic digestion of rice straw with 15% total solid (TS).

Exploring the functional significance of novel cellulolytic bacteria for the anaerobic digestion of rice straw

The purpose of this study is to evaluate the potential of isolated novel bacterial strains for rice straw (RS) hydrolysis in terms of total sugar and COD (chemical oxygen demand) solubilization to improve overall biomethane yield. Four out of seven pretreatment setup with isolated bacterial strains i.e., Bacillus paralicheniformis VKVVG3 (CDf), Perlucidibaca piscinae VKVVG6 (CDd1), Bacillus clausii VKAK2 (RSa1) and Bacillus mojavensis VKAK1 (CDb1) exhibited higher saccharification compared to untreated RS. The CDf pretreated RS showed highest efficiency with 137% COD solubilization and 320% sugar accumulation at optimal dosage of 109 CFU/mL within 4-day of incubation. The batch reactor (20L) study with CDf pretreated RS produced 476 mL/g VSsubstrate compared to 310 mL/g VSsubstrate for untreated RS which corresponds to 53.6% higher than untreated RS. The FESEM, FTIR, and XRD analysis also support the overall results, indicating excellent degradation of the structural morphology of the RS microcrystalline structure. Furthermore, the fitting error in bio-kinetic parameters using modified Gompertz, Fitzhugh, and Monomolecular models were 5.47, 2.44, and 4.28% respectively, with R2 values above 0.99, also supports the experimental data. The results of this study revealed many positive interpretations concerning the future expansion of the existing system for bacterial pretreatment of RS.