Anaerobic Digestion Of Straw Research Articles

Review of Pretreatment Technology for Corn Straw Anaerobic Digestion

Corn straw is mainly composed of hemicellulose, cellulose, and lignin, which together form a crystal structure with extremely high stability. Anaerobic fermentation is an important means of straw resource utilization. Due to the complex composition of corn straw, the hydrolysis rate during anaerobic fermentation is limited, which affects the gas production efficiency. Therefore, it is necessary to pretreat corn straw. This article analyzes the advantages and disadvantages of different pretreatment methods and their applications in anaerobic digestion in order to provide optimal pathways for the pretreatment of corn straw.

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.

Optimal design of a sector-coupled renewable methanol production amid political goals and expected conflicts: Costs vs. land use

Methanol is an important bulk chemical which can be produced from renewable resources with the currently available technologies and doing so has a high potential for greenhouse gas (GHG) emission reductions for the chemical sector. Reaching the targets for climate change mitigation and biodiversity protection will require designing not only renewable, but also land-efficient chemical production systems. However, under the current economic imperative of cost minimization, the efficient use of land is often not considered during production system design and compromise solutions are left undiscovered, the potential of land-use intensifying technologies stays unknown and the impact of their exclusion, e.g. due to political reasons, is not quantified. This study addresses these issues for renewable production of methanol through the biogas- and power-to-methanol production pathways, which are considered concurrently with processes allowing intensified land use (agrivoltaics, wheat straw anaerobic digestion, heat pumps, wind turbines, etc.) in a previously unexplored technological scope. The designs, as well as the effect of coupling with other production systems (residential heat, electricity, and food) as a strategy to reduce the total annualized costs (TAC) and direct land use, are investigated using the FluxMax approach, an optimization-based design methodology. It simultaneously accounts for the, often neglected, dynamics of renewable energy harvesting, waste-heat utilization and biomass production under the fluctuating renewable resource and product-demand conditions of an example location in Saxony-Anhalt, Germany. Reductions of the TAC of 19 %, direct land use of 9 % and GHG emissions of 12 % for the production system by coupling all four of these products were determined. Furthermore, Pareto fronts were constructed to quantify the trade-off between the conflicting objectives of minimizing TAC and direct land use, demonstrating that land use can be reduced by up to 10 % with minimal extra costs among the available technologies. Political conflicts and goals, which may influence the deployment of the considered technologies, are discussed from a political science perspective and highlight the need for further interdisciplinary collaboration.

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.

Application of Ammoniation Pretreatment in Anaerobic Digestion of Straw

Straw is a widely available and highly renewable biomass resource with good utilization value. However, its dense structure is not conducive to methane production during anaerobic fermentation and requires pretreatment. To achieve high-value conversion, pretreatment technologies can effectively destroy the rank structure of straw and increase gas production. Ammoniation pretreatment has unique advantages in pretreating straws. This article reviews the ammoniation pretreatment mechanism, the impact of ammoniation pretreatment parameters on anaerobic fermentation, and ammoniation pretreatment technology, providing a reference for the ammoniation pretreatment of straw.

Low-temperature torrefaction assisted with solid-state KOH/urea pretreatment for accelerated methane production in wheat straw anaerobic digestion

Low-temperature torrefaction assisted with solid-state KOH/urea applied onto wheat straw was proposed to break down the lignocellulosic material to enhance biomethane production in anaerobic digestion (AD). The optimization of key parameters applying the Box-Behnken design and response surface methodology showed that an addition of 0.1 g/gstraw KOH/urea at 180 °C while torrefying for 30 min was the optimal condition for producing biomethane. Results indicate that co-applying KOH and urea in torrefaction synergistically enhanced the biodegradability of straw by effectively removing lignin and largely retaining cellulose, giving rise to a 41 % increase in the cumulative methane production compared to untreated straw (213 mL/g-volatile solids (VSraw)) from batch AD. Additionally, the nitrogen- and potassium-rich digestates helped to improve soil fertility, thus achieving a zero-waste discharge. This study demonstrated the feasibility of using solid-state KOH/urea assisted low-temperature torrefaction as an effective pretreatment method to promote methane production during AD.

Modeling and optimization of the hydrolysis and acidification via liquid fraction of digestate from corn straw by response surface methodology and artificial neural network

This study investigated liquid fraction of digestate (LFD) assisted hydrolysis and acidification (HA) of corn straw (CS) for enhanced biogas production. Response surface methodology-central composite design (RSM-CCD) and artificial neural network-genetic algorithm (ANN-GA) tools were used to optimize the acidogenic performance. Optimized performance was obtained at the hydraulic retention time of 8 d, temperature of 41 °C, the ratio of substrate and inoculum of 4, and pH 10. As a result of combining LFD and HA modification, performance in anaerobic digestion was improved. The highest observed methane yield under the optimal condition was 305.6 mL g−1·TS−1, which was 92.3% higher than the control group. In comparison to the RSM model (R2 = 0.921, RMSE = 20.3), the ANN-GA model indicated a higher R2 and a lower RSME value (R2 = 0.965, RMSE = 13.4), which demonstrated its advantages in determining the non-linear behavior of corn straw anaerobic digestion. The supplementation of LFD along with HA can be useful for enhancing the VFAs yield and bioenergy recovery from CS.

Investigating the Effects of Aerobic Hydrolysis on Scum Layer Formation during the Anaerobic Digestion of Corn Stalk Particles

The scum layer of straw anaerobic digestion significantly impacts biogas production efficiency. The initial floating of straw after entering the reactor is an important reason for scum layer formation. Improving the settleability of straw particles and reducing the initial floating time of straw are crucial to suppressing the scum layer, and accelerating the water absorption rate of straw entering the reactor is the key to reducing the floating time. Therefore, in this study the corn stalks were kneaded and rolled, and the stalk particles were tested for water absorption and aerobic hydrolysis. The results showed that the water absorption rate of the stalks after conditioning was significantly accelerated, and the water absorption rate was 120% higher than that of the untreated stalks after absorbing water for 12 h. Simultaneously, aerobic hydrolysis destroys the lignocellulose structure to a certain extent, increases the porosity of the stalk particles, and further improves the settleability of the stalk particles. In the subsequent anaerobic digestion process, scum decreased significantly: the scum layer volume ratio was 13% lower than untreated stalks. The methane production efficiency of anaerobic digestion was significantly improved, and the optimal hydrolysis time was 12 h. At this time, the cumulative methane production of the milled treated stalks reached the maximum value of 319.64 mL/g VS, which was 26.59% higher than that of the untreated stalks.

Biogas and Volatile Fatty Acid Production During Anaerobic Digestion of Straw, Cellulose, and Hemicellulose with Analysis of Microbial Communities and Functions.

The anaerobic digestion efficiency and methane production of strawwas limited by its complex composition and structure. In this study, rice straw (RS), cellulose, and hemicellulose were used as raw materials to study biogas production performance and changes in the volatile fatty acids (VFAs). Further, microbial communities and genetic functions were analyzed separately for each material. The biogas production potential of RS, cellulose, and hemicellulose was different, with cumulative biogas production of 283.75, 412.50, and 620.64mL/(g·VS), respectively. The methane content of the biogas produced from cellulose and hemicellulose was approximately 10% higher than that produced from RS after the methane content stabilized. The accumulation of VFAs occurred in the early stage of anaerobic digestion in all materials, and the cumulative amount of VFAs in both cellulose and hemicellulose was relatively higher than that in RS, and the accumulation time was 12 and 14days longer, respectively. When anaerobic digestion progressed to a stable stage, Clostridium was the dominant bacterial genus in all three anaerobic digestion systems, and the abundance of Ruminofilibacter was higher during anaerobic digestion of RS. Genetically, anaerobic digestion of all raw materials proceeded mainly via aceticlastic methanogenesis, with similar functional components. The different performance of anaerobic digestion of RS, cellulose, and hemicellulose mainly comes from the difference of composition of raw materials. Increasing the accessibility of cellulose and hemicellulose in RS feedstock by pretreatment is an effective way to improve the efficiency of anaerobic digestion. Since the similar microbial community structure will be acclimated during anaerobic digestion, there is no need to adjust the initial inoculum when the accessibility of cellulose and hemicellulose changes.

Biomass Pretreatment with the Szego Mill™ for Bioethanol and Biogas Production

Results from an investigation of the mechanical size reduction with the Szego Mill™ as a pretreatment method for lignocellulosic biomass are presented. Pretreatment is a highly expensive and energy-consuming step in lignocellulosic biomass processing. Therefore, it is vital to study and optimize different pretreatment methods to find a most efficient production process. The biomass was milled with the Szego Mill™ using three different approaches: dry milling, wet milling and for the first time nitrogen assisted wet milling was tested. Bioethanol and biogas production were studied, but also fibre analysis and SEM (scanning electron microscope) analysis were carried out to characterize the effect of different milling approaches. In addition, two different process flows were used to evaluate the efficiency of downstream processing steps. The results show that pretreatment of barely straw with the Szego Mill™ enabled obtaining glucose concentrations of up to 7 g L−1 in the hydrolysis mixture, which yields at hydrolysis efficiency of 18%. The final ethanol concentrations from 3.4 to 6.7 g L−1 were obtained. The lowest glucose and ethanol concentrations were measured when the biomass was dry milled, the highest when nitrogen assisted wet milling was used. Milling also resulted in an 6–11% of increase in methane production rate during anaerobic digestion of straw.

Biomethane production by typical straw anaerobic digestion: Deep insights of material compositions and surface properties

Straws as lignocellulosic agricultural biomass have a huge amount and are widely used for biomethane production by anaerobic digestion (AD). However, the mechanism of impacts of straw composition and surface properties on biomethane production remain unclear. Here, a lab-scale AD incubation experiment was conducted and the characterization of four types of straws (corn straw, wheat straw, sweet sorghum straw, and rice straw) were also determined. The straw compositions and net cumulative methane production showed significant difference. Although the relative contents of key organic components and carbon had no significant correlation to the biomethane production (r = -0.36, P > 0.05), there existed differences of non-polar characteristics, steric hindrance effect and special surface morphology in four types of straws, indicating that the surface characteristics affected anaerobic biomethane production process. In addition, the straw matrix associating with silicon might hinder the biotransformation.

Full-scale anaerobic reactor samples would be more suitable than lab-scale anaerobic reactor and natural samples to inoculate the wheat straw batch anaerobic digesters

This study evaluated the effects of the inocula from natural wetland, lab-scale and full-scale anaerobic reactors on wheat straw anaerobic digestion. Three replicate batch reactors were constructed for each inoculum to investigate the reactor performances and microbial communities. Reactors seeded with full-scale reactor samples were started up most rapidly, achieved the highest methane production, and were recognized as the higher efficient reactors. The dominance of acetoclastic methanogens, including Methanosaeta and Methanoscrina, was crucial for the higher efficient reactors, whereas hydrogenotrophic methanogens were dominant in other reactors. Genus Treponema, which could enhance the cellulose degradation and conduct homoacetogenesis, was first reported to be dominant in the bacterial communities of high efficient reactors. Inoculum sources and process conditions were suggested to be the deterministic factors in shaping the microbial communities in the higher efficient reactors. These findings contribute to the startup of new anaerobic reactors.

Hydrothermal pretreatment of rice straw at relatively lower temperature to improve biogas production via anaerobic digestion

Although the degradation mechanism of straw anaerobic digestion is still obscure, lower temperature thermophysical pretreatment might be a feasible way to improve biogas fermentation efficiency and net energy production in whole slurry. In this study, the performances of rice straw (RS) degradation and biogas production were examined at different pretreatment temperatures from 90 °C to 130 °C to identify the optimal process. With increasing pretreatment temperature, the change in cellulose and hemicellulose degradation in all the tests was directly related to volatile fatty acids (VFAs) content, but did not correspond to the variation in cumulative methane production. Both 100 °C and 130 °C presented similar ideal digestion performances with highest methane yields of 127.6 and 124.6 mL/g TS, respectively, which were 22.80% and 19.83% higher than that noted in the control. Although test at 100 °C pretreatment, which achieved 12.8% higher net energy production from RS than that observed in the control, could be considered as the optimal choice, the surplus biogas could only meet 75.9% of energy requirement for pretreated water temperature shift. Nevertheless, mesophilic or thermophilic fermentation, lower pretreatment water input, and reuse of excess heat are recommended as feasible working conditions for improving net biogas production.

Minimizing mixing intensity to improve the performance of rice straw anaerobic digestion via enhanced development of microbe-substrate aggregates

The aim of this work was to study the effect of the differential development of microbe-substrate aggregates at different mixing intensities on the performance of anaerobic digestion of rice straw. Batch and semi-continuous reactors were operated for up to 50 and 300days, respectively, under different mixing intensities. In both batch and semi-continuous reactors, minimal mixing conditions exhibited maximum methane production and lignocellulose biodegradability, which both had strong correlations with the development of microbe-substrate aggregates. The results implied that the aggregated microorganisms on the particulate substrate played a key role in rice straw hydrolysis, determining the performance of anaerobic digestion. Increasing the mixing speed from 50 to 150rpm significantly reduced the methane production rate by disintegrating the microbe-substrate aggregates in the semi-continuous reactor. A temporary stress of high-speed mixing fundamentally affected the microbial communities, increasing the possibility of chronic reactor failure.

Improvement of wheat straw anaerobic digestion through alkali pre-treatment: Carbohydrates bioavailability evaluation and economic feasibility

Lignocellulosic biomasses such as wheat straw are widely used as a feedstock for biogas production. However, these biomasses are mainly composed of a compact fibre structure and therefore, it is recommended to treat them prior to its usage for biogas production in order to improve their bioavailability. The aim of this work is to evaluate, in terms of performance stability, methane yield and economic feasibility, two different scenarios: a mesophilic codigestion of wheat straw and animal manure with or without a low-energy demand alkaline pre-treatment (0.08gKOHgTS−1of wheat straw, for 24h and at 25°C). Besides this, said pre-treatment was also analysed based on the improvement of the bioavailable carbohydrate content in the untreated versus the pre-treated wheat straw. The results pointed out that pre-treated wheat straw prompted a more stable performance (in terms of pH and alkalinity) and an improved methane yield (128% increment) of the mesophilic codigestion process, in comparison to the “untreated” scenario. The pre-treatment increased the content of cellulose, hemicellulose and other compounds (waxes, pectin, oil, etc.) in the liquid fraction, from 5% to 60%, from 11.5% to 39.1% TS and from 57% to 79% of the TS in the liquid fraction for the untreated and pre-treated wheat straws, respectively. Finally, the pre-treated scenario gained an energy surplus of a factor 13.5 and achieved a positive net benefit of 90.4€tVS-WS−1d−1, being a favourable case for an eventual scale-up of the combined process.

The Effect of Feeding Frequency and Organic Loading Rate on the Anaerobic Digestion of Chinese Rice Straw

Abstract China produces over 200 tonnes of rice straw (RS) a year. This is an underutilized energy source that is often burned in the fields causing pollution and health problems for populations near and far. Anaerobic digestion (AD) can produce methane (CH 4 ) rich biogas (45-55%) from waste RS as an alternative to burning whilst being affordable. Five 2L reactors were used to test the effect of feeding frequency (FF) and organic loading rates (OLR) on the anaerobic digestion of rice straw with input rates of between 5 feeds per week and one feed every 3 weeks. Two OLRs were used: 1gVS/L/d (OLR1) for 56 days and 2gVS/L/d (OLR2) for 83 days. At the lower OLR1, the best average biogas yield was 300 ml/L of reactor/d at 50% CH 4 and at OLR2 the best reactor achieved a mean biogas yield of 447 ml/L/d at 52%CH 4 . The best performing FF at OLR1 was 1/21 day whilst at OLR2 the 5/7 day FF produced the highest volume and quality of biogas. Results confirm that biogas from rice straw anaerobic digestion could be used with combined heat and power (CHP) technology to potentially produce 0.5-0.8MWh of electricity per day per tonne of rice straw.

Pyrolysis-GC–MS to assess the fungal pretreatment efficiency for wheat straw anaerobic digestion

Cost-effective and environment-friendly pretreatments, such as fungal pretreatments, are required for anaerobic digestion of lignocellulosic biomass particularly because the amount of methane produced is often limited by the lignin content. Anaerobic digestibility is estimated using a Biochemical Methane Potential (BMP) test, which lasts several weeks. Since the Py-GC–MS technique is considered to be a rapid method for obtaining information on various organic components, its suitability for the study of fungal pretreatment efficiency in anaerobic digestion was investigated here, to our knowledge for the first time. In this goal, mycelium of the white-rot fungi Polyporus brumalis BRFM 985, untreated wheat straw and straw pretreated with different fungal strains and under different conditions were analysed with Py-GC–MS. In the mycelium pyrolysate, diverse compounds, often considered as unspecific, probably derive from proteins (toluene, etc.). A strong presence of tyrosine and phenylalanine among the fungus amino acids was also suspected.As for pretreated straw samples, a correlation was observed between the amount of fungal biomass determined by qPCR (used as a reference method) and the sum of relative areas of toluene, styrene and ethylbenzene in the pyrograms, showing that it is feasible to estimate the fungal biomass amount on pretreated straws using Py-GC–MS.In addition, the H/L-Py (Holocelluloses/Lignin) ratio, determined by dividing the sums of areas of pyrolysis compounds that have a polysaccharide (PS) and lignin (LIG) origin, was correlated to the BMP values of pretreated straws, thus showing that the pretreatment efficiency can be rapidly estimated with Py-GC–MS in the tested conditions.

Effect of Ca(OH)2 pretreatment on extruded rice straw anaerobic digestion

It has been proven that extrusion can change the structure of rice straw and increase biogas production, but the effect of a single pretreatment is limited. Ca(OH)2 pretreatment was used to enhance the enzyme hydrolysis and biogas production of extruded rice straw. After Ca(OH)2 pretreatment, the glucose and xylose conversion rates in enzymatic hydrolysis increased from 36.0% and 22.4% to 66.8% and 50.2%, respectively. The highest biogas production observed in 8% and 10% Ca(OH)2 pretreated rice straw reached 564.7mL/g VS and 574.5mL/g VS, respectively, which are 34.3% and 36.7% higher than the non-Ca(OH)2-loaded sample. The Ca(OH)2 pretreatment can effectively remove the lignin and increase the fermentable sugar content. The structural changes in the extruded rice straw have also been analyzed by XRD, FTIR, and SEM. Considering all of the results, an 8% Ca(OH)2 loading rate is the best option for the pretreatment of extruded rice straw.

Effect of inoculum sources on the anaerobic digestion of rice straw

The aim of this study was to evaluate the effect of different inoculum sources on the rice straw anaerobic digestion. Six different digestates (DM, SM, CM, MS, AGS and PS) were applied as inoculums and their effects were evaluated in batch reactors. The results indicated that digested manures were more suitable than sludge. Reactors inoculated with digested manures achieved higher, biogas production and lignocellulose degradation. The better adaptability of digested manures had relationship with its higher cellulase and xylanase activities and sufficient nutrients content. DM had the best effect among all three digested manures. Reactors inoculated with DM achieved the highest biogas production (325.3 mL/g VS) and enzymes activities. The synergism between cellulase and xylanase activities played an important role in lignocellulose degradation.

Improving the Mixing Performances of Rice Straw Anaerobic Digestion for Higher Biogas Production by Computational Fluid Dynamics (CFD) Simulation

As a lignocellulose-based substrate for anaerobic digestion, rice straw is characterized by low density, high water absorbability, and poor fluidity. Its mixing performances in digestion are completely different from traditional substrates such as animal manures. Computational fluid dynamics (CFD) simulation was employed to investigate mixing performances and determine suitable stirring parameters for efficient biogas production from rice straw. The results from CFD simulation were applied in the anaerobic digestion tests to further investigate their reliability. The results indicated that the mixing performances could be improved by triple impellers with pitched blade, and complete mixing was easily achieved at the stirring rate of 80 rpm, as compared to 20-60 rpm. However, mixing could not be significantly improved when the stirring rate was further increased from 80 to 160 rpm. The simulation results agreed well with the experimental results. The determined mixing parameters could achieve the highest biogas yield of 370 mL (g TS)(-1) (729 mL (g TS(digested))(-1)) and 431 mL (g TS)(-1) (632 mL (g TS(digested))(-1)) with the shortest technical digestion time (T 80) of 46 days. The results obtained in this work could provide useful guides for the design and operation of biogas plants using rice straw as substrates.