Anaerobic Digestion Of Corn Straw Research Articles

Enhancement of Anaerobic Digestion of Corn Straw: Effect of Biological Pretreatment and Heating with Bio-Heat Recovery from Pretreatment

Biological pretreatment can promote the degradation of biomass and enhance methane production via the subsequent anaerobic digestion. In addition, a large amount of bio-heat can be generated during the pretreatment process to provide heat for the anaerobic digestion process. In this study, composite microorganisms were employed for pretreating corn straw. The impact of different pretreatment times and the heat generated by the pretreatment process on subsequent anaerobic digestion were studied. The results show that the maximum temperature of the pretreatment process was 56.2 °C, obtained on day 6. After 14 days of pretreatment, the degradation rate of the pretreatment group increased by 41% compared with the control group. As a consequence, straws with different pretreatment times were used for anaerobic digestion. The group that underwent 6 days of pretreatment and utilized bio-heat generated from pretreatment achieved the highest cumulative methane production of 401.58 mL/g VS, which was 60.13% higher than in the control group without pretreatment. After 6 days of composite microorganism pretreatment, the group that utilized bio-heat achieved a 29.08% increase in cumulative methane production compared to the group that did not utilize bio-heat. In conclusion, this study highlights the potential of biological pretreatment with composite microorganisms followed by anaerobic digestion using bio-heat as an effective method for treating corn straw.

Green and chemical-free pretreatment of corn straw using cold isostatic pressure for methane production

In this study, the effect of cold isostatic pressure (CIP) pretreatment on the physicochemical properties and subsequent anaerobic digestion (AD) performance of corn straw (CS) was explored. The CS was subjected to CIP pretreatment by pressures of 200, 400 and 600 MPa, respectively, while AD was carried out at medium temperature (35 ± 2 °C). The results showed that CIP pretreatment disrupted the dense structure of the CS and altered the crystallinity index and surface hydrophobicity of the CS, thereby affecting the AD process. The presence of CIP pretreatment increased the initial reducing sugar concentration by 0.11–0.27 g/L and increased the maximum volatile fatty acids content by 112.82–436.64 mg/L, which facilitated the process of acidification and hydrolysis of the AD. It was also observed that the CIP pretreatment maintained the pH in the range of 6.37–7.30, maintaining the stability of the overall system. Moreover, the cumulative methane production in the CIP pretreatment group increased by 27.17 %–64.90 % compared to the control group. Analysis of the microbial results showed that CIP pretreatment increased the abundance of cellulose degrading bacteria Ruminofilibacter from 21.50 % to 27.53 % and acetoclastic methanogen Methanosaeta from 45.48 % to 56.92 %, thus facilitating the hydrolysis and methanogenic stages. The energy conversion analysis showed that CIP is a green and non-polluting pretreatment strategy for the efficient AD of CS to methane.

Positive effect of antibiotics on methane production from corn straw

Anaerobic digestion (AD) of corn straw (CS) inoculated with waste sewage sludge (WSS) is a promising approach for energy utilization of both lignocellulosic wastes and WSS. However, few studies about the effect of antibiotics contained in WSS on AD of CS are reported, which hinders the efficient conversion from CS to methane (CH4). Antibiotics including tetracycline (TC) and azithromycin (AZM) were used to evaluate their effects on AD of CS inoculated with WSS in this study. As results, the reactor with AZM addition achieved 167.67 mL/g VS CH4 yield, which was increased 65.22% compared with CTRL (without any antibiotics addition, 101.48 mL/g VS CH4 yield) by playing roles at the hydrolysis, acidogenesis/acetogenesis and methanogenesis stages during 20 days of AD. Similarly, addition of TC performed 25.38% (127.27 mL/g VS) higher CH4 yield than CTRL mainly by promoting the acidogenesis/acetogenesis and methanogenesis stages. Specifically, phyla Bacteroidetes, Actinobacteria and genera Methanosarcina, Methanobrevibacter were considered as functional microorganisms for AD of CS with AZM addition. Results from this study provide a new insight for enhancing CH4 yield from CS.

Effects of biogas slurry reflux mode and reflux rate on methane production by mixed anaerobic digestion of corn straw and pig manure

Biogas slurry reflux is a promising method to realize biogas slurry reduction and improve biogas production performance of anaerobic digestion. The purpose of this study was to investigate the effects of reflux mode and reflux ratio on mixed anaerobic digestion of corn straw and pig manure to obtain the best biogas slurry reflux process. The influence of reflux mode and reflux ratio on the internal environment during anaerobic digestion were clarified by kinetic analysis. The results showed that compared with the control group, the degree of substrate hydrolysis in the hydrolysis phase reflux (HPR) and two-phase synergistic reflux (TPSR) treatment groups increased, and the initial concentration and peak value of volatile fatty acids (VFAs) increased by 20.35%–85.81% and 24.72%–74.37%, respectively. The modified Gompertz model fitting results that the three biogas slurry reflux modes all significantly shortened the lag period of anaerobic digestion (17.29%–48.32%) and increased the peak gas production (7.54%–88.07%). And the maximum daily gas production (65.82 mL/(g VS∙d)), methane production (422.86 mL/g VS) and biodegradation rate (83.65%) were obtained under the TPSR mode with reflux ratios of 75% and 100%. This study provides a theoretical basis for the development of biogas slurry reflux technology in the mixed anaerobic digestion of corn straw and pig manure, and realizes the reduction and resource utilization of biogas slurry.

Simultaneous addition of CO2-nanobubble water and iron nanoparticles to enhance methane production from anaerobic digestion of corn straw

In this research, CO2-nanobubble water (CO2-NBW) and iron nanoparticles (Fe0NPs) were added simultaneously to exploit individual advantages to enhance the methanogenesis process from both the stability of anaerobic digestion (AD) system and the activity of anaerobic microorganism aspects. Results showed that the AD performance was enhanced by supplementing with CO2-NBW or Fe0NPs individually, and could be further improved by simultaneous addition of the two additives. The maximum methane yield was achieved in the CO2-NBW + Fe0NPs reactor (141.99 mL/g-VSadded), which increased by 26.16% compared to the control group. Similarly, the activities of the electron transfer system (ETS) and enzyme were improved. The results of microbial community structure revealed that the addition of CO2-NBW and Fe0NPs could improve the abundance of dominant bacteria (Anaerolineaceae, Bacteroidales, and Prolixibacteraceae) and archaea (Methanotrichaceae and Methanospirillaceae). Additionally, the functional metabolic prediction heatmap indicated that metabolic functional genes favorable for AD of corn straw were enhanced.

Supplementation of CO2-nanobubble water to enhance the methane production from anaerobic digestion of corn straw

Nanobubble water (NBW) could improve methane production from anaerobic digestion (AD) of corn straw without secondary contamination. In this study, the effect of carbon dioxide nanobubble water (CO2-NBW) volumes (0%, 25%, 50%, 75%, 100%) on methane production from corn straw was investigated. The results showed that addition of CO2-NBW could improve methane production and promote substrate degradation in AD process. The highest cumulative methane production of 132.16 mL g−1VSadded was obtained in the 100% CO2-NBW added reactor, which was 17% higher than that in the control group. Additionally, the addition of CO2-NBW could mitigate the sharp decrease in pH by acting as a buffer. CO2-NBW could also enhance microorganism activity throughout the AD process. The electron transport system (ETS) activity was increased by 23%, while the β-glucosidase, dehydrogenase (DHA), and coenzyme F420 activities were increased by 15%, 23%, and 11%, respectively, at optimum addition of CO2-NBW. Meanwhile, addition of CO2-NBW accelerated the production and consumption of reducing sugar and volatile fatty acids (VFAs), promoting the reduction rates of TS (Total solid) and VS (Volatile solid).

Use of nanobubble water bioaugmented anaerobically digested sludge for high-efficacy energy production from high-solids anaerobic digestion of corn straw

An increasing attention has been paid to the secure and sustainable management of agricultural wastes, especially lignocellulosic biomass. Nanobubble water (NBW) contains 106–108 bubbles/mL with diameter <1000 nm. Although previous studies have examined the enhancement effects of NBW on methane production from organic solid wastes, the NBW-based anaerobic digestion (AD) system is still restrained from practical application due to the large increase in AD reactor volume, generation of wastewater, and increase in energy consumption as well. In this study, NBW bioaugmentation of anaerobically digested sludge for the first time was performed for high-solids AD of corn straw. Results show that cellulase, xylanases and lignin peroxidase activities were increased by 2–55% during the NBW bioaugmentation process. Significant enrichment of hydrolytic/acidogenic bacteria and methanogenic archaea were noticed in the NBW bioaugmented sludge. This study clearly demonstrated 47% increase in methane production from high-solids AD of corn straw when O2-NBW bioaugmented sludge was applied, achieving a net energy gain of 5138 MJ/t-volatile solids of corn straw with an energy recovery of 34%. The NBW-based high-solids AD system can provide a novel and sustainable management solution for renewable energy production from agricultural wastes, targeting the reduction of environmental pollution and energy crisis.

The effects of micro-aeration on semi-continued anaerobic digestion of corn straw with increasing organic loading rates

The benefits of micro-aeration on batch anaerobic digestion (AD) of organic wastes have been intensively studied. However, the effects of micro-aeration on the semi-continued AD under different organic loading rates (OLRs) were still lacking. This study investigated the effects of micro-aeration on semi-continued AD of corn straw with increasing OLRs from 1.1 to 2.1 volatile solid (VS)/(L·day). Results showed micro-aeration could benefit the AD process by increasing the median daily methane yields for 6%, 10% and 8% at OLRs of 1.1, 1.5 and 2.1 VS/(L·day), respectively. Moreover, micro-aeration stimulated the growth of facultative bacteria (Clostridia), which secreted more critical enzymes (e.g., cellulase and xylanase) and led faster degradation of corn straw as well as higher soluble humic acids (SHAs) concentration. The SHAs might act as electron shuttle to facilitate the direct interspecies electron transfer (DIET) among syntrophic bacteria (Cloacimonadia) and hydrogenotrophic methanogens (Methanobacterium), which led to a faster volatile fatty acids (VFAs) conversion into methane. This study confirmed the beneficial effects of micro-aeration on the semi-continued AD at different OLRs and unraveled the mechanisms behind.

Understanding the mechanisms behind enhanced anaerobic digestion of corn straw by humic acids

Humic acids (HAs) are abundant on earth, yet their effects on anaerobic digestion (AD) of cellulosic substrate are not fully uncovered. The effects of HAs on AD of corn straw and the mechanisms behind were analyzed in this study. Results showed that the effects of HAs on methane yield were closely related to the total solids (TS) content. At relative high TS content of 5.0%, HAs benefited AD process by increasing 13.8% of methane yield, accelerating methane production rate by 43% and shortening lag phase time by 37.5%. Microbial community analysis indicated that HAs increased the relative abundance of syntrophic bacteria (Syntrophomonadaceae and Synergistaceae), facilitating the degradation of volatile fatty acids. HAs might act as electron shuttles to directly transfer electrons to hydrogenotrophic methanogens for CO2 reduction to CH4. This study provides a simple and efficient strategy to facilitate the AD of cellulosic substrate by HAs addition.

Effect of Pretreatment by Freeze Vacuum Drying on Solid-State Anaerobic Digestion of Corn Straw

As a common agricultural waste, corn straw (CS) has a refractory structure, which is not conducive to anaerobic digestion (AD). Appropriate pretreatment is crucial for addressing this problem. Thus, freeze vacuum drying (FVD) was proposed. In this study, fresh CS (F-CS) pretreated (5 h, −40 °C) by FVD and naturally dried CS (D-CS) were compared. Differences in substrate surface structure and nutrient composition were first investigated. Results show that a loose and porous structure, crystallinity, and broken chemical bonds, as well as higher proportions of VS, C, N, cellulose, hemicellulose, and crude proteins in F-CS show a potential for methane production. Besides, process performance and stability were also examined in both high (4, VS basis) and low (1, VS basis) S/I ratio AD. A higher degradation ratio of hemicellulose as well as richer dissolved microbial metabolites, coenzymes, tyrosine-like proteins, and hydrolysis rate of particulate organic matter in the F-CS system enhanced the efficiency of methane conversion. The cumulative methane yield increased from 169.66 (D-CS) to 209.97 (F-CS) mL/gVS in the high S/I ratio system (p = 0.02 &lt; 0.05), and 156.97 to 171.89 mL/gVS in the low S/I ratio system. Additionally, 16S-rRNA-gene-based analysis was performed. Interestingly, the coordination of key bacteria (Clostridium_sensu_stricto_1, Bacillus, Terrisporobacter, Clostridium_sensu_stricto_7, Thermoclostrium, UCG-012, and HN-HF0106) was more active. Poorer Methanosarcina and Methanomassiliicoccus as well as richer Methanobrevibacter and Methanoculleus stimulated the co-relationship of key archaea with diverse methanogenesis pathways. This study aims to verify the positive effect of FVD pretreatment on AD of CS, so as to provide a reference for applications in waste management.

Understanding the mechanisms behind micro-aeration to enhance anaerobic digestion of corn straw

Micro-aeration has been shown to be favorable for anaerobic digestion (AD) process. However, the underlying mechanisms are not fully revealed. In this study, the effects of micro-aeration on AD process were investigated, the underlying mechanisms were also explored by comprehensively analysis of the substrate degradation, intermediate products, electron-transfer capacity, key enzymes and microbial communities. Results showed micro-aeration could benefit the AD process, and the beneficial effects were oxygen intensity-dependent. Maximum methane yield (262.0 ± 6.0 mL/(g·VS)) was achieved at micro-aeration of 0.2 mL/(g·VS·day), which was 7.8% higher than that of the control (without micro-aeration). The volatile fatty acids concentration, cellulase activity, soluble humic acids (SHAs) concentration and substrate degradation rate were all enhanced under micro-aeration condition. Moreover, micro-aeration could regulate the bacterial and archaeal communities: bacterial diversities and relative abundances of facultative and acetate-oxidizing bacteria (e.g., Firmicutes, Synergistota and Spirochaetota) increased, leading to higher substrate utilization rate; archaeal diversities decreased while oxygen-tolerating methanogens (e.g., Methanobacterium) became dominant to promote the methanogenesis. AD system with micro-aeration showed higher electron-transfer capacity and better conductive environment due to the increased SHAs concentration. The increased relative abundance of direct-interspecies-electron-transfer (DIET)-associated microbes could be favorable to DIET-based syntrophic methanogenesis which promotes AD under micro-aeration.

Improving anaerobic digestion of corn straw by using solid-state urea pretreatment

The resistant structure and high carbon/nitrogen ratio (C/N) of cellulosic substrate are the barriers during their anaerobic digestion (AD). Solid-state urea pretreatment was developed in this study to pretreat corn straw and adjust C/N ratio simultaneously for the downstream AD of corn straw. Results showed solid-state urea pretreatment was efficient in lignin removal and achieved the highest lignin reduction of 7.06% with C/N ratio = 15 during pretreatment. Scanning electron microscopy demonstrated the destruction of the dense structure by pretreatment, which benefited to the hydrolysis of corn straw. The cumulative methane yields of the pretreated corn straw ranged from 234.07 to 250.03 mL/g VS, which were obviously higher than that of the untreated corn straw. The maximum methane yield of 250.03 mL/g VS was achieved with C/N = 15 during pretreatment, which was 23.91% higher than that of the untreated group. In addition, AD digestates from the pretreated groups had 9.62% higher nutrients than that from the untreated group. The solid-state urea pretreatment can destroy the dense structure of corn straw and regulate the C/N ratio during AD, thus benefit the methane production and fertilizer use of the digestate, which is a potential choice during the AD of cellulosic substrate.

Enhancement of methane production by anaerobic digestion of corn straw with hydrogen-nanobubble water

Hydrogen-nanobubble water was proposed to enhance methane production by anaerobic digestion (AD) with corn straw. The effects of H2-nanobubble water (H2-NBW) amounts (0%, 20%, 40%, 60%, 80%, and 100%) on methane production characteristics of corn straw were explored. The results showed that the methane yields were increased by 11.54%∼25.29% compared with the control group(CK), and the maximum cumulative methane production reached to 254.36 mL·g-VS-1 when the H2-NBW addition was of 60%. Interestingly, the maximum methane concentration increased by 4.37% compared with CK. H2-NBW addition can destroy the cellulose structure of corn straw, reduce the crystallinity of cellulose, and promote the hydrolysis. The degradation rate of cellulose and hemicellulose were increased by 20%∼33% and 13% ∼25.7% respectively, and the removal rate of TS and VS were increased by 6.82%-27.93% and 8.52%-21.47%, respectively. The modified Gompertz equation fitted the cumulative methane production curves very well, with high correlation coefficients (R2 > 0.992).

Anaerobic digestion of corn straw pretreated by ultrasonic combined with aerobic hydrolysis

Corn straw (CS) was pretreated by ultrasonic combined aerobic with biogas slurry as medium for anaerobic digestion (AD), that strengthened the degradation efficiency CS, varied in the composition of digestion slurry, thereby the methane production was increased. Central combinatorial design (CCD) test was used to treat CS at ultrasonic power (200, 400, and 600 W), time (10, 20, and 30 min) and AD for 25 days, at 37 ± 1℃. According to data showed that the pH and volatile fatty acids (VFAs) affected methane production directly. With an ultrasonic power 309 W, time 26 min, it reached the maximum content of VFAs with 16.24 g/L, the cumulative methane production achieved the highest with 198.56 mL/g VS, which was 46.73% higher than unpretreated raw material as CK. Ultrasonic-aerobic hydrolysis pretreatment can obtain higher VFAs and methane production content in a short period of time that is great significance to biogas engineering.

Effect of combined addition amount of nano zero-valent iron and biochar on methane production by anaerobic digestion of corn straw

Effect of combined addition amount of nano zero-valent iron and biochar on methane production by anaerobic digestion of corn straw

The solid-state physicochemical properties and biogas production of the anaerobic digestion of corn straw pretreated by microwave irradiation.

The effect of different temperatures used in microwave pretreatment on enhancing methane production of corn straw was comparatively studied in this paper through the analysis of the physicochemical properties of the pretreated materials and the methane yield during anaerobic digestion. Analytic methods such as scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction were performed to detect the surface chemistry of the pretreated corn straw. The results indicated that microwave pretreatment could effectively disrupt the lignocellulosic structure to release cellulose, hemicellulose, and related derivatives and make them available for the process of anaerobic digestion. The outcome of the methanogenic assay demonstrated that methane production could be significantly improved by 73.08% concerning the variation of the temperatures in microwave pretreatment. This study provides technical support for pretreatment methods of lignocellulose materials and deems that microwave pretreatment boosts methane yield efficiently during the process of anaerobic digestion of lignocellulosic materials.

Thermophilic Solid-State Anaerobic Digestion of Corn Straw, Cattle Manure, and Vegetable Waste: Effect of Temperature, Total Solid Content, and C/N Ratio.

Thermophilic solid-state anaerobic digestion (SS-AD) of agricultural wastes, i.e., corn straw, cattle manure, and vegetable waste, was carried out in this study. The effects of temperature (40-60°C), initial solid content (ISC, 17.5-32.5%), and C/N ratio (15-32 : 1) on biogas production were evaluated using a Box-Behnken experimental design (BBD) combined with response surface methodology (RSM). The results showed that optimization of process parameters is important to promote the SS-AD performance. All the factors, including interactive terms (except the ISC), were significant in the quadratic model for biogas production with SS-AD. Among the three operation parameters, the C/N ratio had the largest effect on biogas production, followed by temperature, and a maximum biogas yield of 241.4 mL gVS−1 could be achieved at 47.3°C, ISC = 24.81%, and C/N = 22.35. After 20 d of SS-AD, the microbial community structure under different conditions was characterized by high-throughput sequencing, showing that Firmicutes, Bacteroidetes, Chloroflexi, Synergistetes, and Proteobacteria dominated the bacterial community, and that Firmicutes had a competitive advantage over Bacteroidetes at elevated temperatures. The biogas production values and relative abundance of OPB54 and Bacteroidia after 20 d of SS-AD can be fitted well using a quadratic model, implying that OPB54 and Bacteroidia play important roles in the methanogenic metabolism for agricultural waste thermophilic SS-AD.

Effect of liquid digestate recirculation on biogas production and enzyme activities for anaerobic digestion of corn straw

To accelerate the degradation of substrate, 50% liquid digestate recirculation (LDR) was used in the anaerobic digestion (AD) of corn straw. The effects of recirculation on the enzyme activities and biogas production were investigated by comparing with control reactor (ReactorCK). During the AD process, the fermentation system with 50% LDR was more stable. The average biogas and methane production in ReactorLDR were 7,891 mL·d-1 and 347 mL CH4·g-1 VSadded·d-1 respectively. The total volatile fatty acids (TVFAs) concentration in the two reactors both increased at first and then decreased with time. The LDR made the VFAs accumulation significant, especially propionic acid accumulation in 4 ∼ 16 days. The maximum peak value of cellulase, xylanase, dehydrogenase and coenzyme F420 activities in ReactorLDR were 0.51 mg·g-1·h-1, 0.29 mg·g-1·h-1, 4.88 mL·g-1·h-1 and 6.69 μmol·L-1, respectively, which were higher than that in ReactorCK. With or without recirculation, the concentration of TVFAs was positively correlated with cellulase, xylanase and dehydrogenase activities, while was negatively correlated with coenzyme F420 activity. Besides, a very significant correlation existed between hydrolase and dehydrogenase activities and daily biogas production in ReactorCK. And the peaks of cellulase, xylanase and dehydrogenase activities appeared ahead of the peak of daily biogas production with the LDR.

Impacts of Cellulase and Amylase on Enzymatic Hydrolysis and Methane Production in the Anaerobic Digestion of Corn Straw

The impacts of enzyme pre-treatments on anaerobic digestion of lignocellulosic biomass were explored by using corn straw as a substrate for enzyme pre-treatment and anaerobic digestion and by utilizing starch and microcrystalline cellulose as substrates for comparative analysis. The cellulase pre-treatment effectively improved the enzymatic hydrolysis of cellulose, decreased the crystallinity, and consequently showed 33.2% increase in methane yield. The methane yield of starch increased by 16.0% through amylase pre-treatment. However, when the substrate was corn straw, both the efficiencies of enzymes and methane production were markedly reduced by the lignocellulosic structure. The corn straw’s methane yields were 277.6 and 242.4 mL·CH4/g·VS with cellulase and amylase pre-treatment, respectively, which was 11.7% and 27.9% higher than that of the untreated corn straw. It may imply that the lignocellulose should be broken up firstly, enzyme pre-treatments could have great potentials when combined with other methods.

Enhancing energy recovery from corn straw via two-stage anaerobic digestion with stepwise microaerobic hydrogen fermentation and methanogenesis

Abstract Anaerobic digestion (AD) technology attracts increasing concerns for organic waste disposal, renewable energy production as well as organic fertilizer preparation. However, the AD of cellulosic substrate is limited by low efficiency. Microaeration has recently been used to improve the AD efficiency. However, the inhibition of methanogenesis by microaeration limited its application. To enhance the energy recovery from AD of corn straw and avoid the inhibition of microaeration on methanogenesis, two-stage AD including microaerobic hydrogen fermentation (stage I) and methanogenesis (stage II) was investigated. Results showed microaeration had beneficial effects on hydrogen fermentation, methane production and energy recovery depending on the oxygen loading level. At the optimized initial pH of 7.5 for hydrogen production, microaerobic hydrogen fermentation achieved the maximum hydrogen yield of 24.3 mL/g VS (volatile solid, 37 °C and normal pressure) with the oxygen loading of 5 mL/g VS, which was 70% higher than that without microaeration. Overall, the two-stage AD performed better in methane yield and energy recovery than one-stage AD. When the oxygen loading during hydrogen fermentation was 10 mL/g VS of corn straw, the maximum total energy recovery of 10.6 kJ/g VS was obtained, which was 18% higher than that of one-stage AD. The two-stage AD consisting of microaerobic hydrogen fermentation (stage I) and methanogenesis (stage II) is a promising way to enhance the energy recovery from AD of cellulosic substrates like corn straw.