Alkaline hydrogen peroxide pretreatment of energy crops for biogas production

In this study, the influence of alkaline hydrogen peroxide (H₂O₂) pretreatment of the three different plant sources: Miscanthus giganteus, Sorghum Moench, and Sida hermaphrodita, for biogas production was investigated. The influence of temperature, reaction time, and H₂O₂ concentration on the efficiency of biomass degradation and on the further methanogenic fermentation were studied. The results obtained after chemical pretreatment indicate that using H₂O₂ at alkaline conditions leads to the decomposition of three major structures: lignin, hemicellulose, and cellulose. The best results were achieved for the process performed at 25°C for 24 h with the use of a 5 mass % H₂O₂ solution. Although the degradation level was very high for all three plant sources, the biogas production from the energy crops pretreated chemically was strongly inhibited by byproducts and the residual oxygen formed after H₂O₂ decomposition. This fact indicates that alkaline H₂O₂ pretreatment is a very promising method for plant material degradation for further biogas production, but pretreated biomass must be separated from supernatant before the fermentation process because of the high concentration of inhibitors in the hydrolysates. The best results were obtained for Sida with biogas and methane production of 2.29 Ndm³ and 1.06 Ndm³, respectively.     

Integrated Process for Ethanol,Biogas, and Edible Filamentous Fungi-Based Animal Feed Production from Dilute Phosphoric Acid-Pretreated Wheat Straw

Integration of wheat straw for a biorefinery-based energy generation process by producing ethanol and biogas together with the production of high-protein fungal biomass (suitable for feed application) was the main focus of the present study. An edible ascomycete fungal strain Neurospora intermedia was used for the ethanol fermentation and subsequent biomass production from dilute phosphoric acid (0.7 to 1.2% w/v) pretreated wheat straw. At optimum pretreatment conditions, an ethanol yield of 84 to 90% of the theoretical maximum, based on glucan content of substrate straw, was observed from fungal fermentation post the enzymatic hydrolysis process. The biogas production from the pretreated straw slurry showed an improved methane yield potential up to 162% increase, as compared to that of the untreated straw. Additional biogas production, using the syrup, a waste stream obtained post the ethanol fermentation, resulted in a combined total energy output of 15.8 MJ/kg wheat straw. Moreover, using thin stillage (a waste stream from the first-generation wheat-based ethanol process) as a co-substrate to the biogas process resulted in an additional increase by about 14 to 27% in the total energy output as compared to using only wheat straw-based substrates.

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Biogas Production Potential and Kinetics of Microwave and Conventional Thermal Pretreatment of Grass

Pretreatment methods play an important role in the improvement of biogas production from the anaerobic digestion of energy grass. In this study, conventional thermal and microwave methods were performed on raw material, namely, Pennisetum hybrid, to analyze the effect of pretreatment on anaerobic digestion by the calculation of performance parameters using Logistic function, modified Gompertz equation, and transference function. Results indicated that thermal pretreatment improved the biogas production of Pennisetum hybrid, whereas microwave method had an adverse effect on the performance. All the models fit the experimental data with R ² > 0.980, and the Reaction Curve presented the best agreement in the fitting process. Conventional thermal pretreatment showed an increasing effect on maximum production rate and total methane produced, with an improvement of around 7% and 8%, respectively. With regard to microwave pretreatment, maximum production rate and total methane produced decreased by 18% and 12%, respectively.     

Physical Pretreatment Methods for Improving Microalgae Anaerobic Biodegradability

Microalgae may be a potential feedstock for biogas production through anaerobic digestion. However, this process is limited by the hydrolytic stage, due to the complex and resistant microalgae cell wall components. This fact hinders biomass conversion into biogas, demanding the application of pretreatment techniques for inducing cell damage and/or lysis and organic matter solubilisation. In this study, sonication, thermal, ultrasound, homogeneizer, hydrothermal and steam explosion pretreatments were evaluated in different conditions for comparing their effects on anaerobic digestion performance in batch reactors. The results showed that the highest biomass solubilisation values were reached for steam explosion (65–73%) and ultrasound (33–57%). In fact, only applied energies higher than 220 W or temperatures higher than 80 °C induced cell wall lysis in C. sorokiniana. Nonetheless, the highest methane yields were not correlated to biogas production. Thermal hydrolysis and steam explosion showed lower methane yields in respect to non-pretreated biomass, suggesting the presence of toxic compounds that inhibited the biological process. Accordingly, these pretreatment techniques led to a negative energy balance. The best pretreatment method among the ones evaluated was thermal pretreatment, with four times more energy produced that demanded.     

Direct and selective methanation of biomass via oxygenvacancy‐mediated catalysis

正Producing biofuels from renewable biomass resources is considered to be an effective way to reduce carbon emissions and is helpful for establishing sustainable society [1]. Bio‐methane (CH4) is a promising and available clean energy in the future owing to its properties such as high calorific values, low carbon emissions and full miscibility and interchangeability with natural gas or shale gas. Therefore, the production of me‐thane directly from waste biomass resources like straw is highly attractive. However, because of the robustness and vari‐ety of C–C bonds and C–O bonds existing in biomass molecules,it is very difficult to achieve high‐selective methanation of bio‐     

Fungal Pretreatment by Phanerochaete chrysosporium for Enhancement of Biogas Production from Corn Stover Silage

Corn stover silage (CSS) was pretreated by Phanerochaete chrysosporium in solid-state fermentation (SSF), to enhance methane production via subsequent anaerobic digestion (AD). Effects of washing of corn stover silage (WCSS) on the lignocellulosic biodegradability in the fungal pretreatment step and on methane production in the AD step were investigated with comparison to the CSS. It was found that P. chrysosporium had the degradation of cellulose, hemicellulose, and lignin of CSS up to 19.9, 32.4, and 22.6 %, respectively. Consequently, CSS pretreated by 25 days achieved the highest methane yield of 265.1 mL/g volatile solid (VS), which was 23.0 % higher than the untreated CSS. However, the degradation of cellulose, hemicellulose, and lignin in WCSS after 30 days of SSF increased to 45.9, 48.4, and 39.0 %, respectively. Surface morphology and Fourier-transform infrared spectroscopy analyses also demonstrated that the WCSS improved degradation of cell wall components during SSF. Correspondingly, the pretreatment of WCSS improved methane production by 19.6 to 32.6 %, as compared with untreated CSS. Hence, washing and reducing organic acids (such as lactic acid, acetic acid, propionic acid, and butyric acid) present in CSS has been proven to further improve biodegradability in SSF and methane production in the AD step.     

Effect of rapid batch decompression on hydrolysate quality after hydrothermal pretreatment of wheat straw

The subject of this paper was to study the effect of rapid batch decompression on hydrolysate quality and on biogas yield after the hydrothermal pretreatment of wheat straw. An aqueous batch containing 5 mass % total solids of wheat straw was thermally and thermally-expansionary treated in parallel at the process temperature of 170–200°C and the residence time of 0–60 min. An analysis of the thermal and thermal-expansionary hydrolysate provided identical results in the dependences and values of chemical oxygen demand, acidities, and glucose yields of both treatments based on severity factors including the combined effects of temperature and residence time. Increases in the methane content of 33 % for thermally and of 34 % for thermally-expansionary treated wheat straw were reached in comparison to the methane yield from an untreated sample. This means that the polysaccharide cell wall was dissolved because of the high process temperature and residence time. From this it follows that all its nutrients were subsequently washed out of the cell into liquid where they caused changes in its chemical oxygen demand, glucose content, and acidities. There was therefore no rapid decompression effect on the hydrothermally treated wheat straw.     

In situ Removal of Hydrogen Sulfide During Biogas Fermentation at Microaerobic Condition

In this paper, rice straw was used as a raw material to produce biogas by anaerobic batch fermentation at 35 °C (mesophilic) or 55 °C (thermophilic). The hydrogen sulfide in biogas can be converted to S⁰ or sulfate and removed in-situ under micro-oxygen environment. Trace oxygen was conducted to the anaerobic fermentation tank in amount of 0.5, 1.0, 2.0, 3.0, 4.0, 5.0, or 10.0 times stoichiometric equivalence, respectively, and the control experiment without oxygen addition was carried out. The results showed that the initial H₂S concentrations of biogas are about 3235?±?185 mg/m³ (mesophilic) or 3394?±?126 mg/m³ (thermophilic), respectively. The desulfurization efficiency is 72.3 % (mesophilic) or 65.6 % (thermophilic), respectively, with oxygen addition by stoichiometric relation. When the oxygen feeded in amount of 2～4 times, theoretical quantity demanded the removal efficiency of hydrogen sulfide could be over 92 %, and the oxygen residue in biogas could be maintained less than 0.5 %, which fit the requirement of biogas used as vehicle fuel or combined to the grid. Though further more oxygen addition could promote the removal efficiency of hydrogen sulfide (about 93.6 %), the oxygen residue in biogas would be higher than the application limit concentration (0.5 %). Whether mesophilic or thermophilic fermentation with the extra addition of oxygen, there were no obvious changes in the gas production and methane concentration. In conclusion, in-situ desulfurization can be achieved in the anaerobic methane fermentation system under micro-oxygen environment. In addition, air could be used as a substitute oxygen resource on the situation without strict demand for the methane content of biogas.     

Anaerobic bioconversion of municipal solid wastes using a novel high-solids reactor design

Novel, laboratory-scale, high-solids reactors operated under mesophilic conditions were used to study the anaerobic fermentation of processed municipal solid waste (MSW) to methane. Product gas rate data were determined for organic loading rates ranging from 2.99–18.46 g of volatile solids (VS) per liter (L) per day (d). The data represent the anaerobic fermentation at high-solids levels within the reactor of 21–32%, while feeding a refuse-derived fuel (RDF)/MSW feedstock supplemented with a vitamin/mineral/nutrient solution. The average biogas yield was 0.59 L biogas/g VS added to the reactor system/d. The average methane composition of the biogas produced was 57.2%. The data indicate a linear relationship of increasing total biogas production with increasing organic loading rate to the process. The maximum organic loading rate obtainable with high-solids anaerobic digestion is in the range of 18–20 g VS/L·d to obtain 80% or greater bioconversion for the RDF/MSW feedstock. This loading rate is approximately four to six times greater than that which can be obtained with comparable low-solids anaerobic bioreactor technology.     

Plasma-Assisted Pretreatment of Wheat Straw for Ethanol Production

The potential of wheat straw for ethanol production after pretreatment with O(3) generated in a plasma at atmospheric pressure and room temperature followed by fermentation was investigated. We found that cellulose and hemicellulose remained unaltered after ozonisation and a subsequent washing step, while lignin was degraded up to 95% by O(3). The loss of biomass after washing could be explained by the amount of lignin degraded. The washing water of pretreated samples (0-7 h) was analyzed for potential fermentation inhibitors. Approximately 30 lignin degradation products and a number of simple carboxylic acids and phenolic compounds were found, e.g., vanillic acid, acetic acid, and formic acid. Some components had the highest concentration at the beginning of the ozonisation process (0.5, 1 h), e.g., 4-hydroxybenzladehyde, while the concentration of others increased during the entire pretreatment (0-7 h), e.g., oxalic acid and acetovanillon. Interestingly, washing had no effect on the ethanol production with pretreatment times up to 1 h. Washing improved the glucose availability with pretreatment times of more than 2 h. One hour of ozonisation was found to be optimal for the use of washed and unwashed wheat straw for ethanol production (maximum ethanol yield, 52%). O(3) cost estimations were made for the production of ethanol at standard conditions.     

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.     

Synergistic Effects of Magnetic Nanomaterials on Post-Digestate for Biogas Production

Digestate is characterized by high water content, and in the water and wastewater treatment settings, necessitates both large storage capacities and a high cost of disposal. By seeding digestate with four magnetic nanoparticles (MNPs), this study aimed to recover biogas and boost its methane potential anaerobically. This was carried out via biochemical methane potential (BMP) tests with five 1 L bioreactors, with a working volume of 80% and 20% head space. These were operated under anaerobic conditions at a temperature 40 °C for a 30 d incubation period. The SEM/EDX results revealed that the morphological surface area of the digestate with the MNPs increased as compared to its raw state. Comparatively, the degree of degradation of the bioreactors with MNPs resulted in over 75% decontamination (COD, color, and turbidity) as compared to the control system result of 60% without MNPs. The highest biogas production (400 mL/day) and methane yield (100% CH₄) was attained with 2 g of Fe₂O₄-TiO₂ MNPs as compared to the control biogas production (350 mL/day) and methane yield (65% CH₄). Economically, the highest energy balance achieved was estimated as 320.49 ZAR/kWh, or 22.89 USD/kWh in annual energy savings for this same system. These findings demonstrate that digestate seeded with MNPs has great potential to improve decontamination efficiency, biogas production and circular economy in wastewater management.     

Alkali pre-treatment of Sorghum Moench for biogas production

This work studies the influence of the alkali pre-treatment of Sorghum Moench — a representative of energy crops used in biogas production. Solutions containing various concentrations of sodium hydroxide were used to achieve the highest degradation of lignocellulosic structures. The results obtained after chemical pre-treatment indicate that the use of NaOH leads to the removal of almost all lignin (over 99 % in the case of 5 mass % NaOH) from the biomass, which is a prerequisite for efficient anaerobic digestion. Several parameters, such as chemical oxygen demand, total organic carbon, total phenolic content, volatile fatty acids, and general nitrogen were determined in the hydrolysates thus obtained in order to define the most favourable conditions. The best results were obtained for the Sorghum treated with 5 mass % NaOH at 121°C for 30 min The hydrolysate thus achieved consisted of high total phenolic compounds concentration (ca. 4.7 g L^?1) and chemical oxygen demand value (ca. 45 g L^?1). Although single alkali hydrolysis causes total degradation of glucose, a combined chemical and enzymatic pre-treatment of Sorghum leads to the release of large amounts of this monosaccharide into the supernatant. This indicates that alkali pre-treatment does not lead to complete cellulose destruction. The high degradation of lignin structure in the first step of the pre-treatment rendered the remainder of the biomass available for enzymatic action. A comparison of the efficiency of biogas production from untreated Sorghum and Sorghum treated with the use of NaOH and enzymes shows that chemical hydrolysis improves the anaerobic digestion effectiveness and the combined pre-treatment could have great potential for methane generation.     

Pretreatment of Chicken Feather Waste for Improved Biogas Production

This study deals with the utilization of chicken feather waste as a substrate for anaerobic digestion and improving biogas production by degradation of the compact structure of the feather keratin. In order to increase the digestibility of the feather, different pretreatments were investigated, including thermal pretreatment at 120 °C for 10 min, enzymatic hydrolysis with an alkaline endopeptidase [0.53–2.66 mL/g volatile solids (VS) feathers] for 0, 2, or 24 h at 55 °C, as well as a combination of these pretreatments. The effects of the treatments were then evaluated by anaerobic batch digestion assays at 55 °C. The enzymatic pretreatment increased the methane yield to 0.40 Nm³/kg VS_added, which is 122 % improvement compared to the yield of the untreated feathers. The other treatment conditions were less effective, increasing the methane yield by 11–50 %. The long-term effects of anaerobic digestion of feathers were examined by co-digestion of the feather with organic fraction of municipal solid waste performed with and without the addition of enzyme. When enzyme was added together with the feed, CH₄ yield of 0.485 Nm³/kg VS^?1 d^?1 was achieved together with a stable reactor performance, while in the control reactor, a decrease in methane production, together with accumulation of undegraded feather, was observed.     

Degradation of furfural (2- furaldehyde) to methane and carbon dioxide by an anaerobic consortium

Furfural, a byproduct formed during the thermal/chemical pre-treatment of hemicellulosic biomass, was degraded to methane and carbon dioxide under anaerobic conditions. The consortium of anaerobic microbes responsible for the degradation was enriched using small continuously stirred tank reactor (CSTR) systems with daily batch feeding of biomass pretreatment liquor and continuous addition of furfural. Although the continuous infusion of furfural was initially inhibitory to the anaerobic CSTR system, adaptation of the consortium occurred rapidly with high rates of furfural addition. Addition rates of 7.35 mg furfural/700-mL reactor/d resulted in biogas productions of 375%, of that produced in control CSTR systems, fed the biomass pretreatment liquor only. The anaerobic CSTR system fed high levels of furfural was stable, with a sludge pH of 7.1 and methane gas composition of 69%, compared to the control CSTR, which had a pH of 7.2 and 77% methane. CSTR systems in which furfural was continuously added resulted in 80% of the theoretically expected biogas. Intermediates in the anaerobic biodegradation of furfural were determined by spike additions in serum-bottle assays using the enriched consortium from the CSTR systems. Furfural was converted to several intermediates, including furfuryl alcohol, furoic acid, and acetic acid, before final conversion to methane and carbon dioxide.     

脱油芝麻饼厌氧发酵生物制氢

在批式厌氧反应器中,以厌氧消化污泥作为天然产氢菌源,通过脱油芝麻饼的厌氧发酵生产氢气.考察了菌种来源、培养时间和发酵反应温度对芝麻饼产氢能力的影响以及生物氢发酵过程中液相组成的变化.在实验条件下,脱油芝麻饼的最大产氢量为24.1mL/g,生物气中氢气的最大体积分数为66.1%,生物气中没有检测到甲烷气体.     

Biogas Production from N-Methylmorpholine-N-oxide (NMMO) Pretreated Forest Residues

Lignocellulosic biomass represents a great potential for biogas production. However, a suitable pretreatment is needed to improve their digestibility. This study investigates the effects of an organic solvent, N-Methylmorpholine-N-oxide (NMMO) at temperatures of 120 and 90 °C, NMMO concentrations of 75 and 85 % and treatment times of 3 and 15 h on the methane yield. The long-term effects of the treatment were determined by a semicontinuous experiment. The best results were obtained using 75 % NMMO at 120 °C for 15 h, resulting in 141 % increase in the methane production. These conditions led to a decrease by 9 % and an increase by 8 % in the lignin and in the carbohydrate content, respectively. During the continuous digestion experiments, a specific biogas production rate of 92 NmL/gVS/day was achieved while the corresponding rate from the untreated sample was 53 NmL/gVS/day. The operation conditions were set at 4.4 gVS/L/day organic loading rate (OLR) and hydraulic retention time (HRT) of 20 days in both cases. NMMO pretreatment has substantially improved the digestibility of forest residues. The present study shows the possibilities of this pretreatment method; however, an economic and technical assessment of its industrial use needs to be performed in the future.     

Microbial Pretreatment of Corn Stovers by Solid-State Cultivation of Phanerochaete chrysosporium for Biogas Production

The microbial pretreatment of corn stover and corn stover silage was achieved via the solid-state cultivation of Phanerochaete chrysosporium; pretreatment effects on the biodegradability and subsequent anaerobic production of biogas were investigated. The peak levels of daily biogas production and CH₄ yield from corn stover silage were approximately twice that of corn stover. Results suggested that ensiling was a potential pretreatment method to stimulate biogas production from corn stover. Surface morphology and Fourier-transform infrared spectroscopy analyses demonstrated that the microbial pretreatment of corn stover silage improved biogas production by 10.5 to 19.7 % and CH₄ yield by 11.7 to 21.2 % because pretreatment could decrease dry mass loss (14.2 %) and increase substrate biodegradability (19.9 % cellulose, 32.4 % hemicellulose, and 22.6 % lignin). By contrast, the higher dry mass loss in corn stover (55.3 %) after microbial pretreatment was accompanied by 54.7 % cellulose, 64.0 % hemicellulose, and 61.1 % lignin degradation but did not significantly influence biogas production.     

Influence of selected biowaste materials pre-treatment on their anaerobic digestion

The topic of this study is the pre-treatment of substrates for anaerobic digestion. Two different substrates of algae Scenedesmus subspicatus (SAG 86.81), Chlorella kessleri (LARG/1) and foliage of Prunus serrulata were subjected to anaerobic digestion. A mixture of commercially available cellulolytic enzymes (Analytical science s.r.o., Modra, Slovakia) was used for anaerobic treatment of algae while the foliage of Prunus serrulata was pre-treated by lignolytic fungi. The highest production of methane per mass of volatile solids was reached with untreated Chlorella kessleri at (0.59 ± 0.04) L g⁻¹. The addition of cellulolytic enzymes did not increase the production of methane from the algal substrate; however, a faster substrate degradation and thus also higher speed of methane production at the beginning of cultivation was achieved. After foliage pre-treatment by fungal isolate Pleurotus pulmonarius, isolated from natural habitats, the methane production increased five times. In this way we were able to speed up the processes of biological degradation of ligno-cellulose materials and thereby to increase the production of methane. Our results show the possibility of using algae as a suitable substrate for biogas production. On the other hand, also aerobic pre-treatment of foliage (Pleurotus pulmonarius) presents a successful way for speeding up the degradation of ligno-cellulose waste leading to increased methane yields.