Fungal pretreatment of unsterilized yard trimmings for enhanced methane production by solid-state anaerobic digestion

The Use of Fungi of the Trichoderma Genus in Anaerobic Digestion: A Review

Plant waste biomass is the most abundant renewable energy resource on Earth. The main problem with utilising this biomass in anaerobic digestion is the long and costly stage of degrading its complex structure into simple compounds. One of the promising solutions to this problem is the application of fungi of the Trichoderma genus, which show a high capacity to produce hydrolytic enzymes capable of degrading lignocellulosic biomass before anaerobic digestion. This article discusses the structure of plant waste biomass and the problems resulting from its structure in the digestion process. It presents the methods of pre-treatment of lignocellulose with a particular focus on biological solutions. Based on the latest research findings, key parameters related to the application of Trichoderma sp. as a pre-treatment method are discussed. In addition, the possibility of using the digestate from agricultural biogas plants as a carrier for the multiplication of the Trichoderma sp. fungi, which are widely used in many industries, is discussed.

Efficient short time pretreatment on lignocellulosic waste using an isolated fungus Trametes sp. W-4 for the enhancement of biogas production

Biological pretreatment to the lignocellulosic waste prior to anaerobic digestion is a popular method to increase biogas production. However, the long time needed for the pretreatment is not suitable to the practical application. A fungus strain, which could produce many kinds of lignocellulosic enzymes including CMCase, FPase, xylanase and laccase, was isolated from the soil of Tibet in this study. The fungus was identified as Trametes sp. W-4 by morphological and molecular characterization. The optimum culture temperature was 30 °C and the optimum nitrogen source was peptone. Under the optimum fermentation condition, the activity of CMCase, FPase, xylanase and laccase could reach 2.73 U/mL, 0.41 U/mL, 0.29 U/mL, and 1.11 U/mL, respectively. The results of pretreatment of Trametes sp. W-4 on the mixtures of high land barley straw, cow manure and pig manure for enhancement of biogas production showed that a very short time pretreatment of 3 days could obtain the highest cumulative methane production of 111.51 mL/g-VS, which was 63.81% higher than that of the control group of 68.07 mL/g-VS. The finding indicated that Trametes sp. W-4 pretreatment could be a candidate for the improving of biogas production from lignocellulosic waste.

Rapid lignin quantification for fungal wood pretreatment by ATR-FTIR spectroscopy

Lignin determination in lignocellulose with the conventional two-step acid hydrolysis method is highly laborious and time-consuming. However, its quantification is crucial to monitor fungal pretreatment of wood, as the increase of acid-insoluble lignin (AIL) degradation linearly correlates with the achievable enzymatic saccharification yield. Therefore, in this study, a new attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy method was developed to track fungal delignification in an easy and rapid manner. Partial least square regression (PLSR) with cross-validation (CV) was applied to correlate the ATR-FTIR spectra with the AIL content (19.9 %-27.1 %). After variable selection and normalization, a PLSR model with a high coefficient of determination (R_CV² = 0.87) and a low root mean square (RMSECV = 0.60 %) were obtained despite the heterogeneous nature of the fungal solid-state fermentation. These results show that ATR-FTIR can reliably predict the AIL content in fungus-treated wood while being a high-throughput method. This novel method can facilitate the transition to the wood-based economy.

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.

Sequential fungal pretreatment of unsterilized Miscanthus: changes in composition, cellulose digestibility and microbial communities

A sequential fungal pretreatment of Miscanthus × giganteus was conducted by mixing unsterilized Miscanthus with material previously colonized with the white-rot fungus Ceriporiopsis subvermispora. For three generations, each generation started with inoculation by mixing unsterilized fresh Miscanthus with end material from the previous generation and ended after 28 days of incubation at 28 °C. After the first generation, the cellulose digestibility of the material doubled, compared to that of the unsterilized Miscanthus, but the second and third generations showed no enhancements in cellulose digestibility. Furthermore, high degradation of Miscanthus structural carbohydrates occurred during the first generation. A microbial community study showed that, even though the fungal community of the material previously colonized by C. subvermispora was composed mainly of this fungus (> 99%), by the first generation its relative abundance was down to only 9%, and other microbes had prevailed. Additionally, changes in the bacterial community occurred that might be associated with unwanted cellulose degradation in the system. This reiterates the necessity of feedstock microbial load reduction for the stability and reproducibility of fungal pretreatment of lignocellulosic biomass. KEY POINTS: • Sequential fungal pretreatment of unsterilized Miscanthus was unsuccessful. • Feedstock changes with white-rot fungi favored the growth of other microorganisms. • Feedstock microbial reduction is necessary for pretreatment with C. subvermispora.

Genomic driven factors enhance biocatalyst-related cellulolysis potential in anaerobic digestion

Anaerobic digestion (AD) is a promising technology to recover bioenergy from biodegradable biomass, including cellulosic wastes. Through a few fractionation/separation techniques, cellulose has demonstrated its potential in AD, but the performance of the process is rather substrate-specific, as cellulolysis bacteria are sensitive to the enzyme-substrate interactions. Cellulosome is a self-assembled enzyme complex with many functionalized modules in the bacteria which has been gradually studied, however the genomic fingerprints of the culture-specific cellulosome in AD are relatively unclear especially under processing conditions. To clarify the key factors affecting the cellulosome induced cellulolysis, this review summarized the most recent publications of AD regarding the fates of cellulose, sources and functional genes of cellulosome, and omics methods for functional analyses. Different processes for organic treatment including applying food grinds in sewer, biomass valorization, cellulose fractionation, microaeration, and enzymatic hydrolysis enhanced fermentation, were highlighted to support the sustainable development of AD technology.

Optimization of biogas yield from lignocellulosic materials with different pretreatment methods: a review

Population increase and industrialization has resulted in high energy demand and consumptions, and presently, fossil fuels are the major source of staple energy, supplying 80% of the entire consumption. This has contributed immensely to the greenhouse gas emission and leading to global warming, and as a result of this, there is a tremendous urgency to investigate and improve fresh and renewable energy sources worldwide. One of such renewable energy sources is biogas that is generated by anaerobic fermentation that uses different wastes such as agricultural residues, animal manure, and other organic wastes. During anaerobic digestion, hydrolysis of substrates is regarded as the most crucial stage in the process of biogas generation. However, this process is not always efficient because of the domineering stableness of substrates to enzymatic or bacteria assaults, but substrates' pretreatment before biogas production will enhance biogas production. The principal objective of pretreatments is to ease the accessibility of the enzymes to the lignin, cellulose, and hemicellulose which leads to degradation of the substrates. Hence, the use of pretreatment for catalysis of lignocellulose substrates is beneficial for the production of cost-efficient and eco-friendly process. In this review, we discussed different pretreatment technologies of hydrolysis and their restrictions. The review has shown that different pretreatments have varying effects on lignin, cellulose, and hemicellulose degradation and biogas yield of different substrate and the choice of pretreatment technique will devolve on the intending final products of the process.

Bio-Delignification of Green Waste (GW) in Co-Digestion with the Organic Fraction of Municipal Solid Waste (OFMSW) to Enhance Biogas Production

The organic fraction of municipal solid waste (OFMSW) is recognized as a suitable substrate for the anaerobic digestion (AD) process and is currently considered a mature technology. A promising strategy to enhance biogas yield and productivity is the co-digestion of OFMSW with other organic biomass, such as green waste (GW), a mixture of leaves, grass, and woody materials originated from private yards and public greenspace management. The main limitation to the use of GW for biogas production is the high percentage of the lignocellulosic fraction, which makes necessary a pretreatment of delignification to dissolve the recalcitrant structure. In this study, a new strategy of sustainable bio-delignification using the white-rot fungi Bjerkandera adusta (BA) in comparison with other chemical pretreatments were investigated. Untreated and treated GW were, respectively, submitted to anaerobic co-digestion with OFMSW. AD processes were carried out in a lab-scale plant for 30 days in thermophilic conditions (55 °C). Biogas cumulative production was increased by about 100% in the case of treated GW compared with that of just OFMSW, from 145 to 289 Nm3 CH4/ton SV, and productivity almost doubled from 145 to 283 Nm3/ton FM * day. The measured average methane content values in the cumulative biogas were 55% from OFMSW and 54% from GW. Moreover, over 95% of the biogas was produced in 20 days, showing the potential opportunity to reduce the AD time.

An overview of fungal pretreatment processes for anaerobic digestion: Applications, bottlenecks and future needs

Lignin modifying or extracellular enzymes secreted by the white rot fungi have the ability of degrading wide range of lignocellulosic substrates and organic pollutants. Lignocellulosic biomass, despite being a renewable source of energy, is difficult to hydrolyse (hydrolysis being rate-limiting stage in anaerobic digestion process). Various pre-treatment techniques like physical, chemical, thermo-chemical and biological to enhance the accessibility of microbes to carbohydrates have been studied. Recently, usage of white- rot fungi in a biological pre-treatment technique have received renewed interest due to its low cost and eco-friendly nature. This review deals with: a) lignocellulosic biomass recalcitrance, b) various pre-treatment techniques and its economic feasibility, c) delignification and hydrolysis mechanism using white-rot fungi, d) factors controlling white-rot fungi pre- treatment process, and e) improvement in methane production through solid-state anaerobic digestion of white-rot fungi pre-treated lignocellulosic biomass. Finally a future perspective is also included.

A comprehensive review of the recent development and challenges of a solar-assisted biodigester system

The extensive use of fossil fuels and the environmental effect of their combustion products have attracted researchers to look into renewable energy sources. In addition, global mass production of waste has motivated communities to recycle and reuse the waste in a sustainable way to lower landfill waste and associated problems. The development of waste to energy (WtE) technology including the production of bioenergy, e.g. biogas produced from various waste through Anaerobic Digestion (AD), is considered one of the potential measures to achieve the sustainable development goals of the United Nations (UN). Therefore, this study reviews the most recent studies from relevant academic literature on WtE technology (particularly AD technology) for biogas production and the application of a solar-assisted biodigester (SAB) system aimed at improving performance. In addition, socio-economic factors, challenges, and perspectives have been reported. From the analysis of different technologies, further work on effective low-cost technologies is recommended, especially using SAB system upgrading and leveraging the opportunities of this system. The study found that the performance of the AD system is affected by a variety of factors and that different approaches can be applied to improve performance. It has also been found that solar energy systems efficiently raise the biogas digester temperature and through this, they maximize the biogas yield under optimum conditions. The study revealed that the solar-assisted AD system produces less pollution and improves performance compared to the conventional AD system.

Fungal Pretreatments on Non-Sterile Solid Digestate to Enhance Methane Yield and the Sustainability of Anaerobic Digestion

Fungi can run feedstock pretreatment to improve the hydrolysis and utilization of recalcitrant lignocellulose-rich biomass during anaerobic digestion (AD). In this study, three fungal strains (Coprinopsis cinerea MUT 6385, Cyclocybe aegerita MUT 5639, Cephalotrichum stemonitis MUT 6326) were inoculated in the non-sterile solid fraction of digestate, with the aim to further (re)use it as a feedstock for AD. The application of fungal pretreatments induced changes in the plant cell wall polymers, and different profiles were observed among strains. Significant increases (p < 0.05) in the cumulative biogas and methane yields with respect to the untreated control were observed. The most effective pretreatment was carried out for 20 days with C. stemonitis, causing the highest hemicellulose, lignin, and cellulose reduction (59.3%, 9.6%, and 8.2%, respectively); the cumulative biogas and methane production showed a 182% and 214% increase, respectively, compared to the untreated control. The increase in AD yields was ascribable both to the addition of fungal biomass, which acted as an organic feedstock, and to the lignocellulose transformation due to fungal activity during pretreatments. The developed technologies have the potential to enhance the anaerobic degradability of solid digestate and untap its biogas potential for a further digestion step, thus allowing an improvement in the environmental and economic sustainability of the AD process and the better management of its by-products.

Anaerobic digestion of bean straw applying a fungal pre-treatment and using cow manure as co-substrate

The significant amounts of agriculture residues such as bean straw (BS) in rural areas, advises its valorisation for energy recovery. The feasibility of using BS for biogas production through anaerobic digestion was assessed. Prior to this, a fungal pre-treatment to hydrolyse BS with Pleutorus ostreatus was studied at 30°C and 100 rpm in orbital incubators with 1, 10 and 30 mg fungus/g straw for 14, 21 and 28 days. Then, anaerobic digestion experiments were performed in batch with cow manure (CM) as co-substrate and pre-treated BS at ratios (g/g total solids) of 1/2, 1/3, 1/5 and 0/1. Maximum lignin (18%) and hemicellulose (44%) degradation occurred at 30 mg fungus/g straw and 28 days, along with the highest total methane yield (38 mL CH₄/g VS loaded). The total amount of methane decreased when increasing CM in the experiments (701.4-191.5 mL CH₄), suggesting inhibition owed to a component of CM. Self-sustained biogas production of BS occurred due to the presence of bacteria (i.e. Bacilli and Bacteroidia) and archea (i.e. Methanobacteria and Methanomicrobia). However, the usage of a full-active inoculum should be studied for higher biogas production rates.

Pretreatment strategies for enhanced biogas production from lignocellulosic biomass

The inclusion of a pretreatment step in anaerobic digestion processes increases the digestibility of lignocellulosic biomass and enhances biogas yields by promoting lignin removal and the destruction of complex biomass structures. The increase in surface area enables the efficient interaction of microbes or enzymes, and a reduction in cellulose crystallinity improves the digestion process under anaerobic conditions. The pretreatment methods may vary based on the type of the lignocellulosic biomass, the nature of the subsequent process and the overall economics of the process. An improved biogas production by 1200% had been reported when ionic liquid used as pretreatment strategy for anaerobic digestion. The different pretreatment techniques used for lignocellulosic biomasses are generally grouped into physical, chemical, physicochemical, and biological methods. These four modes of pretreatment on lignocellulosic biomass and their impact on biogas production process is the major focus of this review article.

Novel strategy to improve the colonizing ability of Irpex lacteus in non-sterile wheat straw for enhanced rumen and enzymatic digestibility

Pretreatment with white rot fungi is a promising method to enhance the digestibility of lignocelluloses; however, sterilization of feedstocks prior to inoculation is one of the costliest steps. To improve the colonizing ability of white rot fungi under non-sterile condition, Irpex lacteus, Pleurotus ostreatus, and Phanerochaete chrysosporium were inoculated in the wheat straw ensiled for 28 days and incubated for 56 days to determine the changes in microbe counts, organic acid content, chemical composition, and rumen and enzymatic digestibility. Results showed that ensiling produced abundant organic acids and suppressed most microbes in wheat straw. Significant growth of I. lacteus was observed after 3 days of incubation, and molds were only detectable at day 7 in the group. At the end of incubation, aerobic bacteria and lactic acid bacteria decreased by 18% and 38% in the wheat straw treated with I. lacteus, but molds, aerobic bacteria, and lactic acid bacteria thrived in those treated with P. ostreatus and P. chrysosporium. Even more, P. ostreatus and P. chrysosporium increased the lignin content of the ensiled wheat straw by 34% and 65%. However, I. lacteus selectively degraded lignin by 28% and improved the rumen and enzymatic digestibility by 18% and 34%. The finding indicates that ensiling prior to fermentation with I. lacteus is an effective method to control spoilage microbes and to enhance the rumen and enzymatic digestibility of wheat straw.

Techno-Economic Bottlenecks of the Fungal Pretreatment of Lignocellulosic Biomass

Fungal pretreatment is a biological process that uses rotting fungi to reduce the recalcitrance and enhance the enzymatic digestibility of lignocellulosic feedstocks at low temperature, without added chemicals and wastewater generation. Thus, it has been presumed to be low cost. However, fungal pretreatment requires longer incubation times and generates lower yields than traditional pretreatments. Thus, this study assesses the techno-economic feasibility of a fungal pretreatment facility for the production of fermentable sugars for a 75,700 m3 (20 million gallons) per year cellulosic bioethanol plant. Four feedstocks were evaluated: perennial grasses, corn stover, agricultural residues other than corn stover, and hardwood. The lowest estimated sugars production cost ($1.6/kg) was obtained from corn stover, and was 4–15 times as much as previous estimates for conventional pretreatment technologies. The facility-related cost was the major contributor (46–51%) to the sugar production cost, mainly because of the requirement of large equipment in high quantities, due to process bottlenecks such as low sugar yields, low feedstock bulk density, long fungal pretreatment times, and sterilization requirements. At the current state of the technology, fungal pretreatment at biorefinery scale does not appear to be economically feasible, and considerable process improvements are still required to achieve product cost targets.

Solid-state anaerobic digestion of wheat straw: Impact of S/I ratio and pilot-scale fungal pretreatment

Solid State Anaerobic Digestion (SSAD) of fungal pretreated wheat straw was evaluated in a leach bed reactor. During a first experiment, the effect of Substrate/Inoculum (S/I) ratios on the start-up phase was investigated. High S/I increased methane productivity but also raised the risk of reactor failure due to Volatile Fatty Acid (VFA) accumulation. With S/I ratios between 1.2 and 3.6 (Volatile Solid (VS) basis), the SSAD start-up using wheat straw was successful. Moreover, reactors were able to recover from acidification when the Total VFA/alkalinity ratio was lower than 2 gHAc_eq/gCaCO₃, with VFA concentrations lower than 10 g/L and a pH close to 5.5. The conventional threshold of 0.6 gHAc_eq/gCaCO₃ for stable wet AD is therefore not adapted to SSAD. During a second experiment, after the wheat straw was submitted to a fungal pretreatment in a non-sterile pilot-scale reactor, it was digested with an S/I ratio of 2.8-2.9. Under batch SSAD conditions, the biodegradability of pretreated wheat straw was slightly improved in comparison to the control (254 versus 215 NmL/g VS, respectively). Considering mass losses occurring during the pretreatment step, suboptimal pretreatment conditions caused a slightly lower methane production (161 versus 171 NmL/gTS_initial after 60-days anaerobic digestion). Nevertheless, pretreatment improved the start-up phase with lower acidification relative to controls. It would be particularly beneficial to improve the methane production in reactors with short reaction times.

Effect of glucose and cellulase addition on wet-storage of excessively wilted maize stover and biogas production

In north China, large amounts of excessively wilted maize stover are produced annually. Maize stover wet storage strategies and subsequent biogas production was examined in this study. Firstly, wet storage performances of harvested maize stover, air-dried for different time durations, were evaluated. Results showed that optimal storage performance was obtained when the initial water soluble carbohydrate (WSC) content after air-drying was higher than 8.0%. Therefore, cellulase and glucose were added to the excessively wilted maize stover to achieve the targeted pre-storage WSC levels. Good storage performances were observed in treatments with addition of 76.4 g/kg DM glucose and 12.5 g/kg DM of cellulase; the specific methane yield increased by 23.7% and 19.2%, respectively. However, use of glucose as additive or co-storing with high WSC substrates can serve as economically feasible options to adapt wet storage of excessively wilted maize stover.

Biogas production from different lignocellulosic biomass sources: advances and perspectives

The present work summarizes different sources of biomass used as raw material for the production of biogas, focusing mainly on the use of plants that do not compete with the food supply. Biogas obtained from edible plants entails a developed technology and good yield of methane production; however, its use may not be sustainable. Biomass from agricultural waste is a cheap option, but in general, with lower methane yields than those obtained from edible plants. On the other hand, the use of algae or aquatic plants promises to be an efficient and sustainable option with high yields of methane produced, but it necessary to overcome the existing technological barriers. Moreover, these last raw materials have the additional advantage that they can be obtained from wastewater treatment and, therefore, they could be applied to the concept of biorefinery. An estimation of methane yield per hectare per year of the some types of biomass and operational conditions employed is presented as well. In addition, different strategies to improve the yield of biogas, such as physical, chemical, and biological pretreatments, are presented. Other alternatives for enhanced the biogas production such as bioaugmentation and biohythane are showed and finally perspectives are mentioned.

Comparison of sodium hydroxide and calcium hydroxide pretreatments of giant reed for enhanced enzymatic digestibility and methane production

NaOH pretreatment with leachate reuse and Ca(OH)₂ pretreatment were compared for improved enzymatic digestibility and biogas production from giant reed, a promising energy crop. The NaOH pretreatment with leachate reuse increased glucose yields during enzymatic hydrolysis by 2.6-fold, and methane yields during anaerobic digestion by 1.4- to 1.6-fold. However, NaOH pretreatment had a negative net benefit (i.e., revenue from increased energy production minus chemical cost). Pretreatment with 7-20% Ca(OH)₂ not only improved glucose yield and methane yield by up to 2.3-fold and 1.4-fold, respectively, but also obtained a net benefit of $1.1-5.8/tonne dry biomass. Thus, Ca(OH)₂ pretreatment was shown to be more feasible than NaOH pretreatment for biogas production from giant reed.

Combinations of fungal and milling pretreatments for enhancing rice straw biogas production during solid-state anaerobic digestion

Rice straw was pretreated by different combinations of physical (milling) and biological (incubation with Pleurotus ostreatus fungus) treatment to improve its biodegradability and biogas production during solid-state anaerobic digestion (SS-AD). Effects of milling (⩽2mm) and incubation time (10, 20 and 30d), on lignin, cellulose, and hemicellulose degradation during fungal pretreatment and methane yield during digestion were assessed by comparison with untreated rice straw. Both incubation time and milling had significant impacts on both lignin removal during fungal pre-treatment and methane yield during digestion. A combination of fungal pretreatment at 30days followed by milling prior to anaerobic digestion resulted in 30.4% lignin removal, the highest selectivity value (the ratio between relative lignin removal and relative cellulose removal) of 4.22, and the highest methane yield of 258L/kgVS. This was equivalent to a 165% increase in methane yield from SS-AD compared to untreated rice straw.

The application of biotechnology on the enhancing of biogas production from lignocellulosic waste

Anaerobic digestion of lignocellulosic waste is considered to be an efficient way to answer present-day energy crisis and environmental challenges. However, the recalcitrance of lignocellulosic material forms a major obstacle for obtaining maximum biogas production. The use of biological pretreatment and bioaugmentation for enhancing the performance of anaerobic digestion is quite recent and still needs to be investigated. This paper reviews the status and perspectives of recent studies on biotechnology concept and investigates its possible use for enhancing biogas production from lignocellulosic waste with main emphases on biological pretreatment and bioaugmentation techniques.

Biological processes for advancing lignocellulosic waste biorefinery by advocating circular economy

The actualization of a circular economy through the use of lignocellulosic wastes as renewable resources can lead to reduce the dependence from fossil-based resources and contribute to a sustainable waste management. The integrated biorefineries, exploiting the overall lignocellulosic waste components to generate fuels, chemicals and energy, are the pillar of the circular economy. The biological treatment is receiving great attention for the biorefinery development since it is considered an eco-friendly alternative to the physico-chemical strategies to increase the biobased product recovery from wastes and improve saccharification and fermentation yields. This paper reviews the last advances in the biological treatments aimed at upgrading lignocellulosic wastes, implementing the biorefinery concept and advocating circular economy.

Corn forage biological pretreatment by Trametes versicolor in a tray bioreactor

Trametes versicolor is a white-rot fungus known to be efficient in lignin removal due to its complex extracellular lignocellulolytic enzymatic system. Therefore, it can be used in the treatment of lignocellulose waste from agro, food, and wood industries. In a first experiment, corn forage treatment with T. versicolor was investigated in laboratory jars. In a second experiment, the process was scaled up to a tray bioreactor. In the tray bioreactor, the process of lignin degradation was improved, resulting in an increase in lignin conversion of up to 71% during seven days' treatment.

Comparison between ensilage and fungal pretreatment for storage of giant reed and subsequent methane production

Ensilage and fungal pretreatment of giant reed harvested from August through December were compared based on their effects on feedstock preservation, glucose yield, and subsequent methane production via anaerobic digestion (AD). Compared to fungal pretreatment, ensilage obtained lower total solids (<1.2%) and cellulose (<3.5%) losses, and comparable hemicellulose degradation, except for giant reed harvested in August. Ensilage increased glucose and methane yields by 7-15% and 4-14%, respectively, for giant reed harvested from August through December. Fungal pretreatment failed for giant reed harvested in August and October with reduced glucose yields, and was effective for that harvested in November and December, with about 20% increases in glucose yield. However, hydrocarbon losses during fungal pretreatment offset the increased glucose yield, resulting in decreased methane yields by AD. In summary, ensilage was found to be more suitable than fungal pretreatment for giant reed storage and its methane production via AD.

Solid-state anaerobic digestion of lignocellulosic biomass: Recent progress and perspectives

Solid-state anaerobic digestion (SS-AD), which has gained popularity in the past decade as an environmentally friendly and cost-effective technology for extracting energy from various types of lignocellulosic biomass, is reviewed in this paper. According to data of biomass and methane yields of lignocellulosic feedstocks, crop residues have the highest methane production potential in the U.S., followed by the organic fraction of municipal solid waste (OFMSW), forestry waste, and energy crops. Methane yield and process stability of SS-AD can be improved by different strategies, such as co-digestion with other organic wastes, pretreatment of lignocellulosic biomass, and optimization of operating parameters. Different models for SS-AD have been developed, and insights into SS-AD processes have been obtained via microbial community analysis, microscope imaging, and tracer techniques. Future research and development in SS-AD, including feedstock identification and co-digestion, feedstock storage and pretreatment, SS-AD reactor development, digestate treatment, and value-added production, are recommended.

Fungal pretreatment of non-sterile miscanthus for enhanced enzymatic hydrolysis

Miscanthus was pretreated with the fungus Ceriporiopsis subvermispora under non-sterile conditions, using sterile miscanthus that had been previously colonized with the fungus as the inoculum. Inoculum ratios equal to or greater than 30% yielded a successful pretreatment, enhancing the enzymatic digestibility of miscanthus by 3- to 4-fold over that of raw miscanthus, which was comparable with the fungal pretreatment under sterile conditions. This enhanced digestibility was linearly correlated with lignin degradation. Although cellulose loss of up to 13% was observed for the successful non-sterile pretreatments, the final glucose yield was 3-4 times higher than that of raw miscanthus and comparable to that of the sterile pretreated miscanthus. A time course study showed that maximum glucose yield can be achieved with a pretreatment time of 21 days.

Isothermal titration calorimetry uncovers substrate promiscuity of bicupin oxalate oxidase from Ceriporiopsis subvermispora

Isothermal titration calorimetry (ITC) may be used to determine the kinetic parameters of enzyme-catalyzed reactions when neither products nor reactants are spectrophotometrically visible and when the reaction products are unknown. We report here the use of the multiple injection method of ITC to characterize the catalytic properties of oxalate oxidase (OxOx) from Ceriporiopsis subvermispora (CsOxOx), a manganese dependent enzyme that catalyzes the oxygen-dependent oxidation of oxalate to carbon dioxide in a reaction coupled with the formation of hydrogen peroxide. CsOxOx is the first bicupin enzyme identified that catalyzes this reaction. The multiple injection ITC method of measuring OxOx activity involves continuous, real-time detection of the amount of heat generated (dQ) during catalysis, which is equal to the number of moles of product produced times the enthalpy of the reaction (ΔH_app). Steady-state kinetic constants using oxalate as the substrate determined by multiple injection ITC are comparable to those obtained by a continuous spectrophotometric assay in which H₂O₂ production is coupled to the horseradish peroxidase-catalyzed oxidation of 2,2′-azinobis-(3-ethylbenzthiazoline-6-sulfonic acid) and by membrane inlet mass spectrometry. Additionally, we used multiple injection ITC to identify mesoxalate as a substrate for the CsOxOx-catalyzed reaction, with a kinetic parameters comparable to that of oxalate, and to identify a number of small molecule carboxylic acid compounds that also serve as substrates for the enzyme.

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ITC is used to assay the catalytic activity of oxalate oxidase.

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ITC enzymatic assay is sensitive, direct, and continuous.

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Mesoxalate and other carboxylic acids are substrates for oxalate oxidase.

Solid-state anaerobic digestion of fungal pretreated Miscanthus sinensis harvested in two different seasons

Solid-state anaerobic digestion of Miscanthus sinensis harvested in fall and spring was compared under different total solids contents and feedstock-to-inoculum ratios. The highest specific methane yields reached 170-175LCH4/kg volatile solids for both harvest seasons. Miscanthus harvested in fall generated a 6% higher methane yield in average than miscanthus harvested in spring. Fungal pretreatment with Ceriporiopsis subvermispora decreased the lignin content of miscanthus harvested in spring by 25.7%, but there was no significant delignification observed for miscanthus harvested in fall. Fungal pretreatment of miscanthus harvested in spring increased the specific methane yield by 25%, but fungal pretreatment caused a slight methane yield reduction for miscanthus harvested in fall. Methane yields for miscanthus were comparable with those from other energy crops.

Integration of Shiitake cultivation and solid-state anaerobic digestion for utilization of woody biomass

Pretreatment technologies that can not only reduce the recalcitrance of woody biomass but also achieve a high benefit-cost ratio are desirable for bioenergy production from woody biomass. In this study, an integrated process was proposed and conducted by pretreating woodchips via Shiitake cultivation for improved methane yield during solid-state anaerobic digestion (SS-AD), and simultaneously producing mushrooms as a high-value co-product. Shiitake cultivation using woodchips as the main substrate ingredient obtained mushroom yields comparable to those using a commercial substrate. Enzymatic digestibility and cumulative methane yields (133-160 L kg(-1)VS during 62 days of SS-AD) of pretreated substrates (spent mushroom substrate) were at least 1.5 times as high as those of untreated woodchips. Compared to a sole SS-AD process, the integrated Shiitake cultivation/SS-AD process increased methane production and solid waste reduction per kilogram of woodchips by about 1.5 and 8 times, respectively.

Solid-state anaerobic co-digestion of spent mushroom substrate with yard trimmings and wheat straw for biogas production

Spent mushroom substrate (SMS) is a biomass waste generated from mushroom production. About 5 kg of SMS is generated for every kg of mushroom produced. In this study, solid state anaerobic digestion (SS-AD) of SMS, wheat straw, yard trimmings, and their mixtures was investigated at different feedstock to effluent ratios. SMS was found to be highly degradable, which resulted in inhibition of SS-AD due to volatile fatty acid (VFA) accumulation and a decrease in pH. This issue was addressed by co-digestion of SMS with either yard trimmings or wheat straw. SS-AD of SMS/yard trimmings achieved a cumulative methane yield of 194 L/kg VS, which was 16 and 2 times higher than that from SMS and yard trimmings, respectively. SS-AD of SMS/wheat straw obtained a cumulative methane yield of 269 L/kg VS, which was 23 times as high as that from SMS and comparable to that from wheat straw.

Biogas energy production from tropical biomass wastes by anaerobic digestion

Anaerobic digestion (AD) is an attractive technology in tropical regions for converting locally abundant biomass wastes into biogas which can be used to produce heat, electricity, and transportation fuels. However, investigations on AD of tropical forestry wastes, such as albizia biomass and food wastes, such as taro, papaya, and sweet potato, are limited. In this study, these tropical biomass wastes were evaluated for biogas production by liquid AD (L-AD) and/or solid-state AD (SS-AD), depending on feedstock characteristics. When albizia leaves and chips were used as feedstocks, L-AD had greater methane yields (161 and 113 L kg(-1)VS, respectively) than SS-AD (156.8 and 59.6 L kg(-1)VS, respectively), while SS-AD achieved 5-fold higher volumetric methane productivity than L-AD. Mono-digestion and co-digestion of taro skin, taro flesh, papaya, and sweet potato achieved methane yields from 345 to 411 L kg(-1)VS, indicating the robustness of AD technology.