Optimization of biogas production from anaerobic co-digestion of fish waste and water hyacinth

Many fresh water bodies face a great challenge of an invasive weed called water hyacinth (WH) which has great impacts on the environment, ecology, and society. Food and Agriculture Organization (FAO) estimates that over nine million tons of Fish wastes (FW) are thrown away each year. The fish waste generated poses environmental and health hazards because in most cases it is either disposed into pits or discarded onto the open grounds. Both WH and FW are potential substrates for biogas production. However, utilization of FW substrate alone has a limitation of producing a lot of amounts of volatile fatty acids (VFAs) and ammonia. Their accumulation in the digester inhibits substrate digestion. Consequently, as stand-alone it is not suitable for anaerobic digestion (AD). This can be overcome by co-digestion with a substrate like WH which has high carbon to nitrogen (C/N) ratio prior to biodigestion. Experimental variable levels for biogas were substrate ratio (WH:FW, 25-75 g), inoculum concentration (IC, 5-15 g/250 mL), and dilution (85-95 mL). Design-Expert 13 was used for optimization and results analysis. Response surface methodology (RSM) was used to examine the effects of operating parameters and identify optimum values for biogas yield. Optimum values for maximum biogas with the highest methane yield of 68% were found to be WH:FW ratio, 25:75 g, 15 g of IC, and 95 mL for dilution. The yield was 16% and 32% greater than FW and WH mono-digestion, respectively. The biogas yield was expressed as a function of operating variables using a quadratic equation. The model was significant (P < 0.05). All factors had significant linear and quadratic effects on biogas while only the interaction effects of the two factors were significant. The coefficient of determination (R²) of 99.9% confirmed the good fit of the model with experimental variables.

Influence of macronutrients and micronutrients on maize hybrids for biogas production

Important in the cultivation of corn for biogas production is the selection of appropriate hybrids, macro- and micronutrient dozing and the evaluation of energy and economic efficiency of their use. Therefore, this article presents the results of 3-year field research (2019-2021) on the yield of maize hybrids of different maturity groups grown for silage. The influence of the application of macronutrients and micronutrients on fresh and dry mass yield, chemical composition, methane yield, energy, and economic efficiency was analysed. It was established that depending on the maize hybrid, the application of macro- and micro-fertilizers increased the yield of the fresh mass of maize by 1.4-24.0% compared to options without their use. The evaluation of the theoretical yield of CH₄ based on the content of fats, protein, cellulose, and hemicellulose is also presented in different samples of maize. The findings show that the application of macro-and micro-fertilizers is suitable from the energy and economic points of view - profitability begins to appear at the price of biomethane of 0.3-0.4 euros per 1 m³.

Cellulose Fibre Degradation in Cellulose/Steel Hybrid Geotextiles under Outdoor Weathering Conditions

Risks from rockfall and land sliding can be controlled by high-tensile steel nets and meshes which stabilise critical areas. In many cases, a recultivation of the land is also desired. However, high-tensile steel meshes alone are not always sufficient, depending on the location and the inclination of the stabilised slope, to achieve rapid greening. Cellulose fibres exhibit high water binding capacity which supports plant growth. In this work, a hybrid structure consisting of a nonwoven cellulose fibre web and a steel mesh was produced and tested under outdoor conditions over a period of 61 weeks. The cellulose fibres are intended to support plant growth and soil fixation, and thus the biodegradation of the structure is highly relevant, as these fibres will become part of the soil and must be biodegradable. The biodegradation of the cellulose fibres over the period of outdoor testing was monitored by microscopy and analytical methods. The enzymatic degradation of the cellulose fibres led to a reduction in the average degree of polymerisation and also a reduction in the moisture content, as polymer chain hydrolysis occurs more rapidly in the amorphous regions of the fibres. FTIR analysis and determination of carboxylic group content did not indicate substantial changes in the remaining parts of the cellulose fibre. Plant growth covered geotextiles almost completely during the period of testing, which demonstrated their good compatibility with the greening process. Over the total period of 61 weeks, the residual parts of the biodegradable cellulose web merged with the soil beneath and growing plants. This indicates the potential of such hybrid concepts to contribute a positive effect in greening barren and stony land, in addition to the stabilising function of the steel net.

Variimorphobacter saccharofermentans gen. nov., sp. nov., a new member of the family Lachnospiraceae, isolated from a maize-fed biogas fermenter

Strain MD1^T is an anaerobic, Gram-stain-negative bacterium isolated from a lab-scale biogas fermenter fed with maize silage. It has a rod-shaped morphology with peritrichously arranged appendages and forms long chains of cells and coccoid structures. The colonies of MD1^T were white, circular, slightly convex and had a smooth rim. The isolate is mesophilic, displaying growth between 25 and 45 °C with an optimum at 40 °C. It grew at pH values of pH 6.7-8.2 (optimum, pH 7.1) and tolerated the addition of up to 1.5% (w/v) NaCl to the medium. The main cellular fatty acids of MD1^T are C_14:0 DMA and C_16:0. Strain MD1^T fermented xylose, arabinose, glucose, galactose, cellobiose, maltose, maltodextrin10, lactose starch, and xylan, producing mainly 2-propanol and acetic acid. The genome of the organism has a total length of 4163427 bp with a G+C content of 38.5 mol%. The two closest relatives to MD1^T are Mobilitalea sibirica P3M-3^T and Anaerotaenia torta FH052^T with 96.44 or 95.8 % 16S rRNA gene sequence similarity and POCP values of 46.58 and 50.58%, respectively. As MD1^T showed saccharolytic and xylanolytic properties, it may play an important role in the biogas fermentation process. Closely related variants of MD1^T were also abundant in microbial communities involved in methanogenic fermentation. Based on morphological, phylogenetic and genomic data, the isolated strain can be considered as representing a novel genus in the family Lachnospiraceae, for which the name Variimorphobacter saccharofermentans gen. nov., sp. nov. (type strain MD1^T=DSM 110715^T=JCM 39125^T) is proposed.

Techno-Economic Analysis of ZnO Nanoparticles Pretreatments for Biogas Production from Barley Straw

The aim of this study was to analyze the effect of ZnO nanoparticles (ZnO NPs) on the biogas production from mechanically treated barley straw and to perform a techno-economic analysis based on the costs assessment and on the results of biogas production. The structural changes of mechanically pretreated barley straw were observed using FTIR, XRD, TGA, and SEM. Additionally, both green ZnO NPs prepared from red alga (Antithamnion plumula) extract and chemically prepared ZnO NPs were characterized by FTIR, XRD, SEM, and TEM, surface area, and EDX. The results revealed that the biogas production was slightly improved by 14.9 and 13.2% when the barley straw of 0.4 mm was mechanically pretreated with 10 mg/L of both green and chemical ZnO NPs and produced 390.5 mL biogas/g VS and 385 mL biogas/g VS, respectively. On the other hand, the higher concentrations of ZnO NPs equal to 20 mg/L had an inhibitory effect on biogas production and decreased the biogas yield to 173 mL biogas/g VS, which was less than the half of previous values. It was also clear that the mechanically treated barley straw of 0.4 mm size presented a higher biogas yield of about 340 mL/g VS, in comparison to 279 mL biogas/g VS of untreated biomass. The kinetic study showed that the first order, modified Gompertz and logistic function models had the best fit with the experimental data. The results showed that the nanoparticles (NPs) of the mechanically treated barely straw are a suitable source of biomass for biogas production, and its yields are higher than the untreated barley straw. The results of the cost-benefit analysis showed that the average levelized cost of energy (LCOE), adopting the best treatments (0.4 mm + 10 mg/L ZnO), is 0.21 €/kWh, which is not competitive with the other renewable energy systems in the Egyptian energy market.

Metal Catalyst-Free Oxidative C-C Bond Cleavage of a Lignin Model Compound by H2 O2 in Formic acid

Selective cleavage of the β-O-4 ether bond of lignin to produce aromatics is one of the most important topics for the sustainable production of chemicals from biomass. A simple system has been developed for C_α -C_β bond cleavage of a β-O-4 ketone-structured lignin model compound (LMC) by H₂ O₂ in formic acid under metal catalyst-free conditions. By using this simple system, with H₂ O₂ , formic acid, and mineral acid catalyst, over 90 % product yield is achieved in 6 h at room temperature. The reaction proceeds through the classic Baeyer-Villiger oxidation and in situ-generated performic acid serves as the key oxidant. The cleavage of alcoholic LMCs by using the presented method in a two-step process is also demonstrated.

Enhanced hydrolysis of lignocellulose in corn cob by using food waste pretreatment to improve anaerobic digestion performance

This study aims to enhance hydrolysis and anaerobic digestion of corn cob (CC) by using food waste (FW) pretreatment. FW, which tends to be acidification in fermentation, was applied in this process as an acid-like agent to accelerate lignocellulose hydrolysis, aiming to promote methane yield in further digestion process. The effect of FW pretreatment on pH, soluble chemical oxygen demand (SCOD), volatile fatty acids (VFAs), cellulose/hemicellulose contents and cellulose crystallinity are specially focused. FW:CC = 1:3 based on volatile solid (VS) was found to be the optimal mixing ratio in pretreatment and its hydrolysis efficiency was 28% higher than the control group. An increase of 13.2% in cellulose reduction and a decrease of 6.7% in cellulose crystallinity was achieved at this ratio. Supplementation of FW increased VFA concentrations in slurry mixture that directly change the activities of enzymes and microorganisms. In the stage of methane production, the digester A3 (FW:CC = 1:6 based on VS) with higher hydrolysis efficiency presented the best performance in methane production with a specific methane yield of 401.6 mL/g·VS, due to the recovery of the pH in this digester to the optimal pH range for methanogens' metabolism (pH 6.3-7.2). Kinetics studies of cellulose/hemicellulose degradation indicated that the pretreatment of FW could improve the degradation of cellulose. Three-dimensional excitation emission matrix (3DEEM) results further confirmed that FW play an important role in lignocellulose hydrolysis. In addition, variations of lignocellulosic textures during the pretreatment were also cleared by using field emission-scanning electron microscopy (FE-SEM) analysis.

Screening and Bioprospecting of Anaerobic Consortia for Biofuel Production Enhancement from Sugarcane Bagasse

The genera Dysgonomonas, Coprococcus, Sporomusa, Bacteroides, Sedimentibacter, Pseudomonas, Ruminococcus, and Clostridium predominate in compost residue, and vadimCA02, Anaerobaculum, Tatlockia, Caloramator, and Syntrophus prevail in soil used as inoculum in batch rectors. This mixed consortium was used as inoculum for biogas production using different concentrations of sugarcane bagasse (SCB) (from 1.58 to 4.42 g/L) and yeast extract (YE) (from 0.58 to 3.42 g/L) according to a composite central design. The maximum ethanol production (20.11 mg L^-1) was observed using 2.0 and 3.0 g L^-1 of YE and SCB, respectively (C6). Likewise, the highest hydrogen production (0.60 mmol L^-1) was observed using 3.0 and 4.0 g L^-1 of YE and SCB, respectively (C1). Methane was also observed, reaching the maximum production (1.44 mmol L^-1) using 1.0 and 4.0 g L^-1 of YE and SCB, respectively (C2). The archaeal similarity between these conditions was above 90%; however, the richness and diversity were higher in the C2 (12 and 2.42, respectively) than in C1 (5 and 1.43, respectively) and C6 (11 and 2.29, respectively). Equally, the bacterial similarity between C1 and C6 was 60% while richness of 24 and 17 and diversity of 3.13 and 2.81 were observed in C1 and C6, respectively.

Biological strategies for enhanced hydrolysis of lignocellulosic biomass during anaerobic digestion: Current status and future perspectives

Lignocellulosic biomass is the most abundant renewable bioresource on earth. In lignocellulosic biomass, the cellulose and hemicellulose are bound with lignin and other molecules to form a complex structure not easily accessible to microbial degradation. Anaerobic digestion (AD) of lignocellulosic biomass with a focus on improving hydrolysis, the rate limiting step in AD of lignocellulosic feedstocks, has received considerable attention. This review highlights challenges with AD of lignocellulosic biomass, factors contributing to its recalcitrance, and natural microbial ecosystems, such as the gastrointestinal tracts of herbivorous animals, capable of performing hydrolysis efficiently. Biological strategies that have been evaluated to enhance hydrolysis of lignocellulosic biomass include biological pretreatment, co-digestion, and inoculum selection. Strategies to further improve these approaches along with future research directions are outlined with a focus on linking studies of microbial communities involved in hydrolysis of lignocellulosics to process engineering.

Enhanced biomethane production rate and yield from lignocellulosic ensiled forage ley by in situ anaerobic digestion treatment with endogenous cellulolytic enzymes

BACKGROUND

Enzymatic treatment of lignocellulosic material for increased biogas production has so far focused on pretreatment methods. However, often combinations of enzymes and different physicochemical treatments are necessary to achieve a desired effect. This need for additional energy and chemicals compromises the rationale of using enzymes for low energy treatment to promote biogas production. Therefore, simpler and less energy intensive in situ anaerobic digester treatment with enzymes is desirable. However, investigations in which exogenous enzymes are added to treat the material in situ have shown mixed success, possibly because the enzymes used originated from organisms not evolutionarily adapted to the environment of anaerobic digesters. In this study, to examine the effect of enzymes endogenous to methanogenic microbial communities, cellulolytic enzymes were instead overproduced and collected from a dedicated methanogenic microbial community. By this approach, a solution with very high endogenous microbial cellulolytic activity was produced and tested for the effect on biogas production from lignocellulose by in situ anaerobic digester treatment.

RESULTS

Addition of enzymes, endogenous to the environment of a mixed methanogenic microbial community, to the anaerobic digestion of ensiled forage ley resulted in significantly increased rate and yield of biomethane production. The enzyme solution had an instant effect on more readily available cellulosic material. More importantly, the induced enzyme solution also affected the biogas production rate from less accessible cellulosic material in a second slower phase of lignocellulose digestion. Notably, this effect was maintained throughout the experiment to completely digested lignocellulosic substrate.

CONCLUSIONS

The induced enzyme solution collected from a microbial methanogenic community contained enzymes that were apparently active and stable in the environment of anaerobic digestion. The enzymatic activity had a profound effect on the biogas production rate and yield, comparable with the results of many pretreatment methods. Thus, application of such enzymes could enable efficient low energy in situ anaerobic digester treatment for increased biomethane production from lignocellulosic material.

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.

Horse manure as feedstock for anaerobic digestion

Horse keeping is of great economic, social and environmental benefit for society, but causes environmental impacts throughout the whole chain from feed production to manure treatment. According to national statistics, the number of horses in Sweden is continually increasing and is currently approximately 360,000. This in turn leads to increasing amounts of horse manure that have to be managed and treated. Current practices could cause local and global environmental impacts due to poor performance or lack of proper management. Horse manure with its content of nutrients and organic material can however contribute to fertilisation of arable land and recovery of renewable energy following anaerobic digestion. At present anaerobic digestion of horse manure is not a common treatment. In this paper the potential for producing biogas and biofertiliser from horse manure is analysed based on a thorough literature review in combination with mathematical modelling and simulations. Anaerobic digestion was chosen as it has a high degree of resource conservation, both in terms of energy (biogas) and nutrients (digestate). Important factors regarding manure characteristics and operating factors in the biogas plant are identified. Two crucial factors are the type and amount of bedding material used, which has strong implications for feedstock characteristics, and the type of digestion method applied (dry or wet process). Straw and waste paper are identified as the best materials in an energy point of view. While the specific methane yield decreases with a high amount of bedding, the bedding material still makes a positive contribution to the energy balance. Thermophilic digestion increases the methane generation rate and yield, compared with mesophilic digestion, but the total effect is negligible.

The biotransformation of brewer's spent grain into biogas by anaerobic microbial communities

The present study reports on the biotransformation of the brewer's spent grain (BSG) in co-digestion with Jerusalem artichoke (JA, Helianthus tuberosus L.) phytomass by thermophilic (+55 °C) and mesophilic (+30 °C) anaerobic methanogenic communities. BSG is a by-product of the beer-brewing process generated in large amounts, in which utilization provokes a negative effect on the environment. In this study, we will show an effective conversion of BSG into biogas by selected microbial communities, obtained from different sources (animal manure and previously isolated microbial consortia). The stimulation of methanogenesis was reached by the co-digestion of JA's phytomass (stem and leaves). The optimized conditions for microbial stable cultivation included the use of nutrient medium, containing yeast extract and trace element solution. The optimal BSG concentration in biogas production was 50 and 100 g L(-1). Under thermophilic conditions, the maximum total methane production reached 64%, and it comprised around 6-8 and 9-11 of L CH4 per 100 g of fermented BSG without and with co-digested JA, respectively, when the fresh inoculum was added. Although, after a year of re-cultivation, the values reduced to around 6-7, and 6-10 L CH4/100 g BSG, correspondingly, the selected microbial communities showed effective biotransformation of BSG. The supplementation of soil with the residual fermented BSG (10%, w/w) resulted in the promotion of lettuce (Lepidium sativum L.) growth. The results obtained demonstrate a potential for complete BSG utilization via biogas production and application as a soil additive.

Characterization of microbial community structure during continuous anaerobic digestion of straw and cow manure

Responses of bacterial and archaeal communities to the addition of straw during anaerobic digestion of manure at different temperatures (37°C, 44°C and 52°C) were investigated using five laboratory-scale semi-continuous stirred tank reactors. The results revealed that including straw as co-substrate decreased the species richness for bacteria, whereas increasing the operating temperature decreased the species richness for both archaea and bacteria, and also the evenness of the bacteria. Taxonomic classifications of the archaeal community showed that Methanobrevibacter dominated in the manure samples, while Methanosarcina dominated in all digesters regardless of substrate. Increase of the operating temperature to 52°C led to increased relative abundance of Methanoculleus and Methanobacterium. Among the bacteria, the phyla Firmicutes and Bacteroidetes dominated within all samples. Compared with manure itself, digestion of manure resulted in a higher abundance of an uncultured class WWE1 and lower abundance of Bacilli. Adding straw to the digesters increased the level of Bacteroidia, while increasing the operating temperature decreased the level of this class and instead increased the relative abundance of an uncultured genus affiliated to order MBA08 (Clostridia). A considerable fraction of bacterial sequences could not be allocated to genus level, indicating that novel phylotypes are resident in these communities.

Assessment of energy crops alternative to maize for biogas production in the Greater Region

The biomethane yield of various energy crops, selected among potential alternatives to maize in the Greater Region, was assessed. The biomass yield, the volatile solids (VS) content and the biochemical methane potential (BMP) were measured to calculate the biomethane yield per hectare of all plant species. For all species, the dry matter biomass yield and the VS content were the main factors that influence, respectively, the biomethane yield and the BMP. Both values were predicted with good accuracy by linear regressions using the biomass yield and the VS as independent variable. The perennial crop miscanthus appeared to be the most promising alternative to maize when harvested as green matter in autumn and ensiled. Miscanthus reached a biomethane yield of 5.5 ± 1 × 10(3)m(3)ha(-1) during the second year after the establishment, as compared to 5.3 ± 1 × 10(3)m(3)ha(-1) for maize under similar crop conditions.

Lignin: characterization of a multifaceted crop component

Lignin is a plant component with important implications for various agricultural disciplines. It confers rigidity to cell walls, and is therefore associated with tolerance to abiotic and biotic stresses and the mechanical stability of plants. In animal nutrition, lignin is considered an antinutritive component of forages as it cannot be readily fermented by rumen microbes. In terms of energy yield from biomass, the role of lignin depends on the conversion process. It contains more gross energy than other cell wall components and therefore confers enhanced heat value in thermochemical processes such as direct combustion. Conversely, it negatively affects biological energy conversion processes such as bioethanol or biogas production, as it inhibits microbial fermentation of the cell wall. Lignin from crop residues plays an important role in the soil organic carbon cycling, as it constitutes a recalcitrant carbon pool affecting nutrient mineralization and carbon sequestration. Due to the significance of lignin in several agricultural disciplines, the modification of lignin content and composition by breeding is becoming increasingly important. Both mapping of quantitative trait loci and transgenic approaches have been adopted to modify lignin in crops. However, breeding goals must be defined considering the conflicting role of lignin in different agricultural disciplines.

Towards a carbon-negative sustainable bio-based economy

The bio-based economy relies on sustainable, plant-derived resources for fuels, chemicals, materials, food and feed rather than on the evanescent usage of fossil resources. The cornerstone of this economy is the biorefinery, in which renewable resources are intelligently converted to a plethora of products, maximizing the valorization of the feedstocks. Innovation is a prerequisite to move a fossil-based economy toward sustainable alternatives, and the viability of the bio-based economy depends on the integration between plant (green) and industrial (white) biotechnology. Green biotechnology deals with primary production through the improvement of biomass crops, while white biotechnology deals with the conversion of biomass into products and energy. Waste streams are minimized during these processes or partly converted to biogas, which can be used to power the processing pipeline. The sustainability of this economy is guaranteed by a third technology pillar that uses thermochemical conversion to valorize waste streams and fix residual carbon as biochar in the soil, hence creating a carbon-negative cycle. These three different multidisciplinary pillars interact through the value chain of the bio-based economy.