High yielding tropical energy crops for bioenergy production: Effects of plant components, harvest years and locations on biomass composition

Performance and mechanism of various microaerobic pretreatments on anaerobic digestion of tobacco straw

Tobacco straw is an abundant biomass in China's agricultural ecosystems, and has high potential for methane production. However, the anaerobic digestion (AD) efficiency is limited by the recalcitrant lignocellulose structure of the tobacco straw. In this study, three microaerobic pretreatments were performed for the AD of tobacco straw to increase methane production. Among them, microbial pretreatment with biogas slurry at an oxygen concentration of 4 mL/g VS resulted in the highest methane production of 349.1 mL/g VS, increasing by 19.8 % than that of untreated. During this pretreatment, the relative abundances of Enterococcus and Clostridium sensu stricto 12, which are closely related to acetic acid production and cellulose degradation, were high, and these bacteria might have an important contribution to substrate hydrolysis and the methanogenesis efficiency of the AD process. This study advances the understanding of microaerobic pretreatment processes and provides technological guidance for the efficient utilization of tobacco straw.

Biochemical methane potential of dairy manure residues and separated fractions: An Australia-wide study of the impact of production and cleaning systems

This study investigated biochemical methane potential (B0) of manure residues and solid-liquid separation fractions from Australian dairies. This is important for country-specific sector emissions and biogas potential estimates. A range of samples were collected from 12 farms across 4 Australian states, and B0 was measured. A first B0 value for grazing dairy effluent is reported, at 161 LCH4·kgVS-1. The B0 of manure residues from intensive dairies with total mixed ration feeding was not significantly different, at 202 LCH4·kgVS-1. Passive solid-liquid separation decreased B0 with potential fugitive methane losses. Mechanical separation preserved B0, allowing organic matter diversion to reduce fugitive methane emissions. Cleaning method at a dairy significantly influenced residue total solids content, important for solid-liquid separation and selection of anaerobic digestion technology. Overall, B0 for Australian dairy residues was estimated at 76.2 million m3N methane per annum, with a total energy content of 2.8 petajoules·annum-1.

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.

Recent advancements in strategies to improve anaerobic digestion of perennial energy grasses for enhanced methane production

Perennial energy grasses (PEGs) are supposed to be a momentous heading to the development of biomass energy on account of their characteristic superiorities of high yield, strong adaptability and no direct competition with food crops. Anaerobic digestion of PEGs with great biogas-producing potential occupies an irreplaceable status despite a variety of pathways for conversion to renewable energy. However, efficient digestion of PEGs suffers from severe challenges in connection with feedstock properties such as recalcitrant structures. This review highlights recent research in anaerobic digestion of PEGs and focuses on essential aspects enhancing anaerobic digestion performance: types and properties of grasses, diverse pretreatments, various co-feedstocks for co-digestion, dosing of different additives, and improvements in reactors. General discussions on the future prospects of anaerobic digestion of PEGs are proposed. Overcoming knowledge gaps and technical limitations will facilitate further application of PEGs on an industrial scale.

Development and Utilization of an Isolation Box Test to Characterize Personality Traits of Dairy Calves

The use of an isolation box test (IBT) to characterize personality traits has been used in non-bovine species with success. We aimed to develop an IBT for dairy calves and determine if the behavioral responses to an IBT were associated with personality traits found from traditional tests (novel person, novel object, and a startle tests) and average daily gain (ADG; Kg/d) through weaning. Calf movement while in the IBT was measured via accelerometers attached to 5 locations on the exterior of the box. A total movement index (TMI) was calculated based on accelerometer readings during the IBT. We performed a principal component analysis on the traditional tests and identified 3 influential factors that we labeled as “fearful,” “bold,” and “active.” Calves were weighed biweekly to track liveweight ADG. Factor scores and ADG were regressed against TMI. A significant negative association was found between the TMI and the factor “active,” indicating the validity of IBT as a tool for assessing some personality traits of dairy calves. Furthermore, TMI had a positive association with ADG through the entire experimental period and thus has potential to help predict performance through weaning. IBT has potential to be used as a personality test in research scenarios. Further development is needed to produce an IBT that would be appropriate to measure animals' responses reliably in production settings. An automated test that can accommodate a wide range of ages and developing a computer learning model to interpret output from the IBT would be a possible option to do so.

Irrigating digestate to improve cadmium phytoremediation potential of Pennisetum hybridum

The bioavailability of heavy metal and growth of hyperaccumulator are key factors controlling the phytoextraction of heavy metal from soil. In this study, the efficacy and potential microbial mechanisms of digestate application in enhancing Cd extraction from soil by Pennisetum hybridum were investigated. The results showed that digestate application significantly promoted the height, tiller number, and biomass yield of Pennisetum hybridum. The application also increased the activities of urease, sucrase, dehydrogenase, available Cd contents of rhizosphere soils (from 2.21 to 2.46 mg kg^-1), and the transfer factors of Cd from root to shoot and leaf. Assuming three annual harvests, digestate application would substantially reduce time needed for Pennisetum hybridum to completely absorb Cd from soil-from 15-16 yr-10 yr. Furthermore, the results of microbial community diversity analysis showed that digestate irrigation was more facilitated for the growth of the predominant bacteria, which were Actinobacteria and Chloroflexi at phylum level, and Sphingomonas and Nitrospiraat genus level, which mainly have the functions of promoted plant growth and metal resistance. The results suggested that the enhanced phytoextraction of Cd by Pennisetum hybridum with digestate application might mainly attributed to the increased Cd bio-availability and the enhanced plant growth, indicating that an approach combining digestate and Pennisetum hybridum could be a promising strategy for remediating Cd-contaminated soils.

Improving the biogas yield of manure: Effect of pretreatment on anaerobic digestion of the recalcitrant fraction of manure

Anaerobic digestion of animal manure show a maximum of ca. 50% conversion of volatile solids due to recalcitrance of lignin and crystalline cellulose under anaerobic conditions. The aim of this study is to evaluate different pretreatments on anaerobic digestion of manure fibers after anaerobic digestion. Physical, chemical, thermal, and thermal combined with alkaline pretreatments using sodium hydroxide were tested on manure fiber fraction separated out after anaerobic digestion of cow manure. The anaerobic digestion after pretreatment along with untreated controls were done in semi-continuous anaerobic bioreactors. All pretreatments showed positive effect and the highest increase in VS conversion (42.4%) and methane yield (ca. 127%) was found for 3% NaOH pretreated sample at 180 °C. Composition analysis showed that cellulose, hemicellulose and lignin in digested manure fibers were optimally reduced by 24.8, 29.1 and 9.5% respectively during pretreatment and 76.5% of cellulose and 84.9% of hemicellulose was converted to methane during AD.

Analysis of Plant-Production-Obtained Biomass in Function of Sustainable Energy

This research analyzed the degree of utilization of the agricultural biomass for energy purposes (combustion), in order to indicate the reasons that limit its use. The biomass potential was studied by means of the methodology of the biomass potential, whereas the factors suggesting a low degree of biomass utilization were identified by means of factor analysis. The research results reveal that there is an enormous potential of the unused agricultural biomass. This dissertation research significantly contributes to the establishment of a genuine mathematical model based on multiple linear regression. The solution obtained by this analysis, in both a mathematical and a scientific manner, conveys the primary reasons for an insufficient utilization of the biomass for energy purposes. Moreover, the paper suggests the measures to be applied for a more substantial use of this renewable source of energy and presents the expected benefits to be gained.

Hot water pretreatment of lignocellulosic biomass: Modeling the effects of temperature, enzyme and biomass loadings on sugar yield

Experimental conditions of liquid hot water (LHW) pretreatment were tested for two dedicated energy crops, Napiergrass (Pennisetum purpureum) and Energycane (Saccharum officinarum × Saccharum robustum). Both crops showed differential resistance to temperature during pretreatment and differences in response to biomass and enzyme loadings during subsequent enzymatic hydrolysis. Sugar response surfaces, for both glucose release per g pretreated biomass and as percent yield of glucose present in the initial biomass, were estimated using a General Additive Model (GAM) in R to compare non-linear sugar release as temperature, and biomass and enzyme loadings were manipulated. Compared to Napiergrass, more structural glucose is estimated to be recovered from Energycane per g of pretreated biomass under relatively less harsh pretreatment conditions, however, Napiergrass had the highest measured glucose yield. Sugar degradation products (furfural and hydroxymethylfurfural), pH, and biomass recovery differed significantly between crops across pretreatment temperatures, which could adversely affect downstream biochemical processes.

Biotransformation of methane into methanol by methanotrophs immobilized on coconut coir

This study aimed to establish a unique approach for the production of methanol from methane (CH₄) in the presence of paraffin oil mediated by methanotrophs immobilized on coconut coir (CC). Immobilization of different methanotrophs through covalent method increased the immobilization yield and relative efficiency for methanol production to 48.6% and 96.8%, respectively. In the presence of paraffin oil, methanol production was 1.6-fold higher by Methylocystis bryophila than by control. Compared to free cells, whole cells immobilized on CC showed higher stability for methanol production. Under repeated batch conditions, cumulative methanol production by immobilized cells and free cells, after eight cycles of reuse, was 52.9 and 30.9 mmol/L, respectively. This study effectively demonstrated the beneficial influence of lignocellulosic biowaste CC as support for immobilization of methanotrophs and paraffin oil on bioconversion of CH₄ to methanol.

Biomethane Production From Lignocellulose: Biomass Recalcitrance and Its Impacts on Anaerobic Digestion

Anaerobic digestion using lignocellulosic material as the substrate is a cost-effective strategy for biomethane production, which provides great potential to convert biomass into renewable energy. However, the recalcitrance of native lignocellulosic biomass makes it resistant to microbial hydrolysis, which reduces the bioconversion efficiency of organic matter into biogas. Therefore, it is necessary to critically investigate the correlation between lignocellulose characteristics and bioconversion efficiency. Accordingly, this review comprehensively summarizes the anaerobic digestion process and rate-limiting step, structural and compositional properties of lignocellulosic biomass, recalcitrance and inhibitors of lignocellulose and their major effects on anaerobic digestion for biomethane production. Moreover, various type of pretreatment strategies applied to lignocellulosic biomass was discussed in detail, which would contribution to cell wall degradation and improvement of biomethane yields. In the view of current knowledge, high energy input and cost requirements are the main limitations of these pretreatment methods. In addition to optimization of fermentation process, further studies should focus much more on key structural influence factors of biomass recalcitrance and anaerobic digestion efficiency, which will contribute to improvement of biomethane production from lignocellulose.

Anaerobic digestion of hydrothermally-pretreated lignocellulosic biomass: Influence of pretreatment temperatures, inhibitors and soluble organics on methane yield

Anaerobic digestion (AD) of lignocellulosic biomass has received significant attention for bioenergy production in recent years. However, hydrolysis is a rate-limiting in AD of such feedstock. In this study, effects of hydrothermal pretreatment of Napier grass, a model lignocellulosic biomass, on methane yield were examined through series of batch and semi-continuous studies. In batch studies, the highest methane yield of 248.2 ± 5.5 NmL CH₄/g volatile solids (VS)_added was obtained from the biomass pretreated at 175 °C, which was 35% higher than that from the unpretreated biomass. The biomass pretreated at 200 °C resulted in formation of 5-hydroxymethylfurfural and furfural, which significantly inhibited methanogenesis. In semi-continuous studies, digester fed with the biomass pretreated at 200 °C at organic loading rate (OLR) of 4 g VS/L.d resulted in digester failure. Thus, OLR_soluble/OLR_total ratio <200 is proposed as an operating criterion for effective operation of digester fed with pretreated biomass slurry.

Anaerobic digestion of high-yielding tropical energy crops for biomethane production: Effects of crop types, locations and plant parts

This study examined the composition and anaerobic digestibility of the different plant parts of two high-yielding tropical energy crops, Energycane and Napier grass, collected across three locations and two seasons. Both biomass composition and biomethane yields varied significantly with crop types, plant parts and harvest seasons. In Energycane, specific methane yield (SMY) (Nm³ (kg VS_added)^-1) was higher from stems (0.232 ± 0.003) than leaves (0.224 ± 0.003), while in Napier grass, SMY was higher from leaves (0.243 ± 0.002) than stems (0.168 ± 0.002). Energycane had higher specific and total (Nm³ ha^-1 year^-1) methane yields (0.230 ± 0.002 and 8749 ± 494, respectively) than Napier grass (0.192 ± 0.002 and 5575 ± 494, respectively). The SMYs from biomass correlated negatively with acid detergent fiber, cellulose and lignin content in the biomass. Energycane and Napier grass had lower specific but comparable total methane yields (TMYs) with maize. The ecological, economic and environmental merits associated with perennial crops suggest they could outperform maize as a substrate for bioenergy production.