Synergetic effect of combined ensiling of freshly harvested and excessively wilted maize stover for efficient biogas production

Suitable fermentation temperature of forage sorghum silage increases greenhouse gas production: Exploring the relationship between temperature, microbial community, and gas production

Silage is an excellent method of feed preservation; however, carbon dioxide, methane and nitrous oxide produced during fermentation are significant sources of agricultural greenhouse gases. Therefore, determining a specific production method is crucial for reducing global warming. The effects of four temperatures (10 °C, 20 °C, 30 °C, and 40 °C) on silage quality, greenhouse gas yield and microbial community composition of forage sorghum were investigated. At 20 °C and 30 °C, the silage has a lower pH value and a higher lactic acid content, resulting in higher silage quality and higher total gas production. In the first five days of ensiling, there was a significant increase in the production of carbon dioxide, methane, and nitrous oxide. After that, the output remained relatively stable, and their production at 20 °C and 30 °C was significantly higher than that at 10 °C and 40 °C. Firmicutes and Proteobacteria were the predominant silage microorganisms at the phylum level. Under the treatment of 20 °C, 30 °C, and 40 °C, Lactobacillus had already dominated on the second day of silage. However, low temperatures under 10 °C slowed down the microbial community succession, allowing, bad microorganisms such as Chryseobacterium, Pantoea and Pseudomonas dominate the fermentation, in the early stage of ensiling, which also resulted in the highest bacterial network complexity. According to random forest and structural equation model analysis, the production of carbon dioxide, methane and nitrous oxide is mainly affected by microorganisms such as Lactobacillus, Klebsiella and Enterobacter, and temperature influences the activity of these microorganisms to mediate gas production in silage. This study helps reveal the relationship between temperature, microbial community and greenhouse gas production during silage fermentation, providing a reference for clean silage fermentation.

Effects of nanobubble water on digestate soaking hydrolysis of rice straw

This study investigated the performance of combined nanobubble water (NW) and digestate in the soaking hydrolysis process. Two types of NW (CO2NW and O2NW) with digestate were used to soak rice straw for 1, 2, 3, 5, and 7 days. During soaking process, the volatile fatty acids (VFA) concentration in the treatment with O2NW and digestate for 3 days (O2NW-3 d) reached 7179.5 mg-HAc/L. Moreover, the highest specific methane yield (SMY) obtained in this treatment could reach 336.7 NmL/gVS. Although the addition of NW did not significantly increase SMY from digestate soaking, NW could accelerate the rate of methane production and reduce digestion time of T80. The enrichment of Enterobacter in the soaking process was observed when using CO2NW and O2NW as soaking solutions which played important roles in VFA production. This study provides a new insight into environment-friendly enhanced crop straw pretreatment, combining NW and digestate soaking hydrolysis.

Co-ensiling of rice straw and distillers grains to increase methane production and maximise energy output

High organic matter preservation during ensiling promotes material conversion and energy output. In this study, the effects of co-ensiling distillers grains and rice straw on methane production was evaluated, as distillers grains are highly acidic. For co-ensiling, distillers grains and rice straw were mixed to produce methane at five carbon/nitrogen (C/N) ratios. RD20 (C/N20) and RD25 (C/N25) were defined as high-distillers-grain groups and other mixed groups as low-distillers-grain groups. The results showed that Lactobacillus was enriched in RD25, with the highest lactic acid content reaching 54.0 g/kg of dry matter. The pH and organic dry matter loss of RD25 were lower than those of low-distillers-grain groups, but the result for lignocellulose degradation rate was reversed. An 8.6% increase in methane yield and 7.9% increase in energy output were achieved in RD25. Ensiling-anaerobic digestion systems of C/N25 provide high organic matter preservation and energy output.

Two-step anaerobic digestion of rice straw with nanobubble water

Lignocellulose usually requires pretreatment to improve biogas production. To enhance lignocellulose biodegradability and improve anaerobic digestion (AD) efficiency, different types (N₂, CO₂, and O₂) of nanobubble water (NW) were applied in this study as soaking agent and AD accelerant to increase the biogas yield of rice straw. The results showed that the cumulative methane yields of treating with NW in two-step AD increased by 11.0%-21.4% compared with untreated straw. The maximum cumulative methane yield was 313.9±1.7 mL/gVS in straw treated with CO₂-NW as soaking agent and AD accelerant (P_CO2-M_CO2). The application of CO₂-NW and O₂-NW as AD accelerants increased bacterial diversity and relative abundance of Methanosaeta. This study suggested that using NW could enhance soaking pretreatment and methane production of rice straw in two-step AD; however, combined treatment with inoculum and NW or microbubble water in the pretreatment needs to compare in future.

Steam explosion processing intensifies the nutritional values of most crop byproducts: Morphological structure, carbohydrate-protein fractions, and rumen fermentation profile

To investigate the feasibility of steam explosion on the exploitation of ruminant feedstuff, the morphological structure, carbohydrate-protein fractions, and rumen fermentation profile of five typical crop byproducts (corn cob, rice straw, peanut shell, millet stalk, and sugarcane tip) were analyzed before and after steam explosion processing. The results showed that these crop byproducts had different physicochemical properties and rumen fermentation profiles, most of which could be improved by steam explosion processing, i.e., more rough morphological surface, much-broken structure, more digestible carbohydrate fraction (non-NDF +49.92–452.24%), faster gas production rate (c +9.72–68.75%), higher dry matter digestibility (DMD48 +11.38–47.36%), more available energy (ME −3.69–+42.13%, except for peanut shell), along with more unavailable protein fraction (ADICP +27.16–102.70%). It is suggested that steam explosion processing could intensify the feeding value of most crop byproducts for ruminants, but with a caution of heat damage to proteins.

An innovative strategy to enhance the ensiling quality and methane production of excessively wilted wheat straw: Using acetic acid or hetero-fermentative lactic acid bacterial community as additives

Ensiling is an effective storage strategy for agricultural biomass, especially for energy crops (mainly energy grasses and maize). However, the ensiling of excessively wilted crop straw is limited due to material characteristics, such as a high lignocellulosic content and low water-soluble carbohydrate and moisture contents. In this study, acetic acid or hetero-fermentative lactic acid bacterial community (hetero-fermentative LAB) were employed as silage additives to improve the ensiling process of excessively wilted wheat straw (EWS). The results showed that the additives inhibited the growth of Enterobacteriaceae and Clostridium_sensu_stricto_12, whose abundances decreased from 55.8% to 0.03-0.2%, respectively. The growth of Lactobacillus was accelerated, and the abundances increased from 1.3% to 80.1-98.4% during the ensiling process. Lactic acid fermentation was the dominant metabolic pathway in the no additive treatment. The additives increased acetic acid fermentation and preserved the hemicellulose and cellulose contents, increasing the methane yield by 17.7-23.9%. This study shows that ensiling with acetic acid or hetero-fermentative LAB is an effective preservation and storage strategy for efficient methane production from EWS.

Ensiling process for efficient biogas production from lignocellulosic substrates: Methods, mechanisms, and measures

Ensiling has been developed as mainstream technologies to preserve lignocellulose biomass for biogas production. However, the lack of general evaluation methods and process mechanism research hinders the understanding of its effectiveness. In this context, we reviewed existing studies and proposed some key considerations: (1) For assessing the ensiling process, determined dry matter contents should be corrected according to the volatilization loss in oven-drying method to obtain accurate storage loss and methane yield; (2) For comprehensive assessments, the trade-off between storage loss and enhanced biomethane yield should be evaluated from the entire-chain process; (3) The mechanism to enhance methane yield is primarily attributed to increased lignocellulosic biodigestibility through acid-based hydrolysis and biological degradation during ensiling; (4) Measures including co-storage, increasing buffering capacity, adjusting carbon/nitrogen ratio, and additives can be adopted to increase biogas production. The proposed methods, mechanisms, and measures (3Ms) could help initiate the specific quality criteria of biogas-oriented silages.

Agricultural Residue Management for Sustainable Power Generation: The Poland Case Study

The European Union has set targets for renewable energy utilization. Poland is a member of the EU, and its authorities support an increase in renewable energy use. The background of this study is based on the role of renewable energy sources in improving energy security and mitigation of climate change. Agricultural waste is of a significant role in bioenergy. However, there is a lack of integrated methodology for the measurement of its potential. The possibility of developing an integrated evaluation methodology for renewable energy potential and its spatial distribution was assumed as the hypothesis. The novelty of this study is the integration of two renewable energy sources: crop residues and animal husbandry waste (for biogas). To determine agricultural waste energy potential, we took into account straw requirements for stock-raising and soil conservation. The total energy potential of agricultural waste was estimated at 279.94 PJ. It can cover up to 15% of national power generation. The spatial distribution of the agricultural residue energy potential was examined. This information can be used to predict appropriate locations for biomass-based power generation facilities. The potential reduction in carbon dioxide emissions ranges from 25.7 to 33.5 Mt per year.

Urea-assisted ensiling process of wilted maize stover for profitable biomethane production

Low contents of water-soluble carbohydrates and/or low indigenous microbial activity in wilted maize stover (WMS) usually hinder the establishment of the ensiling process, thereby resulting in a low biogas production because of high loss of dry matter (DM). To enhance the biological activity and substrate biodegradability, this study applied the synergistic regulation of sucrose (carbon source) and increasing levels of urea (nitrogen source) during the ensiling process of WMS. Compared with the application of only sucrose, a higher organic acid content (lactic acid (85 g/kg-DM) and acetic acid (14 g/kg-DM)) and higher degradation ratios for lignocellulose (hemicellulose (28%), cellulose (22%), and lignin (17%)) were observed with urea applications of 1.7% (DM) and 3.9% (DM), respectively. This was caused by the enhanced activities of the hetero-fermenter (Weissella) and cellulolytic bacteria (Cellulosimicrobium). A simultaneous addition of urea and sucrose during the ensiling of WMS increased the specific methane yield by 11.2%-21.1% in comparison to raw WMS. Moreover, an economic cost estimation revealed that this approach could be an effective storage strategy for the efficient production of methane when employing a 1.7% (DM) urea application.

Ensiling excessively wilted maize stover with biogas slurry: Effects on storage performance and subsequent biogas potential

This study evaluated the ensiling performance of excessively wilted maize stover (EWMS) with biogas slurries and the effect on the subsequent biomethane potential. Chicken and pig manure biogas slurries with or without solid-liquid separation were used to amend the stover humidity before ensiling for 60 d. The hetero-lactic-acid fermentative bacteria Atopostipes and Lactobacillus were enriched by the biogas slurry regardless of the solid-liquid separation. Significant increases in the total organic-acid content were observed in silages with chicken (41%) and pig (15%) manure biogas slurries without solid-liquid separation, which was not the case for treatments with solid-liquid separation. During the ensiling process, more lignocellulose was degraded under the high buffer-capacity provided by the ammonia-nitrogen in the biogas slurry. An increase of 7.1%-9.6% was observed for the specific methane yieldmeasured, which offset a storage loss of 5.0%-7.3%. Ensiling EWMS with biogas slurry therefore provides a viable strategy for biogas production.

Effects of different simulated seasonal temperatures on the fermentation characteristics and microbial community diversities of the maize straw and cabbage waste co-ensiling system

Ensiling is considered as a suitable method to preserve seasonal agricultural residues to enable long-term supply for wastes valorization. In this study, the effects of simulated seasonal temperatures (-3, 18 and 34 °C) on the organic compositions, ensiling fermentation characteristics, and microbial community evolution during 120 days co-ensiling of maize straw and cabbage wastes were investigated. Successful storage performance was obtained at all these three temperatures. Comparatively, silages at 18 and 34 °C showed lower ammonia nitrogen, lower pH and more intensive lactic acid bacteria fermentation than that at -3 °C. Both silages at -3 and18 °C were well-preserved for 120 days with higher biodegradation potential (BDP), accompanied by lower content of acid detergent lignin (ADL). However, the silages at 34 °C could only preserved for 90 days due to low carbohydrate, low BDP and higher ADL content than that at -3 or18 °C. The storage temperature is a critical parameter that significantly affected the silage quality by influencing the microbial community diversity in silages. Proteobacteria and Firmicutes were dominant bacteria at phylum level for all silages while the dominant lactic acid bacteria at genus level were Lactobacillus and Leuconostoc, which restrained the undesirable microbes such as Enterobacteriaceae, Pseudomonas, Flavobacterium, and Pantoea during co-ensiling. Co-ensiling of maize straw with vegetable wastes may provide a promising strategy for long-term preservation of air-dried crop straw while using vegetable wastes as regulatable supplement to achieve silages of desired quality. This study could provide valuable information for conservation and management of agricultural wastes.

Improving the quality of rice straw silage with Moringa oleifera leaves and propionic acid: Fermentation, nutrition, aerobic stability and microbial communities

Mixed ensiling is believed an effective way to improve nutrient preservation and utilization. The effect of mixing Moringa oleifera leaves (MOL) on silage quality, aerobic stability and microbial communities of rice straw ensiled with/without propionic acid were investigated after 140 days fermentation. The results showed that mixing MOL decreased the pH (4.69 vs 3.85), butyric acid (17.4 g/kg DM vs not detected), ammonia-N (3.36 vs 2.17 g/kg DM) and fiber contents (626 vs 462 g/kg DM) but increased protein content (88.4 vs 125 g/kg DM) of rice straw silages. It also increased the relative abundance of Lactobacillus (12.96% vs 50.82%) at unsealing and Issatchenkia (2.02% vs 36.03%) after exposure to air, and might improve aerobic stability of silages. The addition of propionic acid could inhibit deaminization activity during ensiling and exposure to air. It is suggested mixing MOL could improve the fermentation quality and nutrition of rice straw silage.

Dynamics of fermentation quality, physiochemical property and enzymatic hydrolysis of high-moisture corn stover ensiled with sulfuric acid or sodium hydroxide

A better understanding of biomass usability during storage would offer basis for management decisions in production. High-moisture corn stover was ensiled with sulfuric acid (H₂SO₄, 0.3% and 0.6%) or sodium hydroxide (NaOH, 0.5% and 1.0%) and ensiling characteristics, lignocellulosic profile and enzymatic saccharification were investigated on day 3, 7, 15, 30 and 60 of ensiling. The results showed that 0.6% H₂SO₄ reduced dry matter loss (9.81% to 6.34%) and ammonia-N content (3.89 to 1.04 g/kg DM) during ensiling, whereas it was converse for NaOH treatment (19.89%, 5.74 g/kg DM). Hemicellulose was reduced (27.98% to 22.61%, 16.81% DM) by 0.6% H₂SO₄ or 1.0% NaOH. Saccharification yield was decreased (306 to 229 mg/g DM) during ensiling, which was improved (229 to 356, 277 mg/g DM) by H₂SO₄ and NaOH treatments. This study suggests that ensiling with addition of 0.6% H₂SO₄ could improve nutrient preservation and saccharification yield of high-moisture corn stover.

Coupling of Rural Energy Structure and Straw Utilization: Based on Cases in Hebei, China

China’s coal-based energy structure is the main reason for the current high-level air pollution and carbon emissions. Now in the North China Plain, the government is vigorously promoting “coal to gas” and “coal to electricity” in the country and the vast rural areas. The development and utilization of biomass resources in agricultural areas is also an effective means of replacing coal. We propose the idea of forming a complementary rural energy structure of “biogas, briquetting, electricity (BBE)” model based on centralized biogas production (CBP) and straw briquetting fuel (SBF) to improve the rural energy structure. This article uses emergy analysis methods to analyze actual cases. It needs to have strengths and avoid weaknesses in mode selection. The process of the analysis reveals the disadvantages and improvement measures. Under the current capacity load, the emergy input and output, eco-economic indicators, sustainable development indicators, environmental load indicators, and economic value have their own advantages and disadvantages. Assuming 100% capacity load, the indicators have great optimization space. Reducing labor input during the planting phase can effectively reduce emergy input. The government needs to provide corresponding support based on the strengths and weaknesses of the project to keep the project sustainability. The development of complementary integration based on local conditions is an important measure to optimize the energy consumption structure in rural areas and improve the ecological environment.

Maize Straw as a Valuable Energetic Material for Biogas Plant Feeding

Maize has great potential, especially as a substrate for biofuels production. The aim of this paper is to analyze the possibility of usage in methane fermentation maize straw harvested in different weather conditions, which had an influence on different physical parameters, mainly the dry mass content. The research has shown that maize straw harvested in Central-Eastern Europe can have a broad spectrum of dry mass content, which is related to diverse weather conditions during autumn. However, independently from moisture content, maize straw can be a good (for more wet material) or very good (for more dried straw) substrate for the biogas plant. With the methane productivity reaching 201–207 m³/Mg of fresh mass, this material is a significantly better substrate than that typically used in Europe maize silage (approximately 105 m³/Mg FM). It was noted that the retention time for maize straw (36–42 days) is longer than in the case of maize silage (less than 30 days). However, this difference is quite small and can be accepted by the biogas plant operators.