Biogas Engineering Research Articles

Deciphering the Impact of Lignin on Anaerobic Digestion: Focus on Inhibition Mechanisms and Methods for Alleviating Inhibition.

China has abundant lignocellulosic biomass resources. These resources are converted into biogas by anaerobic digestion (AD), which not only realizes the comprehensive utilization of waste resources but also obtains abundant biomass energy. However, the low biodegradability of lignocellulosic biomass caused by the complex structure has seriously hindered its utilization by enzymes and microorganisms, resulting in low biogas production and limited development of biogas engineering. The purpose of this work is to analyze the mechanism of lignin inhibiting AD and summarize the main methods for alleviating inhibition. Based on this, this review examines the factors influencing lignin's inhibition of methane production during AD from two key perspectives: (1) discussing lignin's biodegradability challenges, with a focus on its structure, functional groups, and the impact of lignin content in lignocellulosic biomass on its methanogenic potential, and (2) analyzing lignin's impact on each stage of AD. In addition, we provide insights into future research directions in this field.

Does Scaling Up Pig Farming Promote Carbon Neutrality Among Pig Farmers?

Pig farming is a major source of carbon emissions in China's livestock industry, and the promotion and application of carbon neutral technologies dedicated to carbon reduction and sequestration is a key measure to promote the realization of carbon neutrality in pig farming industry. In the absence of a system for carbon emission reduction in agriculture, it is important to explore whether large-scale pig farming can spontaneously promote the application of carbon neutral technologies by pig farmers. Combined with the technical background of carbon neutrality in pig farming industry and using the field survey data of 468 pig farmers in Shandong Province, this paper empirically analyzed the effect of large-scale pig farming on the carbon neutral behavior of pig farmers. The findings are threefold. Firstly, because of the effect of economies of scale in the application of carbon neutral technologies, large-scale pig farming can promote the carbon neutral behavior of pig farmers. However, the effect of economies of scale in the application of carbon neutral technologies has a boundary, and the annual output of pigs should be maintained at 3000 to 4999. Secondly, among the effects of pig breeding scale on the application and its degree of composting project, state of planting and breeding cycle has no regulating effect. Thirdly, among the effects of pig breeding scale on the application and its degree of biogas engineering, both state of planting and breeding cycle and subsidy for construction of biogas digester have negative regulating effects. In this paper, the pig farming industry is taken as a typical example to reveal the endogenous incentive mechanism of promoting agricultural carbon emission reduction, which provides theoretical reference and experience enlightenment for the formulation of effective policies to promote agricultural carbon neutrality, which are different from industrial industries.

Synergistic mechanism of substrate hydrolysis and methanogenesis under “gradient anaerobic digestion” process

The destruction of the synergistic effect of the hydrolysis-methanogenesis process (HMP) of substrate may lead to the serious carbon loss of substrate and low biogas yield in traditional straw biogas engineering. In this study, the influence of substrate composition on anaerobic digestion (AD) was investigated under pilot conditions, and the relationship between HMP was further investigated under full-scale plants. The results showed that straw with a high content of soluble substances had the highest methane yield (264.25 L/kg VS) and degradation rate (59.32 %). At HRT = 20 d, the full-scale plant achieved the highest biogas yield (576.92 L/kg VS, 3.47 L/L/d) and degradation rate (67.50 %). Microbial analysis showed that substrate composition affected microbial community and methanogenic metabolic pathway. The analysis results of PICRUSt2 confirm that gradient AD guarantees the synergistic relationship of HMP. This study provides the theoretical basis and engineering guidance for improving the AD process in traditional straw biogas engineering.

Biogas upgrading by biotrickling filter: Effects of temperature and packing materials

Biological hydrogen-methane conversion technology can combine Power-to-Gas technology with biogas engineering and showed great potential in breaking through the limitations of both hydrogen storage and CO2 removal for biogas upgrading. However, the low gas–liquid mass transfer rate of hydrogen greatly limited its conversion efficiency and actual application. This study used a biotrickling filter (BTF) to address this limiting factor, and the effects of temperature and packing materials on hydrogen-methane conversion were investigated. Results showed that higher temperature was beneficial for hydrogen-methane conversion, and the highest conversion efficiency of 8.3 L/Lw·d was obtained at 55 °C with the archaeal community dominated by Methanothermobacter (99.97 %). The reactor using activated carbon as packing material showed the best hydrogen-methane conversion efficiency of 91.9 %, with the most methanogens fixed on the surface. Due to the electronic conductor property of activated carbon, the microbial communities of the biofilm were also different from the other two packing materials. Finally, the H2/CO2 ratio of the gas inflow was optimized, and the most suitable result was 2.5:1 (H2/CO2, v/v), which was far below the previously reported results and indicated higher efficiency in carbon dioxide removal. This study provided a promising way for biogas upgrading.

Retracted: Energy Efficient Utilization toward Rural Biomass Waste by Straw Biogas Engineering

Retracted: Energy Efficient Utilization toward Rural Biomass Waste by Straw Biogas Engineering

Effect of raw material and application rate of biogas slurry on Cucumber growth, Fusarium wilt suppression, and soil properties

With the popularization and application of biogas engineering, byproduct biogas slurry has excellent application potential as organic liquid fertilizer, while its source and application rate significantly affect its effect. Irrational application of biogas slurry, can reduce crop yields and cause environmental problems such as soil salinization and diffuse source pollution. In this study, the impact of different types of biogas slurry from various materials (i.e., pig manure, chicken manure, vinasse, and kitchen waste) and their required application rates on the growth and incidence of cucumber were investigated by analyzing the dry weight of cucumber, soil chemical properties, soil extracellular enzyme activity, and the incidence of cucumber wilt disease. The results showed that the effects of the four selected types of biogas slurry on cucumber growth and disease were similar. It was shown that 3% was the most suitable application rate considering the dry weight of cucumber plants and the incidence of wilt disease. At this application rate, it was achievable to increase soil pH, soil AN, AK, Olsen P content, and enzyme activities without increasing the risk of salinization. In summary, despite different sources, biogas slurry showed the best growth promotion and disease suppression ability in 3% (v/w) application, without the risk of soil salinization.

Anaerobic co-digestion scheme of biogas engineering based on feedstock and temperature

This article investigates the current status and distribution of the feedstock of biogas engineering in China, evaluates the temperature conditions for anaerobic co-digestion (AcoD), and assesses the biogas production potential of feedstock in AcoD, including six feedstocks, namely, maize straw (M), wheat straw (W), rice straw (R), pig manure (P), cow manure (C), and sheep manure (S). The total amount of M, W, and R was 3.89 × 108, 2.10 × 108, and 1.50 × 108 tons, respectively, and that of P, C, and S was 8.46 × 108, 1.31 × 109, and 4.95 × 108 tons, respectively. However, the spatial distributions and amount of those resources were found to be uneven in China. Heilongjiang has abundant maize straw, and Henan has abundant wheat resources. Sichuan is rich in cow manure, while Inner Mongolia is rich in sheep manure. The analysis of total biogas production (TBP) by mono-digestion and co-digestion (using two feedstocks at ratio of 1:9, 3:7, 5:5, 7:3 and 9:1) showed that co-digestion outperforms mono-digestion under 15 and 25 °C. Thus, it is necessary to study anaerobic co-digestion scheme (AcoDS), which will provide a reference for biogas engineering in different regions to promote the biogas yield based on their actual situation.

Influence of Biochar on Physico-Chemical, Microbial Community and Maturity during Biogas Residue Aerobic Composting Process

With the rapid development of large and medium-sized biogas projects, the high-value utilization of anaerobic fermentation residues has become a hot spot in recent years. In this study, biogas residue from biogas engineering was used as composting raw material, and 0 (CK), 2.5% (T1), 5.0% (T2), 7.5% (T3), and 10.0% (T4) biochar was added to investigate its effects on physico-chemical properties, microbial populations, and maturity degree during the aerobic composting process. Results show that the addition of biochar shortens the time (3 days) to reach the high-temperature period, increases the composting temperature (63.8 °C) and germination index (GI), decreases the electrical conductivity (EC), reduces the loss of C and N elements, and increases the microbial population during composting. These results suggest that biochar can improve the maturity and fertility of compost products, and significantly regulate the structure and function of microbial communities during the composting process.

Effect of Biochar Addition on Mechanism of Heavy Metal Migration and Transformation in Biogas Residue Aerobic Compost

In this study, biogas residue fermented by biogas engineering was used as compost raw material, and different quality biochar was added in the composting process to explore the effect of biochar on the transformation of heavy metals in the composting process. The composting process was comprehensively analyzed with the potential ecological risk assessment of heavy metals and redundancy analysis. The addition of 10.0% biochar during composting had a strong passivation effect on exchangeable Cu and Cd, with passivation rates of 11.75 and 63.89%, respectively; the addition of 2.5 and 7.5% biochar had strong passivation ability for exchangeable Zn and Pb, and the passivation rates were 15.26 and 45.02%, respectively. At the end of composting, the potential ecological risk indexes of each treatment were T4 (10.0% biochar) > T3 (7.5% biochar) > T2 (5.0% biochar) > T1 (2.5% biochar) > CK (no biochar added). The risk of heavy metal pollution during the aerobic composting of biogas residue was low, which significantly reduced secondary pollution during the composting process.

Energy Efficient Utilization toward Rural Biomass Waste by Straw Biogas Engineering

In this article, we summarize and analyze the constraints and technical difficulties of biogas plants in clusters, storage and transportation yards, pretreatment yards, and anaerobic fields. Combined with Tyre’s own experience, several major techniques have been proposed. To guide and recommend the suitable technicians to decision makers, to acquire operation courses suitable for the general requirements of our biogas, and to promote the development of booth biogas seedlings in China, the use of environmental slam objects in a small and sufficient nonscale biogas program is formulated by the use of biogas funding alone. Current rating measures leverage the World Age Assessment (LCA) for the Integrated Booth Biogas Swing Type (typically 40,000 kWh) and Bio-Natural Gasoline Program (daily gasoline workload of 12,000 cubic curves). This is built upon the Environmental Impact Assessment and Analogy for Warships Both environmental stroke and sensitivity component analysis. These techniques include termination outlines, register analysis, dynamism drops for each performance stagecoach, and environmental issue calculations. According to the above summarization, when biogas dominates the family, the highest environmental emission becomes the biogas fermentation layer of the booth. Meanwhile, the most sympathetic substitute is the work cost of physical and chemical farting (mL g-1TS). The above two indicators denote the essence of biogas purification, and the choice of biogas purification technology. By evaluating the change in the impact of suppressing environmental emissions, the biogas substitute of scorpion charcoal has a remarkable improvement in the biogas equivalent of the charcoal-bright swing family. Comprehensive experimental results have demonstrated this conclusion.

Resource Utilization of Biogas Waste as Fertilizer in China Needs More Inspections Due to the Risk of Heavy Metals

The utilization of livestock waste has attracted increasing attention in recent years. The presence of high levels of heavy metals is a major obstacle to the utilization of biogas as a fertilizer resource. In this study, the heavy metal contents in biogas residue, slurry, and discharged sewage from three representative farms of gooseries, henneries, and dairy farms in the Yangtze River Basin were investigated and assessed. The results demonstrated that heavy metals, including Cd, Mn, As, Cu, Pb, Cr, Zn, etc., could be detected in all biogas residues, with significantly different contents between farm types (p < 0.005). Specifically, biogas residues from the goosery and the dairy farms met “China’s Organic Fertilizer Standards” (COF Standards); however, Cd concentrations in biogas residues from hennery farms exceeded the limits by five times. The concentrations of Cd and Pb in biogas slurries from all of the farms exceeded the limits of the “China Farmland Irrigation Water Quality Standard” (CFIWQ Standard). In particular, the Pb concentrations in biogas slurry from the dairy farms exceeded the limits by 29 times, and the discharged sewage from all three farm types complied with the comprehensive sewage discharge standards in China; however, only that from the goosery farms was suitable for irrigation. Thus, it is recommended to increase the feed selection, biogas engineering, and biological-purification-supporting technology, and to carry out regular sampling inspections of the biogas residue, slurry, and discharged sewage for heavy metals, so that environmental and crop pollution risks can be reduced when they are used as sources of nutrients for eco-friendly agriculture.

Rapid Biochemical Methane Potential Evaluation of Anaerobic Co-Digestion Feedstocks Based on Near Infrared Spectroscopy and Chemometrics

Biochemical methane potential (BMP) of anaerobic co-digestion (co-AD) feedstocks is an essential basis for optimizing ratios of materials. Given the time-consuming shortage of conventional BMP tests, a rapid estimated method was proposed for BMP of co-AD—with straw and feces as feedstocks—based on near infrared spectroscopy (NIRS) combined with chemometrics. Partial least squares with several variable selection algorithms were used for establishing calibration models. Variable selection methods were constructed by the genetic simulated annealing algorithm (GSA) combined with interval partial least squares (iPLS), synergy iPLS, backward iPLS, and competitive adaptive reweighted sampling (CARS), respectively. By comparing the modeling performances of characteristic wavelengths selected by different algorithms, it was found that the model constructed using 57 characteristic wavelengths selected by CARS-GSA had the best prediction accuracy. For the validation set, the determination coefficient, root mean square error and relative root mean square error of the CARS-GSA model were 0.984, 6.293 and 2.600, respectively. The result shows that the NIRS regression model—constructed with characteristic wavelengths, selected by CARS-GSA—can meet actual detection requirements. Based on a large number of samples collected, the method proposed in this study can realize the rapid and accurate determination of the BMP for co-AD raw materials in biogas engineering.

Effects of acid modification on the structure and adsorption NH4+-N properties of biochar

The adsorption by biochar can effectively alleviate the problem of ammonia inhibition in biogas engineering. Based on batch adsorption experiments, the effect of acid modifier on physicochemical and adsorption NH4+-N properties of biochar was explored, and anaerobic digestion (AD) with addition of modified biochar (MB) was designed and carried out. The results showed that after modification, the adsorption capacity of biochar was significantly improved, and the maximum adsorbance of MB was 1.57 times higher than that of original biochar. Acid modifier had demineralization and increased the number of acidic oxygen-containing functional groups. Chemical adsorption was the dominant adsorption mechanism, mainly including surface electrostatic adsorption and the interaction between ammonium ions and surface functional groups of biochar. With the addition of MB, gas production rate of the AD of chicken manure was increased and the effective gas production period was shortened to 18 days. This research has guidance significance for alleviation ammonia inhibition during the AD by adding MB.

Biochemical methane potential prediction for mixed feedstocks of straw and manure in anaerobic co-digestion

To rapidly estimate the biochemical methane potential (BMP) of feedstocks, different multivariate regression models were established between BMP and the physicochemical indexes or near-infrared spectroscopy (NIRS). Mixed fermentation feedstocks of corn stover and livestock manure were rapidly detected BMP in anaerobic co-digestion (co-AD). The results showed that the predicted accuracy of NIRS model based on characteristic wavelengths selected by multiple competitive adaptive reweighted sampling outperformed all regression models based on the physicochemical indexes. For the NIRS regression model, coefficient of determination, root mean squares error, relative root mean squares error, mean relative error and residual predictive deviation of the validation set were 0.982, 6.599, 2.713%, 2.333% and 7.605. The results reveal that the predicted accuracy of NIRS model is very high, and meet the requirements of rapid prediction of BMP for co-AD feedstocks in practical biogas engineering.

提升中小型集中供气沼气工程效益途径研究分析

提升中小型集中供气沼气工程效益途径研究分析

Development Strategy of Biomass Economy in China

Developing biomass economy is conducive to economic growth and rural development; it reduces fossil energy consumption and improves ecological environment. Biomass economy has great development potentials, but it still faces various challenges. In this article, the biomass resources in China are comprehensively analyzed, the industry and its current situation and trend are evaluated, and the strategic objectives, key projects, and policy suggestions for industrial development are proposed. China is rich in biomass resources, and biomass briquette fuel, large-scale biogas engineering, biomass power generation and cogeneration technologies are mature. These technologies have exhibited a good momentum of large-scale development and will be the main utilization approaches for a period of time in the future. The development idea proposed in this article for the biomass economy in China regards each county-level region as a unit and considers regional resource endowment, economic development level, and industrial development requirements. The development goals of the biomass economy in China are clarified as becoming mature, system innovation, and large-scale replacement by 2025, 2035, and 2050, respectively. Furthermore, policy suggestions are proposed in terms of technology research and development, incentive policy, market cultivation, and capital investment.

Anaerobic co-digestion of chicken manure and cardboard waste: Focusing on methane production, microbial community analysis and energy evaluation

This study aimed to investigate the synergistic effect and microbial community changes between chicken manure (CM) and cardboard (CB) during anaerobic co-digestion. Meanwhile, the energy balance of biogas engineering was extrapolated based on the batch tests. In batch tests, co-digestion system achieved the highest improvement (14.2%) and produced 319.62 mL CH4/gVS with a 65:35 ratio of CB: CM. More extracellular polymeric substance secretion promoted the electron transfer for acidogenesis and more hydrolase was provided with 31.6% improvement. The microbial analysis illustrated that higher acetoclastic Methanosaeta abundance was achieved, leading to 211% enhancement of acetoclastic pathway. Moreover, associated network illustrated that the higher methane production was mainly achieved through matching of hydrolytic bacteria and acidogenesis bacteria. As for energy balance, the synergistic effect increased the energy output by 38% and energy recovery to 46.4%.

Effect of different aerobic hydrolysis time on the anaerobic digestion characteristics and energy consumption analysis

Aerobic hydrolysis of stover before anaerobic digestion is beneficial to improve the biodegradability of corn stover. Aerobic hydrolysis of corn stover at 43 °C was conducted to investigate the effects of hydrolysis time (0 h, 8 h, 16 h, and 24 h) on the degradation of lignocellulose from corn stover and material conversion. Further anaerobic digestion and energy consumption analysis with the digestion temperature of 36 °C were carried out. The accumulation rate of volatile fatty acids began to slow down after 16 h of hydrolysis, and the concentration of acetic acid reached 221.85 mmol/L at 24 h of hydrolysis. The degradation rate of lignocellulose was obviously increased after hydrolysis. When the hydrolysis time was 16 h, it reached the maximum cumulative methane production with 268.75 ml/g VS. In terms of biogas production and energy conversion efficiency, it is more appropriate to choose 16 h as hydrolysis time in biogas engineering.

Study of Gas Production by Anaerobic Fermentation and Microbial Community Changes by In-Situ Microaerobic Desulphurization

The enhancement of biogas quality at low cost and high efficiency process was one of the purposes of biogas engineering. In this work, we designed a reactor for microaerobic desulphurization. We used this reactor to study the anaerobic fermentation in systems that used cow manure with total solid (TS) concentrations of 18.5%, 15% and 10%. The influence of anaerobic fermentation on the stability of gas production and the characteristics of the gas produced with different concentrations of fermentation materials was studied. The strain structure of the fermentation system was obtained by high-throughput sequencing and taxonomy was compared. The H2S removal results showed that the average rates of the H2S removal in concentrations of fermentation materials of 18.5%, 15%, and 10% TS were 99.2%, 97.8%, and 78.8%, respectively. 16SrRNA sequencing was performed in different fermented samples as well as a comparison between samples in order to determine the number of unique species (NUS) and the number of common species (NCS). By comparing TS 18.5 with TS 15 and TS 10 samples, it was determined that under fermentation conditions, NUS were 113 and 106, respectively. Whereas NUS were 31 and 41, respectively, when comparing TS 15 and TS 10. These demonstrated that the number of strain species in the fermentation system with TS 18.5% was far more than those found in the systems with low concentration of fermentation. Also, the ability for disturbance resistance of the microaerobic desulphurization system was stronger at high concentration of the fermentation.

Biogas standard system in China

Standardization of biogas technology is immensely important for the promotion of the biogas industry worldwide. China has built a complete biogas standard system, which is divided into common, household biogas, biogas engineering, biogas digester for domestic sewage treatment, output utilization, and service system standards. The problems and potential barriers for biogas standardization in China are analyzed and come down to sluggish standard, overlapped standard, government-dominated standard, and lagging international standard. Accordingly, all potential biogas standards should be evaluated and placed under the same department. China Biogas Society and China Association of Rural Energy Industry play leading roles in developing enterprise or group/association biogas standards and ISO biogas standards. The bio-natural gas standard system and experimental standardization should be developed as well to replenish biogas standard system. A paradigm shift in biogas standardization should be from government-dominated to market-oriented model. The lessons learned for other developing countries includes expanding standardization to multi-aspects to realize full lifecycle control and management, building rapid responding mechanism of standardization to adopt industry transformation, integrating outdated standards into new versions, and establishing market-based standard system.