Rural Household Biogas Research Articles

Performance Testing and Case Studies of Rural Household Biogas Micro-CHP Systems

Against the backdrop of clean rural heating and dual carbon targets, this paper investigates and develops a household combined heat and power (CHP) unit. The performance of the unit under natural gas operating conditions was tested and evaluated in the laboratory. The test results show that at rated operating conditions the unit has an electrical efficiency of 29% and an overall efficiency of 96%. The micro-CHP was then tested in a civil building in a demonstration site in Xuzhou, Jiangsu province, for trial operation under biogas working conditions. The test results show that when the unit in biogas working condition is heating the room, the unit has a rated working condition power generation of 3.2 KW and still has an average electrical efficiency of about 26.8% and a thermal efficiency of 65.6%, which remains at a high level. And the room temperature data shows that the heat supply meets the heating demand. Finally, this paper compares the performance with micro-CHP units available in the European and American markets. The results show that the performance of this unit is superior to many micro-CHP units available overseas. This paper demonstrates through test results that rural micro-CHP system can meet the daily energy needs of farmers, improve energy use efficiency and reduce carbon emissions.

Design and numerical analysis of a composite system of a household biogas digester with pretreatment

The rural household biogas digesters are studied in this paper, and numerical analysis is used to simulate the effects of light climates in the cold season and the heat of sunlight on the temperature distribution in the pool. The numerical results show that the uneven distributions of light intensity and temperature in the biogas digester have a great influence on its cumulative gas production. The central area has a significant heat collection effect, the inner wall is weaker, and the temperature near the top is slightly higher than that in the lower area, and the vertical temperature changes in a decreasing trend. Aiming at the different photo-climatic conditions of the household biogas digester and the uneven heat collection and temperature distribution in different periods, the traditional slag pumping work is cumbersome, and the utilization rate of the biogas residue is low, so a new household with pretreatment is proposed. An intelligent temperature control system is designed for the biogas tank to analyze the adverse effects of straw fermentation at low temperature, insufficient gas production and low resource utilization.

Anaerobic digestion characteristics and key microorganisms associated with low-temperature rapeseed cake and sheep manure fermentation.

In this study, gas production from mixed anaerobic fermentation of rapeseed cake and sheep manure at low temperature (15.2-17.8°C) was investigated in Qinghai rural household biogas digesters to understand the temporal dynamics of key microbial populations involved in fermentations. Different raw material ratios resulted in significantly different effects on biogas yields and microbial community compositions over 40days. When the dry weight ratio of sheep manure to rapeseed cake was 1:2, the highest level of cumulative gas production was observed (122.92 m3·t-1). Firmicutes, Proteobacteria, Bacteroidetes, and Actinobacteria were the dominant bacterial phyla among the 29 digester samples (total relative abundances > 79.23%), followed by Synergistetes (4.09-10.7%). Lactobacillus was the most abundant genus in the biogas digesters with high rapeseed cake contents (average relative abundances: 14.68%), while Peptoniphilus exhibited higher abundances (12.69%) in the mixed treatments. In addition, unclassified Synergistaceae abundances (6.64%) were positively associated with biogas production variation among treatments. Bacteroides (5.74%) and Pseudomonas (5.24%) both accounted for larger proportions of communities in the digesters that used more sheep manure. Methanomicrobiales (66.55%) was the most dominant archaeal group among digesters, with Methanogenium (41.82%) and Methanoculleus (16.55%) representing the main gas-producing archaeal genera; they were more abundant in biogas digesters with higher sheep manure contents and higher rapeseed cake contents, respectively. VFAs and pH were the main factors associated with differences in microbial communities among the 29 samples. Specifically, VFA concentrations were positively correlated with Lactobacillus, Methanoculleus and Methanothrix abundances, while pH was positively correlated with Bacteroides, Pseudomonas, and Methanobacterium abundances.

Archaeal and bacterial community structures of rural household biogas digesters with different raw materials in Qinghai Plateau.

The present study aims to investigate microbial community structures household biogas digesters with different raw materials in Qinghai Plateau rural. High-throughput 16S rRNA gene sequencing analysis revealed that Firmicutes, Bacteroidetes, and Proteobacteria are the most abundant bacterial phyla (64.08%). Prevotella group 7 was the most abundant genus in digester YL9 and YL10 (69.72% and 26.96%, respectively) using vegetable waste raw materials. Trichococcus exhibited the highest abundance (14.55%) in YL1 digester using sheep and pig manure. Clostridium sensu stricto 1 (13.89%) and Synergistaceae_uncultured (15.52%) comprised the highest abundances in digester YL5 with mixed raw materials (i.e., dairy manure, sheep manure, and human feces). In addition, Proteiniphilum and Pseudomonas exhibited the highest abundances among bacterial genera in YL4 digester using pig manure. Methanomicrobiales was the most dominant archaeal communities, ranging from 13.35% to 81.34% in abundance. Methanocorpusculum exhibited dominant abundances in all digesters using various raw materials. Methanogenium was the most abundant archaeal genera in YL4 and YL6 digesters, which consume pig manure as primary raw material. In addition, Methanosarcina and Methanosaeta exhibited the highest abundances in digester YL1 (55.03%) and YL9 (51.40%), respectively. Moreover, fermentation temperatures and pH both contributed to the archaeal and bacterial community structures in all the investigated digesters. Specially, fermentation temperature showed positive correlation with the abundances of Synergistaceae_uncultured, Methanogenium, and Methanosaeta, and pH was positively correlated with the abundances of Prevotella group 7 and Methanosarcina abundances.

Economic Feasibility and Comprehensive Benefit Evaluation of Rural Household Biogas Utilization: Evidence from China

It is of great significance for the scientific formulation or adjustment of rural energy policy in the new era to explore the current situation of rural household biogas utilization and make a comprehensive evaluation of the benefits of biogas and its derivatives. Based on the field survey data of Qionglai, Sichuan Province, this study uses AHP to build a comprehensive evaluation index system, uses financial indicators to calculate the economic benefits of household biogas, and establishes the weight and score of the index system to comprehensively evaluate the economic, ecological and social benefits of biogas and its derivatives utilization in the survey area. The research results show that the economic benefits and social benefits of rural household biogas are good, but the ecological benefits are not up to the ideal level. Under the background of rapid development of new rural construction and urbanization, the government still needs adjusting policies, so as to meet the challenges of structural changes in the domestic energy consumption market.

The effect of temperature fluctuation on the microbial diversity and community structure of rural household biogas digesters at Qinghai Plateau.

Seasonal temperature-fluctuation has been regarded as a key environmental factor affecting rural biogas fermentation yields. The present study investigated the impact of seasonal temperature-fluctuation on operating-temperatures and biogas production in rural household digesters at Qinghai Plateau and revealed the related changes in microbial diversity and community structure by 16S rRNA gene high-throughput sequencing (HTS) analysis. Our results showed closely positive correlation between operating-temperatures and biogas production. HTS analysis indicated the highest diversity for bacteria community in autumn (at highest operating-temperatures) and late winter (at lowest operating-temperatures) and for archaea community only in autumn. HTS analysis classified bacteria into 21 phyla and 346 genera with the most predominant phyla Firmicutes, Bacteroidetes and Proteobacteria (> 72.4% in total) and the most predominant genera Proteiniphilum, Clostridium sensustricto 1, Petrimonas, Pseudomonas and Fastidiosipila (37.09-38.61% in total). HTS analysis also revealed two main archaea orders (Methanomicrobiales and Methanobacteriales) and one predominant genus Methanogenium to support plateau biogas fermentation. Especially, a remarkable impact of temperature on the community abundances of bacteria phyla Synergistetes and archaea genera Methanogenium and Thermogymnomonas was observed, and such microbial community structure changes were positively consistent with the biogas production. The present work provided the first set of evidences to link temperature-controlled modulation of microbial community structure with rural household biogas production at Qinghai Plateau.

Efficiency measures of the Chinese biogas project subsidy policy using an additive two stage DEA

In this study, based on the perspective of effectiveness, the entire process of the biogas project is divided into two sub-processes (biogas production and biogas consumption). We utilize the additive two-stage Data Envelopment Analysis to evaluate the efficiency of biogas project subsidy policy. Our finding indicates that from the perspective of input-output efficiency, the efficiency of biogas project subsidy policy is low in China. There are two main reasons for this result: the subsidy is inadequate and its purpose deviates from the actual demand. First, because the subsidy is inadequate and the construction cost of the rural biogas project is high, farmers are unable to build rural household biogas digesters by raising funds themselves. Second, the biogas project subsidy policy only stimulates the increase in biogas production through increasing the construction of large and middle scale biogas projects. But the construction of a household biogas digester is ignored. Furthermore, macro-affecting factors have a significant influence on the implementation of biogas project subsidy policy. When formulating new biogas project subsidy policy, the government should consider the influence of urbanization, per capita annual income, and international oil price fluctuations. The above analysis could provide theoretical guidance for the government to formulate new biogas project subsidy policy.

PCR-DGGE Analysis on Microbial Community Structure of Rural Household Biogas Digesters in Qinghai Plateau.

To investigate contribution of environmental factor(s) to microbial community structure(s) involved in rural household biogas fermentation at Qinghai Plateau, we collected slurry samples from 15 digesters, with low-temperature working conditions (11.1-15.7°C) and evenly distributed at three counties (Datong, Huangyuan, and Ledu) with cold plateau climate, to perform polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and further sequencing. The bacterial communities in the total 15 digesters were classified into 38 genera with Mangroviflexus (12.1%) as the first dominant, and the archaeal communities into ten genera with Methanogenium (38.5%) as the most dominant. For each county, the digesters with higher biogas production, designated as HP digesters, exclusively had 1.6-3.1°C higher fermentation temperature and the unique bacterial structure composition related, i.e., unclassified Clostridiales for all the HP digesters and unclassified Marinilabiliaceae and Proteiniclasticum for Ledu HP digesters. Regarding archaeal structure composition, Methanogenium exhibited significantly higher abundances at all the HP digesters and Thermogymnomonas was the unique species only identified at Ledu HP digesters with higher-temperature conditions. Redundancy analysis also confirmed the most important contribution of temperature to the microbial community structures investigated. This report emphasized the correlation between temperature and specific microbial community structure(s) that would benefit biogas production of rural household digesters at Qinghai Plateau.

Greenhouse Gas Mitigation of Rural Household Biogas Systems in China: A Life Cycle Assessment

Rural household biogas (RHB) systems are at a crossroads in China, yet there has been a lack of holistic evaluation of their energy and climate (greenhouse gas mitigation) efficiency under typical operating conditions. We combined data from monitoring projects and questionnaire surveys across hundreds of households from two typical Chinese villages within a consequential life cycle assessment (LCA) framework to assess net GHG (greenhouse gas) mitigation by RHB systems operated in different contexts. We modelled biogas production, measured biogas losses and used survey data from biogas and non-biogas households to derive empirical RHB system substitution rates for energy and fertilizers. Our results indicate that poorly designed and operated RHB systems in northern regions of China may in fact increase farm household GHG emissions by an average of 2668 kg CO2-eq· year−1, compared with a net mitigation effect of 6336 kg CO2-eq per household and year in southern regions. Manure treatment (104 and 8513 kg CO2-eq mitigation) and biogas leakage (-533 and -2489 kg CO2-eq emission) are the two most important factors affecting net GHG mitigation by RHB systems in northern and southern China, respectively. In contrast, construction (−173 and −305 kg CO2-eq emission), energy substitution (−522 emission and 653 kg·CO2-eq mitigation) and nutrient substitution (−1544 and −37 kg CO2-eq emission) made small contributions across the studied systems. In fact, survey data indicated that biogas households had higher energy and fertilizer use, implying no net substitution effect. Low biogas yields in the cold northern climate and poor maintenance services were cited as major reasons for RHB abandonment by farmers. We conclude that the design and management of RHB systems needs to be revised and better adapted to local climate (e.g., digester insulation) and household energy demand (biogas storage and micro power generators to avoid discharge of unburned biogas). More precise nutrient management planning could ensure that digestate nutrients are more effectively utilized to substitute synthetic fertilizers.

Alternative policies to subsidize rural household biogas digesters

Existing policies of household biogas projects focus mainly on supports on construction, but less consider management and maintenance, resulting in high scrap rate and waste of resources. Alternative policies must be explored to balance construction and operation. Taking the costs and benefits from a typical rural household biogas project, this paper assesses the economic performance at three different subsidy levels, i.e., no subsidy, existing standard and positive externality based standard. Furthermore three subsidy alternatives, one-time, annual and combined option are applied to the externality based standard. The results show that household biogas digesters have unsatisfactory economic performance without any subsidy and even in current subsidy policies. Environmental benefits of the digester were estimated as 2732 Chinese Yuan, significantly larger than existing subsidy standard. To keep continuous work during the 20-year lifespans of digesters, the income disparity of farmers among regions must be considered for policy application. With the increasing of labor costs, the ratio of initial subsidies must be reduced. These results provide policy implications to the future development of biogas projects in terms of both their construction and follow-up management, reuse of the abandoned digesters as well as the exploitation of other emerging renewable energy projects.

Development of Biofuels in China: Progress, Government Policies and Future Prospects

China is the largest energy consumer in the world, but has limited energy resources. Energy security is thus a primary concern for China. Over reliance on the consumption of fossil energy has resulted in severe environmental pollution, which puts pressure on the government to adjust its energy mix. To strengthen its energy supply and prevent further environmental degradation, China has been committed to developing renewable energies, such as biofuels.
 This article provides a comprehensive assessment of the development of biofuels, rural household biogas, and bioethanol, in particular. It also examines related government policies and the future prospects of the biofuel sector. The analysis shows that remarkable achievements have been made in the development of biogas in rural areas and in bioethanol at the industrial level. This progress is largely credited to government's strong support for the biofuel sectors. Nonetheless, although ongoing energy insecurity and environmental pollution continues to motivate the central government to support the development of biofuels, widening domestic food supply and demand gap, changes in rural life and agricultural industrialization constrain the further expansion of rural household biogas and cereal-based bioethanol. This article suggests that while China urgently needs to find alternative feedstock for the existing rural household biogas digesters and bioethanol plants, centralized biogas and non-cereal-based bioethanol projects should be prioritized for future development.

Impact of government subsidies on household biogas use in rural China

In this paper, we evaluate empirically the impact of biogas subsidies on household biogas energy use in rural China. Special attention was given to the problem of sample selection bias in assessing the impact of subsidies on biogas energy use because biogas subsidies often change the propensity for installing biogas digesters. Using data from a large-scale household survey, the results indicate that biogas subsidies did promote the construction of biogas digesters. The results suggest that a 10 percentage point increase in subsidy-cost ratio would lead to a 3% increase in digester installations. We also found that biogas subsidies correlated negatively with average time of digester use. A 10 percentage point increase in the subsidy-cost ratio would result in a 4.3% reduction in the average working time of digesters. These results suggest that the net effect of the current subsidy policy on rural household biogas use was near-negligible. Indeed, a 10 percentage point increase in the subsidy-cost ratio resulted in a mere 1.15% increase in biogas use. These findings indicate that biogas subsidies have possibly not been targeted effectively at households that would actually prefer to use biogas energy.

Publisher's Note: “Analysis on sustainable development countermeasures and barriers of rural household biogas in China” [J. Renewable Sustainable Energy 5, 043116 (2013)

First Page

Energy and GHG Analysis of Rural Household Biogas Systems in China

The Chinese government has taken great efforts to popularize rural household scale biogas digesters, since they are regarded as an effective approach to address energy shortage issues in rural areas and as a potential way of reducing greenhouse gas (GHG) emissions. Focusing on a typical rural household biogas system, the aim of this study is to systematically quantify its total direct and indirect energy, concentrating on non-renewable energy and the associated GHG emission cost over the entire life cycle to understand its net dynamic benefits. The results show that the total energetic cost for biogas output is 2.19 J/J, of which 0.56 J is from non-renewable energy sources and the GHG emission cost is 4.54 × 10−5 g CO2-equivalent (CO2-eq), with respect to its design life cycle of 20 years. Correspondingly, a net non-renewable energy saving of 9.89 × 1010 J and GHG emission reduction of 50.45 t CO2-eq can be obtained considering the coal substitution and manure disposal. However, it must be run for at least 10 and 3 years, to obtain positive net non-renewable energy savings and GHG emission reduction benefits, respectively. These results have policy implications for development orientation, follow-up services, program management and even national financial subsidy methods.

Characteristics of Mixed Fermentation by Alternanthera Philoxeroides and Corn Stalk for Biogas Production

In order to alleviate the shortage of raw materials in rural household biogas production and promote utilization of the formidable alien invasive species-alternanthera philoxeroides, mixed fermentation by alternanthera philoxeroides and corn stalk was designed and the performance was investigated in separated and different dry matter ratios (18.33, 6.25 and 3.46) treatments, by batch model at (35±1)°C.Results indicated that, the best biogas production appeared in the treatment of dry matter ratio of 6.25 when total solid (TS) loading of raw material was 8% and inoculating amount of biogas slurry was 20%, with TS and volatile solid (VS) biogas yields, and methane content of 325.74±5.11 mL/g, 456.06±4.87 mL/g and 60.56±1.23 %, respectively. Highly significant positive correlations (p˂0.01) were found between degradation rate of VS and four indexes such as average daily biogas yield, TS biogas yield, VS biogas yield and rate of change of total organic carbon (TOC) of fermentation liquid, while positive correlation between degradation rate of VS and methane content, and negative correlation between it and rate of change of volatile fatty acid (VFA), were not significant (p>0.05). Mixed fermentation by alternanthera philoxeroides and corn stalk could improve biogas production and achieve the gas peak in advance, therefore it had good feasibility.

Analysis on sustainable development countermeasures and barriers of rural household biogas in China

The paper has been designed based on the experimental survey and questionnaires to 797 farmers, 25 technicians in 41 villages, and 8 towns of Yuxi region, Yunnan, China—to analyze the universal problems in biogas utilization process, including (a) low biogas utilization rate, critical dysfunctional phenomenon; (b) poor comprehensive utilization of biogas, bio-slurry, and residue; and (c) imperfect post-installation service system. Combined with the investigated findings, the article has analyzed the main causes and influencing factors which lead to the different problems. In the end, having based on the adequate interpretation about the studying conclusion, recommendations and countermeasures for the future sustainable development of China's rural household biogas proper measures can be put forward onto consideration table, which includes (a) encourage joint household biogas construction; (b) carry out comprehensive utilization demonstration actively; (c) establish a relatively complete post-installation service system by encouraging technicians to get involved in the maintenance and management initiations. The establishment of incentive systems and co-operative approaches can help to achieve the ultimate target of appropriately “biogas-designed” that are sustainably developed and constructed in China.

Comprehensive Benefit Evaluation of Rural Household Biogas Based on Fuzzy Comprehensive Evaluation Method

The comprehensive benefit evaluation is the key of reasonable development for the rural household biogas. The evaluation index was established according to the economic efficiency, energy efficiency, ecological benefit and social benefits and so on, which was used to resolve the problem that the effect factors of comprehensive benefit evaluation of rural household biogas are more and the quantitative evaluation can't completely be finished. The secondary mathematical model of fuzzy comprehensive evaluation for comprehensive benefit evaluation of rural household biogas was established by fuzzy mathematical method. The case calculation shows that this method is simple and practical, which not only convenient for experts to compare, selection and score, but also has the effect of quantification. It is integrated between the qualitative analysis and quantitative evaluation and the result is satisfactory through.

Carbon emission reduction potential of a typical household biogas system in rural China

Given the rising expectations for the substitution of fossil energy with renewable energy as one of the solutions to cope with climate change, the carbon emission reduction potential of possible solutions should be evaluated in a holistic and systematic way. In this paper, a systematic account of carbon emission reduction potential was conducted for a typical household biogas system with a digester volume of 8 m3, using a hybrid life-cycle assessment method. Using a 20 year operation scenario, the total life cycle CO2 emission of this family-size biogas utilization system is 2.60 tons, i.e., 0.02 kg CO2/MJ, of which 98.46% is attributed to indirect emissions from building materials and labor inputs. Considering the carbon emission savings due to energy and fertilizer substitution, the annual CO2 emission reduction potential is 1.25 tons for the biogas system that is under consideration. Consequently, such rural household biogas systems should be operated for at least 1.78 years to achieve a positive reduction benefit, i.e., cumulative CO2 emission savings could offset the life-cycle-related CO2 emissions. The results also indicate that long-term, stable running and maintenance are key points to maximize the benefits of household biogas as an effective approach for carbon emission abatement in the rural areas of China.

Greenhouse gas emission reduction potential of rural household biogas CDM project

Greenhouse gas emission reduction potential of rural household biogas CDM project