Household Biogas Digesters Research Articles

Current Status and Future Prospects of Small-Scale Household Biodigesters in Sub-Saharan Africa

Despite the age of the technology, sub-Saharan African (SSA) countries have numerous challenges that hinder biogas from being widely adopted. This review investigates the current gap between holistic use and the need for small-scale household biodigester adoption and effectiveness in rural and semiurban households of SSA. It reviews the present situation and potential of small-scale household digesters for sustainable future energy and biofertilizer use, with a focus on SSA. A literature survey was performed on small-scale household biogas digesters, and issues relating to the distribution, use, and implementation status with their implications on the future of small-scale household digesters in SSA were briefly reviewed. In recent years, the overall number of domestic biogas digesters installed across SSA countries has shown a significant increase due to the efforts of the National Domestic Biogas Programs such as the African Biogas Partnership Program with the Netherlands Development Organization and the Humanist Institute for Development Cooperation. However, based on an extensive literature review on small-scale household biodigesters in SSA, the study highlights that the success of biogas technology as a clean domestic cooking fuel has been relatively low. The findings of this review show that SSA countries still face a number of hurdles, the most significant of which can be boiled down to the need for technological advancement according to local context, social acceptance, and large initial investment costs. In order to overcome these obstacles and advance technological capability, social acceptance, financial benefits, and environmental impacts in order to improve its use and widespread dissemination as a renewable energy source, a highly effective organic fertilizer, and economic benefits for the betterment of SSA communities, more well-organized work and adequate research activities should be initiated and supported. The findings may be useful to researchers, practitioners, and policymakers who support/promote sustainable energy and waste management strategies in low-resource settings.

A systematic review of the design considerations for the operation and maintenance of small-scale biogas digesters

This review investigates small-scale biogas digesters' design and construction considerations to address biogas digesters' failures shortly after installation. The frequent failures of small-scale or household biogas digesters negatively affect its adoption as a clean domestic cooking fuel in developing countries, affecting the achievement of Sustainable Development Goal (SDG) 7. The study considered Scopus database-indexed peer-reviewed journals published between 2000 and 2022. Selected papers focussed on real-time monitoring, stirring mechanisms, and temperature control systems based on predefined inclusion and exclusion criteria with initial search results of 4751 documents, narrowing to 55 papers. The PRISMA 2020 statement was adopted to conduct the study. The study highlights the importance of incorporating a real-time monitoring system as a design factor in small-scale biogas digesters for successful operation and maintenance. The study's findings may be helpful to practitioners, policymakers, and researchers promoting sustainable energy and waste management solutions in low-resource settings.

Unlocking the power of synergy: Cosubstrate and coculture fermentation for enhanced biomethane production

The energy crisis, shortage of conventional fuels, and increasing pollution have directed the research toward renewable energy. Methane is one such form of energy that can be used as fuel directly or for electricity generation. It is one of the conventional fuels produced as biogas in triable and rural areas from organic waste using household biogas digesters. However, adapting such technology at commercial and global scales needs to withstand many challenges like purity and quality of methane, yield, cost of production, and efficient utilization of biomass residues. Generally, organic residues from industries and agricultural fields have higher applicability due to availability in abundance but their complex nature slower down the degradation process. In addition, some of the residues are rich in carbon while some are rich in nitrogen which might affect the product yield hence coculture and codigestion are effective approaches to valorize the waste. Coculture provides the possibility to exploit multiple pathways to degrade polymer compounds along with transformation into methane while codigestion might balance the availability of nutrients. The approach has proved promising but commercial exploitation needs further exploration for the compatibility and stability of coculture.

Dissemination of antibiotic resistance genes through fecal sewage treatment facilities to the ecosystem in rural area

Infection of antibiotic-resistant pathogens mostly occurs in rural areas. In this paper, the dissemination of antibiotic resistance genes (ARGs) through fecal sewage treatment facilities to the ecosystem in a typical rural area is investigated. Household three-chamber septic tanks (TCs), household biogas digesters (BDs), wastewater treatment plants (WWTPs), vegetable plots, water ponds, etc. Are taken into account. The relative abundance of ARGs in fecal sewage can be reduced by BDs and WWTPs by 80% and 60%, respectively. While TCs show no reduction ability for ARGs. Fast expectation-maximization microbial source tracking (FEAST) analysis revealed that TCs and BDs contribute a considerable percentage (15–22%) of ARGs to the surface water bodies (water ponds) in the rural area. Most ARGs tend to precipitate in the sediments of water bodies and stop moving downstream. Meanwhile, the immigration of microorganisms is more active than that of ARGs. The results provide scientific basic data for the management of fecal sewage and the controlling of ARGs in rural areas.

Assessment of biogas production and fertilizer properties of digestate from cow dung using household biogas digester

Assessment of biogas production and fertilizer properties of digestate from cow dung using household biogas digester

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.

Research on the Non-Point Source Pollution Characteristics of Important Drinking Water Sources

In recent years, freshwater resource contamination by non-point source pollution has become particularly prominent in China. To control non-point source (NPS) pollution, it is important to estimate NPS pollution exports, identify sources of pollution, and analyze the pollution characteristics. As such, in this study, we established the modified export coefficient model based on rainfall and terrain to investigate the pollution sources and characteristics of non-point source total nitrogen (TN) and total phosphorus (TP) throughout the Huangqian Reservoir watershed—which serves as an important potable water source for the main tributary of the lower Yellow River. The results showed that: (1) In 2018, the non-point source total nitrogen (TN) and total phosphorus (TP) loads in the Huangqian Reservoir basin were 707.09 t and 114.42 t, respectively. The contribution ratios to TN export were, from high to low, rural life (33.58%), farmland (32.68%), other land use types (20.08%), and livestock and poultry breeding (13.67%). The contribution ratios to TP export were, from high to low, rural life (61.19%), livestock and poultry breeding (21.65%), farmland (12.79%), and other land use types (4.38%). The non-point source pollution primarily originated from the rural life of the water source protection zone. (2) Non-point source TN and TP pollution loads and load intensities showed significantly different spatial distribution patterns throughout the water source protection area. Specifically, their load intensities and loads were the largest in the second-class protected zone, which is the key source area of non-point source pollution. (3) When considering whether to invest in agricultural land fertilizer control or rural domestic sewage, waste, and livestock manure pollution control, the latter is demonstrably more effective. Thus, in addition to putting low-grade control on agricultural fertilizer loss, to rapidly and effectively improve potable water quality, non-point source pollution should, to a larger extent, also be controlled through measures such as establishing household biogas digesters, introducing village sewage treatment plants, and improving the recovery rate of rural domestic garbage. The research results discussed herein provide a theoretical basis for formulating a reasonable and effective protection plan for the Huangqian Reservoir water source and can potentially be used to do the same for other similar freshwater resources.

Analysis of the types of animal husbandry and planting that influence household biogas in rural China

Producing biogas from agricultural waste by using a household biogas digester has a critical role in increasing energy supply and reducing greenhouse gas emissions in rural areas. However, only a few studies have analyzed the type of animal husbandry and planting that influence household biogas. This paper analyzes the spatial-temporal distribution of household biogas and its proportion in the total biogas produced in rural China from 2009 to 2018. The correlation between household biogas in rural China and animal husbandry and planting from 2009 to 2018 is also examined. The types of animal husbandry and planting that influence household biogas are then respectively determined via ordinary least squares and geographically weighted regression. Results show that the spatial-temporal distributions of household biogas with maximum and minimum values of 1.384 × 1010 m3 in 2011 and 0.8420 × 1010 m3 in 2018, respectively and its proportion with maximum and minimum values of 94.83% in 2009 and 75.07% in 2018, respectively significantly vary and show a declining trend from 2009 to 2018. The number of cattle and pigs is identified as the main animal husbandry factor that influences household biogas, whereas the planting areas of vegetables, fiber, and tobacco were identified to be the main planting factors. Considering fitting effects, R2 and adjusted R2 values of 0.8620 and 0.8100 obtained by geographically weighted regression respectively, were higher than those of ordinary least squares (0.6480 and 0.6220, respectively), respectively in animal husbandry factors, whereas R2 and adjusted R2 values of 0.8400 and 0.7990 obtained by geographically weighted regression, respectively, were higher than those of ordinary least squares (0.7190 and 0.6880, respectively) in planting factors. These results provide a reference for planning the production of biogas and the utilization of agricultural waste.

Challenges and strategies for biogas production in the circular agricultural waste utilization model: A case study in rural China

As a renewable energy source, production and utilization of biogas is of great benefit to mitigation of greenhouse gas (GHG) emissions, reduction of the dependency on fossil fuels, and promotion of the utilization of livestock manure and crop straw. It has been widely popularized in rural China, yet the benefits and drawbacks of the operation of household biogas digesters (HBD) are not well-understood, resulting in the operation of HBD failing to live up to expectations. This study used propensity score matching (PSM) to estimate the true benefits of the HBD process, explored the drivers and barriers for households to continue using HBD with the logit model, and identified the determinants of HBD operation time by using the tobit model. Results showed that of the 1743 households interviewed, 42% had adopted HBD and the average biogas production time using HBD was 6.66 months per year. It was estimated that HBD owners could save 474 Chinese yuan (CNY) annually by using HBD and that the net present value of the HBD program would be generated after eight years of operation. However, lack of technical training and subsidies for HBD operation were the key barriers for households to carry on using HBD. Conversely, a warm local climate and HBD with larger size had positive effects on households deciding to continue using HBD. Thus, comprehensive policies addressing construction and operation of HBD, as well as new methods for a high-value supply chains to comprehensively utilize biogas products could solve dilemmas in HBD operation.

Factors contributing to abandonment of household biogas digesters in rural China: a study of stakeholder perspectives using Q-methodology

Factors contributing to abandonment of household biogas digesters in rural China: a study of stakeholder perspectives using Q-methodology

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.

Environmental, social and health benefits of alternative renewable energy sources. Case study for household biogas digesters in rural areas

In rural areas of Colombia, liquefied petroleum gas (LPG) is the preferred option available for cooking. However, the poorest households rely on firewood (FW) to meet their daily cooking needs, because is the most accessible and affordable energy source. This high level of dependence on traditional solid fuels and the use of non-optimized cook stoves results in high health, environmental, economic and social costs on developing countries’ households. This study aimed at assessing the environmental and health benefits of implementing grass-fed household biogas digesters in rural areas of Colombia, through Life Cycle Assessment (LCA) methodology. Functional Unit was the annual demand of cooking energy by a typical family in those rural areas, which means 2400 MJ of useful heat. There were evaluated two sources of biogas obtained from Pennisetum grass: Biogas from minerally fertilized grass (BMFG) and from organically fertilized one (BOFG). Results showed that FW had the highest impacts from fuels assessed, while the lowest impacts were found with BOFG, showing half of LCA total impacts compared with LPG and more than two orders of magnitude lower in non-methane volatile organic compounds and particulate matter (PM2.5eq) emitted compared with FW. Therefore, BOFG appears as an environmentally feasible alternative for cooking, which allowed the reduction LCA impacts among most of the categories assessed, as the fuel purchase expenses and of the wood collection time. Moreover, health impacts including the indoor emissions exposure showed also more than two orders of magnitude less impact compared with FW. It can be concluded that household digesters could improve the living standard of rural families.

Life cycle assessment of household biogas production in Egypt: Influence of digester volume, biogas leakages, and digestate valorization as biofertilizer

Biogas production from animal manure can address many negative impacts of traditional energy generation and also improve living conditions in rural communities in Egypt, the case study herein, and further afield. Even though techno-economical aspects of the household biogas digester technology have been thoroughly studied, its environmental sustainability, especially under Egypt’s conditions, remains largely unknown. To this end, life cycle inventory data were collected from typical fixed-dome digesters operating in Egypt. Environmental modelling was based on the life cycle assessment methodology using SimaPro. It was identified that the 100-year global warming potential for producing 1 m3 of biogas under Egypt’s conditions amounts to 2.72 kg CO2eq., while its total environmental footprint was 160.1 mPt. The main contributor was the operational phase (89.1%), while the construction phase had a much smaller contribution (10.9%). The main environmental hotspots were identified as the manure required to drive the process, closely followed by biogas leakages and intentional releases. By minimizing biogas losses, the system’s environmental sustainability largely improves (∼60% reduction) and could be on the same level with the one of larger biogas units operating in developing countries. Furthermore, it was identified that the digester volume plays an overall small role in the system’s environmental performance; however, oversized digesters grossly affect the environmental sustainability, due to the large amounts of biogas intentional releases. Finally, the use of digestate as a biofertilizer appears to be environmentally sustainable (∼38% reduction of total environmental footprint). Taken together, the results obtained in this study provide substantial information for policy- and decision-making on renewable energy development in rural Egypt and beyond.

Design of a household biogas digester using co-digested cassava, vegetable and fruit waste

Apart from solar photovoltaic and energy from wind turbine, biogas has also been identified as one of the alternatives for the replacement of fossil fuel at a modular level. With respect to the adoption of biogas for household application, extensive research has been conducted on the optimal techno-economic design of biogas digesters. However, available studies and case studies do not often provide simplified details that can be used for replicative studies. Hence, this study presents a simplified stepwise illustration of a household anaerobic digester for sustainable co-digestion of cassava, vegetable and fruit waste. Using a scenario-based approach, the digester was designed to produce biogas energy that will cater for five (5) families; each comprising eight (8) members. It is expected that the stepwise example presented in this study will help in expanding the frontier knowledge directed at presenting the optimal design of biogas digesters.

Beyond climatic intervention: The social dimension of a biogas project in Sogwala village, Zimbabwe

There is now considerable interest to understand how local communities experiencing climatic risks can benefit from climate change responses. As this agenda unfolds, there is need to understand the impact of climate-related interventions from the perspective of local populations targeted by such projects. Existing assessment approaches tend to concentrate on the environmental and economic impacts of projects that minimise greenhouse gas emissions. This study assesses the social aspect of a domestic biogas project that was intended to address the twin challenges of poverty and climate change in Sogwala village, Zimbabwe. A three-tier methodological execution process was adopted, involving field reconnaissance, household survey and key informant interviews. The focus was on measuring the social dimension of the changes brought about by the project, from the experiences of participating households. With a consciousness of assessment challenges associated with community projects, social capital parameters were used to assess the project’s contribution to the social well-being of the villagers. Overall, results show that the biogas project has the potential to facilitate social development through improved trust and social networks. Despite the contested climatic benefits associated with small-scale household biogas digesters, projects of this nature can enhance community relationships and networks, upon which other development interventions can be operationalised.

Materials for the design and construction of household biogas digesters for biogas production: A review

Materials for the design and construction of household biogas digesters for biogas production: A review

Analysis of revolution in decentralized biogas facilities caused by transition in Chinese rural areas

Decentralized biogas facilities have become an important component of agricultural sectors in Chinese rural area. This study is the first attempt to investigate how transition in Chinese rural areas affects the revolution of decentralized biogas facilities and its sustainability. The characteristics of the household biogas digesters (HBD), simple biogas plants (SBP), and well equipped biogas plants (WEBP) with higher level of technologies were clarified, and their practical feasibility was correspondingly investigated through a comprehensive survey of 15 selected villages. More effort was devoted to the adoption of feedstock availability, energy supply stability, and digestate distribution optimization for each facility. The results showed that feedstock collection and insufficient biogas production were the main restraining factors for HBD, while SBP found to be ineffective facilities for competitive energy production due to the un-guaranteed biogas supply. The survey results demonstrated that the average biogas expenditure of dwellers, who were connected to WEBP, accounted for 39.61% commercial energy cost. According to the one-year operation data collected from a 52-household club revealed that WEBP would effectively maintain stability and continuous biogas supply with the average feeding interval of 6.2 d. Accordingly, WEBP groups were found as the best option for regional development respected with the professional management unit. Overall, commercial biogas is the orientation of decentralized biogas facility construction. However, to form a robust biogas-centric industrial chain, future research should focus on how to establish relative policies and regulations supporting the comprehensive operation framework of a multi-participant collaboration leadership system.

Evaluation of methane emission flux from a typical biogas fermentation ecosystem in China

To reduce greenhouse gas emissions and promote sustainable agricultural practices in China, this study used conventional method to examine methane (CH4) production from hydraulic biogas digesters in Jiuxi Town, Yunnan Province, China. The static chamber technique was utilized to measure CH4 emission fluxes from the inlet and outlet of the biogas digesters. For the 100 m3 biogas digester, CH4 emission fluxes from the inlet, outlet, and the biogas digester were 1.043 g/(m2·h), 2.328 g/(m2·h), and 52.669 g/(m3·d); while those for the 8 m3 biogas digester were 0.156 g/(m2·h), 0.083 g/(m2·h), and 23.580 g/(m3·d), respectively. The diurnal and monthly variation of CH4 emission fluxes were further analyzed from the 100 m3 biogas digester. Among the environmental factors, the fermentation temperature and feeding quantity had significant effects on the CH4 emission fluxes. Especially, CH4 leakage from the digesters was evaluated, which would help identify and adjust the methane conversion factor for the typical biogas fermentation ecosystem used in China. For the hydraulic biogas digesters of 8 m3 and 100 m3, the respective leakage ratios were 3.01% and 14.56%. Therefore, it is very important for rural farmers in China to improve the management of household biogas digesters for reducing greenhouse gas emissions.

Numerical study of heat transfer performance of helical coiled tubes for heating high-solids slurry in household biogas digester

A computational fluid dynamics model to simulate conjugate heat transfer between a helical coiled tube and high-solids fermentation slurry in a household biogas digester was developed. The model simulation results were then verified using field experiment results. The effect of total solids concentration, pitch, helical diameter, and tube materials on the thermal performance of the helical coiled tubes were analysed. The results show that the accuracy of the numerical model that was based on the rheological and thermal parameters of the fermentation slurry was significantly improved compared with that based on the corresponding water parameters. As the total solids concentration increased, the zero-shear viscosity of the slurry significantly increased and the heat transfer performance of the helical coiled tubes was notably weakened. In the high-solids fermentation slurry, the influence of pitch on the heat transfer coefficient of the coiled tubes was greater than that of the helical diameter. The difference in the rates of total thermal resistance between cross-linked polyethylene (PEX) and metal (stainless steel and copper) coiled tubes was small for the high-solids fermentation slurry compared to that for the water. Therefore, low-cost PEX coiled tubes are more suitable for high-solids fermentation slurry than metal tubes in household biogas digesters.

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.