Biogas energy from family-sized digesters in Uganda: Critical factors and policy implications

Dependence on fossil energy sources is increasingly becoming unsustainable due to ecological and environmental problems and rapid depletion. Biogas energy could augment these conventional energy sources but despite its advantages and favourable conditions for its production, biogas energy use in Uganda remains low due to technical, economic and socio-cultural impediments. Based on primary data on households in Central and Eastern Uganda and the use of logistic regression, this study analyses factors affecting the adoption of biogas energy in Uganda. The empirical results suggest that the probability of a household adopting biogas technology increases with decreasing age of head of household, increasing household income, increasing number of cattle owned, increasing household size, male head of household and increasing cost of traditional fuels. In contrast, the likelihood of adoption decreases with increasing remoteness of household location and increasing household land area. Policy options and recommendations including educational and awareness campaigns on biogas benefits and successes, the provision of financial and non-financial incentives to households and establishment of an institutional framework could bolster wider biogas energy acceptance in Uganda.     

Design Biogas Production from Mixed Napier Pak Chong I/Food Waste at Thermophilic Temperature by Anaerobic Digestion in Cow Dung and Chicken Dung

AD （anaerobic digestion） is a beneficial and efficient technique for the treatment of agricultural wastes, food wastes and wastes water to produce renewable energy. Solid agricultural are potential renewable energy resoures. Biogas production by co-digestion of mixed Napier Pak Chong I and food waste at thermophilic temperature using anaerobic digestion in cow dung and chicken dung as the seed inoculums were investigated. The total reactor volume of the co-digester reactor was 7.94 m^3, which was equipped with pump, and it was operated continuously for the 20 days as a pilot scale at 50 ℃. The Napier Pak Chong I was cut into 2 mm sections, and the initial VS （volatile solids） was 30%. The initial VS of food waste were 70%. Two pilot-scale digesters filled with Napier Pak Chong I and food waste, which both digesters contained 476 kg of Napier Pak Chong I mixed 305 L of food waste, and 1305 L of water. There were carried out to investigate the optimum C/N （carbon to nitrogen） ratio for effective biogas production. The slurry raw materials provided sufficient buffering capacity to maintain appropriate pH values （between 7.0 and 8.0）. Digester I was designed for 1.98 m^3 of cow dung as the seed inoculum while digester II was designed to establish 1.98 m^3 of chicken dung as the seed inoculum. Gas detector performs analysis gas production. The m^3/day in digester I and 1.86 m^3/day from digester II, resulting in added, respectively. Biogas production in digester I was directly experimental results indicate that total biogas production was 2.19 specific methane yields of 1.26 m^3 CH4/kgVS and 1.07 m^3 CH4/kgVS correlated with temperature.     

牛粪、鸡粪发酵产氢潜力的研究

采用恒温厌氧发酵工艺,用乳酸调控发酵pH值,进行了牛粪和鸡粪发酵产氢的实验研究。实验结果表明,pH为4.7～5.5时,牛粪的产氢潜力为32.33ml/g(TS)和41.39ml/g(VS);鸡粪的产氢潜力为33.58ml/g(TS)和50.88ml/g(VS)。     

Biogas steam and oxidative reforming processes for synthesis gas and hydrogen production in conventional and microreactor reaction systems

In this work, a renewable source, biogas, was used for synthesis gas and hydrogen generation by steam reforming (SR) or oxidative reforming (OR) processes. Several Ni-based catalysts and a bimetallic Rh–Ni catalyst supported on magnesia or alumina modified with oxides like CeO₂ and ZrO₂ were used. For all the experiments, a synthetic biogas which consisted of 60% CH₄ and 40% CO₂ (vol.) was fed and tested in a fixed bed reactor system and in a microreactor reaction system at 1073 K and atmospheric pressure. The catalysts which achieved high activity and stability were impregnated in a microreactor to explore the viability of process intensification. For the SR process different steam to carbon ratios, S/C, varied from 1.0 to 3.0 were used. In the case of OR process the O₂/CH₄ ratio was varied from 0.125 to 0.50. Comparing conventional and microreactor reaction systems, one order of magnitude higher TOF and productivity values were obtained in the microreactors, while for all the tested catalysts a similar activity results were achieved. Physicochemical characterization of catalysts samples by ICP-AES, N₂ physisorption, H₂ chemisorption, TPR, SEM, XPS and XRD showed differences in chemical state, metal–support interactions, average crystallite sizes and redox properties of nickel and rhodium metal particles, indicating the importance of the morphological and surface properties of metal phases in driving the reforming activity.     

Low cost tubular digesters as appropriate technology for widespread application: Results and lessons learned from Bolivia

This paper presents the results and lessons learned from four and a half years of implementing low cost tubular digesters in Bolivia. The selection of this technology is justified in comparison with other popular technologies such as fixed dome or floating drum digesters. The highlighted weakness of the tubular model (its short life expectancy), is transformed into a strength, making the low cost tubular digester an appropriate technology for widespread application. The experiences in Bolivia show that the success of biogas programs depend more on socio-economic factors than on the validated technology selected, suggesting that local circumstances are a critical, and often underestimated, factor to be taken into consideration in the praxis. Finally, some testimonies of the use of biol (bio-slurry or effluent) are reported, identifying the high potential of this anaerobic digestion product that provides a food sovereignty approach, reduced expansion of the agricultural frontier, increased agricultural productivity and hence family income, that other household energizing systems do not have. A brief report of lessons learned is also included.     

Popularizing household-scale biogas digesters for rural sustainable energy development and greenhouse gas mitigation

Biogas utilization has undergone great development in rural China since the government systematically popularized household-scale biogas digesters for meeting the rural energy needs in the 1970s. In order to comprehensively estimate the significance of biogas utilization on rural energy development and greenhouse gas emission reduction, all types of energy sources, including straw, fuelwood, coal, refined oil, electricity, LPG, natural gas, and coal gas, which were substituted by biogas, were analyzed based on the amount of consumption for the years from 1991 to 2005. It was found that biogas provided 832749.13 TJ of energy for millions of households. By the employment of biogas digesters, reduction of greenhouse gases (GHG) was estimated to be 73157.59 Gg CO₂ equivalents (CO₂-eq), and the emission by the biogas combustion was only 36372.75 Gg CO₂-eq of GHG. Energy substitution and manure management, working in combination, had reduced the GHG emission efficiently. The majority of the emission reduction was achieved by energy substitution that reduced 84243.94 Gg CO₂, 3560.01 Gg CO₂-eq of CH₄ and 260.08 Gg CO₂-eq of N₂O emission. It was also predicted that the total production of biogas would reach to 15.6 billion m³ in the year 2010 and 38.5 billion m³ in the year 2020, respectively. As a result, the GHG emission reductions are expected to reach 28991.04 and 46794.90 Gg CO₂-eq, respectively.     

Biogas reforming for hydrogen production over nickel and cobalt bimetallic catalysts

Ni/Co bimetallic catalysts supported by commercial γ-Al₂O₃ modified with La₂O₃ for biogas reforming were prepared by conventional incipient wetness impregnation. The catalysts were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), BET surface area and porosity analysis (BET), H₂ temperature-programmed reduction (H₂-TPR), transmission electron microscopy (TEM) and thermogravimetry coupled to differential scanning calorimetry (TG–DSC). XRD and XPS analysis revealed that a Ni/Co alloy was formed in the bimetallic catalysts. The Ni/Co ratio could be adjusted to improve pore textural properties, which enhanced the metal particle dispersion and resulted in smaller metal particle size, and thus increased the catalytic activity and resistance to carbon deposition. The activity and stability of the catalysts for biogas reforming was tested at 800 °C, ambient pressure, GHSV of 6000 ml g_cat⁻¹ h⁻¹ and a CH₄/CO₂ molar ratio of 1 without dilute gas. Experimental results showed that the catalytic activity could be closely related to the Ni/Co ratio. The bimetallic catalyst 7Ni3Co/LaAl exhibited better catalytic and anti-coking performance due to smaller metal particles, higher metal dispersion, uniform pore distribution, surface enrichment of Co, as well as the synergetic effect between Ni and Co. During a 290 h stability test over the catalyst 7Ni3Co/LaAl, the average conversion of CH₄ and CO₂, selectivity to H₂ and CO, and ratio of H₂/CO were 93.7%, 94.0%, 94.9%, 97.8%, and 0.97, respectively. The average coking rate was 0.0946 mg g_cat⁻¹ h⁻¹.     

Biogas production from sewage sludge and microalgae co-digestion under mesophilic and thermophilic conditions

Isochrysis galbana and Selenastrum capricornutum, marine and freshwater microalgae species respectively, were co-digested with sewage sludge under mesophilic and thermophilic conditions. The substrates and the temperatures significantly influenced biogas production.Under mesophilic conditions, the sewage sludge digestion produced 451 ± 12 mL_Biogas/g_SV. Furthermore, all digesters were fed with I. galbana, or mixed with sludge, resulting in an average of 440 ± 25 mL_Biogas/g_SV. On the contrary, S. capricornutum produced 271 ± 6 mL_Biogas/g_SV and in the mixtures containing sludge produced intermediate values between sludge and microalgae production.Under thermophilic conditions, the sewage sludge digestion achieved yet the highest biogas yield, 566 ± 5 mL_Biogas/g_SV. During co-digestion, biogas production decreased when the microalgae content increased, and for I. galbana and for S. capricornutum it reached minimum values, 261 ± 11 and 185 ± 7 mL_Biogas/g_SV, respectively. However, no evidence of inhibition was found and the low yields were attributed to microalgae species characteristics.The methane content in biogas showed similar values, independently from the digested substrate, although this increased by approximately 5% under thermophilic condition.     

Biogas steam reformer for hydrogen production: Evaluation of the reformer prototype and catalysts

This work aims to investigate a biogas steam reforming prototype performance for hydrogen production by mass spectrometry and gas chromatography analyses of catalysts and products of the reform. It was found that 7.4% Ni/NiAl₂O₄/γ-Al₂O₃ with aluminate layer and 3.1% Ru/γ-Al₂O₃ were effective as catalysts, given that they showed high CH₄ conversion, CO and H₂ selectivity, resistance to carbon deposition, and low activity loss. The effect of CH₄:CO₂ ratio revealed that both catalysts have the same behavior. An increase in CO₂ concentration resulted in a decrease in H₂/CO ratio from 2.9 to 2.4 for the Ni catalyst at 850 °C, and from 3 to 2.4 for the Ru catalyst at 700 °C. In conclusion, optimal performance has been achieved in a CH₄:CO₂ ratio of 1.5:1. H₂ yield was 60% for both catalysts at their respective operating temperature. Prototype dimensions and catalysts preparation and characterization are also presented.     

Effect of temperature and retention period on biogas production from lignocellulosic material

The extensive utilization of biogas for energy needs of rural dwellers would reduce their dependence on fossil fuels and fuelwoods and henoe camplement Government afforestation programes. In this investigation, effect of temperature and retention period on biogas production from lignooellulosic material, hereafter referred to as cow dung were studied. Maximum gas production was dotained at thermophilic temperature. The results of the effect of retention period shows that gas production was qotimum at 4th and 7th weeks of production.     

Biogas: A promising renewable technology and its impact on rural households in Nepal

Nepal, one of the least developed countries, is characterized by very low per capita energy consumption. Because of a lack of other commercial sources of energy, the country relies heavily on traditional fuel source, especially firewood. In order to solve the energy problem in rural areas, the country initiated production and distribution of several renewable energy technologies. Among several technologies, biogas has been proved to be viable and emerged as a promising technology. It has been one of the most successful models for the production of clean, environmental friendly, cost effective source of energy and has multiple benefits. In this paper we present the current state and discuss benefits of the biogas technology in Nepal. Improved health, increased crop productivity, saved time for women are some of the major benefits to the users. It provides economic benefit to the country through reduced deforestation and carbon trading. In addition, by reducing green house gas emission, the technology helps in mitigating global warming and climate change. Thus biogas is a renewable, sustainable and clean source of energy that provides multiple benefits; locally and globally. With some exception, cattle dung has been used primarily as an input and the technology is limited to households only. More systematic and comprehensive study supported by research and development is required to use other degradable waste such as municipal waste to produce biogas on a large scale.     

Biogas scrubbing, compression and storage: perspective and prospectus in Indian context

Biogas is a clean environment friendly fuel. Raw biogas contains about 55–65% methane (CH₄), 30–45% carbon dioxide (CO₂), traces of hydrogen sulfide (H₂S) and fractions of water vapours. Presently, it can be used only at the place where it is produced. There is a great need to make biogas transportable. This can be done by compressing the gas in cylinders which is possible only after removing its CO₂, H₂S and water vapour components. Pilot level trials to compress the biogas have been carried out by a number of earlier investigators working on the subject. This paper reviews the efforts made to improve the quality of biogas by scrubbing CO₂ and the results obtained. There is a lot of potential if biogas could be made viable as a transport vehicle fuel like CNG by compressing it and filling into cylinders after scrubbing and drying. Thus the need emerges for a unified approach for scrubbing, compressing and subsequent storage of biogas for wider applications.     

Thermodynamic and environmental study on synthetic natural gas production in power to gas approaches involving biomass gasification and anaerobic digestion

The main goal of this paper is to assess and compare three hybrid systems for the production of synthetic natural gas (biomethane) from biogas or process gas. Mathematical models were built to determine the main performance indicators and plant efficiency of the proposed solutions, such as mass and energy flows and gas composition in characteristic points of the systems, as well as the efficiencies of the full chains. The carbon footprint of the three approaches was calculated using a streamlined life cycle assessment. The results show that both methanation cases may be an interesting option for SNG production and energy storage. The energy efficiency of the solutions reaches a value of 84% for Case 1 (methanation from syngas) and 90% for Case 2 (methanation of biogas) and 3 (biogas upgrading), respectively. If the manure credit is accounted for emissions, the carbon footprint of biomethane from Case 3 is the lowest.     

中国北方农村户用沼气池可持续发展的对策及建议

针对近年来中国北方农村户用沼气池推广使用过程中出现的问题,通过实地考察、发放问卷调查,与使用者、管理者、技术人员交流等方式,对河南省焦作、济源、濮阳、武陟等地区的沼气池使用情况进行了实地调查.结果表明,目前主要存在政策缺乏、后续服务能力薄弱、用户自我解决问题能力不足、原料缺乏、综合效益较低等问题.针对这些问题,提出了一些有利于沼气池可持续发展的建设性意见和措施.     

低温下沼气促进剂驯化菌种及其应用研究

针对冬季低温(<17℃)条件下,如何以优良厌氧发酵菌种和沼气促进剂提高农村户用沼气池产气量,进行了研究.研究中以特制的5L厌氧消化罐作反应器,以猪粪为底物,设计了Fe3 ,Ni2 ,木炭3因素4水平的正交实验,研究厌氧发酵过程中产气量的变化,以获得微量元素和木炭的最佳的投加量组合配比,在此基础上驯化出优良的产甲烷菌种.沼气促进剂和菌种的实验室和农户应用效果表明,在厌氧发酵过程中微量元素和木炭都能够增强甲烷菌活性,提高产气量,并对低温具有一定的抵抗作用.其最佳配比Fe3 ∶ Ni2 ∶木炭为2∶ 1∶ 5,投加绝对量为0.61%(相对于原料干重).驯化出的菌种微生物生物量较高,较驯化前提高了27.3%,作为接种物在农村沼气实际运用中取得较好效果.     

Biogas production from thermophilic codigestion of air‐dried rice straw and animal manure

In order to evaluate the effects of organic loading rate (OLR) on thermophilic codigestion of air‐dried rice straw (RS) with pig manure (PM), cow manure (CM), and chicken manure (CHM), continuous bench experiments (40 L) were carried out at OLRs of 3.0, 3.6, 4.2, 4.8, 6.0, 8.0, and 12.0 kg VS/(m³ · d). Stable biogas production without inhibition by volatile fatty acids (VFA) or ammonia and foaming was achieved at OLRs of 3–12, 3–6, and 3–4.8 for the codigestions of RS + PM, RS + CM, and RS + CHM, respectively. Maximum average volumetric biogas production rates of 4.98, 2.64, and 2.03 m³/(m³ · d) were obtained at OLRs of 12, 6, and 4.8 kg VS/(m³ · d) for the codigestions of RS + PM, RS + CM, and RS + CHM. Foaming was occurred at OLRs of 8 kg VS/(m³ · day) for the codigestions of RS + CM. The codigestion of RS + CHM was inhibited by the accumulation of ammonia instead of VFA when the OLR was ≥6 kg VS/(m³ · d). This study provided references for the engineering application of codigestion of RS and animal manure. Copyright © 2016 John Wiley & Sons, Ltd.     

Biogas plants in Denmark: technological and economic developments

Biogas plants are one of the important elements in the Danish energy-policy of having reduced CO₂ emissions by 20% by 2005. Since 1984, development efforts concerning centralised biogas plants in Denmark have been carried out, and Denmark now has approximately 20 large centralised biogas plants. All Danish biogas plants have increased gas production as a result of admixing industrial organic wastes with manure. This is predominantly regarded as a great advantage for both biogas plants and waste suppliers. The paper will describe the technological development of this renewable energy source in terms of biogas production prices. The price has dropped dramatically during the last 15 years. Based on this analysis, the paper discusses the socio-economic costs of technology development including state budget and employment effects. Also the paper refers to socio-economic feasibility studies from the early 1990s, when biogas production prices were much higher than natural gas. Still, employment effects made the development feasible in socio-economic terms.     

Investigation and application of polysiloxane-based gel electrolyte in valve-regulated lead-acid battery

Polysiloxane-based gel electrolyte (PBGE) is prepared and investigated as a new gel electrolyte for valve-regulated lead-acid (VRLA) batteries. PBGE particles, characterized by means of Fourier transform infrared (FTIR) spectroscopy, cyclic voltammetry (CV) and scanning electron microscopy (SEM), reveal good stability and their particle sizes are 30–50 nm. The initial cyclic properties of the absorptive glass mat (AGM)–PBGE and AGM–colloid silica gel electrolyte (CSGE) hybrid batteries are investigated by electrochemical techniques, scanning electron microscopy and X-ray diffraction (XRD). The addition of PBGE improves the utilization efficiency of positive active material (PAM) in AGM–PBGE hybrid batteries and thus enhances the batteries capacity compared with the AGM–CSGE reference batteries. Cyclic overdischarge tests show that the AGM–PBGE hybrid batteries have superior recharge and discharge during partial-state-of-charge (PSoC). It is also found that the greatly enhanced electrochemical performance of the AGM–PBGE batteries may be due to higher charge efficiency, good conductivity with lower internal resistance and the open three-dimensional network structure of the polyelectrolyte. The analysis results of SEM and XRD indicate that softening and shedding of positive active material are the main causes of failure for the two hybrid batteries.