The fixed dome digester: An appropriate design for the context of Sub-Sahara Africa?

The fixed dome digester design is the most deployed small scale biogas technology in sub-Sahara Africa (SSA). This design is deployed on mono-feedstock-wet anaerobic digestion (WAD) principle. Little or nothing has been reported in the literature on the sustainability in terms of the actual field operation and performance of this design within the SSA context. This study aims at bridging this gap and bringing additional insights to the scientific literature by investigating the sustainability of the Nepali–type fixed dome digester within the context of rural Cameroon. The investigations were evaluated in terms of operating parameters, biogas production, production rate and productivity of the digester. In addition the local investment cost of the design was analyzed. The design was operated on multiple-locally-available feedstock mixed with water at an average of 3:1 ratio resulting in a higher than design TS of 16%. The design, thus was operated towards the dry anaerobic digestion principle, highlighting insufficient mono-feedstock and water scarcity for a sustainable operation of the design within the context of rural SSA. The average biogas production was 1.2 m³_biogas/day, giving average volumetric production rate of 0.16 m³_biogas/m³_digester day⁻¹ and yields of 0.18 m³_biogas/kg VS respectively. This low performance compared with the potential mesophilic biogas production rate of 0.27 m³_biogas/m³_digester day⁻¹ could be linked to insufficient mixing of digester content and low operating temperatures. Gas storage facility (dome), skilled labour and cement made significant contributions to the investment cost of the digester. The Levelized cost of Energy from the digester was less than 1 € cents/MJ.     

A COMPARISON OF ACTIVE HEATING OF BIOGAS SYSTEMS FOR HIGHER PRODUCTION

In this communication, a thermal analysis of biogas systems has been presented in terms of the system and climatic parameters. The biogas systems of floating and fixed dome type have been analysed for higher production rate after integrating the digester with a panel of collector through a heat exchanger. A comparison of their performances, under similar climatic condition, has been carried out. The paper concludes that (i) there is no difference between the performance of the horizontal floating gas holder and fixed dome type biogas plant, and (ii) the performance of the vertical floating gas holder type biogas plant is better than the horizontal floating and fixed dome type biogas plant.     

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.     

4m3商品化户用玻璃钢沼气池的结构与性能

4m^3商品化户用玻璃钢沼气池为水压式沼气池，最大贮气量为1．1m^3，最大压力100cm水柱，设置进料口水压间和出料口水压间，不设天顶盖，实现自动进出料。该沼气池密封性好，使用寿命可达20a，整池重量轻，仅120kg，建池方便快捷，不受地下水位的影响，发酵启动快，产气率高。     

Reduced hydraulic retention times in low-cost tubular digesters: Two issues

Low-cost tubular digesters have been implemented in several developing countries. One of the problems reported from field surveys is that biogas generation that does not meet the user’s expectations. This report provides two reasons for the discrepancy between the biogas generation rate estimated in the design phase and the actual rate measured after construction, due to a lower final hydraulic retention time (HRT). The hydraulic retention time is normally determined from the liquid volume calculated from the cylindrical shape of the bag and not from the trench dimensions. The result is a reduction in HRT of 6%-51%, depending on the dimensions of the trench recommended by various authors. Another factor that is not normally considered is the influence of the biogas pressure on the liquid level inside the digester which negatively affects the liquid volume of the digester, reducing HRT by as much as 15%.     

Performance of semi-continuous fixed-bed digester for thalassic biogas production of the brown seaweed,Ecklonia spp.

Ecklonia spp. is available during summer (June–September), making it a possible rotational brown seaweed feedstock for biogas production. Hence, biogas production of Ecklonia was tested in a pilot-scale (120 L volume) semi-continuous fixed-bed digester under thalassic (high salinity) condition – seeded with marine bacteria. The biogasification efficiency obtained for Ecklonia in terms of its theoretical methane yield (345.6 mL CH₄/g VS) was 68.5%. This is higher than obtained in a batch digester (5.8%). The successful thalassic biogas production of Ecklonia may help secure the continuous operation and lower the biogas operation cost by directly using seawater as liquid substrate.     

4m3商品化户用玻璃钢沼气池的实际运行效果

在云南省已试验示范和推广了4m^3商品化户用玻璃钢沼气池1000多口，基本上能够解决5口之家的日常生活用能，使用管理方便，深受农户欢迎。实际运行的统计分析表明，平均年产沼气600m^3以上，原料产气率为0．377m^3/kg，沼气的甲烷含量超过65％。     

Economic assessment of biogas-to-electricity generation system with H2S removal by activated carbon in small pig farm

This study was conducted to assess the economic feasibility of electricity generation from biogas in small pig farms with and without the H₂S removal prior to biogas utilisation. The 2% potassium iodide (KI) impregnated activated carbon selected as H₂S adsorbent was introduced to a biogas-to-electricity generation system in a small pig farm in Thailand as a case study. With the average inlet H₂S concentration of about 2400 ppm to the adsorption unit, the H₂S removal efficiency could reach 100% with the adsorption capacity of 0.062 kg of H₂S/kg of adsorbent. Under the reference scenario (i.e., 45% subsidy on digester installation and fixed electricity price at 0.06 Euro/kWh) and based on an assumption that the biogas was fully utilised for electricity generation in the system, the payback period for the system without H₂S removal was about 4 years. With H₂S removal, the payback period was within the economic life of digester but almost twice that of the case without H₂S removal. The impact of electricity price could be clearly seen for the case of treated biogas. At the electricity price fixed at 0.07 Euro/kWh, the payback period for the case of treated biogas was reduced to about 5.5 years, with a trend to decrease at higher electricity prices. For both treated and untreated biogas, the governmental subsidy was the important factor determining the economics of the biogas-to-electricity systems. Without subsidy, the payback period increased to almost 7 years and about 11 years for the case of untreated and treated biogas, respectively, at the reference electricity price. Although the H₂S removal added high operation cost to the system, it is still highly recommended not only for preventing engine corrosion but also for the environment benefit in which air pollution by H₂S/SO₂ emission and impact on human health could be potentially reduced.     

大中型沼气池抗裂设计与构造

在料液压力、沼气压力等外力作用下，钢筋混凝土结构大中型沼气池池体易产生裂缝，裂缝的存在对池体是十分不利的。文章针对500m^3大型钢筋混凝土沼气池池壁的抗裂设计等问题进行了深入探讨，并提出了提高池体抗裂度的主要技术措施。     

“三位一体”沼气池建设整体质量评价指标体系

随着我国沼气事业的发展,全国"三位一体"沼气建设规模不断扩大,评价某一地区的"三位一体"沼气池建设整体质量水平,评估沼气项目建设实施水平和生态效果,制定"三位一体"沼气池整体质量评价指标体系至关重要。文章从"三位一体"沼气建设区域适宜性指标体系、沼气建设质量体系、沼气服务体系等方面,可以评估出某一区域的沼气建设的科学性和整体建设质量水平。     

寒区太阳能和沼气锅炉联合增温系统及试验研究

发展应用沼气可有效利用农作物等废弃资源,降低能源消耗,减少环境污染.但我国北方冬季气温低,致使沼气池产气率极低,甚至发生池体冻裂,无法正常使用.通过建立太阳能沼气锅炉联合增温系统,试验测试并分析了沼气池内温度变化,确定了太阳能与沼气锅炉联合运行的匹配方式.结果表明联合增温系统能使沼气池体处于较好的发酵温度范围内,保证了...     

陕西户用沼气池越冬使用技术研究

为了有效解决陕西省农村户用沼气池使用时间短的难题,结合陕西农村的实际情况,对传统沼气池的结构形式进行了改进,增加预处理池为沼气池提供热量,并对沼气池的池墙、进(出)料口进行保温,以达到增加冬季沼气池池温的目的。以榆林市为代表,通过理论计算、试验等手段,证明冬季最低室外温度条件下,沼气池产气率可以达到0.1 m3/(m3.d)以上,一口6～8 m3的沼气池就可以满足一个普通农户一天的炊事用气要求。     

新型管式进出料户用沼气池

探讨了一种新型户用沼气池的结构特点及其商品化生产的可能性。为户用沼气池的推广，提供了省工省时、文明卫生、产气率高的新设备。图３。     

Inline NH3 removal from biogas digesters

During biogas production from various types of substrates such as animal manure, fats and proteins, bacterial growth and biogas production can be inhibited by excessive ammonia (NH₃) concentrations. If NH₃ is removed from the biogas digester without damaging the digestion process, inhibition of the methane (CH₄) producing bacteria will diminish. This study shows that it is possible to remove a significant quantity of NH₃ from the biogas digester headspace and liquid phase by a simple gas circulation method where gas bubbles free of NH₃ is forced through the upper 30 cm of the liquid phase in the biogas digester, into the headspace and out of the digester. The suggested method improves conditions for anaerobic bacteria exposed to high concentrations of NH₃ by simply removing NH₃ from the digester.In full-scale biogas production the system presented in this study can be improved by circulating headspace gas through an ammonia absorber and returning the NH₃ depleted biogas into the biogas digester. This method can also replace the need for mixing in biogas digesters.     

解决牛粪厌氧发酵中浮渣结壳的几种方法

在畜禽养殖场沼气发电工程中,牛粪具有固体及纤维物质含量高的特点.在厌氧发酵过程中极易在厌氧反应器内部形成浮渣层并硬化结壳,如不及时解决,将导致沼气无法顺利进入气室,严重影响厌氧反应器的正常运行.针对这个问题,文章介绍几种在实际工程中经常用到的防止浮渣结壳的方法(高位出料、机械搅拌、反冲回流等),供工程设计人员参考.     

Trace compounds of biogas from different biogas production plants

Biogas composition and variation in three different biogas production plants were studied to provide information pertaining to its potential use as biofuel. Methane, carbon dioxide, oxygen, nitrogen, volatile organic compounds (VOCs) and sulphur compounds were measured in samples of biogases from a landfill, sewage treatment plant sludge digester and farm biogas plant. Methane content ranged from 48% to 65%, carbon dioxide from 36% to 41% and nitrogen from <1% to 17%. Oxygen content in all three gases was <1%. The highest methane content occurred in the gas from the sewage digester while the lowest methane and highest nitrogen contents were found in the landfill gas during winter. The amount of total volatile organic compounds (TVOCs) varied from 5 to 268 mg m⁻³, and was lowest in the biogas from the farm biogas plant. Hydrogen sulphide and other sulphur compounds occurred in landfill gas and farm biogas and in smaller amounts in the sewage digester gas. Organic silicon compounds were also found in the landfill and sewage digester gases. To conclude, the biogases in the different production plants varied, especially in trace compound content. This should be taken into account when planning uses for biogas.     

When does decentralized production of biogas and centralized upgrading and injection into the natural gas grid make sense?

The production of biogas through anaerobic digestion is one of the technological solutions to convert biomass into a readily usable fuel. Biogas can replace natural gas, if the biogas is upgraded to green gas. To contribute to the EU-target to reduce Green House Gases emissions, the installed biogas production capacity and the amount of farm-based biomass, as a feedstock, has to be increased. A model was developed to describe a green gas production chain that consists of several digesters connected by a biogas grid to an upgrading and injection facility. The model calculates costs and energy use for 1 m³ of green gas. The number of digesters in the chain can be varied to find results for different configurations. Results are presented for a chain with decentralized production of biogas, i.e. a configuration with several digesters, and a centralized green gas production chain using a single digester. The model showed that no energy advantage per produced m³ green gas can be created using a biogas grid and decentralized digesters instead of one large-scale digester. Production costs using a centralized digester are lower, in the range of 5 €ct to 13 €ct per m³, than in a configuration of decentralized digesters. The model calculations also showed the financial benefit for an operator of a small-scale digester wishing to produce green gas in the cooperation with nearby other producers. E.g. subsidies and legislation based on environmental arguments could encourage the use of decentralized digesters in a biogas grid.     

A mathematical model for fixed dome type biogas plant

This paper describes the development of a mathematical model for determining the dimensions of a fixed dome type Deenbandhu model biogas plant, the most popular model constructed in India. The developed model could estimate the different dimensions within an absolute variation of 6%. This will help the designers to determine the dimensions of various capacities of a Deenbandhu model biogas plant for different hydraulic retention times to suit the local climatic conditions.     

Experimental study of co-digestion of food waste and tall fescue for bio-gas production

Chinese food waste (CFW) and Tall fescue (Tf) are obtainable at low cost, and the digestibility of the mixture is superior to mono-digestion. The major objective of this study was to determine optimal CFW/Tf ratio and organic loading rate (OLR) for biogas yields and organics removal rate in batch and hydraulic pressure semi continuous anaerobic treatment. Batch digestion of mixed substrates was carried out at CFW/Tf ratios of 8.89, 2.75, 1.52, 0.99 and 0.7 based on volatile solid (VS). For CFW/Tf ratio of 1.52, increasing OLR in hydraulic pressure semi continuous digester was evaluated. Results showed that positive synergistic effects of co-digestion took place at CFW/Tf ratios of 1.52 and 0.99. In semi continuous anaerobic digester, the reliability daily methane yield and effective organic matter removal was observed at OLR of 15.8 g VS/(L·d). This study showed that the co-digestion of CFW and Tf improved biogas yield and degradation efficiency. The improved characteristics indicated the co-digestion process had better stability.     

太阳能辅助加热户用沼气池系统设计

沼气开发利用是发展可再生能源的重要选择,户用沼气是我国农村能源的重要组成部分.文中介绍了沼气的产生原理及发展现状,针对北方寒冷地区冬季气温低,沼气产气少利用率低问题,在调研常规保温增温方法的基础上提出了家用太阳能热水器辅助加热户用沼气池系统,并对系统经济性进行了分析.