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Biogas
Biogas is a methane rich gas produced through the anaerobic digestion (ie. without air) of organic wastes. It can be generated from cattle dung and animal wastes, and with substantially more difficulty, from some crop residues. Although these feedstocks are frequently used directly as cooking fuel, in most areas they are not preferred fuels and are used only when wood is not available.

Biogas systems offer multiple benefits. The digester-effluent is usually a good fertiliser, and, if connected to latrines, biogas plants can provide valuable sanitation services. For cooking and other thermal household tasks, it is simple and reasonably efficient to use the gas directly in conventional low-pressure gas burners. Biogas can also provide lighting when used in mantle lamps. In societies where suitable feedstocks are readily available, small family-sized biogas digesters were thought to have considerable potential.

International experience

A number of countries have initiated biogas programmes - China and India have on a large scale, and there is significant experience of commercial biogas in Nepal. Results have been mixed, especially in the early stages. Quality control and management problems have resulted in a large number of failures.

Biogas experience in Africa has been on a far smaller scale and has been often disappointing at the household level. The capital cost, maintenance, and management support required have been higher than expected. Under subsistence agriculture, access to cattle dung and to water that must be mixed with slurry has been more of an obstacle than expected. Possibilities are better where farming is done with more actively managed livestock and where dung supply is abundant - as in rearing feedlot-based livestock. The initial enthusiasm for biogas has thus been somewhat dampened by experience. Because of its requirement for relatively large amounts of animal dung, the niche for household biogas plants is likely to remain small. Poor families often do not have access to the necessary quantity of dung, and better-off families with sufficient animals often prefer to purchase fuel and fertiliser rather than spend time gathering dung and managing the often-temperamental digesters. Even so, in the right social and institutional context, and with appropriate technical expertise, the potential for biogas remains significant. A new initiative on Biogas was launched in May 2007 called the Biogas Africa Initiative.

Benefits of biogas technology

What makes biogas an attractive option is the fact that this technology can provide solutions to a variety of problems simultaneously: In general it has been proven that the energy aspect alone does not justify the cost for biogas technology. But the essential benefits of biogas plants are not manifested in individual cost-efficiency calculation. The overall objective, to which biogas technology contributes, is environmental protection which includes energy-related objectives (decrease of greenhouse gas emissions as well as deforestation) and the improvement of livelihoods of biogas users.

Well-functioning biogas systems can yield a whole range of benefits for their users, the society and the environment in general:

• production of energy (heat, light, electricity)
• transformation of organic waste into high quality fertilizer
• improvement of hygienic conditions through reduction of pathogens, worm eggs and flies
• reduction of unpleasant odors
• reduction of workload, mainly for women, in firewood collection and cooking
• environmental advantages through protection of soil, water, air and woody vegetation
• micro-economical benefits through energy and fertilizer substitution, additional income sources and increasing yields of animal husbandry and agriculture
• macro-economical benefits through decentralized energy generation, import substitution and environmental protection
• Biogas technology can substantially contribute to conservation and development, if the concrete conditions are favorable

[top] [end]II. Limitations of Biogas Technology

Biogas systems are functioning under a variety of climatic conditions. However, a widespread acceptance and dissemination of biogas technology has not yet materialized in many countries. One main reason is the required high investment capital. Often the reasons for failure were also the unrealistically high expectations of potential users. Biogas technology cannot solve every problem of a farm, a village or a big animal production unit. If disappointment is to be avoided, the limitations of biogas technology should be clearly spelt out.

• An obvious obstacle to the large-scale introduction of biogas technology is the fact that the majority of rural populations often cannot afford the cost of investment for a biogas plant. The installation of a few biogas plants often can only be afforded by better-off farmers. High up-front investment costs for even small biogas units are still not affordable for poor households.
• The technical viability of biogas technology has been generally proven in field test and projects; the economic viability of biogas digesters is under discussion and did not prove to be viable for some contexts. The establishing of an efficient and sustainable dissemination structure continues to remain the key problem of numerous biogas projects. Numerous problems have arisen when mass dissemination of biogas units/digesters is attempted: in particular the dung collection has proved more problematic than anticipated, particularly for farmers who do not keep their livestock in one location. The viability and reliability of biogas projects usually depend on a number of factors, such as:
• • Quantity of available biomass/animal waste: Sufficient biomass/manure on a continuous basis should be available to maintain installed biogas units. Project experiences show that if more biogas units were installed than biomass manure has been available, unreliable and disrupted energy services were a consequence.
  • Location of biogas project: if a project combines the provision of energy services with income-generation, such as the production and selling of manure as fertilizer, the local market situation plays a role, as it is critical to have a sustainable local demand for fertilizers and a critical mass of users. Users, such as farmers, will loose interest in using biogas units if there is no financial benefit associated with producing and marketing manure.
  • Ownership issue: Users of biogas units should, if possible, make a financial contribution to the installation of biogas units, to develop an ownership perception of the energy provider.
  • Combined biogas units: General consensus emerged from practice is that larger combined septic tanks/biogas units run by institutions such as schools or hospitals are more viable than small-scale biogas digesters.

III. Dissemination & promotion strategies for biogas

The implementation of biogas projects and programmes, even on a small-scale level, must take into account the underlying socio-cultural, political, economic and ecological conditions. As an appropriate technology, mainly for rural areas, the realization of economically viable and sociologically and ecologically beneficial biogas projects heavily relies on social and political acceptance. The basic prerequisite for successful, comprehensive introduction and popularization of biogas technology is the effective motivation and mobilization of potential target groups.

A successful dissemination strategy will require steps within the following fields of activity: information and public relation campaigns; educational and training programs; financial promotion; politico-administrative and organizational aspects; social acceptance.

Checklist for introduction & promotion of biogas technology:

• region with favorable climatic conditions
• existence of a potential target group
• private sector involvement
• informal sector involvement
• government involvement
• organizations/networks to cooperate with
• economic viability on micro- and macro level
• financing program and the cost of programme
• material requirements
• technological standards
• available know-how on planning, management, technician and artisan level
• the role of subsidies
• kinds of information, propagation, awareness creation
• assessment of sustainability

IV. The Technology

There are various types of plants. Concerning the feed method, three different forms can be distinguished: (1) Batch plants; (2) Continuous plants; (3) Semi-batch plants. Batch plants are filled and then emptied completely after a fixed retention time. Each design and each fermentation material is suitable for batch filling, but batch plants require high labor input. As a major disadvantage, their gas-output is not steady. Continuous plants are fed and emptied continuously. They empty automatically through the overflow whenever new material is filled in. Therefore, the substrate must be fluid and homogeneous. Continuous plants are suitable for rural households as the necessary work fits well into the daily routine. Gas production is constant, and higher than in batch plants. Today, nearly all biogas plants are operating on a continuous mode. If straw and dung are to be digested together, a biogas plant can be operated on a semi-batch basis. The slowly digested straw-type material is fed in about twice a year as a batch load. The dung is added and removed regularly.

Resources

• Beginners guide of biogas - an introduction to biogas
• Nepal Biogas Plant -- Construction Manual
• Clean Energy for Development and Economic Growth: Biomass and other renewable energy options to meet energy and development needs in poor nations, policy discussion paper (2002): The policy paper discusses the following topics related to biomass energy services: energy for the poor; biomass (Energy) for household use: resources and impacts; biomass energy beyond the household: scaling up; biomass energy conversion technologies; renewable energy technologies: markets and costs; biomass, bioenergy and climate change mitigation; eight case studies (i.e. Nepal, Mexico, Morocco, Brazil)
• Bioenergy Primer: Modernized Biomass Energy for Sustainable Development, 2000 - PDF file 2.9MB: This report discusses topics related to bioenergy sources; environmental and socio-economic issues; technologies to convert biomass into modern energy; implementation and replication; and features case studies (India, Brazil, China)
• World Energy Assessment Report, 2000: in particular Chapter 7 on Renewable Energy Technologies, biomass energy (pp. 222-230) and Chapter10 on Rural Energy in Developing Countries, fuels in rural areas: climbing the energy ladder (pp.369-373)
• Sustainable Energy Strategies: Materials for Decision-Makers, 2000, (ed.) Minoru Takada, Ellen Morris and Sudhir Chella Rajan, Chapter 4: Renewable Energy for Rural Development
• International Conference for Renewable Energies, Bonn/Germany, June 2004, Conference thematic background paper: Traditional Biomass Energy - improving its use and moving to modern energy use - PDF file 1.5MB

A number of useful publications are available from the meeting "How to create a market for domestic biogas plants?" of the "Network of Experts on Domestic Biogas" held on 5 and 6 April 2006 in Hanoi and focused on the promotion of biogas.

• First Meeting of Network of Experts on Domestic Biogas – Meeting Summary (395 KB)
• Biogas Promotion in Bangladesh (62 KB)
• Biogas Promotion in Cambodia (133 KB)
• Biogas Promotion in China (144 KB)
• Biogas Promotion in India (914 KB)
• Biogas Promotion in Lao PDR (948 KB)
• Biogas Promotion in Nepal (448 KB)
• Biogas Promotion in Rwanda (214 KB)
• Biogas Promotion in Vietnam (181 KB)
• A presentation showing the ways and methods for the promotion of quality biogas plants in Bangladesh (201 KB)
• A pilot program in Laos for the promotion of biogas (952 KB)
• A proposal for biogas promotion in the Domestic Programme in Rwanda (71 KB)
• A National Programme for the promotion of Biodigesters in Cambodia (2,046 KB)
• An assessment of the Rural Domestic Biogas Plants and how they can be promoted in P. R. China (119 KB)

[top] [end]External links and references

• http://en.wikipedia.org/wiki/Biogas
• http://www.ashdenawards.org/winners/shaanxi
• http://practicalaction.org/?id=biogas_expertise
• http://www.ashdenawards.org/winners/bsp
• http://www.ashdenawards.org/winners/vknardep
• http://www.ashdenawards.org/winners/arti06
• http://www.ashdenawards.org/winners/kist05
• Biogas Africa Initiative
• Nepal Biogas Programme
• Vietnam Biogas Programme
• Bangladesh Biogas Programme
• Cambodia Biogas Programme
• SNV, click ‘practise areas/biogas’

Rural Decentralized Energy Production from Animal Waste Biogas Plant : Evaluation of Options for Water Minimization Using Process Simulation Software.


Pannirselvam P.V, Souza .E,Costa.G.B ,Gilson.G.M and Melo H.N.S ; Departamento de Engenharia Química /CT. Universidade Federal do Rio Grande do Norte, Natal-RN. 59078400.Brazie-mail: pannirbr@gmail.com;

www.biomassa.eq.ufrn.br and ww.ecosyseng.wetpaint.com



In the past,farm waste did not pose a problem as themanure made great fertilizer, so farmers simply spread it on their fields. Today, many of the big farms are specialized and these "farm machines" are designed to produce in bulk and the farm waste problem began to mount. So this huge amount of centralized production began to runoff into nearby stream, and other water supplies not only in developed countries , but also in the country like Brazil .In conjunction with these problems associated with farm waste ,posing contamination of water resource , we need to study them as the resource for water and energy recovery .This is the objective of our research work where the effort is made to design and develop ecologically sound integrated bio systems for small community using the anaerobic digestion of rural and animal waste.A viableand successful practical small scale biogas and rural power production in the semiarid the rural area of North East is also illustrated . In this context of the biogas production ,the water also plays important role as much as the energy for the integrated sustainable local development and was observed to be the limiting factor resource for future insataltions.“Good Quality” water is increasingly a scarce resource and wastewater treatment costs rise. The once-through use of this water is becoming uneconomical and environmentally unacceptable, principally to the semi arid region of the Northeast of Brazil.Instead, recovery and recycling of used wastewater is becoming more attractive from both an economic and environmental perspective. In this context , the water minimization and recycling is our second objective of this work as this lead to substantial savings through reduced wastewater disposal cost and rural water requirements , as our region is semiarid and dry.The Integrated Bio-Systems (IBS) approach follows three basic principles. The first principle is to useall biological organic materials and wastes instead of throwing them away. The second principle is to obtain at least two products from a waste. The third principle is to close the loop for the material and nutrient flows to achieve total use of a resource and zero waste disposal. The IBS approach has many benefits and potentials but it also has limitations.The anaerobic digestion of animal waste produces "biogas",which is typically made up of 70% methane and 30% carbon dioxide. Since methane is easily combusted, it makes for a good source of decentralized small scale energy production .However the viable and successful process of producing biogas and eletrcity using internalcombustion in the intermediate scale in the semiarid the rural area of North East are detailed this work..In this context of the biogas production based on wastes from cow and chicken , water plays importante role as much as the energy for the integrated sustianable localdevelopment and was observed to be the limiting factor resource for future insataltions.“Good Quality” water is increasingly a scarce resource and wastewater treatment costs rise, the once-through use of this water is becoming uneconomical and environmentally unacceptable , principly the semi arid region of the Northeast of Brazil. Instead, recovery and recycling of used wastewater is becoming more attractive from both an economic and environmental perspective. In this context , the water minimization and recycling is the other objective of this work as this lead to substantial savings through reduced wastewater disposal cost and rural water requirements , as our region is semiarid and dry.. Further, it improves the environmental aspact of the surrounding communities.. To address the need for efficient design, evaluation, and operation of integrated wastewater treatment and recycling processes, our research group are evaluating and expanding the scope of a software tool called SuperPro Designer. The use of computational modeling and dynamic simulation approach and the system design based on energy and environment concerns were also used . The fundamental approaches in process analysis (synthesis, modeling, and design) of energy and water recovery from animal waste and effluents have particular attributes, require different types of information and provide results applicable in several ways. The system design for small scale energy production from wastes integrated with water conservation using reuse treatments involve complex dynamic system design and operation. The focus of this paper is on modeling of water recycling options as they apply to the smallscale biogas energy gereation plant using animal wastes.Recently several process simulation software were reported that can be applied to biomass utilization process, which also focus on the computer aids for engineering economics. To use this one, several input data and mathematical model need to be developed first for material balance, preliminary design and process economics. SuperPro , the process simultaor used in this work features an intuitive graphical interface that enhances human-computer interaction and makes the software easy to learn and simple to use, even for occasional users with a limited process modeling and water treatment/recycling background. To model a process, we created several flow diagrams by putting together unit procedures, aerobics and anaerobic bioreactors and waste treatments ponds and connecting them with material streams.Besides water recycling applications. This system is used for the evaluation of diferent option for water the conservation and reuse at the small scale biogas energy generation in the farm level.The main equipments used are anaerobic biodigester, compressed biogas storage tanks , oxidation pond for micro algae production , hidrophonic biofiter system.The first case study was made the water consumption related with intermediate scale technology of biogas production from animal wastes based on the wastes from animal residuos.The second case study was to evaluate water reuse option . Two integrated subsystems for bioconversion of biomass sresidues were developed. They were based on (i) energy--manure-recycled water system, (ii) composting and co-composting system., inwhich the reuse and recycle of water had been studied with two option :
Water Minimization Options : Processing wastewater of biogas plant for reuse require that the organic matter in this used water need to be significantly reduced. This can be done in a number of different ways as intensively studied recently by Brazilian , National Research Program of Sanitation(PROSAB) :

• Fertirrigation for hydrophonics foragem : The water is used for green feed
• Gravelbed and sand bed hydroculture filter: The water is filterd for recucling

SuperPro softwerewas used to evaluate these options and performs material balances on individual components and, based on stream composition and estimates Environmental /Aqueous characterization of streams. Recycling the optimum amount was achived after several case studies and process optimization. This was found to reduces the cost of waste disposal but results in increased equipment-dependent operating cost. The cost of utilities also increases because of the additional power consumed by the recovery process.At a first case study , it appears that recycling of wastewater is not an attractive process modification since it increases the unit cost of purified water . The investment is very significantly high to operate the plant .In addition to potential future financial benefits, the main selling point of wastewater recycling in such a facility is the reduced dependency on supply of city water and the improved water supply for the surrounding communities.In the second case study , the role that process simulation was found to play in facilitating the undestanding of the recycling and reuse of wastewater from small scale biogas energy production A water recycling effort was analyzed. With a modest increase in the cost , a water recycling effort would become attractive even from an economic point of view. Several tecnoeconomical parameter of the energy from waste production integrated with the best reuse option to gother with effluent stream characteristics made possible the comparative evaluations. To model the process, several flow diagrams were created by putting together unit procedures, aerobics and anaerobic bioreactors and waste treatments ponds and connecting them with material streams.. This system is used for the evaluation of different option for water the conservation and reuse at the small scale biogas energy generation in the farm level. The main equipments used are anaerobic biodigester, compressed biogas storage tanks , oxidation pond for micro algae production , hidrophonic biofilter system. .The case study was made to evaluate the water reuse options .The material balances on individual components based on stream composition and estimates were obtained.Recycling the optium amount was achieved after several case studies, simulations and process optimization. This was found to reduces the cost of waste disposal but results in increased equipment-dependent operating cost. Even though the integratedsmall biogas system design were made possible ,but several problems were encountered to design and implement the project for community or for the small family farmer
Keywords:Wastewater treatment, Water reuse, computer-aided process design, process modeling, Process simulation, Animal waste, Biogas , Bioenergy, Algae.

Bibliographical References.

1. Li ,K& Wang Q,Digester Fishpond Interaction in Integrated Biomass System,Proceed of the Internet Conference on Material Flow Analysis of Integrated Bio-Systems ,March-Oct 2000.
2. Pannirselvam P.V. et al. Process, Cost modeling and simulations for integraded project development of biomass for fuel and protein, Journal of scientific and industrial research, vol.57, Oct, Pp. 567-574,1998.
3. Carioca, J, et al. Energy from Biomass-Impact of Science on Society, nº 148, 1988.
4. Pearson, H. W., D. D. Mara, L. R. Cawley, H. M. Arridge and S. A. Silva, 1996. The performance of an innovative tropical experimental waste stabilization pond system operating at high organic leadings. Wat. Sci.Techn., 33(7) : 63-73.
5. Shehata SM , et al. Integrated waste management for rural development in Egypt, J Environ Sci Health A Tox Hazard Subst Environ Eng. 2004;39(2):341-9.

Acknowledment :CNPQ/MCT/DEQ/PPGEQ/CT