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Biogas as a means of solid waste management


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Biogas as a means of solid waste management

  1. 1. BIOGAS TECHNOLOGY AS A MEANS OF SOLID WASTE MANAGEMENT<br /> 1ADEWUMI, A. A .J, 1OBAJEMU, O. AND 2OYELEKE, S.B.<br /> 1 Department of Applied Science, CST,<br /> Kaduna Polytechnic, Kaduna<br /> 2 Department of Microbiology,<br /> Federal University of Technology,<br /> Minna, Niger State<br /> <br /> <br /> PAPER PRESENTED AT THE MAIDEN ANNUAL CONFERENCE,<br /> NIGERIAN ENVIRONMENTAL SOCIETY (NES),<br /> KADUNA CHAPTER,<br /> 3 - 5TH JUNE, 2010,<br /> SCIENCE LECTURE THEATRE,<br /> KADUNA STATE UNIVERSITY (KASU),<br /> TAFAWA BALEWA WAY, KADUNA.<br />ABSTRACT<br />Solid wastes are collected and disposed off at a large number of unprotected sites in Nigeria. About 85% of solid wastes disposed on land in Nigeria are organic in nature. Biogas (Anaerobic Digestion –AD) technology can be used to implement a sustainable waste management programme suitable for both urban and rural areas as biodegradable wastes are transformed into biogas and slurry. Biogas technology can serve as a waste disposal technology and help to solve garbage and solid waste environmental problems. Biogas technology is a renewable, alternative and sustainable form of energy. It is an attractive method of solid waste and waste water treatment. Biogas technology can thus play a vital role in Nigeria in solving some of the major environmental problems such as solid waste, chemical fertilizer use, deforestation(use of wood fuel). Biogas technology is extremely appropriate to ecological and economic demands of the future as it can provide pollution free environment, efficient energy for cooking, lighting, and improve health conditions of the people. Highlighted in this paper are the fundamentals of the biogas(Anaerobic) process, feed stocks for anaerobic digestion, environmental impacts of anaerobic digestion, benefits of anaerobic digestion and biogas. <br />I n t r o d u c t i o n<br />Around the world, pollution of the air and water from municipal, industrial and agricultural operations continues to grow. The concept of the ‘four R's’, which stands for Reduce, Reuse, Recycle, and Renewable energy, has generally been accepted as a useful principle for waste handling. The emission of CO2 and other greenhouse gases (GHG) has become an important issue. Governments and industries are therefore increasingly on the lookout for technologies that will allow for more efficient and cost-effective waste treatment while minimizing Green House Gases (GHG).The CO2-trade will even further increase the need for CO2-neutral technologies(IEA,Bioenergy, 2005). The increasing population and the development demands in the Third World have caused an increasing demand on traditional fuels. The fast rate of forest destruction and low rate of reforestation has simultaneously reduced the availability of firewood. To arrest the environmental and agricultural deterioration it is imperative to introduce other sources of renewable energy, such as hydro-power, wind and solar energy and biogas. Biogas is considered one of the cheapest renewable energies in rural areas in developing countries. Production of biogas would not only save firewood but also be beneficial for integrated farming systems by converting manure to an improved fertilizer for crops or ponds for fish and water plants. Other benefits of biodigestion include the reduction of manure smell, elimination of smoke when cooking and the alleviation of pathogens and thereby improving hygiene on farms (Bui Xuan, 2002).<br />The environmental aspects and the need for renewable energy are receiving interest and considerable financial support in both developed and developing countries, leading to an increase in research and development in this area. Many systems using biodigestion have been constructed in different countries. Despite the potential benefits, the expansion of biogas technology has gone slowly, especially in countries where there has been no financial support (subsidy) from governments or development agencies. The main constraint has been the high cost of the biogas plant for people in rural areas with limited financial resources (Bui Xuan, 2002).<br />Anaerobic digestion (AD) is the most promising method of treating the organic fraction of municipal solid waste (MSW) and other organic wastes. Anaerobic bacteria convert the biomass into a biogas or landfill gas that can be used to generate energy (Mshandete and Parawira, 2009).<br />One technology that can successfully treat the organic fraction of wastes is AD. When used in a fully-engineered system, AD not only provides pollution prevention, but also allows for energy, compost and nutrient recovery. Thus, AD can convert a disposal problem into a profit centre. As the technology continues to mature, AD is becoming a key method for both waste reduction and recovery of a renewable fuel and other valuable co-products. Worldwide, there are now approximately 150 AD plants in operation and a further 35 under construction using MSW or organic industrial waste as their principal feedstock. The total annual installed capacity is more than five million tonnes, which has the potential to generate 600 MW of electricity. Waste managers have found that AD provides environmental benefits allowing waste disposal facilities to meet increasingly stringent regulations. Controlling odour and recovering nutrients are major drivers in their decision making. The use of AD for sewage sludge stabilization is well established and the use of AD as a (pre-) treatment step for industrial wastewater is increasing rapidly, to the point where there are now more than 2,500 vendor-supplied systems in operation or under construction throughout the world (IEA, Bioenergy, 2005).<br /> Digestion<br /> In southern countries e.g. Italy, Portugal, Spain the technology is widely used only as a wastewater <br />treatment technology. Climatic conditions and intensive production systems result in the use of<br />large quantities of water. Thus manure contains a very low dry matter content and is handled<br />and treated similarly to wastewater. In countries such as Germany, Denmark, Switzerland the<br />composition of manure is different: it is concentrated, with higher solids content and is<br />regarded as a fertilizer. This difference makes it necessary to look at the biogas technology in <br />two ways:<br />1. Biogas or anaerobic technologies as an option for slurry/wastewater treatment <br />2. Biogas technology as an option for improvement of the value of the residues as organic fertilizers<br />There are inevitable overlaps between the two, as the environmental aspects of importance in<br />option 2 is also relevant tor option 1. However, they are generally of less importance when the<br />treatment type is selected.<br />Considering biogas technology as a wastewater treatment system following major<br />environmental impacts are mentioned1:<br />low sludge production: 50 to 75 % less excess sludge is produced. Although sludge can be<br />used as soil conditioner and fertilizer, the handling (post composting, spreading) causes<br />additional costs. In some cases sludge is also incinerated or just dumped. The reduction of<br />excess sludge can be considered as an environmental positive impact of anaerobic digestion<br />(AD).<br />low land demand: Depending on the anaerobic system applied land demand can be reduced<br />up to 5 times compared with aerobic systems. Especially in those areas where land is rare<br />and/or expensive AD is given the priority and thus preserves valuable land resources.<br />positive energy balance: Anaerobic treatment processes have only a small demand for<br />process energy. The gas generated during the treatment process, depending on the type of<br />wastewater, allows a surplus of energy and saves fossil fuels (see also option 2).<br />low emissions: Capturing and utilization of biogas contributes to the protection of our<br />climate (see also option 2). (GTZ, 1998).<br />Biogas is generated when bacteria degrade biological material in the absence of oxygen, in a process known as anaerobic digestion. Since biogas is a mixture of methane (also known as marsh gas or natural gas, CH4) and carbon dioxide it is a renewable fuel produced from waste treatment. Anaerobic digestion is basically a simple process carried out in a number of steps that can use almost any organic material as a substrate - it occurs in digestive systems, marshes, rubbish dumps, septic tanks and the Arctic Tundra. Humans tend to make the process as complicated as possible by trying to improve on nature in complex machines but a simple approach is still possible (University of Adelaide, 2010). Biogas can provide a clean, easily controlled source of renewable energy from organic waste materials for a small labour input, replacing firewood or fossil fuels (which are becoming more expensive as supply falls behind demand). During the conversion process pathogen levels are reduced and plant nutrients made more readily available, so better crops can be grown while existing resources are conserved (University of Adelaide, 2010). Biogas technology may be a possible means of reducing or eliminating the menace and nuisance of solid wastes in many cities of Nigeria (Akinbami et al., 2001). <br />Fundamentals of the Anaerobic Process:<br /> Biogas generation basically takes place in four successive phases (Hydrolytic, Acidogenic, Acetogenic and Methanogenic) by decomposition of organic substances to water and Biogas (methane). Mixed cultures of facultative anaerobic and strictly anaerobic microorganisms are involved in the decomposition process, with different microorganisms involved in each step of degradation. Biogas quality is highly dependent on the composition of the substrate. Biogas is a renewable biofuel produced by anaerobic digestion or fermentation of biodegradable materials (Stefan, 2009; Wikipedia, 2010). <br />The typical composition of Biogas consists of Methane(CH4): 50-75%; Carbon dioxide(CO2):25-50%; Nitrogen(N2): 0-10%; Hydrogen(H2): 0-1%; Hydrogen sulphideH2S): 0-3%; Oxygen(O2): 0-2% (Stefan, 2009; Wikipedia, 2010). <br />Available feed stocks for Anaerobic Digestion<br />In principle, most types of biomass can be used as feedstock for biogas production. Manure from many types of domestic animals, waste from kitchens, gardens, agriculture and slaughterhouses, and even human excreta have all been used for anaerobic digestion. Gas yields will depend on the feedstock used. One tonne of cow manure produces around 36m3 biogas. Figures from a demonstration biogas plant in Ludlow, Shropshire, suggest that one tonne of UK household kitchen waste produces 140m3.<br />Available <br />Sewage Sludge<br />Digestion of sewage sludge provides significant benefits when recycling the sludge back to land. The digestion process sanitizes and also reduces the odour potential from the sludge. Typically between 30 and 70% of sewage sludge is treated by AD depending on national legislation and priorities. In countries like Sweden and Switzerland limitations for the field application of sludge have been introduced. However, AD is still considered an important step since it produces renewable energy and improves the ability of the sludge to settle which makes it easier to dry.<br />In less developed countries, direct AD is the only treatment of waste water. If the digester is adequately designed and the retention time of the water is long enough, the quality of the treated water can be excellent.<br />Agricultural Wastes<br />Digestion of animal manure is probably the most widespread AD application worldwide. It produces a valuable fertilizer as well as biogas. Today more and more organic industrial waste materials are added to the manure which brings increased gas production and creates an additional income from the gate fee. In countries like Denmark, Austria and Germany the easily degradable wastes are becoming scarce and farmers are looking for alternative substrates (energy Cattle manure is an excellent substrate for biogas production. The yield is not the highest however; it guarantees high methane content of up to 63% and makes the process more stable. <br /> Industrial Wastes<br />Organic solid wastes from industry are increasingly treated in biogas plants. Even if some of the substances might be difficult to digest as a sole substrate, in mixture with manure or sewage sludge they don’t pose any problem. The combined digestion of different wastes is called co-digestion. Most of the waste products from the food industry have excellent gas potential and therefore are in demand by plant operators. Until recently the industry paid the operators reasonably high gate fees (up to 35 Euro per ton) to accept the waste products. Now, the operators are starting to pay for the waste materials with the highest gas potential like fat and vegetable oil. With current high feed-in tariffs they can easily recover the cost of these wastes. AD of industrial waste waters is becoming a standard technique. Whilst AD is only an initial stage in the treatment of high quality water discharge, it can significantly reduce the cost and size of plant compared to wholly aerobic treatments.<br />Municipal Solid Wastes(MSW)<br />Organic wastes from households and municipal authorities provide potential feedstock for anaerobic digestion. The treatment of clean source separated fractions for recycling of both the energy content and the organic matter is the only method in which the cycle can be completely closed. In most of the participating countries, the source separation of MSW is actively encouraged. This includes separation of the putrescible organic fraction, also known as ‘green waste’ or ‘biowaste’. Experience has shown that source separation provides the best quality feedstock for AD. The digested material is a valuable fertilizer and soil improver, especially after aerobic post-treatment. Where source separation has been widely introduced, the results are encouraging. Alternatively, the unsegregated wastes or the ‘grey waste’ after separation of the ‘biowaste’ can be treated to gain the biogas from the waste as well as stabilizing it to prevent further problems in landfill. The latter technologies are called mechanical biological treatment (MBT).The EU has set the goal of reducing the amount of organic waste to landfill by 65% by 2014. Some countries have completely banned the disposal of untreated organic waste. Odour free storage and efficient collection of source separated waste are the key components for a successful introduction of an MSW system (Pulford, 1988; Zamani, 2009).<br />gas Production<br />Farm-scale digestion plants treating primarily animal wastes have seen widespread use throughout the world, with plants in developing and technically advanced countries. In rural communities small-scale units are typical; Nepal has some 50,000 digesters and China is estimated to have 8 million small-scale digesters. These plants are generally seed for providing gas for cooking and lighting for a single household. In more developed countries, farm-scale AD plants are generally larger and the gas is used to generate heat and electricity. These farm-scale digestion plants are simple stirred tank designs that use long retention times to provide the treatment required. In Germany more than 2,000 farm-scale biogas digesters are in operation; Austria has approximately 120, and Switzerland 69.Two designs are prevailing throughout Europe: the so-called rubber top digester, and the concrete top digester usually built in the ground. Both have a cylindrical form with a height to diameter ratio of 1:3 to 1:4.They are intermittently mixed tank reactors with hydraulic retention times (HRT) of the waste in the digester of 15 to 50 days. The longer HRT applies where an energy crop is used as a co-substrate or even the only source of energy. There are digesters with a single and a double membrane cover. The advantage of the rubber top digester is the price. A membrane is cheaper than a concrete cover. At the same time, the membrane serves as gas storage whereas concrete top digesters need additional gas storage. On the other hand, the latter are easy to insulate and can take high snow The most applied digester technology is the family sized Chinese dome digester with over 8 million plants. This modern version of ADRA in Suck Chon (DPRC) is built in a glass house to maintain elevated temperature in the cold winters of North Korea.<br />Environmental Impacts of Anaerobic Digestion (AD):<br /> Considering the technology as a fertilizer treatment option environmental impact can be<br /> divided into impacts at farm and public level :<br /> Farmers Interests<br /><ul><li>Quality improvement of organic fertilizer/Reduction of mineral fertilizer
  2. 2. Risk of increased NH4 loss
  3. 3. Reduction of phytotoxic substances
  4. 4. Reduction of the use of pesticides
  5. 5. Fertility/reduction of desertification</li></ul> P ublic Interests<br /><ul><li>Reduction of pollutants
  6. 6. Reduction of odour
  7. 7. Positive impact on resource protection
  8. 8. Positive impact on climate protection
  9. 9. Compared to other fuels positive emission behavior of biogas (Klinger, 2000).</li></ul>Quality improvement of organic fertilizer<br />The most important advantage of organic fertilizer is their participation in the natural nutrient<br />cycle, while inorganic fertilizers are additional to it. A characteristic of organic fertilizers is the<br />wide nutrient spectrum, which is very similar to the demand of the plants.<br />Although in many European regions surpluses of manure cause groundwater and air pollution,<br />farmers are still using additional mineral fertilizer. This is, mainly due to the comparative<br />ease of calculating the nutrient (especially Nitrogen) content and the more convenient handling.<br />After anaerobic digestion about 25 to 40% of the organic dry matter is converted to methane<br />(CH4) and carbon dioxide (CO2). This reduction results in a decreased carbon/nitrogen<br />proportion and improves the quality of manure.<br />In addition the fluidity is increased, which allows for easier handling (less clogging) and an<br />increased infiltration after spreading2.<br />Odour causing compounds are degraded and weed seeds and pests are reduced.<br />With increasing retention time the ammonia content increases. Thus anaerobically treated manure acts more like mineral fertilizer and can be utilized more on demand by plants (Knuz, 1996; Munasinghe, 1996a, 199 6b ; GTZ, 1998; Parawira , 2009 ).<br />This effect was also measured in an 8 years trial with digested manure. The ammonia content<br />increased from 58 to 62 %. An average increase of ammonia from 5 to 10 % was found.<br />This effect and a slightly increased nutrient release measured in the soil resulted in an improved<br />fertilizer effect from digested manure compared to untreated manure and generally allows<br />fertilization more appropriate to the plant needs.<br />Many farmers have observed improved yields after using digested manure. Measurements<br />show a yield increase of 2 to 3 % compared to untreated manure. The effect is more<br />significant if the manure is directly injected into or covered with soil and when applied before<br />seeding.<br />Another observation from farmers after use of digested manure is that the grass variety is<br />higher than with untreated manure.<br />Through co-fermentation (addition of agro-industrial residues such as slaughterhouse wastes,<br />fat etc.) the nutrient content can easily be increased. Through addition of co-substrates and<br />improved fertilization techniques an average of 20% more ammonia (ca. 0.7 kg/m³ biomass)<br />and 30% more phosphate (ca. 0.3 kg/m³ biomass) is achieved, which substitute the use of<br />mineral fertilizer (Taftrup, 1993).<br />To produce one kg of nitrogen, 2 kg mineral oil is needed (Haber Bosch System). An average<br />of 30 MJ per m³ of biomass (manure and co-substrates) can be saved through co fermentation.<br />The anaerobic treatment of animal manure with co-substrates increases the quality of the<br />digested manure, which results in a better handling and increased yield. In Addition the range<br />of application possibilities and the acceptance by farmers is increased(Taftrup, 1993).<br />Increased risk of ammonia losses<br />The increased ammonia content of digested manure combined with a slightly increased pH<br />causes a higher risk of ammonia losses in treated manure compared to untreated manure.<br />Therefore digested manure must be handled more carefully and farmers have to follow manure<br />handling instructions given by the national advisory services. Anaerobically treated manure<br />should be injected into the soil or covered to minimize ammonia emissions.<br />Reduction of phytotoxic substances and odour<br />Phytotoxic substances in the manure can cause necroses and scleroses when applied to growing<br />plants. This is the main the reason why overhead fertilizing of a growing field is not done with<br />organic fertilizer, but mineral fertilizer. Untreated manure with a dry matter content of 7 to<br />10% spread on plants, covers leaves and reduces assimilation.<br />Through anaerobic digestion phytotoxic acids are degraded and dry matter content is<br />decreased. Therefore digested manure can be applied to a growing field (e.g. maize) which<br />usually has a high demand for nutrients. Farmers are able to reduce their amount of mineral<br />fertilizer (Kunz, 1996).<br />Odour causing substances are degraded in the same way. This is the major reason to install a<br />biogas plant for many farmers. . In particular, farmers situated near housing areas face<br />problems with the local population due to odour complains. Anaerobically treated manure<br />allows farmers to spread manure also close to villages and thus increase the application<br />possibilities.<br />Anaerobically treated manure increases the range application possibilities in terms of time,<br />crops, housing.<br />Reduction of weed seeds and pests<br />Organic fertilizer generally contains weed seeds and microorganisms causing pests. The<br />anaerobic digestion process lowers the ability of seeds to germinate. This loss of ability to<br />germinate can occur after 10 to 16 days. Differences have been registered for different weeds.<br />In general the longer seeds are kept in an anaerobic environment, the lower the ability to<br />germinate and greater the reduction in the infectious potential of manure(Taftrup, 1993; Kunz, 1996).<br />This effect is a major reason for German organic farmers to integrate a biogas plant in their<br />farming system, since they are not allowed to use herbicides and pesticides in general.<br />To quantify the effect and whether biogas technology is able to reduce the amount of pesticides<br />additional scientifically measurements are needed.<br />Improvement and stabilization of soil fertility<br />Organic fertilizer (liquid and solid animal manure) and mineral fertilizer differentiate not only<br />in nutrient content, composition and variance but also in qualitative aspects. While organic<br />fertilizer contributes directly to the humus household of the soil, mineral fertilizer does not.<br />Lack of humus ultimately results in desertification. A productive soil system needs a balance<br />between incoming humus and degradation of humus. Manure, compost or any organic fraction<br />will increase or stabilize the humus level in soil.<br />Humus is one of the most important compounds in the soil since it is responsible for the<br />temperature of the soil;, the water capacity, structure and pore volume (which is very important<br />against desertification) and absorption of nutrients.<br />During the anaerobic process most of the low molecular substances (less than 1000 g/Mol) are<br />degraded, while lignin substances still contribute to the humus pool of the soil . Thus fermented manure still contributes with its humus building substances to soil fertility.<br />Findings from a study in southern Germany on the use of digested manure confirmed the above:<br />100 % of the farmers found digested manure easier to handle, as they are able to use the<br />digested manure more on demand.<br />100% experienced the odour reduction, which was a very important side effect for farmers<br />near housing areas.<br />81 % stated a higher crop yield through the better and demand driven handling.<br />75% agreed that digested manure is similar to mineral fertilizer and 50 % were able to<br />reduce the amount of mineral fertilizer.<br />40% of the farmers said that digested manure reduces weed seeds and pests (GTZ, 1998; Klinger, 2000).<br />Reduction of pollutants<br />Reduction of heavy metals is not feasible. Organic compounds can be reduced through the<br />anaerobic treatment process. Tests have shown that organic carbon compounds, mainly<br />resulting from the use of pesticides, can be degraded. Organic compounds that can be degraded through anaerobic treatment includes <br /> <br /> Trichlormethane<br /> Tetrachlormethane<br /> 1, 2-Dichlorethane<br /> 3-Chlorbenzoesäure<br /> 3, 5-Dichlorbenzoesäure<br /> Phenol<br /> Cresol<br /> Xylol,<br /> Toluol<br /> 2-,3-,4-Chlorphenol<br /> 2,4-Dichlorphenol<br /> 3,4-Dichlorphenol<br /> 3,5-Dichlorphenol<br /> Pentachlorophenol<br /> low condensate PCB<br /> low condensate PAC<br />There is no information available on whether benzol, dioxin and furans (PCDD, PCDF) are<br />degraded through anaerobic processes. But similarities to the structure of other carbohydrogens<br />compounds suggest there is a possibility that they could be.<br />It has been shown that anaerobic treatment is able to eliminate a number of organic<br />pollutants. Further research is needed to quantify the effect.(Klinger, 2000).<br />Contribution to the water resource protection<br />Within the agricultural sector anaerobic digestion may contribute through a double effect to<br />save water resources <br />1. Through the increased ammonia content in the digested manure an accelerated plant up take<br />occurs. Roots prefer ammonia than nitrate, if they are available at the same time. When<br />ammonia is more and faster absorbed by the plants it cannot be transformed into nitrate and<br />leached downwards in direction of the groundwater level. Thus groundwater pollution through<br />nitrate is prevented.<br />Trials on cereals have demonstrated the higher uptake of ammonia from digested manure which<br />resulted in an equivalent of mineral fertilizer between 79 to 101 % (mineral fertilizer is 100%).<br />Raw manure achieved an equivalent of 35 to 42% only. This increased up take of accessible<br />nitrogen during the growing period implies for the following period (autumn and winter) a<br />reduced nitrogen content in the soil. Unwanted mineralization of nitrogen at this time is reduced<br />and the risk of transfer to the groundwater is also reduced (Taftrup, 1993; Klinger, 2000).<br />2. Decentralized biogas plants with a co-generation unit reduce the technical water demand for<br />electricity supply. For example: 1988 in Germany about 360 TWh electricity was produced<br />resulting in a water demand of 300 Bill m3 fresh water. For about 18% of the final electricity<br />use, half of Germans water demand was spent!<br />Decentralized energy production saves water resources.<br />Contribution to the climate change protection<br />Methane is the second most important greenhouse gas in the world, with a global warming<br />potential (GWP) of 25 times higher than CO2 (in a time horizon of 100 years). Methane<br />emissions occur in any anaerobic processes with organic materials. It has been estimated that<br />methane emissions from agriculture contribute about 33% to the global greenhouse effect.<br />About 7 % alone result from animal excrement which is similar to 20-30 Million<br />tonnes of methane per year( Cassada and Safley, 1990; Kunz, 1996).<br />Through anaerobic treatment of animal excrement a renewable source of energy is generated,<br />which has an important dual climatic effect: The use of renewable energy reduces the CO2-<br />emissions through a reduction of the demand for fossil fuel (1 m3 biogas substitutes 0,5 kg oil<br />for energy purposes reducing 2,6 kg CO2-emissions, see also table 4). At the same time the<br />process can diminish uncontrolled methane generation by capturing methane (Japan Environment Agency, EPA, 1990).<br />Half of the methane emissions could be reduced through implementation of biogas technology.<br />In particular in developing countries smaller agricultural biogas units reduce the use of forest<br />resources for household energy purposes and thus slow down deforestation (about 1 ha of<br />forest per rural biogas plant), soil degradation and resulting natural catastrophes like flooding<br />or desertification.<br />Nitrous oxide emissions that are much more harmful to the climate change through their very<br />high GWP of 320 are also diminished through the anaerobic process.<br />Nitrous oxide generation is a natural microbial process. It is produced during nitrification and<br />denitrification processes in soils, stables and animal waste management systems. In general<br />nitrous oxides emissions appear in soils without anthropogenic influence. Fertilizing as well as<br />special conditions during storage can immensely increase the emissions.<br />Very few detailed information is available about the reduction potential of nitrous oxides<br />through anaerobic digestion of animal waste. There is still a need for further research.<br />Nevertheless recent research results lead to the opinion that anaerobic digestion of animal<br />waste significantly reduces nitrous oxide emissions by<br />1. Avoidance of emissions during storage of animal waste.<br />2. Avoidance of anaerobic conditions in soils.<br />3. Less N2O-losses through increased nitrogen availability for plants and faster nitrogen absorption through crop plants.<br />4. Reduced application of inorganic nitrogen fertilizer and N2O avoidance during production of<br />nitrogen fertilizer.<br />5. Avoidance of changes of land use (saving of forest resources).<br />Considering all these effects an N2O-reduction potential through anaerobic treatment of about<br />10 % could be assumed.<br />Anaerobic treatment of agricultural residues reduces the global climate change effect (Taftrup, 1993; Klinger, 2000).<br />Biogas composition and emissions after burning in comparison with other fuels<br />There are four major gas components in biogas: methane, carbon dioxide, nitrogen and oxygen.<br />Besides those other gases such as ammonia, chloride, etc. could be a minor part of the biogas<br />and disturb either the burning process or harm the environment. Recent research on biogas<br />composition confirmed that biogas from animal excrement and co-fermentation does not have<br />an increased content of disturbing gases. There was a non-significant correlation visible<br />between co-fermentation and other gases in the biogas.<br />For H2S values under 100 mg/m³ have been found, when the normal desulphuration with air is<br />installed.<br />For ammonia, chloride, fluoride, mercaptane detectable limit of 0,1 mg/m³ was not exceeded.<br />The same stands for benzol, toluol, ethylbenzol, xylol and cumol and PAC with its limit of 0,01<br />micrograms/m³.<br />These data are supported by the emission data after burning from different fuels. Biogas shows<br />positive emission behaviour in comparison to other fossil and renewable fuels. Measurements<br />on a cogeneration unit showed that parameters like NOx and SO2 can fulfill emission standards<br />like in Germany (GTZ, 1998). Problems have occurred with carbon monoxide.<br />In comparison to other fuels biogas has cleaner emissions after burning.<br />Resource protection, an appropriate technology<br />Fossil fuels are limited and contribute to the greenhouse effect. Biogas is renewable and can<br />help to reduce the climate change as well as support the protection and conservation of limited<br />resources.<br />Gases as fuels have one big advantage in comparison to other fuels. There is no need for<br />refining and processing of the fuel; and the exhaust usually does not need an expensive and<br />sophisticated cleaning facility before use. The output after burning is nothing more than the<br />exhaust gases.<br />With co-generation the highest efficiency in the energy supply is achieved. This way of<br />electricity and heat generation saves water and energy resources in comparison to conventional<br />power stations.<br />Biogas can be stored and transformed to energy when it is needed.<br />Biogas is in terms of its application mode a competitive energy source and protects limited<br />fuel resources(Taftrup, 1993; Klinger, 2000).<br />Reduction of waste disposal<br />Through the introduction and support by the EC of separated waste collection the amount of<br />organic residuals has been increased tremendously, while possibilities to re-use have not been<br />considered. Therefore disposal problems are evident in many communities. Composting is<br />limited, mainly due to limited market potential. Incineration does not always contribute to the<br />common understanding of sustainable development.<br />In many of the agricultural biogas plants in Europe additional organic residues from separated<br />household waste, or agro-industrial wastes are co-treated with manure. This contributes<br />strongly to a closed nutrient cycle system, where nutrients are not lost but re-used in the<br />agriculture (see figure 6). At the same time energy is generated. However the re-use of waste in<br />the agriculture is limited due to many factors, such as public acceptance, input of pollutants,<br />overload of nutrients, organization and infrastructure.<br />The participation of the agricultural sector is and should be a major and important step in a<br />sound waste management.<br /> There are a number of benefits resulting from the use of Anaerobic Digestion(AD) technology.<br />The Anaerobic Digestion Process<br />In the absence of oxygen, anaerobic bacteria will ferment biodegradable matter into methane and carbon dioxide, a mixture called biogas. Approximately 90% of the energy from the degraded biomass is retained in the form of methane. Hence, very little excess sludge is produced. Biogas is formed solely through the activity of bacteria.<br />The AD process occurs naturally in the bottom sediments of lakes and ponds, in swamps, peat bogs, intestines of ruminants, and even in hot springs. Methane formation is also the process which stabilizes landfill sites. The widespread natural occurrence of methane bacteria demonstrates that anaerobic degradation can take place over a wide temperature range from 10°C to over 100°C and at a variety of moisture contents from around 50% to more than 99%. The potential to operate digesters at temperatures above 50°C makes the AD process particularly interesting for promoting hygiene. In addition to temperature, the anaerobic chemical environment multiplies the sanitation effect (IEA, Bioenergy, 2005; Mshandete and Parawira, 2009).<br /> Waste treatment benefits:<br />_ Natural waste treatment process <br />_ Requires less land than aerobic composting<br /> _ Reduces disposed waste volume and weight<br /> Energy benefits:<br /> _ Net energy producing process<br /> _ Generates high quality renewable fuel<br /> _ Biogas proven in numerous end-uses to be land filled applications <br />l Benefits Economic Benefits<br /> Environmental benefits:<br /> _ Significantly reduces greenhouse gas<br /> _ Eliminates odours<br /> _ Produces a sanitized compost and Nutrient-rich liquid fertilizer<br /> _ Maximizes recycling benefits<br /> <br /> Economic benefits:<br /> Considering the whole life-cycle, it is more emissions cost-effective than other treatment options<br />Advantages of biogas over wood as a cooking fuel:- <br />Less labour than tree felling<br />Trees can be retained<br />Biogas is a quick, easily controlled fuel<br />No smoke or smell (unless there is a leak - then you need to knowanyway!) so reduced eye/respiratory irritation<br />Clean pots<br />Sludge is a better fertilizer than manure or synthetic fertilizers (andis cheaper then manufactured products)<br />Reduced pathogen transmission compared to untreated waste(University of Adelaide,2010)<br /> Biogas can provide a clean, easily controlled source of renewable energy from organic waste materials for a small labour input, replacing firewood or fossil fuels (which are becoming more expensive as supply falls behind demand). During the conversion process pathogen levels are reduced and plant nutrients made more readily available, so better crops can be grown while existing resources are conserved.<br />The benefits of biogas:<br />_ Biogas systems make clean energy for household use. After an initial investment in the system,<br />there is no need to spend money on fuel and no more smoke from wood or charcoal<br />_ Cooking on biogas is quicker and easier than cooking with firewood<br />_ Biogas systems kill the bacteria in livestock manure. A farm with a biogas system is a cleaner<br />and safer place.<br />_ Biogas systems produce excellent safe fertilizers for use on the farm<br />_ Biogas systems can help in the fight against global warming by allowing us to burn methane<br />from organic waste, instead of letting it escape into the atmosphere where it adds to the<br />greenhouse effect. It also helps by letting us leave more trees standing!<br />Biogas and climate change<br />Carbon dioxide released by burning fossil fuels is the primary cause of global warming. Burning methane, for example for cooking or to run a generator, produces carbon dioxide and water. However, all the carbon contained in biogas (in the form of carbon dioxide and methane) has previously been absorbed from the atmosphere by the plants that produced the feedstock. Hence burning biogas will only release as much carbon dioxide into the air as the plants have taken out of it, and as long as the biomass is allowed to regenerate, biogas is a carbon-neutral source of energy.<br />However, methane is a potent greenhouse gas, many times more powerful than carbon dioxide in causing climate change. It is therefore important that all gas is burned, with no leakage during production and distribution(Centre for Alternative Technology, 2007) .<br />Uses of the slurry<br />Only a small proportion of the total mass of the feedstock is converted into biogas. The remainder is converted into nutrient-rich slurry which can be used as a biofertilizer. The anaerobic digestion process eradicates most pathogens. Studies show that counts of fecal coliform bacteria can be reduced by 99.9%. Biogas effluent does not attract flies. These factors can contribute positively to the health of the people (Ellegard, et al., 1983; Sinha and Kazaglis, 2006; Centre for Alternative Technology, 2007).<br /> <br /> <br />Conclusions<br />Biogas technology contributes in a wide range of aspects and effects to the environment.<br />The major effect for farmers is the improved quality of anaerobically treated manure. This<br />results in a better handling (less clogging), increased ammonia content, increased possibility to<br />apply on demand of the plants, less odour and potential decreased use of mineral fertilizer and<br />pesticides. Considering all positive impacts an increased crop yield is observed. The overall<br />and most important effect is the higher acceptance of organic fertilizers through AD by farmers<br />and the public. <br />A potential reduction of the use of mineral fertilizer and pesticides is feasible but needs to be<br />quantified scientifically.<br />The risk of an increased ammonia emission should be minimized by proper application<br />(injection, covering).<br />Anaerobic treatment and gas use contributes to the reduction of greenhouse gases.<br />Biogas is a competitive energy source and protects limited fuel resources.<br />The participation of the agricultural sector is and should be a major and important step in a<br />sound waste management due to its resource saving potential.<br />It becomes evident that with the implementation and promotion of biogas technology in the<br />agricultural sector interactive implications can be achieved especially for the protection of the<br />environment. This is confirmed by the growing number of agricultural biogas plants in the<br />European community. In respect of the global harm, “Climate change” and it's range of positive<br />impacts for farmers and the public the technology should gain more importance and should be<br />included in promotion programmes.<br />Biogas technology blends with our culture and society. However the success of promoting this technology depends on careful planning, management, implementation, training and monitoring. Biogas technology can help in maintaining the environment and improvement of health conditions. <br /> <br />REFERENCES<br />Akinbami, J.R.K., Ilori, M.O., Oyebisi, T.O., Akinwumi, I.O. and Adeoti.O. (2001). Biogas energy<br /> use in Nigeria: Current status , future prospects and policy implications. Renewable and<br /> Sustainable Energy Review 5:97-112.<br />Bui Xuan, A. (2002). Biogas technology in Developing Countries-Vietnam case study. Proceedings <br /> Biodigester<br />Cassada, M. 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