16th European Biomass Conference & Exhibition, 2-6 June 2008, Valencia, Spain BIOGAS POTENTIAL FROM LIVESTOCK AND POULTRY WASTES IN THE REGION OF WESTERN MACEDONIA, GREECE Goula Ma., Bereketidou Oa,b., Economopoulos Ca., Charisiou Na. aPollution Control Technologies Department, Technological Educational Institute of Western Macedonia, Koila, Kozani, 50100, Greece, b Department of Engineering and Management of Energy Resources, University of Western Macedonia, Bakola & Sialvera, Kozani, 50100, Greece *Corresponding author. Tel: +302461068296, Fax : +302461039682, email:[email protected] ABSTRACT: Animal wastes constitute a high proportion of biomass in the region of Western Macedonia, Greece, and are able to play an important role towards the satisfaction of heat and/or energy and related material supply, with respect to environmental protection targets. Significantly, such wastes could be a significant source of energy if conventional energy prices continue to rise. This paper describes anaerobic digestion as a potential animal waste exploitation method. The aim of the present work is to strengthen the interest in animal waste potential for energy production in the region, through a methodology for the feasibility of utilization of those kinds of wastes as renewable energy resources. A combination of technical, economic and environmental issues is presented here. This study estimates the economically recoverable energy potentially available from livestock and poultry wastes in the region of Western Macedonia, Greece for the base year 2000. Anaerobic digestion of dairy cow, fed beef, goat, sheep and laying hen manures could have produced approximately 129,084 m3/d or 47x106 3 6 m /year of biogas, containing approximately 61.5 x 10 KWh/year that could result at a reduction in CO2 of over 80 x 103 tonnes per year and significant economic savings. Keywords: biogas, anaerobic digestion, animal manure oxygen and various trace hydrocarbons. Due to its low 1 INTRODUCTION methane content (and therefore lower heating value) compared to NG, biogas is considered a low quality gas The promotion of biogas production and utilization is which is only suitable for use in enginegenerator sets strongly suited to the Mediterranean region as, to a great and boilers specifically designed to combust biogas as extent, the economies of the countries of the region rely fuel. on agriculture and related activities [16]. Currently, the vast majority of agricultural/ animal wastes are not being taken advantage of, despite the potential that they have as 2 BACKGROUND an energy resource. The successful development of such wastes into energy sources can go some way towards 2.1 The anaerobic digestion process mitigating the adverse economic, environmental and The biological conversion of the organic fraction of political effects that the over reliance on imported fossil animal wastes under anaerobic conditions is thought to fuels has upon the Mediterranean countries. This is a occur in three steps. The first step involves the enzyme- particularly urgent for two main reasons. Firstly, the mediated transformation (hydrolysis) of higher current climate of uncertainty over security of oil supply molecularmass compounds into compounds suitable for due to the political instability that characterizes the use as a source of energy and cell tissue. The second step majority of oil producing countries, fears over global involves the bacterial conversion of the compounds terrorism and the emergence of the economies of China resulting from the first step into identifiable lower and India as major oil demanding economies, are pushing molecularmass intermediate compounds. The third step the prices of crude oil at record prices, affecting involves the bacterial conversion of these intermediate adversely the economies of the Mediterranean countries compounds into simpler end products, principally and the living standards of their people. Secondly, the methane and carbon dioxide. effects of global climate change are expected to be In the anaerobic decomposition of wastes, a number of particularly negative in the region, due to limited water anaerobic organisms work together to bring about the resources and the sensitivity of local ecosystems. conversion of the organic portion of wastes into a stable Biogas is a renewable energy source similar to natural end product. One group of organism is responsible for gas and is derived from renewable biomass sources, hydrolyzing organic polymers and lipids to basic primarily via a process called anaerobic digestion [7 - structural building blocks such as fatty acids, 20]. The most common types of biogas projects involve monosaccharides, amino acids, and related compounds. A biogas collected at landfills (i.e. landfill gas), waste water second group of anaerobic bacteria ferments the treatment plants, and dairy or swine farms where biogas breakdown products from the first group to simple is created from animal manure in anaerobic digesters. organic acids, the most common of which is acetic acid. The processes and equipment for converting biomass This second group of microorganisms, described as sources (such as dairy manure) into biogas via anaerobic nonmethanogenic, consists of facultative and obligate digesters are well known, commercially available and anaerobic bacteria that are often identified in the economically reasonable. In its raw state, the major literature as “acidogens” or “acid formers”. components of biogas are methane (typically 60 – 70%) A third group of microorganisms converts the hydrogen and carbon dioxide (typically 30 – 40%). Additional and acetic acid formed by the acid formers to methane smaller components of biogas include hydrogen sulfide gas and carbon dioxide. The bacteria responsible for this (typically 50 – 2,000 ppm), water vapour (saturated), conversion are strict anaerobes, called methanogenic, and are identified in the literature as “methanogens” or 385 16th European Biomass Conference & Exhibition, 2-6 June 2008, Valencia, Spain “methane formers”. Many methanogenic organisms system, which may be either mechanical or gas- identified in landfills and anaerobic digesters are similar based, helps to increase the efficiency of the to those found in the stomachs of ruminant animals and in digestion process as well as accelerate it. Likewise a organic sediments taken from lakes and river. The most built-in heating system also increases the efficiency important bacteria of the methanogenic group are the of the digestion process. Typically 10 – 15% of the ones that utilize hydrogen and acetic acid. They have biogas output is used to provide heating for the very slow growth rates, as a result, their metabolism is digester and electricity for other biogas plant usually considered ratelimiting in the anaerobic processes. treatment of an organic waste. Waste stabilization in anaerobic digestion is accomplished when methane and • PlugFlow – This type of anaerobic digester is carbon dioxide are produced. Methane gas is highly intended for ruminant animal manure (cows) with 11 insoluble, and its departure from a landfill or solution – 14% solids and is therefore not appropriate for represents actual waste stabilization. manure collected via a flush system. The design is Anaerobic digestion can occur within three different similar to the complete mix digester but without the temperature ranges: psychrophilic, mesophilic, and mixing system. Plugflow digesters are cheaper to thermophilic [8]. construct and operate than complete mix digesters Psychrophilic digestion occurs at temperatures below but are also less efficient. 68°F and is usually associated with systems that operate at ground temperature. Psychrophilic AD has the lowest • MultipleTank (2Stage) – This type of anaerobic biogas production rate of the three temperature ranges. digester is similar to the complete mix digester The production rate is susceptible to seasonal and diurnal design except that digestion occurs sequentially in fluctuations in temperature, making it difficult to predict two phases. The first phase is a higher temperature how much biogas will be available. (thermophilic) phase at 55ºC followed by a second, The mesophilic range is between 68°F and 105°F. The lower temperature (mesophilic) phase at 35ºC. optimal temperature for mesophilic AD is approximately While laboratory tests of this design show promise 100°F, which is nearly the same as the body temperature for increased digester efficiency, there is very little of dairy cattle. This allows the same bacteria at work in a data on fieldscale systems yet. cow’s ruminant system to continue breaking down the excreted organic matter for a period of several days. 2.3 Biogas usage Digesters operating in the mesophilic range require 2.3.1. Heat Production constant heating in order to maintain a temperature of Mediumcalorific heating value biogas can be used in a 100°F. number of ways. Typically after condensate and The thermophilic range is between 110°F and 160°F. The particulate removal, the biogas is compressed, cooled, elevated temperature allows for the highest rate of biogas dehydrated and then be transported by pipeline to a production and the lowest hydraulic retention time nearby location for use as fuel for boiler or burners. (HRT). The HRT is the amount of time material must Minor modifications are required to naturalgas fired remain in the digester before it is sufficiently processed. burners when biogas is used because of its lower calorific Digesters that operate in the