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substances are solubilized into simpler ones (especially volatile acids, which are low molecular weight organic acids) with the help of extracellular enzyme excreted by the acid forming bacteria. The phase is also known as polymer breakdown stage. For example, the cellulose consisting of polymerised glucose units are first broken down to dimers (disaccharides), and then to monomers (monosaccharides) such as glucose by cellulolytic bacteria, which excrete enzyme called cellulose. The most common anaerobic cellulose fermenters in nature appear to be members of the genus Clostridium. These bacteria are found in soil, compost, manure, river mud, sewage, etc. 3.3.2 Acidogenesis During acidogenesis (conversion of high volatile acid to acetic acid and CO;), the second group of 3 bacteria i.e. facultative anaerobic and hydrogen producing acidogenic bacteria convert the simple organic materials via oxidation-reduction reactions into acetate, hydrogen and carbon dioxide. These substances serve as food for the final stage. Fatty acid is converted into acetate. H2 and CO;, via acetogenic dehydrogenation by obligate H 2 producing acetogenic bacteria. There is other group of acetogenic bacteria, which produce acetate and other acids from H 3 and via acetogenic hydrogenation. The monomer such as glucose, which is produced in stage 1, is fermented under anaerobic condition into various organic acids with the help of enzymes produced by the acid forming bacteria. At this stage, the acid forming bacteria break down molecules of six atoms of carbon (glucose) into molecules of less atoms (acids) which are more reduced state than glucose. The principal acids produced in this process are acetic acid, propionic acid, butyric acid and ethanol. The bacteria involved in acidification are Bacillus cereus, Bacillus megathorium, Closdtridium carnofeetidium, Psedomonas formacans etc. 3.3.3 Methanogenesis or Methanisation This is the final stage of anaerobic digestion where acetate and H 3 plus CO 2 are converted by methane producing bacteria (methanogens) into methane, carbon dioxide, water and other products. The principal acids produced by acid forming bacteria in stage 2 are processed by methane producing bacteria to produce methane. The reaction that takes place in this process of methane production is called methanisation and expressed by the following equation: CH 3 COOH → Acetic acid 2CH 3 CH a OH + Ethanol CH 4 Methane CO 2 Carbon dioxide + CO 2 Carbon dioxide → CH 4 + Methane 2CH 3 COOH Acetic acid 3 CO 2 + Carbon dioxide 4H 2 Hydrogen → CH 4 + Methane 2H 2 O Water The above equation shows that many products, by products and intermediates are produced in the process of digestion of inputs in an anaerobic before the final product (methane) is produced. Different species of methanogens are involved in breakdown of complex organic matter into acetate or other organic acids. Acetate is one of the substrates of methanogenic bacteria. Hydrogen with CO 2 is a general substrate for methanogenesis. Numbers of these bacteria differ with type of substrates. For example counts of 10-10 6 per ml and 10 5 -10 8 per ml of hydrogen utilizing bacteria were determined from the pig waste and sewage sludge digesters respectively. a. Microbial Activities of Metbanogenic Bacteria Methanogens are a unique group of bacteria. They are obligate anaerobes and have slow growth rate. They play a major role in breakdown of substrate into gas form. They are the only organisms that can anaerobically 3 23
catabolize acetate and H 2 to gaseous products in the absence of exogenous electron accepiors other than CO 2 or light energy. In their absence effective degradation would cease because of accumulation of non gaseous reduced fatty acid and alcohol products of the fermentative and other H 2 using bacteria that have almost the same energy content as the original organic matter. In morphology they are of different types of such as cocci, bacilli, spiralli and sarcinea. In 1940, Barker isolated a pure culture of Methanobacterium omehanskii capable of reducing carbon dioxide into methane. In 1956, based upon morphology, Barker classified the methane producing bacteria into the following four groups. Carbon substrates are oxidized by methogenic bacteria to form methane as given in Table 3.1. Table 3.1: Caron Substrates Oxidized by Methanogenic Bacteria S.N. Genus Morphology Substrates Used End Products 1. Methanobacterium Rods (variable) Formate CH 4 + HCO 3 2. Methanobacillus Cocci Formate CH 4 + HCO 3 3. Methanococcus Vibrios Formate CH4+HCO3 4. Methanosarcina Cocci in regular Acetate, Methnol CH 4 + HCO3 Cubical packages Active species of methanogenic bacteria are widely distributed in nature such as water-logged soils, marshes swamps, manure piles, marine and fresh water sediments and intestines of higher animals b. Mechanism of Methane Formation Metabolically the Methanogens arc very peculiar. Carbon dioxide fixations, Calvin cycle, serine or hexulose pathways are absents in them. The mechanism of methane formation is not well understood. Several new coenzymes are involved which are not present in any other group of bacteria. These coenzymes are methylcoenzymes. M hydroxy methyl coenzyme, M coenzyme, F 420 coenzyme, F 430 component, B corrinoids, Methanofuran of carbon dioxide reducing factor, Methanopterin and formaldehyde activating factor. Primary reaction in which carbon monoxide takes part is as below: CO+H 3 O → CO 2 +H 2 The secondary reaction takes lace in the presence of sufficient hydrogen: CO + 4H 2 O → CO 2 +4H 2 Other reactions showing methane formation from various substrates are given below: 4CH 3 + 4OH → 3CH 4 +CO 2 +2H 2 O (Methanol) 4HCOOH → CH 4 +3CO 2 +2H 2 O (Formate) 12CH 3 COOH →12CH 4 +12CO 2 (Acetate) 24
Page 2 and 3: BIOGAS As Renewable Source of Energ
Page 4 and 5: FOREWORD I have the pleasure to go
Page 6 and 7: EDITORS NOTE Since its inception fr
Page 8 and 9: IBS IEIA IOE INGO IQC IRR JBT KfW K
Page 10 and 11: TABLE CONTENTS FOREWORD EDITOR'S NO
Page 12 and 13: 13.5 Long-term Government Policy 11
Page 14 and 15: List of Tables Table 1.1 Table 1.2
Page 16 and 17: Figure 5.6 Figure 5.7 Figure 5.8 Fi
Page 18 and 19: CHAPTER I CHARACTERISTICS OF BIOGAS
Page 20 and 21: Figure 1.1 clearly indicates that t
Page 22 and 23: CHAPTER II DESIGN CONCEPT AND RELAT
Page 24 and 25: Chinese model fixed dome biogas pla
Page 26 and 27: 2.2.4 Other Designs Figure 2.4: Dee
Page 28 and 29: Anaerobic Filter: The anaerobic fil
Page 30 and 31: ■ Suitable foundation condition -
Page 32 and 33: Solution: From Table 2.2: 1 cow yie
Page 34 and 35: 2.6.2 Volume Calculations for Chine
Page 36 and 37: The resultant force is as follows:
Page 38 and 39: CHAPTER III MICROBIAL ACTIVITIES IN
Page 42 and 43: 3.4 FACTORS AFFECTING MICROBIAL ACT
Page 44 and 45: CHAPTER IV VARIOUS USES OF BIOGAS A
Page 46 and 47: Figure 4.5: Sketch of Ujeli Biogas
Page 48 and 49: The volume of water form the 5 HP p
Page 50 and 51: . Availability of Fertilizer Cattle
Page 52 and 53: d. Needs Match Sticks More matchsti
Page 54 and 55: In which Q = rate of heat loss, (en
Page 56 and 57: . Integration of Solar Energy Integ
Page 58 and 59: 5.4.1 Biogas Reactor at Lukla/Mosi
Page 60 and 61: Figure 5.8: The Flat View of the Pi
Page 62 and 63: CHAPTER VI BIOGAS IN RELATION TO OT
Page 64 and 65: Table 6.1: Impact of Biogas on vari
Page 66 and 67: Chinese experience shows that if th
Page 68 and 69: 7.2 NITROGEN CYCLE Bio-slurry is ri
Page 70 and 71: 7.4.2 Nutrient Content of Bio-slurr
Page 72 and 73: To avoid the loss of ammonia (NH 4
Page 74 and 75: Experiment with Bio-slurry on Maize
Page 76 and 77: stated that cucumber yielded double
Page 78 and 79: 7.8.5 Philippines In the Philippine
Page 80 and 81: Cross Section—B-B Figure 7.4: Mod
Page 82 and 83: CHAPTER VIII BIOGAS PRODUCTION FROM
Page 84 and 85: ■ ■ ■ Excreta available /day
Page 86 and 87: It is to be noted that the settling
Page 88 and 89: 8.43 Operation of Biodigester After
Page 90 and 91:
9.1.2 Raw Materials Utilized for Fe
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help design large anaerobic digeste
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Inlet and outlet of the biodigester
Page 96 and 97:
CHAPTER X IMPLICATIONS OF BIOGAS ON
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10.43 Substitution of Agricultural
Page 100 and 101:
10.8 CARBON EMISSION SAVED FROM THE
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industrial, military or other organ
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apidly. The techniques that have fo
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11.2.7 Contingency Approach The ess
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have to deal not only with one leve
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REFERENCES [1] CES/IOE (2001) Role
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. Internal rates of return (IRRS) a
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Other assumptions made while calcul
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Table 12.1: Summary of Financial Ra
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Table 12.4: Summary of Financial Ra
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Table 12.7: Financial Rates of Retu
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IRRs are higher when increased nutr
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CHAPTER XIII BIOGAS POTENTIAL AND F
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would be available since the number
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13.2 FUTURE PERSPECTIVE IN NEPAL 13
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13.3.1 Institutional Strengthening
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■ ■ Reducing dependency on impo
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CHAPTER XIV ROLE OF VARIOUS ACTORS
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■ ■ ■ To construct 13,000 bio
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utilization of bio-slurry as fertil
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and NBPG. Sometimes a company may b
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CHAPTERXVI IMPACT OF BIOGAS ON USER
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of dung, On the other hand, 33 perc
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CHAPTER XVII IMPACT OF BIOGAS ON HE
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Figure 17.1: Perceived Reduction in
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27 percent of households with bioga
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Majority of biogas households (95.5
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Table 18,1: Sampling of Biogas Hous
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as the probable reasons for non-ope
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Table 18.7 shows that majority of t
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variations. Assuming that 1 hour of
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Status Table 18.15: Comparison of t
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contributes to the saving of Rs. 6.
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Table 18.22: Kerosene Replacement a
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The survey results on Carbon emissi
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CHAPTER XIX WORKLOAD OF WOMEN AND G
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Looking into the division of activi
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19.3 STUDIES OF BIOGAS USERS WITH F
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co-operative manner so that the wea
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Biogas user women perceived that bi
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20.1 INTRODUCTION CHAPTER XX FINANC
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portion of the construction cost of
Page 184 and 185:
CHAPTER XXI CONSTRAINTS AND PROBLEM
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21.6.4 Mosquito Breeding after Biog
Page 188 and 189:
(FAOm:P/Nep/4451-T). [33] CMS (1996
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