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3.4 FACTORS AFFECTING MICROBIAL ACTIVITIES IN DIGESTER 3.4.1 Slurry For proper solubilization of organic materials, the ratio between solid and water should be 1:1 when the domestic wastes are used (see Chapter II). 3.4.2 Seeding or Bacterial Population Acetogenic (acid forming bacteria) and methanogenic are naturally present in cow dung. However, their number is quite small. Acid forming bacteria proliferate fast and increase their number, while methanogenic bactera develop very slowly. Therefore, for die initial reaction, small amount of sludge of another digester is generally used as seeding or inoculum. This sludge contains high concentration of acetogenic and methanogenic bacteria, which could enhance the process of anaerobic digestion of organic materials. Some study has shown that the seeding materials can be mixed with the input slurry up to the ratio of 30 to 50 percent. If inoculum is increased further, less volume of gas is obtained due to reduced inputs fed to the digester. 3.4.3 Stabilization of pH Value Methane producing bacteria are very sensitive to pH level. For high amount of methane, optimum pH of digester should be maintained between 6 and 8. The acidic condition lowers down methane formation (see Chapter I). 3.4.4 Temperature Temperature factor is critical value in the beginning of methane formation. Once metabolism occurs exothermic reaction is helpful for the methane production. In case of mesophilic digestion, temperature range should be maintained between 30 to 40°C. In case of thermophilic digestion, it should be between 45 to 60 °C. In cold climate, the temperature of digester area should be raised upto 35 °C (see Chapter I). 3.4.5 Nitrogen Concentration Methane production is the activity of Carbon metabolism, thus excess amount of nitrogen inhibits the bacterial metabolism and lower down the methane production. 3.4.6 Carbon-Nitrogen (C:N) Ratio C:N ratio is one of the important factors in digester for methane production. High metabolism occurs when C:N ratio is 30:1. The ratio is only maintained when other substrates are used ratlier man the cow dung or other animal dung (see Chapter I). 3.4.7 Maintain of Anaerobiosis Methanogenic bacteria are anaerobic organisms. In aerobic condition, most of these bacteria are inactive in metabolism, thus digesters should be totally airtight to maintain strictly anaerobic condition. In many places, digesters are buried in the Earth to maintain anaerobiosis condition. 3.4.8 Addition of Succulent Plant or Algae For the effective and high production of biogas from cow dung and animal dung many succulent plants or algae are added. Green algae, water hyacinth and lemon grass are added in the digester. The amount of biogas produced from the algae was twice (344 ml/g dry algae) of that obtained from cow dung (179/g dry cow dung) alone. Also, the duration of gas evolution increased with increasing the proportion of slurry. The calorific value of the gas was 4800 K cal/m 3 and the percentage of methane was 55.4 percent. 25
REFERENCES [1] Alexander, M. (1961) Introduction to Soil Microbiology. John Wiley & Sons, Inc. [2] CMS (1996) Biogas Technology: A Training Manual for Extension. Food and Agriculture Organization of the United Nations. Support for Development of National Biogas Programme (FAO/TCP/Nep/4451-T). [3] Karki, A. B. and K. Dixit (1984) Biogas Fietdbook, Sahayogi Press, Kathmandu, Nepal. [4] Lagrange, B. (1979) Biomethane 2. Principes-techniques Utilisations, EDISUD. La Calade, 13100 Aix-en-Provence. [5] Sathianathan, M.A (1975) Biogas Achievements and Challenges, Association of Voluntary Agencies of Rural Development, New Delhi, India. 26
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 40 and 41: substances are solubilized into sim
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
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CHAPTER X IMPLICATIONS OF BIOGAS ON
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10.43 Substitution of Agricultural
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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
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CHAPTER XXI CONSTRAINTS AND PROBLEM
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21.6.4 Mosquito Breeding after Biog
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(FAOm:P/Nep/4451-T). [33] CMS (1996
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