This presentation discusses biogas production from garbage through anaerobic digestion. It defines biogas as a combustible gas produced through biological breakdown of organic matter without oxygen. The presentation outlines the four stages of anaerobic digestion: hydrolysis, acidogenesis, acetogenesis, and methanogenesis. It also discusses factors that affect biogas production such as temperature, pH, carbon/nitrogen ratio, organic loading rate, and hydraulic retention time. Applications of biogas include electricity generation, transportation fuel, and cooking fuel.

1. A PRESENTATION
ON
BIOGAS PRODUCTION FROM GARBAGE
BY
H NELANI
BS MKHWANAZI
L DUKU
&
T NKOSI
DEPARTMENT OF BIOTECHNOLOGY & FOOD TECHNOLOGY

2. Introduction
 Biogas is a colorless combustible gas produced by the biological breakdown of organic
matter, occurring in absence of oxygen
 The process involves the breakdown of organic matter under anaerobic environment
releasing methane and carbon dioxide gas.
 It has a high methane content making it highly flammable which is beneficial for its usage
as an energy source.
 generated from biodegradable materials such as biomass, cow dung, green waste,
agricultural residue such as cassava, sugar cane and can also be produced from garbage
 It is environmentally friendly since it uses nature's ability to recycle substances into
valuable resource by the conversion of waste into energy

3. Introduction cont.
 The benefits are it reduces pollution, avoids toxic usage of chemicals for sewage
treatment plants, it can save money, energy and material by treating waste-on-site.
 Biogas is made up of mixture of gases such as methane (CH4), carbon dioxide (CO2), 1–
5% other gases, including hydrogen (H2).
 It is produced by bacteria that occur during the biodegradation of organic materials
under anaerobic conditions.
 There are multiple biogas systems and plant designed for the utilization of biogas
efficiently
 Each model is different depending on its input, size, output and type but the process of
conversion of organic matter to waste remains the same.

4. Stages of biogas production using anaerobic digestion
4 steps
 Hydrolysis
 Acidogenesis
 Acetogenesis
 Methanogenesis
Hydrolysis of CO2
 Biomass is made up of large organic polymers
 Complex polymers hydrolysed to monomers
 complex organic molecules → simple sugars, amino acids, and fatty acids. Done by
hydrolytic fermentative bacteria

7. Model of a biogas generator

8. Advantages of Biogas Technology
 Renewable Energy Source
 Contribution to EU Energy and Environmental Targets
 Reduced Greenhouse Gas Emissions and Mitigation of Global Warming
 Waste Reduction
 Flexible and Efficient End Use of Biogas
Disadvantages
 Explosion chances
 High capital cost
 Incorrect handling of liquid sludge cause pollution
 Requires control and maintenance
 Needs proper conditions
 If used as a fuel, it requires removal of CO2 and H2S

9. Main factors affecting biogas production
The biogas is affected by many factors these include:
1.Temperature
 The internal temperature of the digester greatly affects the production of biogas.
 The microorganisms participating in the process of anaerobic digestion are divided into large categories namely
psychrophiles (less than 15⁰C), mesophiles (15⁰C- 45⁰C), thermophiles (45⁰C-65⁰C).
 The anaerobes are most active in mesophilic and thermophilic temperature range and hence commonly used
temperature during AD of organic wastes.
2.pH
 pH is also one of the main operational factors that affect digestion. During AD, there are various microorganisms that
require different optimal pH value.
 This depends on the temperature maintained inside the digester.
3.Carbon/ Nitrogen (C/N) ratio
 C/N ratio is expressed as the relationship between carbon and nitrogen present in organic materials .
 Benefits of nitrogen present in the feedstock are that it is an essential element for synthesis of amino acids and
proteins, It will also be converted to ammonia which helps to maintain favourable pH conditions for microorganism.
 Too much nitrogen will cause toxic effect and too little nitrogen cause nutrient limitation.
 C/N ratio varies depending on the type of substrate, trace elements and biodegradability .

10. 4.Organic loading rate (OLR)
 Biogas production is highly influenced by organic loading rate, it indicates the amount of waste that needs to be fed daily.
 The actual loading rate depends on the types of wastes fed into the digester.
 The under loading and overloading reduce biogas production.
 If OLR is increased, metabolic activity of microorganism will be high and hence improve biogas yield.
5.Volatile Fatty Acids (VFAs)
 During start-up or when there is organic overloading of the digester, high concentrations of VFA are generally observed.
 They are usually associated with toxicity and inhibitory effects.
 Although it is generally understood that VFA inhibition is due to their accumulation and subsequent pH reduction, some
VFA are themselves toxic to anaerobic microbes.
6.Hydraulic retention time (HRT)
 This indicates the time period for which the fermentable material remains inside the digester.
 Longer HRT will require larger digester volume which increases capital cost.
 Short HRT will wash away active bacterial population. Maximum methane production occurs at an optimum value of HRT.
 If retention time is less than optimal value, VFA will accumulate which will cause server fouling and will result in a reduced
biogas production.
 If the retention time period is above optimal value, biogas component will not be utilized effectively and hence biogas
production will be reduced.

11. 7.Stirring
 Agitation or stirring is done to make sure that the contact between substrate and microorganism are intimate and hence
results in enhanced degradation rate substrate .
 If not stirred, the slurry will tend to settle out and form a hard scum on the surface, which will prevent release of biogas.
 Biogas production enhanced by 62% compared to gas production without agitation.
8.Nutrients
 The inadequate availability of nutrient concentration in energy crops have resulted in problems such as low methane yields,
acidification and process instability in crop monodigestion.
 This leading to application of low organic loading rates (OLRs) and long HRTs.
 They influence the performance and stability of the AD process.
9.Free ammonia
 Free ammonia concentrations above 100 mg/l can cause inhibition, although the ionic form, NH+4, will only cause
inhibition at much higher concentrations .

12. Use and applications of biogas
 Electricity generation
 In combined heat and power (CHP) plants
 Waste Management in agriculture
 Cooking fuel as a sustainable energy source
 Injection into a natural gas pipeline
 As a Clean Renewable Fuel for Transport Vehicles
 In Biogas Fuel Cells

13. Biogas around the world
 Family-sized biogas units have major focus and polarity since it helps reduces waste in the household providing
clean renewable energy for the families throughout the world.
 Countries are adopting this biogas system for small-scale and large-scale anaerobic digestion.
 Small-scale system can digest animals waste and food waste that can be used as electricity, gas, transportation
fuel and heat.
 In Swedan, most cars and buses use biogas that is produced from sewage treatment plants and landfill.
 UK uses the anaerobic digestion plant to process diary residue converting them into bio-methane for the gas grid.
 India and China have an abundance of the small-scale biogas digester.
 African countries, the bio-slurry by-product produced by the biogas system has made so much profit for some
biogas owners since they are selling it.

14. Conclusion
 The biogas system and anaerobic digestion are of so much value as means of renewable energy
generation.
 Factors affecting the process like pH, temperature, etc. should be closely monitored.
 There should be an evaluation and optimization of the anaerobic process since it is of high
importance for the optimal biogas production.
 Furthermore, study needs to be conducted on the biogas system to provide more information
to people about it that way their usage of it could increase.

15. References
Arsova, L. (2011), Anaerobic Digestion of Food Waste: Current Status, Problems and an
Alternative Product. MSc Degree, Thesis Columbia University
Bailey, J., Ollis, D. (1986), Applied enzyme catalysis. Biochemical Engineering Fundamentals,
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Chandra, R., Takeuchi, H., Hasegawa, T. (2012), Methane production from lignocellulosic
agricultural crop wastes: Areview in context to second generation of biofuel production.
Renewable and Sustainable Energy Reviews, 16(3), 1462-1476.
Molino, A., Nanna, F., Ding, Y., Bikson, B. & Braccio, G. (2013). Biomethane Production by
Anaerobic Digestion of Organic Waste. Fuel. 103: 1003-1009.
Nges, I.A., Lovisa, B., Hinrich, U. (2012), Anaerobic Digestion of Crop and Waste Biomass:
Impact of Feedstock Characteristics on Process Performance. Denmark: Lund University
Obrecht, M. & Denac, M. (2011). Biogas- A Sustainable Energy Source: New Measures and
Possibilities for Slovenia. Journal of Energy Technology. 5: 11-24