Biogas -A way out for Garbage

Biogas -A way out for Garbage

1. Introduction

Biogas generation is an intriguing method for recovering nutrients and renewable energy from a variety of organic waste sources. The method might be used to make value-added compounds from mixed cultures, and it could also be used in integrated bioenergy production systems.

Methane (50–75%) and carbon dioxide (25–50%) are the most common gases found in biogas, along with tiny amounts of other gases and water vapor. In the anaerobic digestion (AD) process, microbes degrade various organic materials to produce biogas. Carbohydrates, proteins, lipids, cellulose, and hemicelluloses should all be present in the biomass inputs for a successful anaerobic digestion process. The carbohydrate, protein, and fat composition all affect the ultimate gas production. The biogas digestion process may be broken down into four stages. The metabolic transformation is carried out by various groups of microorganisms in each step.

The four phases are:

·      Hydrolysis: complex organic matter, such as proteins, is converted into simple soluble products, such as amino acids. 

·      Hydrolysis: complex organic matter, such as proteins, is converted into simple soluble products, such as amino acids.

·      Acidogenesis: soluble products are converted to volatile fatty acids and CO₂.

·      Acetogenesis: volatile fatty acids are converted to acetate and H₂.

·      Methanogenesis: acetate and CO₂ + H₂ are converted to methane gas.

This ability has been used in man-made systems (bioreactors) to produce energy for centuries. Biogas is a good energy source that produces 5.5–7 kWh/m3, and the total energy is proportional to the amount of methane present.

 2. Working of biogas plant

 2.1. Raw Materials for Biogas

 Organic input materials like food scraps, fats, and sludge can be used as substrates in a biogas plant. Renewable resources like maize, beets, and grass are used to feed both animals like cows and pigs and microorganisms in the biogas plant. The biogas facility also receives manure and feces.

2.2. Process of Biogas formation

The substrate is degraded by the microorganisms in the fermenter, which is heated to around 38-40°C and is light and oxygen-free. Biogas, primarily composed of methane, is the product of this fermentation process. However, biogas also contains strong hydrogen sulfide.

A stainless-steel fermenter has the distinct benefit of withstanding hydrogen sulfide assaults and remaining functional for decades. Furthermore, a stainless-steel fermenter allows the biogas plant to be operated in the thermophile temperature range (up to 56 °C). After fermentation, the substrate is carried to the fermentation leftovers end storage tank, where it may be recovered for future use.

2.3. Handling byproducts

The leftovers can be used to make high-quality fertilizer. The benefit: Biogas manure has a reduced viscosity, which allows it to infiltrate the ground more rapidly. Furthermore, the fermentation byproduct frequently has a greater fertilizer value and is less smell strong.

However, drying it and utilizing it as a dry fertilizer is another alternative. The biogas produced is kept in the tank's roof and then burnt to create electricity and heat in a combined heat and power plant (CHP). Electricity is immediately supplied to the electricity grid. The heat produced can be used to heat a structure, dry wood, or harvest items.

3. The basic factors that affect anaerobic digestion are

 3.1 .Temperature:

In this factor, a distinction is made between 3 different temperature regimes mesophilic (20 – 40 ºC), psychrophilic (10 – 20 ºC), and thermophilic (50 – 60 ºC). The lower the temperature, the slower the bacterial growth and conversion processes. Therefore, a longer retention time is needed.

· In psychrophilic temperatures, the bacteria will be stable, and no additional heat is required but there will be low production of the biogas, the lowest pathogen reduction. The advantage is it is the least costly to construct and easiest to manage

· In the mesophilic temperature range, in this range the bacteria are more stable than the thermophilic bacteria, they have a shorter retention time. There will be moderate management and moderate monitoring required. The drawbacks are that additional heat is required, there will be moderate pathogen reduction, and costly to construct.

· And in the thermophilic temperature range, there is the shortest retention time, highest biogas production, and highest pathogen reduction. The disadvantages of these temperature ranges are, that the bacteria are least stable, additional heat is required for digestion, the monitoring should be intensive, most costly to construct, and hardest to manage.

3. 2. pH:

When compared to other pH range values, it has been experimentally proven that substrates with an optimal range value of pH 7 have a greater biogas generation yield and degradation efficiency. Because microorganism, particularly methanogens, is very sensitive to acidic ambient circumstances, the pH value plays a crucial role. As a result of the acidic environment, they are unable to thrive and produce methane. Increasing the pH value over 7.5 and approaching 8 can, on the other hand, lead to the growth of methanogens, which hinders the acetogenesis process. A particular quantity of buffer solution, such as CaCo3 or lime, is given to the system to keep the pH value in an equilibrium state. Although to produce a better production of biogas, the ideal pH value should be kept between 7.5 and 8.

 3.3. Composition of the food waste

Knowing the composition is necessary for predicting the reaction's course and pace, as well as the amount of biogas produced. The bio-methanization potential or rate of methane generation is determined by four key concentrations: lipids, proteins, carbs, and cellulose. High lipid content AD systems have a high bio-methanization efficiency, but due to their complicated structure, they require a longer retention time. Proteins have the shortest retention time span, followed by carbs and cellulose.

 4. Sources of biogas production

Biogas may be obtained in several different methods:

1.    landfill sites.

2.    wastewater treatment.

3.    co-digestion of manure.

4.    other sources.

5. What will the remaining Digested substrate be used for? 

Anaerobic digestion of organic materials results in the production of digestate in addition to biogas. After digestion, the latter is the substrate that remains. Because of its nitrogen concentration and the fertilizing effects of its flow characteristics, digestate is a desirable fertilizer. Anaerobic digestion can also inactivate weed seeds, germs, viruses, and other potential pathogens, especially when longer retention durations and higher temperature regimes are utilized.

6 . Biogas End Uses

Biogas may be utilized to heat buildings, power boilers, and even power the digester itself with little to no processing on-site. Biogas can be used in CHP systems or simply converted to electricity via a combustion engine, fuel cell, or gas turbine, with the resulting electricity being used on-site or sold to the grid.

Digestate is the nutrient-dense solid or liquid that remains after digestion; it contains all the recycling nutrients included in the original organic material, but in a form that is more readily available to plants and soil builders. The feedstock used in the digester will determine the digestate's composition and nutritional value. Liquid digestate may be sprayed on farms as a fertilizer, reducing the need for synthetic fertilizers. Solid digestate can be used as cow bedding or composted after mild processing. To assure digestate safety and quality control, the biogas industry has lately taken steps to develop a digestate certification framework.

6.1 Renewable Natural Gas

Biomethane, also known as renewable natural gas (RNG), is biogas that has been purified to remove CO2, water vapor, and other trace gases to fulfill natural gas market requirements. Renewable Natural Gas (RNG) may be injected into the existing natural gas system (including pipelines) and utilized in place of conventional natural gas. The remaining natural gas is utilized for commercial and industrial applications (heating and cooking).

6.2 Compressed Natural Gas and Liquefied Natural Gas

Renewable Natural Gas may be converted to compressed natural gas (CNG) or liquefied natural gas (LNG) for use as a motor fuel, much like regular natural gas (LNG). CNG-powered vehicles are equivalent to gasoline-powered vehicles in terms of fuel economy, and they may be used in light- to heavy-duty vehicles. LNG is not as widely used as CNG because it is more expensive to produce and store, even though its higher density makes it better fuel for heavy-duty vehicles driving long distances. CNG and LNG are most suited for fleet vehicles that return to a base for refilling, allowing fueling infrastructure expenditures to be maximized.

7. References

1.      https://www.eesi.org/papers/view/fact-sheet-biogasconverting-waste-to-energy

2.      https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5609262/

3.      https://www.youtube.com/watch?v=3UafRz3QeO84.

4.      https://www.youtube.com/watch?v=MYj13FB_Iac

5.      https://energsustainsoc.biomedcentral.com/articles/10.1186/s13705-017-0122-3

1.      https://www.diva-portal.org › get › FULLTEXT01

7.      https://edepot.wur.nl/199056