Biogas: what it is and how it is transformed into energy

Biogas is seen as an alternative for generating electricity to replace natural gas

Biogas

Jan Nijman image by Pixabay

Biogas is the gas produced from the decomposition of organic matter (organic waste) by bacteria. In the generation of energy from biogas, the chemical energy of the gas is converted into mechanical energy through a controlled combustion process. This mechanical energy activates a generator that produces electrical energy. Biogas can also be used in boilers through its direct burning for energy cogeneration.

There are three routes to using biomass as an energy source. The first is through direct combustion, the second is gasification and the third concerns the reproduction of the natural process in which the action of microorganisms in an anaerobic environment produces the decomposition of organic matter and, consequently, emits biogas. Discovered in the 17th century, biogas came to be considered an energy source after a presentation made by Louis Pasteur, in the 19th century, in which biogas generation was demonstrated through a mixture of manure and water.

At the end of the 19th century, biogas started to be collected in effluent treatment plants in England and, in the 1940s, it began to be used from animal manure in power generation plants in India. Since then, the anaerobic process has evolved and expanded to the treatment of agricultural and industrial waste.

Gasification consists of thermochemical reactions that involve a solid fuel in the presence of air or oxygen (in a minimal amount for combustion) and water vapor (which form gases) to be used as thermal or electrical energy, for the synthesis of chemical products and for the production of liquid fuels. Anaerobic digestion occurs naturally in many ecosystems, such as the aquatic sediments of freshwater and saltwater lakes.

Anaerobic reactors, which are like a biogas plant, seek to reproduce natural conditions by creating artificial ecosystems through anaerobic reactor ponds, and their initial use is the treatment of semi-solid waste, such as animal manure, domestic waste and sludge from effluent treatment. Biogas is typically 60% methane, 35% carbon dioxide and 5% a mixture of hydrogen, nitrogen, ammonia, hydrogen sulfide, carbon monoxide, amines and oxygen.

Use of biogas from landfills

The final disposal of solid waste is one of the main environmental problems in urban centers, whose administrations end up resorting to sanitary landfills. Landfilling waste leads to the production of biogas. The distribution of the concentration of these gases varies according to the landfill and according to the composition, age and moisture of the waste.

Landfill LFG generation typically begins within the first three months following disposal and may continue for a period of 30 years or more. Because it contains a high concentration of methane, biogas must be considered in the calculation of greenhouse gases. According to the report of the Intergovernmental Panel on Climate Change (IPCC), methane emissions from landfills vary between 20 teragrams per year (Tg/year) and 70 Tg/year, which indicates that the landfills are responsible for the production of 6 % to 20% of total methane emissions per year worldwide.

The use of biogas can be done by installing drains that reach all layers of waste. The waterproofing of the base and roof of the landfill is a measure that contributes both to collaborate with the process of degradation of organic matter, increasing the production of biogas, and to prevent contamination of the soil and groundwater at the site.

The extraction system directs the gases from the landfill (biogas) to a collection system, taking it to the treatment system, which is composed of a set of blowers and filters so that the condensate droplets and particulate matter are removed. Then, the gas is sent to the flare that takes place in the flares.

Use of biogas from sewage treatment

The sewage that comes from the collection network is transported to the pumping station, where the larger particles are retained, and then it is sent to a Sewage Treatment Station (ETE). Solid waste is sent to a sanitary landfill, while the liquid is sent to a reactor where there is a process of digestion of organic matter by the bacteria present there and from there it goes on to a post-treatment step. The gas produced by bacterial activity can be burned and transformed into carbon dioxide or can be reused in the form of biogas.

Domestic Biodigesters

Conventional biodigesters are subdivided into batch and continuous. The batches, also known as batches, are filled only once, and kept closed for a period of time during which the organic matter will undergo fermentation. On the other hand, continuous biodigesters are those that require periodic supply of organic matter (usually daily). Both models allow the generation of energy through biogas.

indian model

It consists of a mobile dome made of iron or fiberglass, in which the gas is stored as the organic matter undergoes fermentation. This storage and the incessant production of biogas allow for uninterrupted use. The existence of a central wall, which divides the fermentation tank into two chambers, helps to separate the already fermented biomass for future disposal.

Chinese model

It consists of a cylindrical masonry chamber with a vaulted and waterproof roof, intended for the storage of biogas. This reactor works on the basis of pressure differences inside. Thus, when there is an increase in pressure, the biomass is moved from the fermentation chamber to the exit box - and when there is decompression, the inverse movement occurs.

Recolast Residential Biodigester

It can be used both in rural properties and in urban residences. It is compact, efficient and cost effective. The residential biodigester can be supplied with food waste, grass, faeces from domestic animals, chicken, pigs and biomass in general. It has the capacity to produce the equivalent of a canister of cooking gas and 20 liters of biofertilizer for fertilizing vegetable gardens, in addition to having an insecticidal effect. See more equipment details and see prices at eCycle store.

HomeBiogas Residential Biodigester

HomeBiogas is a residential biodigester that promotes the use of resources. This type of product promotes the transformation of organic waste into cooking gas and natural organic biofertilizer, through an anaerobic biodigestion process. Inside the system, it is possible to place bark, bones, food waste, animal manure and also pet feces. All these materials serve as raw material for the generation of biogas. See more equipment details and see prices at eCycle store.

Advantages of Power Generation

Biogas represents an energy generation alternative to supply isolated communities, which can use the waste generated in agriculture and livestock to meet their energy demands. In addition, the use of biogas energy from landfills and sewage treatment represents a more sustainable and intelligent destination for waste. Using biogas to generate energy also prevents the methane from the decomposition of organic matter from being released into the atmosphere by turning into water and carbon dioxide by the burning process. Thus, biogas energy is presented as an alternative that does not generate as many social and environmental impacts as natural gas.



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