Biodigesters Reduce the Emission of Greenhouse Gases

“Another form of GHG sequestration by biodigesters is through the use of liquid effluent as biofertilizer”

Luciano dos Santos Rodrigues is an agricultural engineer, professor at the Federal University of Minas Gerais, with a postdoctoral degree in sanitation from the same institution. Rodrigues also holds a postdoctoral degree in sanitary engineering at the State University of São Paulo.

Luciano Rodrigues, professor at UFMG

At the current rates of greenhouse gas (GHG) emissions, world temperatures could rise by 2°C, that the United Nations Intergovernmental Panel on Climate Change says is the threshold for avoiding “dangerous” levels by 2050. Emissions caused by human activities come from the burning of fossil fuels, mainly coal, oil and natural gas.

Biodigesters are treatment systems via anaerobic digestion, in which organic waste, such as animal waste, food waste, sewage, and crop residues are degraded, resulting in the generation of biogas, basically composed of methane gas (CH4) and carbon dioxide (CO2), responsible for the greenhouse effect and climate change.

Every anaerobic storage and treatment system generates these gases. Since most of the time the gases are not captured, they are emitted into the atmosphere and contribute to global warming.

One of the characteristics of biodigesters is that they capture biogas by means of metallic hoods, and more currently through their own geomembranes, so that the gas can be burned or used.

In burning, only methane is removed and transformed into CO2. As methane is 23 times more capable of polluting than CO2, we can consider that this process “sequesters” carbon.

What is interesting in the case of biodigesters is the use of biogas in the form of heating, electricity production (power generation), or the conversion of biogas into biomethane, that can be used as vehicle fuel.

The contribution of biodigesters to the capture and reduction of GHG emissions occurs directly and indirectly. Directly, it happens when biogas is used in space heating directly or through burning in boilers, or when converted into electricity in biogas generators. In this way, all methane is sequestered, but CO2 is still emitted.

Biomethane production has grown. This production is based on the purification of biogas with the removal of hydrogen sulfide and carbon dioxide, with the gas having values greater than 97% methane, used as fuel in cars, buses, and trucks, either directly or injected into the natural gas, to be used at gas stations.

Another form of GHG sequestration by biodigesters is through the use of liquid effluents as biofertilizers, replacing mineral fertilizers. Because it is a treated effluent, there is a reduction in GHG emissions by more than 50%, compared to organic effluent in natura.

Indirectly, biodigesters, through the use of biogas, will reduce or replace various non-renewable fossil fuels that generate GHGs, such as firewood, coal and diesel oil in burning and/or heating environments, the use of power plants thermal energy, etc. As energy will be produced, there is a decrease in the demand for electricity from hydroelectric plants and there is no need to activate thermal plants.

The use of biomethane replaces the use of fossil fuels, such as gasoline and diesel, and the injection of biomethane into the natural gas network reduces the use of this fossil fuel, that also generates GHG.


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