Biogas is a combination of several gases that are procured through the degradation of various organic matter in the absence of oxygen. Biogas is a form of renewable energy belonging to the class of biofuels. The composition of biogas varies based on the components used in the process of production. The primary components of biogas are methane and carbon dioxide even though it encompasses certain contaminants like Hydrogen Sulfide, siloxanes, and volatile halogenated organics.
Why is it important to remove hydrogen sulfide from biogas?
Bagasse, kitchen, and garden waste are used for producing biogas. These wastes from bagasse, food remains, and garden waste is organic. Therefore, they can be degraded by microorganisms which, in turn, release carbon dioxide, hydrogen sulfide, methane, and ammonia gas into the atmosphere. The suggested industrial exposure limit for hydrogen sulfide is around 8-10 ppm per day. And this makes it imperative to consider various means of hydrogen sulfide removal from biogas.
The easy availability of hydrogen sulfide in the process of ignition causes the formation of this chemical compound. It is extremely harmful to the ecosystem, human beings, and animal health. It might cause nausea, headaches, irritation of the mucous membranes, dizziness, and even sudden death. Thus, it is important to remove hydrogen sulfide and it can be approached through the physical-chemical method and biotechnological method.
What are the methods used for hydrogen sulfide removal from biogas?
The physical-chemical method is the traditional approach and it is most prevalent today. On the other hand, the biotechnological method opted for hydrogen sulfide scavenger chemistry involves biofilters, biotrickling filters, and bioscrubbers. In the method of physical absorption, the hydrogen sulfide gas molecules attract and eventually stick to the absorbent surface through intermolecular forces.
Biological desulphurization
This method involves the use of microorganisms from the family of Thiobacillus. To allow microbiological oxidation of sulfide, it’s critical to add a stoichiometric level of oxygen to the biogas. Based on the level of hydrogen sulfide, it may correspond between 2 and 6 percent air within biogas. The simplest way of desulphurization is adding optimum oxygen into the storage tank or digester simultaneously with the gas holder. Since Thiobacillus is ubiquitous, the process doesn’t require inoculation.
Iron Chloride Dosing
Iron chloride can be placed in the digester directly or in the feed substrate within a pre-storage tank. This compound starts reacting with the hydrogen sulfide present and starts forming particles of iron sulfide salt. This process is considerably effective in lowering the levels of hydrogen sulfide. However, it is not an efficient means of attaining stable and low levels of hydrogen sulfide within the range required for vehicle fuels.
Final words
Hydrogen sulfide is a major contaminant of biogas. As it is corrosive and poisonous, it leads to significant damage to the instruments, equipment, and piping. It’s important to note that the level of different components of biogas impacts the final use. While considering the numerous advantages of biogas, it is important to develop cost-effective means of straining out contaminants like hydrogen sulfide.
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