Biogas is a gaseous renewable energy source produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste, wastewater, and food waste. Biogas is produced by anaerobic digestion with anaerobic organisms or methanogens inside an anaerobic digester, biodigester or bioreactor. The gas composition is primarily methane (CH4) and carbon dioxide (CO2) and may have small amounts of hydrogen sulfide (H2S), moisture and siloxanes.


Benefits of Biogas

It is a renewable energy resource. Since it is a part of the organic cycle in nature, the gas has been emitted into the atmosphere in its raw and direct form. This biogas (Methane, H2S, CO2) has adverse effects on the environment if found in large concentrations, which is exactly the fact in recent decades due to increased biomass production due to population explosion. It would only be wise to tap the benefits for the betterment of humankind and also avert the damage that would otherwise be costly to repair. It is a win-win situation for humans and also for the environment.



Biogas has been in use for nearly half a decade. However, in its early stage, biogas was only considered for heating & as cooking gas. The recent advancements in this field have made it a great alternative to serving the energy needs. With the recent push for clean & renewable energy for sustainability, it is best that we understand it holistically.


The Biogas plant will produce high-quality organic manure apart from the biogas. Organic manure is a great nourishment to plants & trees.


CH4 is the major fuel source in biogas, along with traces of H2S which is also a combustible gas. H2S is considered dangerous when found in significant amounts in a particular region. Let us also understand its perils if we intend to use biogas as a primary energy source.


Hydrogen Sulphide (H2S)

Hydrogen sulfide is a chemical compound with the formula H2S. It is a colourless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odour of rotten eggs.

Risk / Hazard

Hydrogen sulfide is toxic to humans and most other animals by inhibiting cellular respiration in a manner similar to hydrogen cyanide. When it is inhaled or its salts are ingested in high amounts, damage to organs occurs rapidly with symptoms ranging from breathing difficulties to convulsions and could lead to death.

Occurrence

Volcanoes and some hot springs (as well as cold springs) emit some H2S. 
A portion of global H2S emissions are due to human activity. The largest industrial source of H2S is petroleum refineries: The hydrodesulfurization process liberates sulfur from petroleum by the action of hydrogen. 

Other anthropogenic sources of hydrogen sulfide include coke ovens, paper mills (using the Kraft process), tanneries and sewerage. 

Besides living near gas and oil drilling operations, ordinary citizens can be exposed to hydrogen sulfide while living near wastewater treatment facilities, landfills, mass burial sites and farms with manure storage. Exposure occurs through breathing contaminated air or drinking contaminated water.

Safety

Although very pungent at first (it smells like rotten eggs), it quickly deadens the sense of smell, creating temporary anosmia, so victims may be unaware of its presence until it is too late. Safe handling procedures are provided by its safety data sheet (SDS).


Low-level exposure

Exposure to lower concentrations can result in eye irritation, a sore throat and cough, nausea, shortness of breath, and fluid in the lungs. These effects are believed to be due to hydrogen sulfide combining with alkali present in moist surface tissues to form sodium sulfide, a caustic. These symptoms usually subside in a few weeks.


High-level exposure

Short-term, high-level exposure can induce immediate collapse, with loss of breathing and a high probability of death.


Exposure thresholds

  • 10–20 ppm is the borderline concentration for eye irritation.
  • 50–100 ppm leads to eye damage.
  • 100–150 ppm the olfactory nerve is paralyzed after a few inhalations, and the sense of smell disappears, often together with awareness of danger.
  • 320–530 ppm leads to pulmonary edema with the possibility of death.


Risk Aversion

Production of sulfur

Hydrogen sulfide is mainly consumed as a precursor to elemental sulfur. This conversion, called the Claus process, involves partial oxidation to sulfur dioxide. The latter reacts with hydrogen sulfide to give elemental sulfur. The conversion is catalyzed by alumina.

2H2S + SO2→ 3S + 2H2O


The resultant Sulphur can be utilised for industries that use it as a raw material, and the second component in this process is pure water.