first step in biogas production is carried out with the help of obligation aerobes decomposers methangones detrivores

The correct option is 2.
Biogas is practically produced as landfill gas (LFG) or digested gas. A biogas plant is the name often given to an anaerobic digester that treats farm wastes or energy crops. It can be produced using anaerobic digesters. These plants can be fed with energy crops such as maize silage or biodegradable wastes including sewage sludge and food waste. During the process, an air-tight tank transforms biomass waste into methane, producing renewable energy that can be used for heating, electricity, and many other operations that use an internal combustion engine, such as GE Jenbacher or Caterpillar gas engines.