There are many technical approaches and levels of complexity for turning leftover food and manure till biogas. Understanding the underlying science and concepts in a simple way can help to gradually construct and develop own solutions to achieve affordable, efficient and friendly fuctional facilities.
You have input material, i.e. initial reactants that are processed under reduced “anaerobic” conditions, i.e. air free from oxygen through using sealed containers, at a suitable temperature, and more or less neutral conditions. The temperature range can vary around 40 degrees celsius, and to be controlled using heat from the sun along with suitable insolation if necessary, i.e. depending on region and season. The initial reactants have to be crushed to facilitate the bacterial reaction where we have two types of bacteria, e.g. those creating acidity and those producing methane. There are high-energy organic matter, i.e. those with high sugar and high carbohydrate content, and low-energy organic matter such as grass and manure (more or less consumed organic matter). High-energy food promote production of acidity, i.e. “acid” type of bacteria while the other methane-producing bacteria are much more accessible in animal manure. The liquid leftover “effluent” from the whole process may be used fertilizer, however it can be beneficial to do some analysis to see the quality in relation to the composition of the reactants. In this context, adjustment of the control parameters, i.e. temperature, duration and acidity as well as the composition of reactants can be part of development and optimization of the production facilities.