Feed and Reaction:
The SERIGAS process starts from choosing the feed. Feed can be any organic material that is bio degradable as mentioned earlier. There are many steps that happen from feed to fuel. The major steps are as follows :
Feed has to be pre conditioned, where the material is either chopped and dried or is pre-treated with other organic substances and acted upon with Aerobic bacteria to break the cell wall of plant and animal material.
The feed than has to be pre-digested, that is, some of the tough contestants have to be broken down into simpler forms. For example, most plant material contains complex substances like Lignin, Cellulose and Hemi cellulose. These substances cannot be digested easily in a bioreactor, so we need to convert them to carbohydrate using specialised microbes in a specifically designed environment. This process takes anywhere between 48 to 72 hours depending on the type of feed and their cellulolignin characteristics.
The Pre-Digested feed has to be made suitable for the next stage of digestion. This process is called feed enrichment. Here the material is mixed to form the correct consistence, balance the pH and destroy any residual unwanted bacteria that may go to the next stage. This feed that contains high nutritional content is ready for the microbial army in the main digestion stage to produce SERIGAS.
The Digestion Process is a biomimicry of the digestion system of animals. The process is highly controlled and balanced by on board computers. The technology used in the reactors for digestion is called Variable Hydraulic Microbe Incu-bated Auto balanced Anaerobic Bio-Reactor. There are three stages of digestion in the SERI process.
In the first stage, the large organic polymers those are present in the feed that arrives from the previous processes are broken down into their smaller constituent parts to enable the bacteria in the subsequent stages of the reactors to ac-cess the energy potential. These constituent parts or monomers such as sugars are readily available to the large popu-lation of microbes. This process of breaking these long chains structures and dissolving the smaller molecules into solu-tion is also called hydrolysis. Therefore hydrolysis of these high molecular weight polymeric components is the neces-sary first step in the SERIGAS making process. Through this stage, the complex organic molecules are broken down into simple sugars, amino acids, and fatty acids. This stage also produces some quantity of Acetate and hydrogen, which can be directly used in the third stage of the SERI process to form SERIGAS. However there are other molecules such as vola-tile fatty acids that are compounds with chain length greater than acetates that needs to be catabolised into easily con-vertible compounds before it reaches the third stage of the process.
The Second stage in the SERI process, uses a different group of microbes, and starts with further breakdown of the remaining components by fermentative bacteria. Here volatile fatty acids are converted along with ammonia, carbon dioxide and hy-drogen sulfide as well as other by-products. This part of the second stage is similar to the way milk becomes curd. Simultane-ously specific bacterium is made available to handle harmful hydrogen sulfide and convert it into hydrogen and elemental sulphur. Sulphur dissolves in water and hydrogen is used back in the process. A third set of bacterium would use the con-verted fatty acids, ammonia, carbon dioxide and hydrogen to produce largely acetic acid and some more carbon dioxide and hydrogen.
The Third and the terminal stage is where large amount of SERIGAS is produced. Highly specialised microbial population, accurately acclimatised and finely placed utilise all the intermediate compounds from stage one and two and systematically convert them to methane, carbon dioxide and water. It is these compound that make-up the Crude SERIGAS. The remaining, non-digestible material along with the mortal remains of bacterium and used-up water is excreted from the system.
The excreted material from the system is converted into high NPK fertiliser, which are nitrogen fixed and phosphate soluble-ised and an organic high alkaloid pest repellent. The fertiliser from this process is called SERILISER and the pest repellent is called SERIPEST.
There are around 16 different species of microbes in all that perform the above wonderful task of producing SERIGAS. All of these microbes are isolated and purely cultured at the SERI Microbial Biotech Laboratory.