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Home > Business Line > Biogas


Distillery effluent, which is commonly termed, as raw spent wash is one of the most polluting effluent with very high values of BOD, COD, suspended solids & dissolved solids. This dark brown effluent has great potential of biogas generation, which can be used as fuel and burnt directly in boiler or can be used to generate electricity by burning the same in biogas engines. Anaerobic digestion process is used to convert this high strength wastewater into biogas. The Digester based on CSTR process offered by ProEnergy provides higher treatment efficiency and is considered the best available amongst anaerobic processes. The CSTR system gives consistent and higher biogas production. It is not only the most reliable system but extremely easy to operate, as well.


“CSTR” process being offered by ProEnergy is based on the concept of conversion of organic matter into biogas. The process of conversion of organic matter into biogas occurs through a group of bacteria. In ‘‘CSTR’’ process, which is a high rate process, anaerobic digestion takes place in the mesophillic range of temperature, i.e. 36o – 40°C. The pH inside the reactor is usually kept around 7.2 while proper ratio of volatile acid and alkalinity is maintained. In CSTR process the bacteria responsible for digestion process are kept in suspension with the help of Lateral as well as central Agitators.

The following three stages are involved in the process of anaerobic digestion.

  • Hydrolysis:In the process of hydrolysis the complex molecular compounds i.e. polymers are converted into the simple molecular form i.e. monomers.

  • Acidogenesis:The monomers so formed at the end of hydrolysis process are converted into volatile fatty acids. Acetic acid forms the major portion of volatile fatty acids. The process of conversion of monomers into acids is carried out by a group of anaerobic bacteria known acid formers.

  • Methanogenesis:Acids produced at the end of Acidogenesis process are converted into carbon dioxide and methane gases. The process of conversion of acid into gases is carried out by group of anaerobic bacteria known as methane formers.


    The CSTR Reactor is designed on the principle of anaerobic contact process. The raw effluent enters the CSTR at the top in a central shaft. The Recirculated sludge is also mixed with raw effluent in a central shaft. A central agitator is provided at the top to facilitate mixing and downward movement of the mixed effluent. The effluent travels to the bottom of reactor through central shaft. In reactor the effluent comes in the contact with active anaerobic culture maintained in the suspension. In the process the organic matter in the effluent is converted in to biogas and cell mass. The liquid travels upward in the reactor. Lateral agitators are provided for mixing and upward movement of the liquid.

    The effluent is then taken out of the reactor through overflow pipe provided with water seal. The effluent will be received in a lamella clarifier where the active biomass will be separated and part of it is recirculated back to the reactor. Before entering into the lamella clarifier the effluent is passed through degassing tower for removal of dissolved gases to achieve better settling in the lamella clarifier. Lamella clarifier is fabricated with anticorrosive paint and is provided with inclined plates. The clarifier shall also be provided with sludge withdrawal arrangement. Sludge Recirculation pumps is provided to recirculate the sludge back to the CSTR reactor. The post anaerobic effluent is then taken to secondary treatment for further removal of the organics.

    CSTR reactor will be erected and fabricated at site using mild steel plates and structural members. The reactor will be painted from inside with chlorinated rubber paint and synthetic enamel paint from outside.


    Biogas will be collected at the top of the reactor and will be stored in a gasholder separately constructed. Biogas holder is fabricated in MS plated and shall be of floating type. Biogas from biogas holder will be compressed and sent to boiler for burning. Flare stack is provided to flare the excess biogas.