Bio-digester is a vessel or tank which is used for bio-degradation of human faecal matter using Anaerobic Microbial Inoculum (AMI). In essence Bio-digester provides environment for AMI to work on faecal matter in an anaerobic environment. During the Bio-degradation of the faecal matter, CO2, Methane and water are generated along with very little sludge. These digesters come in different sizes and types depending on the environment of installation. Dfferent kinds of bio-digesters are being used in trains, extreme cold climate like Laddakh and Siachen and in high water table areas. Depending on the number of users, the capacity of the bio-digester ranges from 500 ltr to 20,000 ltrs or higher.

Types of Digesters

Plains and dry regions

Digesters for Plains and dry regions:
This is one of the most common type of digesters. They can be made from metals, RCC or FRP. They could be rectangular or cylindercial shapes, depending on the numbers of users, budget availability, site constraints etc. They are suitable for use in plain areas and comes in various sizes starting from 500 liters (for 5 people) to any size depending on number of users. Some of the examples of such bio-digester are shown in picture.

Insulated floating Bio-Digesters

Insulated floating Bio-Digesters
Elefo Biotech has built Insulated floating Bio-Digesters for Dal lake in collaboration with DRDO. It is successfully running for the last several months. This Bio-Digester has capacity to achieve effluent quality standards which is potentially acceptable by Central Pollution Control Board.

High Water Table

Digesters in high water table areas (ex: Island)
Water table in an island is typically very high and chances of contamination of this precious water resource from human waste is highly probable. To eleminate the chances of water contaimination, bio-digester is used. These bio-digesters can be of rectangular shape, made of FRP and have four compartments for providing longer treatment path to the waste.

Indian Railways

Digesters for Indian Railways
Indian Railways is facing the problem of direct discharge of human waste on the tracks, which is not only the public health hazard but also corrodes the precious railway lines. Besides, the workers who are involved with maintenance of tracks and trains are exposed to untreated human excreta. Another challenge has been the limited space available beneath the coaches for housing the bio-digester for on-board treatment of human waste. For this purpose customised bio-digesters are made of mild steel have been designed and are being installed in coaches Indian railways.

High Altitude Regions

Bio-Digesters for soil bound high altitude regions
High altitude regions have their own challenges. Areas like Leh, Kargil and Drass and other Himalayan regions bear the temperature in the range of 0 to -50C and biological decomposition of human waste in these areas has always been a challenge. However a bio-digester is condusive for such extreme conditions. These bio-digesters are of cylindrical shape, incorporate immobilization matrix. The bio-digesters are installed underground and anaerobic microbial inoculum usually needs to be charged only once during commissioning. A large number of bio-digesters have been installed in Jammu & Kashmir, Ladhak, Himachal Pradesh, Sikkim, Arunachal Pradesh, Uttarakhand, etc.


BIO-TANK with a natural reed bed system can be constructed for secondary treatment of the wastewater that is released from the bio-tank. The reed bed system comprises a bed of sand and pebbles, along with reed plants grown in the bed that are capable of natural amelioration of the wastewater. In doing so the system totally reduces foul smell, suspended particulates, pathogenic micro-organisms (more than 99% of pathogens (disease causing bacteria)) and agents causing sudden nutrient enrichment &/or pollution to the water bodies (eutrophication). Bio-tank cum reed bed system is also used to treat the wastewater of kitchen and bathroom.