Skip links

Comparison with Conventional Twin Pit and Septic Tank

Bio-Digester Technology Comparison

Technical Features:

The biodigester is a readymade device (fermenter) made of mild steel / FRP whereas biotank is made at the site either of RCC or brick & cement. These are closed containers and only treat effluent coming out of the outlet. The conventional twin pit is open system and not meant for fermentation of the human waste (although partial decomposition takes place and untreated waste get absorbed into surrounding soil). The septic tank is also a closed container of cement & brick and constructed on the site.

  • The biodigester / biotank almost does complete bio degradation of the human waste, which is not possible at all in twin pit and only partially possible in septic tank.
  • Biodigester / biotank inactivates the pathogens during fermentation and effluent is almost free of them. Twin pit allows all pathogens to absorb into the soil and finally into underground water.
  • The organic matter is reduced by more than 90% in the biodigester / biotank whereas in twin pit it is degraded partly and accumulates during the usage and has to be removed physically, which is indirect way of manual scavenging.
  • The biodigester / biotank does not require any cleaning throughout its life whereas conventional system needs frequent cleaning.
  • There is no foul smell in the biodigester / biotank effluent and gas whereas it smells badly in conventional systems.
  • Biodigester / biotank are maintenance free (use & forget) whereas conventional systems required to be maintained regularly.


  • It is not worth comparing the cost of twin pit with the biodigester / biotank since the earlier system is not for biodegradation of human waste at all rather it is just for accumulating the waste in a pit and contaminating the soil, water and environment. Septic tank although is much better device than the twin pit but has many drawbacks.
  • The biotank cost can be calculated in much authentic way by civil engineers working in this area on the simple concept that cement & brick structure has the volume of approximately 1/3rd to 1/4th than the septic tank. In general, it is expected to cost less than half of septic tank for the single family and 1/5th to 1/10th if used for apartments / colony.
  • Further, biodigester / biotank need less space and there is no maintenance cost whereas the conventional systems require repeated cleaning which results in recurring cost.


  • The treatment system works in all temperature ranges and geographical conditions of the country like high altitude areas, glaciers, desert, plains and islands.
  • Technology also works in mobile systems like Indian Railways.
  • Bacteria addition is required only once in the life time.
  • The organic matter (human waste) is reduced (converted to gas to the extent of 99%).
  • Effluent & gas is free from any odour
  • System does not require any cleaning throughout the life and no other maintenance.
  • No need of power / electricity.
  • Pathogens are inactivated (more than 90%).
  • Cost effective and space saving as the volume of fermenter is very low.
  • Use of toilet cleaning agents permitted.
  • Effluent is environment friendly.
  • Requirement of water for cleaning the toilet is minimal as P-trap can be avoided. Since water seal has been provided in the bio-digester itself.
  • Effluent can be used for cleaning the toilet pan or irrigation or may be discharged openly.
Return to top of page