With reference to bio-toilets used by the Indian Railways, consider the following statements: 1) The decomposition of human waste in the bio-toilets is initiated by a fungal inoculum. 2) Ammonia and water vapour are the only end products in this decomposition which are released into the atmosphere. Which of the statements given above is/are correct?

Our answer is D, neither statement is correct. Indian Railways bio-toilets, developed with DRDO's help, work on anaerobic digestion. A bacterial consortium inside the bio-digester tank breaks down the human waste in the absence of oxygen.

• Statement 1 is wrong. The inoculum is bacterial, not fungal. The bacteria are what drive the decomposition, and the tank is designed around that bacterial action.
• Statement 2 is wrong. The process does not yield only ammonia and water vapour. Anaerobic breakdown releases gases such as methane and carbon dioxide along with water vapour. The disinfected liquid effluent is what is discharged, so the design is not a simple gas-only release.

The core concept is the difference between aerobic and anaerobic decomposition and what each produces. This ties into Mains GS-II and GS-III on sanitation, the Swachh Bharat Mission, and the problem of human waste discharged on tracks. Railways have since been moving towards vacuum and discharge-free toilet systems, so the bio-toilet is no longer the only design in use.

Trap: Aspirants often assume that 'bio' means fungi, or that a gas-release statement sounds plausible because ammonia has a strong smell. Check the microbe type and the full list of end products rather than going by intuition.