Bio-toilets for Indian Railways

Abstract

Bio-toilets are projected to improve sanitation in the trains to solve the problem of open defecation1,2. Bio-toilets are based on continuous anaerobic microbial digestion of human excreta to biogas. Typical composition of biogas is 55–75% methane and 25–50% carbon dioxide. In these bio-toilets, gases escape into the atmosphere and treated waste water is discharged after chlorination. Bio-toilets welded to passenger coaches have an inlet for human excreta and outlet for biogas. They are an economically viable solution, with one bio-toilet costing Indian rupees 15,000 (US$ 280). There is also a plan of installing these toilets in over 100,000 Gram Panchayats in the next five years. This will help solve the problem of open defecation in rural India. Although this is a good beginning, the concept of bio-toilets in trains will be entirely different from those in Gram Panchayats (houses, schools, institutes, etc.). In the latter case, trapped methane will most probably be used as a cooking gas, whereas in the case of trains it will be released to the atmosphere. The Indian Railways carries 20 million passengers daily and once bio-toilets are equipped in all 53,000 coaches by 2022 as projected, methane emissions will be substantially increased. Methane as a greenhouse gas had a global warming potential of 25 compared to carbon dioxide over a 100-year-period3. The Indian Railways may look for engineering solutions to capture and store methane released from the bio-toilets. Vehicles including trains which are successfully fuelled with compressed and concentrated biogas may be taken for case studies4. Also, railtoilets are generally small and care should be taken to divert methane out, because it is an asphyxiant and may displace oxygen in an enclosed space.