The Swachh Rail-Swachh Bharat programme of the Indian Railways, under which ‘greening’ of the railway tracks is underway, is fast picking up steam. By 2019, two years ahead of the schedule, the Indian Railways is expected to finish fixing 1,40,000 green toilets, technically known as bio-toilets, in all its 55,000 coaches. This should put an end to the harmful practice of disposal of faecal waste on the railway track and convert the rail network across India into a zero- discharge zone. Bio-toilets are eco-friendly toilets that use a bacterial inoculum to convert human waste into biogas (methane) and odourless liquid (water). The gas is released into the environment, whereas the liquid is discharged after chlorination. While the former can also be used as a source of energy, the latter (treated water effluent) can be used for irrigation purposes.
The Indian Railways has the third largest rail network in the world transporting more than eight billion passengers in a year. Spread over a 66,000-km route, it runs over 21,000 passenger and freight trains every day. The toilets in the passenger trains generate about 4,000 tonnes of faecal waste per day, which is directly dumped on to the railway tracks through the traditional ‘open discharge’ toilets in the trains.
Open disposal of human waste from the train toilets is both a health hazard and an environment concern. If not disposed of properly, human waste can cause diseases such as cholera, diarrhoea, typhoid, hepatitis, polio and other water-borne ailments.
When disposed on the railway tracks, the human waste gets mixed with other kinds of waste disposed in and around the railway tracks such as plastic and food waste among others, which not only pollute land, but also contaminate groundwater. Groundwater is a source of not only irrigation but also drinking purposes. During the rains, human waste gets washed away as run-off and ends up polluting local water bodies and streams.
Waste from the open discharge toilets of the train coaches also gets into the rivers when the trains pass over various bridges. Excreta disposed on tracks at railway
stations create unhygienic conditions and leads to spreading of various diseases. Apart from these hazardous impacts, it is also the primary cause of corrosion of the railway tracks.
To address these problems, the Railways is working towards phasing out of ‘open discharge’ toilets by fixing bio-toilets in all its coaches. This is being done with the help of Defence Research and Development Organisation (DRDO). While the prime goal of DRDO is to develop technologies to meet the requirements of armed forces, it also transfers spin-off benefits to the civil sector. And the biodigester technology of bio-toilets is one such spin-off benefit.
The Indian Army maintains the world’s highest battlefield, Siachen in Jammu and Kashmir at an altitude of 20,000 feet where the winter temperature dips to -50° Celsius. Disposal of human waste becomes a big problem as faecal matter does not decompose and gets buried under snow, which is a source of drinking water. This led researchers to find out how this can be avoided.
The work on bio-toilets started way back in the 1980s when the task of finding a suitable biodegradation technology was given to the Defence Research & Development Establishment (DRDE) Gwalior. As a part of this task, research scientists of the Defence Ministry went to Antarctica to study bacteria capability of degrading excreta and found that psychrotrophic bacteria like Clostridium and Methanosarcina had the natural capability to survive on waste. These organisms breakdown excreta to produce re-usable water and gas through anaerobic (in absence of oxygen) process.
To test the capability of these organisms at -50° Celsius and at +50° Celsius at different altitudes, a toilet was made with a tank fitted below the commode where faeces were deposited. It was found that when human waste comes in contact with the bacteria, it gets converted into methane gas and water through the process of anaerobic digestion.
The DRDE, thus, developed a unique technology called the biodigester for application in low temperature high altitude areas. This biodigester technology was subsequently modified and adopted by the Indian Railways.
The biodigester is a readymade device (fermenter) made of stainless steel, fibre reinforced plastic (FRP) and low-density polyethylene (LDPE). It is a closed container (rectangular or circular) in which fermentation of the human waste is
carried out under anaerobic conditions using the anaerobic microbial consortium (inoculum). The inoculum is the main ingredient of bio-toilets. It is a mixture of different types of bacteria (hydrolytic, acidogenic, acetogenic and methanogenic groups) that is responsible for the breakdown of complex polymers into simple sugars, which are further broken down into low chain fatty acids and finally into biogas.
The inoculum for bio-toilets of the Indian Railways has been developed by acclimatising the slurry of biogas plants to operate at low temperature areas and is further modified by incorporating the bacteria isolated from Antarctica, Siachen and other remote high altitude locations. The inoculum works in a wide temperature range, resists temperature fluctuations, freezing-thawing and also tolerates limited quantity of antiseptics.
The mother culture is maintained at DRDE Gwalior by operating two reactors, one of size 14 cubic metre and another of 75 cubic metre. The biodigester is connected to existing toilets in train coaches, or can be housed below the toilet pan to save space. The design depends on various factors and applications such as insulated or non-insulated, single user or multiple users and quantity of water used among others, and has been modified to cope up with limited space available beneath the coaches.
Initially the biodigester is charged with the seeding material, which then continues to multiply with the usage of toilet. A temperature of five to 30° Celsius is maintained. Night soil degradation occurs through microbial reaction, which converts it into biogas. On the basis of dry waste weight, 90% of the solid waste is reduced. The cost of a single module of bio-toilet is between Rs 75,000 and Rs 80,000. Biodigesters have been tested in various railway coaches across the country with good results. The first prototype rake with bio-digester toilets is running successfully in Gwalior-Varanasi Bundelkhand Express since January 18, 2011. Till March 31 this year, over 35,000 bio-toilets have been installed in 10,000 railway coaches.
The Indian Railways is also adopting bio-tanks (tank made of masonry/concrete as against stainless steel or FRP) at railways stations to replace the conventional septic tanks. Because of the weight of bio-tanks, these are recommended by railways as stationary tanks. Apart from the Indian Railways, bio-tanks are also being promoted in the rural parts of the country. The DRDO has already transferred the biodigester technology to a number of industries in India, which are now setting up biodigester-based toilets on commercial basis.
With these changes underway, a path towards a greener future doesn’t seem to be too hard at all.