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Introduction
The challenge of sanitation in Indian cities is acute. With very poor sewerage networks, a large number of the urban poor still depend on public toilets. Many public toilets have no water supply while the outlets of many others with water supply are not connected to the city’s sewerage system. The sanitation landscape in India is still littered with 13 million unsanitary bucket latrines, which require scavengers to conduct house-to-house excreta collection.
Septic tanks are one of the common forms of urban sanitation facilities in India. Other commonly used on-site sanitation systems in India include pit or vault or tank latrines. The prevalence of onsite sanitation varies dramatically from state to state, with as many as 80 percent of toilets connected to septic tanks in the states of Orissa and Rajasthan. Major part of urban India has not been connected to municipal sewer system, which makes people dependent on the conventional individual septic tanks.
Fecal Sludge
Sludge of variable consistency collected from on-site sanitation systems, such as latrines, non-sewered public toilets, septic tanks and aqua privies is denoted as fecal sludge. Fecal sludge from septic tanks is specifically termed as septage. The fecal sludge comprises varying concentrations of settleable or settled solids as well as of other, non-fecal matter.
Although there are some differences, sewage sludge is, to some extent comparable with fecal sludge and night soil. This means that the technologies that are in use for treatment, resource recovery and reuse of e.g. sewage sludge may be appropriate for fecal sludge treatment as well.
Fecal Sludge Generation and Management in India
As it can be seen fecal sludge/septage is generated either from open defecation or on-site sanitation systems. According to EAI estimates, about 0.12 million tons of fecal sludge is generated in India per day.
In most of the cities, only crude and unhygienic septage handling practices exist and there is no proper municipality infrastructure that performs the task of septage management. In contrast with the large proportion of on-site installations, limited attention has been accorded to proper construction, maintenance management and safe disposal of septage from septic tanks and pit latrines.
According to a WHO-UNICEF report, around 638 million people do not have access to toilets in India, which accounts for about 58% of open defecation. Indians leave about 100,000 tons of fecal matter in the open every day, in the fields, on the river banks and in the middle of the biggest cities.
Open defecation typically happens in one of the three locations:
- Open fields in villages, usually near farms
- Next to water bodies
- Open land areas near residences
The fecal sludge in open fields and in proximity to water bodies usually is not collected and they get naturally assimilated in the surrounding environment. Where the fecal sludge is on open lands near residences and roads, it is sometimes collected as part of the MSW collection and handling program.
Septage management basically consists of collection, treatment and proper disposal of septage. Proper septage management entails regular and safe disposal of liquid overflows and safe removal of septage (semi-solid wastes) from septic tanks and pits.
The basic stages of the septage management are represented in the following figure:
Septage Management Value Chain
Potential of Energy Recovery from Fecal Sludge Generated in India
Fecal sludge (FS) is a potent medium for energy derivation and overall proves to be a versatile, bulk waste commodity for substantial energy production in a renewable way. Its high calorific value is primarily attributed to peptides, fatty acids and sugar fragments, completely undigested cellulosic matters, dead cells, pigments, residual vitamins, mineral salts, miscellaneous secondary organic matter derivatives and defense substances etc. All these constituents determine the energy potential of FS.
There is no authentic source or data for the generation of fecal sludge in India and its potential for power generation. EAI estimates that the total power potential has thus been estimated to be about 3600 MW from the 0.12 million tons of fecal sludge generated in India. While fecal sludge has a higher theoretical potential, its accessible potential could be considerably less than this.
Technological Routes of Energy Recovery from Fecal Sludge
To know about the Processes of energy generation from fecal sludge, Click Here