Biogas produced from human excreta is being used for different purposes e.g. cooking, lighting, electricity generation and body warming. Besides, it can be used as fertilizer, as it contains a good percentage of nitrogen, potassium and phosphate. But simultaneously its unpleasant bad colour, odour and presence of pathogens, and high BOD content limit its use for agricultural/horticultural purposes or for direct discharge into a water body.
Since, Sulabh is maintaining over 8000 public toilet complexes spread all over the country, out of which 200 are linked with biogas plants, it was an important task for the organization to make the effluent free from odour, colour and pathogens, to use it safely for agricultural purposes. After a series of experiments, the organization has developed a new and convenient technology by which the effluent of human excreta based biogas plant turns into a colourless, odourless and pathogen-free liquid manure. The technology is based on filtration of effluent through activated charcoal followed by ultraviolet rays. The filtration unit makes it colourless, odourless and free from organic particles and the UV eliminates the bacteria. It reduces BOD and COD of the waste water drastically. Since such wastewater is from human wastes, its BOD (Biochemical Oxygen Demand) which is around 200 mg/l, comes down to <10 mg/l after treatment – safe for aquaculture, agriculture gardening or discharge into any water body. It can also be used for floor cleaning of public toilets in drought prone areas.
Advantages of Decentralized System of Biogas Plant with SET Technology
- Cost of collection of sewage and operation & maintenance of the system are very low.
- No manual handling of human excreta is required.
- It is aesthetically and socially accepted.
- Biogas is used for different purposes.
- Treated effluent is safe to reuse for agriculture, gardening, or discharge into any water body.
- In drought prone areas treated effluent can be used for cleaning floors of public toilets.
- If discharged into the sewer, pollution load on STP will be much lower.
Thus, the decentralized system of sewage treatment through biogas technology is more effective for minimizing financial burden to combat pollution.
Biogas from Dried Water- Hyacinth and Other Mixed Feeds
Water hyacinth is an aquatic, seasonal and problematic weed of national concern. The Government of India formulated a Task Force to get rid of this weed. However, it has an advantage that it is a good substrate for biogas generation. Since this weed is seasonal, biogas plant based on this feed becomes non-functional during summer due to unavailability of this weed. This organisation has successfully demonstrated that biogas can be produced from this weed throughout the year after harvesting, drying and pulverising it. The pulverised weed can be easily transported and used for biogas generation throughout the year.
The Institute has also carried out a series of experiments on biogas generation from vegetables/fruit wastes and household kitchen wastes with or without mixing with human wastes. Better results were obtained when human waste and vegetable waste were fed in combination. It showed an additive effect.
Use of Digester Effluent for Hydroponics
Biogas digester has a good plant nutrient value. It can be directly used for irrigating grass lawns, flower beds or even for agricultural purposes. The Institute has successfully demonstrated its use as hydroponics i.e., soil-less culture of plants. The effluent is first dried in earthen pots kept in sunlight where owing to the evaporation of the liquid, the concentration of nutrients increases. It is filtered with a thin plastic mesh. Some trace elements are added in the filtered effluent. Such effluent is completely odourless. Various plants have been grown exclusively on such an effluent when mixed (5 to 10% by volume) with tap water. Plants can be grown in glass bottles or any other jars and kept inside or outside the room. Such technology is useful for the culture of rare plants like cactus sps and other ornamental plants.
Sulabh Technology Reduces Green House Effect
In addition to conserving and reusing water the system has additional inbuilt advantage of reducing green house effect arising out of Carbon dioxide and Methane production due to degradation of human wastes. Due to design of leach pit (Sulabh Toilet) produced carbon dioxide is diffused in soil through honey combs. It does not escape in atmosphere as in other cases. During anaerobic digestion of human wastes during biogas production, methane is produced that is used for different purposes. Methane as such is not left to escape in the atmosphere. Thus, both these technologies are helping in reducing green house effect and thus improve environment.