Appropriate rural technologies: Agricultural waste to charcoal and strategies for biogas production from organic garbage

Abstract

Agricultural Waste to Charcoal: Two cottage scale processes have been described for pyrolysing agricultural waste into charcoal. One of the processes uses a kiln working on the "oven and retort" principle, and the other one uses the "top-lit, updraft" principle. Because charred agricultural waste is powdery in nature, it is mixed with a binder and extruded into briquettes. Currently, more than 100 organizations in India and abroad are making charcoal by using these processes. A team of four persons can produce daily about 70-80 kg briquettes. Working for about 200 days in a year, in the post-monsoon period, this team can make about 15 tons of char briquettes having a market value of about Rs.400,000, but the process can be easily scaled up without increasing the manpower component. Sugarcane trash was found to be ideal for continuous supply of raw material, but one can also use leaf litter from roadside trees, plantations and forests. The charcoal briquettes made by this method can be used as cooking fuel, as industrial fuel or also to replace metallurgical grade coke. The charcoal can also be applied to the soil for raising soil fertility. Efforts are on at the author's organization to convert the charcoal into value-added products like active charcoal and water gas. Abstract for Sect. 6.7 A Strategy for Biogas Production from Organic Garbage: In spite of new knowledge gained since the advent of the twenty-first century, the biogas researchers still use some of the older concepts. The new concepts pointed out in this article are: 1. Because the biogas-producing microbes reside in the intestines of animals, they eat what the animals eat. 2. Breeding super-methanogens can be achieved, but their use in a biogas plant would not be practical, as it would be impossible to maintain them in an open system like a biogas plant. 3. All animals represent living biogas plants. The faecal matter of animals is therefore effluent slurry of a biogas plant. The biogas-producing microbes occur in the faecal matter of animals because they exit the animal body along with dung. 4. The anaerobic microbes extract the chemically bound oxygen from their feedstock and use it in their metabolism. Therefore, feedstock of a biogas plant must have oxygen in its chemical makeup. Since animals represent living biogas plants, the same is also true of food eaten by animals. 5. The value called % volatile solids actually represents the % digestibility of the concerned substance. 6. The digestibility of the feedstock is more important than the C/N ratio of a feedstock. 7. In the case of material which is difficult to be digested under anaerobic conditions, use is made of biphasic digestion, in which the feedstock is first treated aerobically and then subjected to anaerobic digestion. This is wrong, because most of the organic carbon, which would have yielded methane in the anaerobic phase, gets oxidized in the aerobic phase itself, leading to drastic reduction in the methane yield.