Dry dung fuel (or dry manure fuel) is feces, generally of domestic animals, that have been dried in order to be burned as a fuel source. It is used in many countries, and in some instances employs human feces. [1] Despite the disadvantage of increasing air pollution, the practice remains a common use of this kind of manure. [2]
Dry dung is more commonly used than moist dung, because it burns more easily. [3] Dry manure is typically defined as having a moisture content less than 30 percent. [4]
"Dung cakes", made from the by-products of animal husbandry, are traditionally used as fuel in India for cooking food in a domestic hearth called a Chulha. They are made by hand by village women, traditionally of cow or buffalo dung. One dung cake of an average size[ clarification needed ] gives 2100 kJ of energy. Dung cakes are also known as goitha, uple, kande, gosse or thepdi.
These cakes are molded with a curvature to keep them stuck to the walls. Once dried, they are put in a pile and covered with thatch called bitauda. These bitaudas can be seen in parts of rural India, albeit with different names. The size and shape of the cake may vary with region. It is also not uncommon to see the cakes directly used in earthen ovens.
This biofuel has been used primarily for two reasons: for easy disposal of cow dung and as easily available and cheap fuel.
Human feces can in principle also be dried and used as a fuel source if they are collected in a type of dry toilet, for example an incinerating toilet. Since 2011, the Bill & Melinda Gates Foundation is supporting the development of such toilets as part of their "Reinvent the Toilet Challenge" to promote safer, more effective ways to treat human excreta. [5] The omni-processor is another example of using human feces contained in fecal sludge or sewage sludge as a fuel source.
Advantages of using dry animal dung include: [6]
Also, camel dung is used as fuel in Egypt.
Dry animal dung was used from prehistoric times, [16] including in Ancient Persia, [12] Ancient Egypt and early modern England. [17] In Equatorial Guinea archaeological evidence has been found of the practice, [18] and biblical records indicate animal and human dung were used as fuel. [19]
The combustion of dried dung cakes has been shown to release many thousands of organic components into gas and aerosol phases, some of which are unique tracers of dung combustion, such as cholestanol and coprostanol. [20] Dung cakes are generally a higher emission fuel, with the combustion of cow dung cake samples collected from the Delhi area of India releasing around four times more volatile organic compounds than fuel wood samples. [21]
The volatile organic compounds released from cow dung cake combustion have been shown to be significantly more reactive with the hydroxyl radical, with the gases released from the combustion of cow dung cake samples collected from Delhi in India around 120 times more reactive with the hydroxyl radical than the emissions from liquefied petroleum gas. The volatile organic compounds from cow dung cake combustion have also been shown to result in 3-4 times more secondary organic aerosol production than fuel wood and release many more toxic polycyclic aromatic hydrocarbons. [22]
