Abstract
The applicability of supercritical water oxidation was investigated to the treatment of livestock excrement, which is a large quantity in Japan and almost 100 million tons in a year. In this method, the livestock excrement was incinerated completely and safely to carbon dioxide, water and nitrogen. The toxic and bad-smelling ammonia was decomposed rapidly and the toxic nitrogen oxide was not produced in supercritical water. As a result, the nitrogen atoms in the waste were converted to harmless nitrogen gas.
The effects of temperature, pressure, reaction time and oxygen supply ratio (ratio of supplied to stoichiometric amount of oxygen) on the combustion efficiency of carbon and product yields of ammonia, nitrous oxide were studied. As a result, the condition of 650°C, 15MPa, 15min and 1.2 of oxygen supply ratio was suitable for clean and complete burning of cow's excrement, where the combustion efficiency of carbon atom was almost 100% and the product yields of ammonia, nitrous oxide were almost zero. Furthermore the thermal energy recovered from the combustion process was estimated to be 2.87x106 kJ per ton of raw excrement. It was equivalent to around 70 liter of C-heavy oil and corresponded to the reduction of about 56kg of carbon dioxide on carbon basis.
