Evaluations of catalysts for wet oxidation waste management in CELSS.

A wet oxidation is considered to be one of the most effective methods of waste processing and recycling in CELSS (Controlled Ecological Life Support System). The first test using rabbit waste as raw material was conducted under a decomposition temperature of 280 degrees C for 30 minutes and an initial pure oxygen pressure of 4.9 MPa (50 kgf/cm2) before heating, and the following results were obtained. The value of COD (Chemical Oxygen Demand) was reduced 82.5% by the wet oxidation. And also the Kjeldahl nitrogen concentration was decreased 98.8%. However, the organic carbon compound in the residual solution was almost acetic acid and ammonia was produced. In order to activate the oxidation more strongly, the second tests using catalysts such as Pd, Ru and Ru+Rh were conducted. As the results of these tests, the effectiveness of catalysts for oxidizing raw material was shown as follows: COD and the Kjeldahl nitrogen values were drastically decreased 99.65% and 99.88%, respectively. Furthermore, the quantity of acetic acid and ammonia were reduced considerably. On the other hand, nitrate was showed a value 30 times as much as without catalytic oxidation.