Our research was carried out with an aim of the design of a commercial plant to treat Transformer oil contaminated with polychlorinated biphenyls (PCBs) by a supercritical water oxidation (SCWO) process The optimal destroying conditions were determined with a lab-scale facility then designed and manufactured a pilot plant facility of 30 kg/h capacity After finishing pilot plant tests dioxin NO NO2 and N2O were analyzed to estimate environmental effects of SOWO process treating transformer oil contaminated with PCBs in and around the pilot plant As the concentration of dioxin was similar to 0 09 pqTEQ/m(3) at four different measuring points we concluded that our SCWO process could be utilized to treat the transformer oil contaminated with PCBs In addition as we have a plan to use the oxygen made from air instead of pure oxygen as an oxidant in commercial plants a mixed gas with 92% oxygen and 8% nitrogen was tested The sample was collected from the exhaust system and estimated the effects of the mixed gas on the SCWO process The total concentrations of NO NO2 and NOx that were measured were less than 5 ppm and N2O was not detected As a result we could ascertain the possibility of the mixed gas prepared from air as an oxidant (C) 2010 Elsevier B V All rights reserved