Abstract
In order to treat the landfill leachate, $UV/TiO_2/H_2O_2$ system connected with biological treatment was investigated, and proper pretreatment methods were examined to reduce the load on the system considering economical and technical efficiency. It was more profitable to put $H_2O_2$ into the system in the early stage for the sample which was treated with $H_2SO_4$ to decrease alkalinity and with $FeCl_3-6H_2O$ flocculation. Because the required reaction time run up by increasing $H_2O_2$ input amount, though the COD was reduced slightly, the optimal $H_2O_2$ input amount should be determined for the desired COD and the economical efficiency. The appropriate way to get the lowest COD in the shortest time was the method to treat the sample which was controlled to pH 3.5 after adjusting to pH 12 and put 500 ppm $H_2O_2$ into the system. In that case, to increase $H_2O_2$ input amount was not profitable for the system efficiency. The sufficient photocatalytic excited time was required to reduce the photocatalytic decomposition time for the sample which was gone through the alkali state.