A waste treatment system connected to a sewage treatment plant comprises: an organic waste supply unit for drying and storing organic wastes; a combustible waste supply unit for supplying combustible wastes; a first combustion device for high-temperature combustion the organic wastes supplied from the organic waste supply unit; a second combustion device for low-temperature combustion the combustible wastes supplied from the combustible waste supply unit; a first power generating device connected to the first combustion device so as to perform high-efficiency combined heat and power generation by high-temperature water vapors; a second power generating device connected to the second combustion device so as to perform low-efficiency combined heat and power generation by low-temperature water vapors; and a hot water generating unit for generating hot water using the waste heat from the first power generating device and the second power generating device and supplying the generated hot water to the sewage treatment plant and the organic waste supply unit. According to the thus-configured waste treatment system connected to a sewage treatment plant, organic wastes can be dried using the waste heat power generation generated in the process of generating electric power by high-temperature water vapors generated during the high-temperature incineration of the organic wastes, a sewage treatment can be performed using the waste heat power generation generated in the process of generating electric power by low-temperature water vapors generated during the low-temperature incineration of combustible wastes, and the offensive odor generated in the organic waste drying plant or in the sewage treatment plant can be removed by incinerating the offensive odor in a high-temperature incinerating device or in a low-temperature incinerating device.
