A zero liquid discharge (ZLD) power plant (20) includes an advanced oxidation system (72) for reducing contaminants in source water (70) to form feed water (40) for a boiler (24). The system (72) includes an ozonation module (86) for applying high concentration ozone to the source water (70) to form a mixed stream (104), an ozone reactor (92) in which the mixed stream is retained (104) under pressure, an ultraviolet reactor (98) downstream from the ozone reactor (92) for enhanced contaminant reduction, and a retention tank (103) downstream from the reactor (98). In one configuration, the source water (70) is evaporator distillate from an evaporator (52) that recycles cooling tower blowdown 30. The system (72) achieves organic contaminant reduction at total organic carbon (TOC) levels of less than three hundred parts per billion.