Processes and devices associated with reducing the amount of organic substances in a fluid are described. In one example method, oxidizing agents may be introduced into a local constriction of flow in a flow-through chamber as the fluid is flowed therethrough. Cavitation bubbles which contain and/or are associated with the oxidizing agents may form. Collapse of the cavitation bubbles may produce pulses of ultraviolet light, thereby ionizing the oxidizing agents, producing hydroxyl radicals, and degrading and/or oxidizing the organic substances in the fluid. An example device may include a flow-through chamber including a local constriction of flow, a port configured to introduce oxidizing agents into the local constriction of flow, and may include an area configured to collapse the cavitation bubbles, thereby initiating events leading to degradation and/or oxidation of organic substances in a fluid flowed through the device.