An ozone purification system for wastewater comprising an ozone diffusion reactor installable in or in fluid communication with wastewater collection tanks of septic or other wastewater systems. The reactor includes a pump that circulates wastewater through a gas-liquid mixing device, a contact volume, and a static mixer. The contact volume comprises an elongate length of contact piping and the static mixing chamber is configured to impart turbulence into the flow of the circulated wastewater and ozone gas.