A wastewater treatment apparatus (10) includes one or more treatment tanks (12, 14). Each treatment tank (12, 14) has an associated oxygenation treatment circuit (18) including a gas and liquid mixing chamber (20), a gas injector (22) upstream of the mixing chamber (20) and one of an oxygen generator (24) or an ozone generator (26) supplying gas to the gas injector (22), and a pump (28, 29) for pumping wastewater from the treatment tank (12, 14) through the mixing chamber (20) and back to the treatment tank (28, 29).