Apparatus and methods for oxidizing an ammonia desulfurization solution. The apparatus may include an oxidation air system. The apparatus may include an oxidation tank. The apparatus may include in the tank, a gas-liquid dispersion enhancer. The enhancer may include a sieve plate layer that includes a sieve plate. The sieve plate layer may be one of a plurality of sieve plate layers. The plurality may include two or three sieve plate layers. The apparatus may include an oxidation enhancing device mated to the tank. The oxidation enhancing device may include an acoustic wave generating device. The oxidation enhancing device includes an ultrasonic wave generating device. The ultrasonic generating device may be configured to provide a sound intensity in the range 12 to 40 Watts/Liter. The ultrasonic generating device may be configured to provide to a liquid sound intensity in the range 12 to 40 Watts/Liter.