Formation of inorganic nitrogenous byproducts in aqueous solution under ultrasound irradiation

The effects of ultrasonic frequency, power intensity, temperature and sparged gas on the generation of nitrogenous by-products NO2- and NO3- have been investigated, and the new kinetics model of NO2- and NO3--generation was also explored. The results show that the highest primary generation rate of NO2- and NO3- by direct sonolysis in the cavitation bubbles (represented by k(1)' and k(2)', respectively) was obtained at 600 kHz and 200 kHz, respectively, in the applied ultrasonic frequency range of 200 to 800 kHz. The primary generation rate of NO2- (represented by k(1)') increased with the increasing ultrasonic intensity while the primary generation rate of NO3- (represented by k(2)') decreased. The lower temperature is beneficial to the primary generation of both NO2- and NO3- in the cavitation bubbles. The optimal overall yields of both NO2- and NO3- were obtained at the N-2/O-2 volume (in the sparged gas) ratio of 3:1 which is near to the ratio of N-2/O-2 in air. The dissolved O-2 is the dominant oxygen element source for both center dot NO and center dot NO2, compared with water vapor. Ultrasonic irradiation can significant enhance the recovery rates of dissolved N-2 and O-2 and thus keep the N-2 fixation reaction going even without aeration.