Research of the effects of various gases on cavitation-based removal of organic pollutants from distillery wastewater

Abstract

The tendency to preserve water resources and rationally use natural waters promotes finding new methods and improving the existing methods of wastewater treatment. Using the phenomenon of cavitation to intensify the treatment processes we have proposed saturating the cavitation zone with various gases such as nitrogen, oxygen, and the mixture of nitrogen and oxygen in the ratio of 1:1. The study focuses on the impact of the nature of bubbled gases, both with ultrasonic treatment and without it, on the changes in the chemical oxygen demand (COD). The calculated effective rate constants for the destruction of organic compounds in distillery wastewater have proved that the highest value of 1.2 10-4 sec-1 is achieved through bubbling nitrogen in the cavitation zone. The use of nitrogen alone allows reaching the effective rate constant value of 0.7 10-4 sec-1 vs. 0.2 10-4 sec-1 in case when ultrasound is used alone. The highest degree of water treatment in cavitation conditions (63 %) is achieved in the presence of nitrogen, and the lowest (38.8 %) - of the mixture of nitrogen and oxygen in the ratio of 1:1. The differences in the effects of various bubbled gases on distillery wastewater are revealed depending on the electronic excitation energy of water molecules and the formation rates of radicals H and HO that are strong oxidants of the process. It is determined that the destruction of organic impurities in distillery wastewater can be described with the use of the firstorder kinetic equation. The research has confirmed the synergistic effect of the joint action of cavitation and nitrogen in the distillery wastewater treatment. The study has determined the relative series of the effects of the nature of certain gases on the cavitation treatment of distillery wastewater and proved that the most effective nitrogen dioxide can increase the degree of the wastewater treatment by 46 % compared to the effect of ultrasound alone. Given the growing problem of inadequate industrial and domestic wastewater treatment, the development of innovative technologies is particularly important. The use of the proposed cavitation technology for the treatment of wastewater from distillery plants can reduce or even completely eliminate the negative impact of contaminants on the environment.