Using quantum chemistry theory to elucidate the mechanism for treating sulfonamide antibiotic wastewater by progressive freezing

Abstract

Progressive freezing is a separation and purification technology that is widely used to treat various kinds of wastewater because of providing energy savings and environmental protection. However, there have been no reports of using it to treat sulfonamide antibiotics (SAs) wastewater and the mechanism of the progressive freezing method for wastewater treatment still needs to be clarified. Therefore, we selected four typical SAs, including sulfadiazine (SD), sulfapyridine (SP), sulfamethazine (SM2) and sulfaquinoxaline (SQ), as research subjects to systematically explore the solid–liquid phase distribution of SAs during the freezing process. We considered the binding energy between an SA and an ice molecule or a water cluster to elucidate the purification mechanism of the freezing process. The results showed that the purification rate of the SAs solution was 65 %–86 % and decreased in the order SD > SP > SM2 > SQ. The Gaussian calculation showed that the binding energy of SAs to the ice phase was less than that to the water phase, resulting in the separation of the SAs in ice-water two-phase and purification of the ice body. The main reason for the difference among the purification rates of the four SAs during the progressive freezing process was the difference in the binding energies of the SAs to the ice-water two-phase.