Heterogeneous catalytic ozonation by Nano-MgO is better than sole ozonation for metronidazole degradation, toxicity reduction, and biodegradability improvement

Abstract

2015): Heterogeneous catalytic ozonation by Nano-MgO is better than sole ozonation for metronidazole degradation, toxicity reduction, and biodegradability improvement, Desalination and Water Treatment, In the current paper, the removal efficiency of metronidazole (MNZ) using a catalytic ozonation process (COP) in the presence of magnesium oxide nanocrystals, as a catalyst, was investigated in deionized water and compared with a sole ozonation process (SOP). The influence of several operational factors on both removal processes was evaluated: solution pH, MgO dosage, initial MNZ concentration, and reaction time. Biodegradability improvement, mineralization rate, oxidation intermediates, and toxicity were also studied for the COP. The results showed that MgO nanocrystals accelerated MNZ removal compared to the SOP. The optimum pH for both SOP and COP was obtained at 10 and optimum MgO dosage for the COP was determined 0.25 g/L. Under optimum conditions, after 20 min and 35 min, the complete removal of 40 mg/L MNZ solution occurred in COP and SOP, respectively. The COP significantly increased the biological oxygen demand/chemical oxygen demand ratio (from 0.09 to 0.43), caused 93.5% MNZ mineralization, and reduced the toxicity of the MNZ.

Catalytic ozonation of nitroimidazole antibiotics using nano-magnesium hydroxide as heavy-metals free catalyst

“…However, the removal efficiency decreased when dosage of nano-Mg(OH) 2 continued to increase due to the limited amount of ozone in the system [54]. Similar studies have been reported on the catalytic ozonation of metronidazole using nano-MgO catalyst [16]. Considering the treatment cost, 0.15 g L -1 was chosen as the optimized catalyst dose for nitroimidazole antibiotics.…”

“…The removal rate constant of MNZ, TNZ, and DMZ after three runs shifted to 0.326, 0.342, and 0.481 min -1 , respectively. The catalytic ozonation of MNZ and TNZ in the presence of other catalysts such as activated carbon, nano-MgO, and brucite have been investigated [13,16,34]. However, rare evaluation has been conducted on the degradation of MNZ, TNZ, and DMZ in the catalytic ozonation process using nano-Mg(OH) 2 as catalyst except this investigation.…”

“…In order to remove nitroimidazole antibiotics, various chemical methods including photo-catalytic oxidation method [12,13], nanoscale zero-valent iron technology [7], and ozonation [14][15][16] have been used for degradation of nitroimidazole antibiotics. The catalytic ozonation has been widely accepted as an efficient degradation approach for various antibiotics with short reaction time and high oxidation rate [17][18][19].…”

“…In addition, the use of brucite can avoid secondary pollutant because Mg 2+ is beneficial to the organisms in water [25,26]. However, with the development of nanotechnology, nanomaterials used as ozonation catalysts have shown high catalytic performance due to high surface area and numerous active sites on surface of the nanoparticles [12,16,27,28]. It is regretful that rare investigations are available on the oxidation of antibiotics in the catalytic ozonation with nano-Mg(OH) 2 as catalyst that is an environment-friendly and economically feasible catalyst.…”

Preparation of MgO nanocrystals and catalytic mechanism on phenol ozonation

“…The acceleration of phenol removal in the presence of magnesium oxide was in agreement with the observation shown in preliminary screening experiments and TBA indeed reduce the rate of phenol removal as expected which indicates the degradation of phenol in the O 3 /MgO system might involves hydroxyl radicals. A similiar observation reported by Kermani M et al that both ozone molecules and radicals participated in the degradation of metronidazole by ozonation with magnesium oxide, 47 and the formation of hydroxyl radicals resulted from the decomposition of ozone which taking place on the catalyst surface. Fig.…”