Micronano-bubble ozonation as an efficient pretreatment technology for raw oxytetracycline production wastewater discharged to biological treatment

Efficient high-strength antibiotic production wastewater treatment is a significant challenge that restricts sustainable pharmaceutical industry development. A novel ozone micronano-bubble (MNB) treatment system has been firstly developed to enhance oxytetracycline (OTC) degradation primarily by ozone and singlet oxygen. For practical applications employing pretreatment combined with biological treatment for raw OTC production wastewater, it is necessary to clarify the treatment performance (including the removal of parent OTC, toxicity, and organic fraction), and the potential impact on following bioprocesses. In this study, three pretreatment technologies (i.e., MNB ozonation, conventional ozonation, and thermal hydrolysis) were developed to treat real raw OTC production wastewater and were comprehensively compared. Conventional ozonation requires treatment time of over 14 h for complete removal of OTC and toxicity. Under the high-temperature operating condition (85 °C), thermal hydrolysis achieves the shortest treatment time (3 h) for complete OTC removal from production wastewater without toxic substance generation. Nevertheless, the hydrolysis products and high-concentration dissolved organic matter (DOM) cannot undergo further transformation. Despite the formation of some toxic oxygen-rich transformation products, these products can be rapidly degraded to innoxious substances with lower molecular weights within 8 h via MNB ozonation. In addition, MNB ozonation can promote a 30.0 % organic fraction transformation to produce more methane (584.0 mL) during the anaerobic inhibition tests than thermal hydrolysis (356.0 mL). Consequently, MNB ozonation technology is more conducive to combination with biological post-treatment. This study demonstrates the promising application potential of MNB ozonation as an efficient pretreatment technology for OTC production wastewater, and provides comprehensive insight into different pretreatment technologies to obtain an optimal treatment strategy for practical applications.