Impact of ozonation on the degradation of organic molecules in aquaculture wastewaters (en ce compris une introduction à la méthodologie de la recherche)

Abstract

Vietnam has become the second largest shrimp exporter worldwide. To meet demand and prevent livestock from viral contamination, farmers heavily rely on antibiotics, such as oxytetracycline (OTC). This extensive use leads to water pollution. Treating the wastewater after shrimp harvesting and before its release into the Mekong River is a necessity. To overcome the inability of conventional biological treatment processes to remove micro-pollutants, advanced oxidation processes (AOP) are a promising alternative. This work evaluated the potential of ozonation for the degradation of organic molecules present in aquaculture water.

A preliminary study on para-nitrophenol validated the ozonation protocol. The degradation of OTC was then thoroughly investigated and the impact of OTC concentration, ozone (O3) dosage, bubbling system and water salinity were assessed. UV-Vis spectrophotometry, Total Organic Carbon (TOC) analysis, and High Performance Liquid Chromatography coupled to Mass Spectrometry (HPLC-MS) were used as complementary characterization techniques. Exploratory experiments were also conducted to broaden the research scope to the rifampicin antibiotic degradation and inactivation of the bacterial strain Pantoea agglomerans.

Results highlighted the fast degradation of a 0.1 mmol/l of OTC solution (-90% after 5 minutes in a 400 ml batch reactor) for given ozonation parameters (31 mmol/h). Only a partial mineralization of the by-products was reached (-35% in TOC after 6 hours). A partial reaction order for OTC of 0.57 was determined through a kinetic study, suggesting a complex degradation involving both direct O3 attack and indirect •OH radical pathways. The bubbling system and the salinity affected the degradation significantly, suggesting mass transfer limitations and the scavenging role of Cl– as key factors. Coupling O3 treatment to other AOP processes could enhance the process efficiency to reach complete mineralization of by-products.