Abstract
The pollution of seawater by both biotic (bacteria, viruses, toxic algae etc.) and abiotic contaminants (toxin, pesticide, pharmaceutical residues, etc.) frequently leads to economic losses in aquaculture activities. The methods of water treatment commonly used in aquaculture (UVC, filtration...) do not allow to eliminate both biotic and abiotic contaminants. Advanced Oxidation Processes (AOPs) such as heterogeneous photocatalysis allow the removal of all organic contaminants present in water and therefore could reduce production losses in land-based farms (closed facilities ). If t his process has already been widely studied for the abiotic decontamination, its application for biotic disinfection is still overlooked (especially on viruses). O ver the past decade the production of the Pacific oyster Crassostrea gigas has been regularly affected by massive mortalities due to the Pacific Oyster Mortality Syndrome (POMS). This syndrome is a complex and polymicrobial disease involving an initial viral infection by the Ostreid Herpes Virus 1 (OsHV-1 µVar ) followed by multiple bacterial infections. In this context, we investigated seawater disinfection by the heterogeneous photocatalysis (UV/TiO2 ) method in the context of POMS by addressing both the impact of the treatment on a single opportunistic pathogenic bacterium ( Vibrio harveyi) and on a complex microbial community refection a natural POMS event (OsHV-1 µVar virus and opportunistic pathogenic bacteria consortium). The viral inactivation has been monitored using experimental infections to see if viral particles were still infectious after UV/TiO2 treatment. Moreover, changes on the total seawater bacterial community have been investigated comparing UV/TiO 2 treatment with UV- irradiated seawater and non-treated seawater. This study gave promising results for UV/TiO2 seawater disinfection. Both oyster’s pathogens tested were efficiently inactivated in a few hours of treatment. Even if treatment impacted transiently the total bacteria community, the seawater microbiota shift toward untreated seawater few days after the end of the treatment. Altogether, these results revealed that heterogeneous photocatalysis could be an interesting alternative process for the disinfection of land-based oyster farm seawater to prevent vibriosis and viral diseases.