Evaluating the treatment performance of filtration & real-time UV irradiation processes for bacteria and pathogens in fresh ballast water

Abstract

Ballast water (BW) is fresh water or seawater taken onboard to stabilize ships. By traveling with the vessels, different species can be introduced into a new area, which has potential impact on human health, economy, and environment. Bacteria are transferred in large numbers through BW. Owing to their diversity and potential pathogenicity, they could pose a direct threat to the prevailing microbiome in the recipient waters and human health. The aim of this paper is to examine the effects of real-time ultra-violet (UV) irradiation on the survival, activity, and diversity of bacterioplankton in fresh water. The treated water was held in the treatment tanks for one day or five days before discharged. After treatment, the density of total viable bacteria and indicator bacteria decreased significantly in discharge water compared with control water, and the density of indicator bacteria met the D-2 standard. The sequencing of 16S rRNA amplicons showed that α-proteobacteria was dominant in Inlet water. In the treated water, γ-proteobacteria was dominant in UV_PD_1d, while α-proteobacteria became the most abundant class again in the UV_PD_5d. Shannon and Simpson indices confirmed the declining trend in bacterial diversity. Further, our result indicated that real-time UV irradiation was likely to cause the change of assemblage of bacteria, and there were still several pathogen bacteria after treatment. By monitoring the physicochemical parameters of ballast water, we found that pH positively correlated with the dominant phylum Proteobacteria. This study provides a further idea for type approval of ballast water management systems.