The Ballast Water Management Convention (BWMC) establishes limits for viable organisms in discharged ballast water. However, organisms smaller than 10 μm are not considered in this regulation although they represent, in some regions, the majority of the phytoplankton organisms in marine water. The objective in this study is to assess three photosynthetic species smaller than 10 μm as potential standard test organism (STO) in experimentation focused on the inactivating efficacy of ultraviolet treatments (UV). A growth modelling method was employed to determine the reduction of the viable cell concentration under either light or dark post-treatment conditions to evaluate the importance of the photoreactivation. In spite of its moderate growth rate, the high UV resistance in combination with the abundance and worldwide distribution of Synechococcus sp. and the environmental importance of this species constitute important reasons for considering Synechococcus sp. as a valuable STO for ballast water treatment.

Ballast water transport is considered as one of the major vectors for dispersal of microplastics around the global oceans. In this commentary, a simple, inexpensive solution has been proposed to reduce microplastic pollution and its mobility via ballast water. A screening chamber (with stainless steel three layered mesh) is proposed to be attached to the existing Ballast Water Treatment Systems (BWTSs) in cargo ships to filter back-flushed sea water from BWTSs. The three layered screens (500, 300 and 100 μm) will not only avoid clogging and easy separation of different size groups of microplastic particles but also help in smooth discharge of water to the sea. This technique is expected to remove a large number of microplastic particles (ranging from 0.0015 to 1020 million) from a single voyage. The proposed chamber may help to collect 0.0003–204 metric tons of particles/day, depending upon the geographical location of ballast intake in the global ocean. These estimations were made by considering a daily turnover of 0.033 billion tonnes of ballast water globally. This proposed screening chamber attached to the existing BWTSs in cargo ships, along with other region-specific ocean cleaning initiatives, will help in mitigating microplastic pollution in the global ocean.

The discharge of ballast water from ocean-going ships is a major pathway by which invasive species are introduced into coastal waters. As a global factory and trade power with extensive shipping networks, China has paid a huge ecological price for its progress. However, current endeavors to protect the nation's biodiversity are largely focused on terrestrial ecosystems. Therefore, for the first time, we conducted a comprehensive risk assessment of ballast water-induced biological invasion in Chinese ports. The results showed that the ports in the Yangtze River Delta, Pearl River Delta, and Southern Taiwan Province face significantly high invasion risks, and the number of donor ports, connected ships, and arriving vessels showed a positive correlation with the invasion risk. Further, we observed that even a low efficacy disinfection of ballast water can still significantly decrease the level of invasion risk.

The sediments inside the ballast tanks might compromise the effectiveness of the ballast water exchange procedure. In the present study, the sediment removal from double bottom ballast tanks due to flow-through ballast water exchange is investigated by simplified experimental and numerical models. Two flow rates and two sediment densities were considered to verify their influence on the process. Besides, the effectiveness of two tank configuration modifications to improve the sediments removal was investigated. The first is the introduction of a flow deflector inside the tank and the second is the water inflow from the bottom. A fully Lagrangian particle-based method is adopted to simulate the sediment removal process with complex tank geometry. A new boundary condition is proposed to model the mesh of the bottom inlet in the bottom inflow configuration. Despite the simplifications of the numerical model, the computational results are in good agreement with the experimental ones. The results show that the flow-through ballast water exchange method might not be effective to remove the sediments entrapped between the bottom stiffeners, and the proposed modifications, despite challenging implementation, improve the sediment removal.

Ship ballast water can transfer harmful organisms, including antibiotic-resistant bacteria (ARB), among geographically isolated waters. In this study, the presence and composition of ARB and multiple ARB (MARB) were investigated in the ballast waters of 30 vessels sailing to the Port of Jiangyin (Jiangsu Province, China). ARB were detected in 83.3% of the ship's ballast water samples. Moreover, penicillin- and cephalothin-resistant bacteria were the most and least prevalent ARB in the ballast waters, respectively. Oxytetracycline-, chloramphenicol-, tetracycline-, and vancomycin-resistant bacteria were also detected at high concentrations. The multiple antibiotic resistance index demonstrated the presence of MARB, which exceeded 200% in the ballast waters of five ships. Furthermore, 15 species, including the human opportunistic pathogens Vibrio alginolyticus and Serratia nematodiphila, were resistant to at least three antibiotics. Therefore, the potential ecological risk of ARB warrants further attention because of their effective invasion by ballast water.

To verify ships' compliance with ballast water regulations, samples may be collected and tested for viable organisms. This task is completed using a sample probe, which is placed in the ballast discharge pipe through a sample port (a flanged opening). To collect representative samples, the placement of the sample port and the size of the sample probe must be appropriate for the shipboard piping arrangement and ballast water flows. The placement of sample ports was evaluated on 72 ships to assess the current condition of ballast water sampling installations against available guidance. Few ships (15%) had sample ports fully aligned with International Organization for Standardization (ISO) standard 11711-1. While current configurations may present challenges in collecting representative samples, these installations likely occurred before the ISO standard was available. Future installations should be in accordance with the standard to facilitate representative sampling.

Despite that the ballast water management (BWM) convention has come into force to prevent the spread of harmful aquatic organisms, to date, very few bacteria can be identified through microbial culture method. In this study, we explored a reduced-representation sequencing of 2b-RAD approach to investigate the bacterial diversity in ballast water and sediments (BWS). Our results indicated a large amount of bacteria species (1496) detected in BWS up to now, including 13 pathogens that are seriously concerning in marine environment and aquaculture like the most harmful Vibrio harveyi and Aurantimonas coralicida. We showed that the ballast water had relative lower species, which was dominated by Proteobacteria. In contrast, the sediments had richer species, which was dominated by Bacteroidetes. Although BWS differed significantly in species composition, sediments shared most of the concerned pathogens with ballast water, highlighting the importance of sediment management. In conclusion, 2b-RAD sequencing shows promise in future BWM.

During the type approval process of ballast water management systems (BWMS) performance tests need to be conducted according to the BWMS Code (previously Guidelines G8) of the International Maritime Organization (IMO). The shipboard tests previously included a control experiment with untreated ballast water to evaluate the BWMS performance by comparing test results of treated and untreated water. Biological results and abiotic parameters of 97 control water tests conducted during the last >10 years during ballast water uptakes and corresponding discharges were summarized. In general, a strong decline of organisms in ballast tanks was observed, especially during the first few days of the holding time. The IMO validity criteria for uptake water phytoplankton in shipboard control tests were met in 82.5% of all tests. Phytoplankton numbers below the validity criteria occurred predominantly in winter and/or when the water was taken up offshore. For zooplankton the validity criteria were always met. The TSS and POC content in our ballast water uptake samples was frequently much higher than required during IMO BWMS type approval tests so that the current testing requirements do not represent a challenge to BWMS. With this a risk is taken that type approved BWMS fail in water conditions which occur frequently in the real world.