Development of an automated ballast water treatment verification system utilizing fluorescein diacetate hydrolysis as a measure of treatment efficacy

Recent progress and challenges facing ballast water treatment - A review

The transoceanic movement of non-indigenous microorganisms and organic and inorganic contaminants through the transfer of ballast water of ocean-going vessels can be considered highly likely. The introduction of contaminants and non-indigenous microorganisms can cause changes in indigenous microorganisms, marine species, and biota, which can create problems for the ecology, economy, environment, and human health. This paper compiles and presents ballast water treatment system concepts, principles of inactivation mechanisms used, and the advantages and challenges of the treatment technologies. In addition, the paper aims to draw attention to the relationship between various organisms and the individual mechanism to be inactivated, including the effect of external factors (e.g., pH, salinity, turbidity) on inactivation efficiency. This review can assist in the choice of a suitable ballast water treatment system, taking into account the water conditions (e.g., pH, temperature, salinity) and indigenous species of the maritime areas where the ships intend to operate. This review also provides information describing the responses of the various organisms to different treatment techniques.

Enhanced bioremediation of diesel oil-contaminated seawater by a biochar-immobilized biosurfactant-producing bacteria Vibrio sp. LQ2 isolated from cold seep sediment

This study investigated the effect of immobilized biosurfactant-producing bacteria on the bioremediation of diesel oil-contaminated seawater. Initially, a biosurfactant-producing bacterium, LQ2, was isolated from a marine cold-seep region, and identified as Vibrio sp. The biosurfactant produced by LQ2 was characterized as a phospholipid, exhibiting high surface activity with strong stability. Meanwhile, the inoculation of biochar-immobilized LQ2 demonstrated superior efficiency in removing diesel oil (94.7%, reduction from 169.2 mg to 8.91 mg) over a seven-day period compared to free-cell culture (54.4%), through both biodegradation and adsorption. In addition, the microbial growth and activity were greatly enhanced with the addition of immobilized LQ2. Further experiment showed that degradation-related genes, alkB and CYP450-1, were 3.8 and 15.2 times higher in the immobilized LQ2 treatment, respectively, than those in the free cell treatment. The findings obtained in this study suggest the feasibility of applying immobilized biosurfactant-producing bacteria, namely LQ2, in treating diesel oil-contaminated seawater.

Electrokinetic detection and separation of living algae in a microfluidic chip: implication for ship's ballast water analysis

Detecting living algae from treated ship's ballast water is an important task for port state control (PSC) under the requirement of the International Ballast Water Convention. In this paper, electrokinetic detection and separation of living algae from NaClO- and UV-treated ship's ballast water in a microfluidic chip are presented. The electrokinetic movement of algae in a straight poly ethylene glycol (PEG)-modified PDMS microchannel filled with 10% PEG solution was measured by using an optical microscope. The experimental results show that the moving velocity of dead algae is lower by more than 80% in comparison with living algae. The decreased velocity is larger for larger dead algae and the velocity is decreased to zero for dead algae larger than 6 μm in diameter. A curve was obtained to evaluate the vitality of algae with similar moving velocity but different sizes. Electrokinetic separation of living algae from a mixture sample in a straight channel was also achieved. The method presented in this paper provides a moving velocity-based approach for quickly evaluating the living status of algae in treated ship's ballast water.

A fungus-bacterium co-culture synergistically promoted nitrogen removal by enhancing enzyme activity and electron transfer

The fungus Penicillium citrinum WXP-2 and the bacterium Citrobacter freundii WXP-9 were isolated and found to have poor denitrification performance. Surprisingly, co-culture of the two strains which formed fungus-bacterium pellets (FBPs) promoted the removal efficiency of nitrate (NO₃^--N; 95.78%) and total nitrogen (TN; 81.73%). Nitrogen balance analysis showed that excess degraded NO₃^--N was primarily converted to N₂ (77.53%). Moreover, co-culture increased the dry weight to 0.74 g/L. The diameter of pellets and cell viability also increased by 1.49 and 1.78 times, respectively, indicating that the co-culture exerted a synergistic effect to promote growth. The increase in electron-transmission system activity [99.01 mg iodonitrotetrazolium formazan/(g·L)] and nitrate reductase activity [8.65 mg N/(min·mg protein)] were responsible for denitrification promotion. The FBPs also exhibited the highest degradation rate at 2:1 inoculation ratio and 36 h delayed inoculation of strain WXP-9. Finally, recycling experiments of FBP demonstrated that the high steady TN removal rate could be maintained for five cycles.

Fluorescein Derivatives as Fluorescent Probes for pH Monitoring along Recent Biological Applications

Potential of hydrogen (pH) is one of the most relevant parameters characterizing aqueous solutions. In biology, pH is intrinsically linked to cellular life since all metabolic pathways are implicated into ionic flows. In that way, determination of local pH offers a unique and major opportunity to increase our understanding of biological systems. Whereas the most common technique to obtain these data in analytical chemistry is to directly measure potential between two electrodes, in biological systems, this information has to be recovered in-situ without any physical interaction. Based on their non-invasive optical properties, fluorescent pH-sensitive probe are pertinent tools to develop. One of the most notorious pH-sensitive probes is fluorescein. In addition to excellent photophysical properties, this fluorophore presents a pH-sensitivity around neutral and physiologic domains. This review intends to shed new light on the recent use of fluorescein as pH-sensitive probes for biological applications, including targeted probes for specific imaging, flexible monitoring of bacterial growth, and biomedical applications.

High efficiency inactivation of microalgae in ballast water by a new proposed dual-wave UV-photocatalysis system (UVA/UVC-TiO2)

A new synergistic method was developed to inactivate marine microalgae using combined longwave ultraviolet (UVA) and shortwave ultraviolet (UVC)-photocatalysis (UVA/UVC-TiO₂) technology. Five kinds of representative marine microalgae in three phyla were used as inactivating targets to examine the inactivation effect. Compared with the photocatalytic systems using UVA or UVC alone as the light source, the algae inactivation ratio in the newly developed system increased by 0.31 log or 0.19 log, and the chlorophyll a removal rate increased by 17.5% or 9.7%, respectively. Total suspended solids (TSS) of the seawater did not cause remarkable impact on the inactivation process, and the increase of UV radiation intensity improved the treatment effect significantly. Further, UVA/UVC-TiO₂ treatment causes irreversible damage to microalgae cell membrane. The content of lipid peroxidation product malondialdehyde (MDA) increased rapidly within a short period of time, and a large number of proteins leaked out. The results of this study indicated that UVA/UVC-TiO₂ was an effective method to solve the challenge of efficient inactivation of plankton in ballast water containing a high density of suspended matter.

Synergistic degradation of crude oil by indigenous bacterial consortium and exogenous fungus Scedosporium boydii

The purpose of this study was to investigate the potential of defined co-culture of indigenous bacterial consortium and exogenous fungus Scedosporium boydii for biodegradation of crude oil. After 7 days of incubation, residual oil, n-alkanes and aromatic fraction were analyzed. The degradation rate of crude oil was increased from 61.06% to 81.45% by the defined co-culture according to the 3:1 inoculation ratio of bacteria to fungi. The microbial activity was enhanced markedly and the formation of biofilms was accelerated after suitable inoculation of Scedosporium boydii. High throughput analysis showed that bacterial evenness and diversity were increased and the relative abundance of Paraburkholderia tropica was increased observably from 7.67% to 56.13% in the defined co-culture. These results indicated that synergistic degradation of crude oil in the bacteria-fungi consortium may be advantageous for bioremediation of petroleum-contaminated site.

Occurrences, composition profiles and source identifications of polycyclic aromatic hydrocarbons (PAHs), polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) in ship ballast sediments

The aim of this study was to investigate the levels of persistent organic pollutants (POPs) including polycyclic aromatic hydrocarbons (PAHs), polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) in ship ballast sediments. The ballast sediment samples were collected from six merchant ships docked in 2015 in Jiangyin City, China. Ballast sediments represent a potential vector for the transport of POPs and invasive species between marine environments. An attempt was also made to determine the sources of these compounds in the ballast sediment. The results indicated ballast sediments generally contain greater amounts of BDE-209 and comparable amounts of PAHs, PBDEs (exclusive of BDE-209) and PCBs compared to those in marine surface sediments. Based on the sediment quality guidelines, PAHs and PCBs in ballast sediments were estimated to have median or high potential of posing ecological risks, respectively, to marine life if ballast sediments were disposed without specific treatment. POPs in ballast sediments were derived from multiple sources with atmospheric deposition being an important origin. Ship activities including diesel exhaust and illegal oil sewage discharge were considerable contributors of certain individual POPs to ballast sediments. Our study is important because it represents the first report on levels, health risk assessment and source apportionments of POPs in ballast sediments and is a first step in the implementation of specific ballast sediment management measures.