Are silicone foul-release coatings a viable and environmentally sustainable alternative to biocidal antifouling coatings in the Baltic Sea region?

Quantification of paint flakes and metal emissions during pro-active in-water hull cleaning

Pro-active in-water hull cleaning is a viable option for reducing greenhouse gas emissions and preventing the transportation of non-indigenous species. Conversely, pro-active in-water cleaning (IWC) might lead to the emission of antifouling paint particles and biocides, posing a risk to the marine environment. However, the analysis of these APPs is particularly challenging. We have therefore adapted a thermoanalytical approach using pyrolysis-gas chromatography/mass spectrometry to analyze the abrasion of APPs. In this approach, the mass of APPs is determined by analyzing the polymer backbone and external calibration. We investigated the particulate abrasion of antifouling coatings for one ship with a self-polishing coating, one with a foul-release coating and one with an abrasion-resistant coating, in order to evaluate the different abrasion behavior and the suitability of the respective coating types for pro-active IWC. In addition, the zinc and copper emissions were analyzed. The extrapolation of the abrasion for ships with 10,000 m2 of wetted surface shows that both the abrasion-resistant coating and the foul-release coating release only small quantities of APPs during IWC, with 1.2-2.1∗10-4 kg for the abrasion-resistant coating and 0.015 kg for the foul-release coating. The potential emissions for self-polishing coatings showed significantly higher abrasion with 1.9-4.3 kg. In addition, copper and zinc emissions showed the same distribution trends for the self-polishing coating samples and were between 2.2-9.5 and 1.1-3.2 mg/L, respectively, exceeding common water quality standards by far. These results demonstrate that caution is required when balancing the advantages and disadvantages of IWC, especially with regard to self-polishing coatings.

Biofouling dynamics and antifouling innovations: Transitioning from traditional biocides to nanotechnological interventions

Biofouling is a common phenomenon caused by waterborne organisms such as bacteria, diatoms, mussels, barnacles, algae, etc., accumulating on the surfaces of engineering structures submerged under water. This leads to corrosion of such surfaces and decreases their moving efficiency. Conventional antifouling agents are synthetic chemicals which are hazardous to non-target species. Further, these agents are mixed with paints, releasing toxins in the water bodies that affect other organisms. Thus, the development of natural alternatives for anti-fouling chemicals is urgently needed. This review examines the development of environmentally friendly antifouling technologies, focusing on the switch from biocidal coatings that leach toxic elements like mercury and copper to sustainable substitutes such as hybrid, biomimetic, and nanotechnology-based antifouling solutions. Research also focuses on increasing antifouling properties and reducing environmental impact by incorporating natural antifouling agents and constructing hybrid coatings that include multiple technologies. The financial effects of implementing these new technologies compared to more conventional approaches highlight the significance of sustainable practices in the maritime industry. This thorough review sheds light on the state of antifouling technology. It recommends future research to maximize ecological compatibility and apply these advancements to broader applications.

A Robust Natural Rubber-Polyzwitterion Composite Hydrogel for Highly Enhanced Marine Anti-Biofouling

Polyzwitterion (PZW) hydrogel has excellent marine anti-biofouling performance, but it is difficult to effectively work for a long time in natural seawater due to its weak mechanical strength. In this study, a new natural rubber (NR)-PZW composite hydrogel has been reported for long-term anti-biofouling by simply dispersing NR latex into the poly(sulfobetaine methacrylate) (PSBMA) hydrogel network. First of all, owing to the PZW hydrogel network having an anti-polyelectrolyte effect, this NR-PZW hydrogel can provide outstanding anti-biofouling performance, including broad-spectrum anti-bacteria, anti-algae, and anti-protein properties in marine environments. Furthermore, it has a composited natural rubber nanoparticle with a hydrophilic negatively charged outer protein membrane, which can uniformly disperse in the hydrogel to significantly improve its mechanical properties. Therefore, this composited hydrogel can provide not only highly enhanced tensile strength (0.52 MPa) but also ultra-high breaking elongation (738%), which can effectually resist harsh seawater environments. As a result, the NR-PZW composite hydrogel can achieve excellent anti-biofouling performance for more than 3 months within a real marine environment. This work can provide an excellent, robust polyzwitterionic hydrogel for long-term marine anti-biofouling, which will also inspire new strategies for anti-biofouling materials.

A novel alternative fate for shrimp fishery wastes as active ingredients in ecofriendly antifouling paints

This study addresses two environmental issues: the fate of fisheries organic wastes and the marine biofouling control. Marine biofouling continues to pose a significant environmental and economic burden, with existing solutions often being environmentally toxic or prohibitively expensive. Natural products, such as enzymes, have emerged as promising alternatives. Shrimp processing wastes are usually dumped to the environment, although they constitute an important source of marine enzymes. In this context, the present study investigates the potential of enzymatic extract derived from shrimp processing waste as an antifouling agent. We focused on the performance and stability of proteolytic enzymes within the extract under various conditions: exposure to seawater (static and dynamic) over time, and resistance to organic solvents. Additionally, we explored field trials using antifouling paints formulated with shrimp extract and we investigated a versatile and simple technology for extract immobilization. The results demonstrate that proteolytic activity in the shrimp extract remained stable over time in seawater and when exposed to organic solvents. Paints containing this extract completely inhibited macrofouling attachment for 7 months. Interestingly, control panels with deactivated enzymes exhibited macroalgae colonization but also showed reduced macroinvertebrate attachment. This suggests that additional compounds within the extract may have antifouling properties. We successfully produced nanocapsules of alginate-chitosan containing the shrimp extract using electrohydrodynamic atomization. While these nanocapsules show promise, further optimization is required. Overall, this study presents encouraging findings for the use of shrimp waste extract in antifouling paint formulations. This approach offers a potentially low-cost and environmentally friendly solution to the biofouling problem.

The contribution of shipping to the emission of water and air pollutants in the northern Adriatic Sea - current and future scenarios

Marine pollution management requires identifying all sources of contaminants, yet shipping's role in marine contamination remains unexplored. To address this gap, we investigated shipping contribution to water and air pollutant loads in the Northern Adriatic Sea in 2018 and under two future scenarios. The approach integrated (i) modelled data of shipping-related emissions, (ii) load from tributaries, and (iii) land-based emissions to the atmosphere. The results showed that shipping significantly contributes to copper, zinc (from antifouling paints), nitrogen (from sewage and food waste), phenanthrene, and naphthalene (from scrubbers and bilge water) loads. Under an increased shipping traffic scenario by 2050, scrubber use reduces atmospheric emissions but increases water pollutants, while alternative fuels reduce air contaminants emission with no significant increase in water pollution. This study sets the foundation to apply water and air quality models to identify areas of concern and assess the environmental impacts of future shipping emission control strategies.

Projected changes of the emission and transport of organic pollutants and metals from shipping in European seas 2018-2050

The ChemicalDrift model is applied to predict concentrations of metals and polycyclic aromatic hydrocarbons emitted from shipping in European seas in 2050, compared to 2018. Sources include antifouling paints (AFPs), discharge water from scrubbers and atmospheric deposition. The fate of pollutants in the marine environment is presented, highlighting the effect of degradation and volatilization, with seasonal and regional differences. A simplified impact assessment is outlined, where predicted environmental concentrations of individual chemicals and whole effluent concentrations of scrubber discharge water are compared to predicted no-effect concentrations (PNECs) or lowest observed effect concentration (LOEC). The 2018 assessment shows scrubber effluent concentrations exceeding LOEC in Baltic and North Sea coastal regions. By 2050, assuming high use of scrubbers, elevated concentrations may extend to all European seas. For AFPs, assuming continued use of primarily copper-based paints, the highest copper concentrations are projected in 2050 for North Sea ports and coasts, potentially exceeding PNECs.

Sustainable Hull maintenance strategies in Baltic Sea region through case studies of RoPax vessels

Determining optimal maintenance strategies in unique maritime environments like the Baltic Sea is challenging, as it should consider various aspects, including ship characteristics and environmental conditions. This study employs the decision support tool HullMASTER (Hull MAintenance STrategies for Emission Reduction) to assess the life cycle costs of different hull maintenance scenarios for RoPax vessels in the Baltic Sea. Findings indicate that optimal hull management can save operators up to €9.3 million and reduce socio-environmental damage costs by €7.9 million over ten years compared to a less proactive baseline. Notably, biofouling pressure decreases from the high-salinity Skagerrak and Kattegat to the low-salinity Baltic Proper, emphasizing the need for tailored maintenance strategies. Among the coatings analyzed, non-biocide foul-release coatings are the most sustainable choice, reducing emissions to the ocean and the atmosphere. These findings will provide practical guidelines for sustainable hull management strategies, contributing to enhanced operational efficiency and marine environmental protection.

Life-cycle cost assessment of hull protection technologies considering their effect on the environmental friendliness of fishing vessels

Biofouling represents a global challenge for the maritime industry, affecting vessel performance and environmental footprint. This paper analyses various antifouling technologies to reduce the vessel's environmental impact and its operating costs by reduced fuel consumption and less frequent dry-docking. It evaluates both passive and active technologies - passive referring to antifouling coatings and active involving systems that continuously prevent biofouling using energy. The methodology employs mathematical models to quantify the additional resistance and emissions caused by biofouling. Using the case of a fishing vessel operating in the Adriatic Sea, operational features and potential economic and environmental benefits resulting implementing an innovative biofouling protection system are analysed. Economic analysis includes a comprehensive cost structure, investment details, maintenance and operating costs, and possible future carbon taxation scenarios. The research indicates that active antifouling protection is more efficient than passive protection, including a potential reduction of the required power of up to 120 kW, leading to decreased fuel consumption and lower environmental impact, particularly at higher speeds. Despite higher initial investments, life-cycle cost analysis favours active protection systems.

Recent advances in emerging integrated anticorrosion and antifouling nanomaterial-based coating solutions

The rapid progress in the marine industry has resulted in notable challenges related to biofouling and surface corrosion on underwater infrastructure. Conventional coating techniques prioritise individual protective properties, such as offering either antifouling or anticorrosion protection. Current progress and innovations in nanomaterials and technologies have presented novel prospects and possibilities in the domain of integrated multifunctional coatings. These coatings can provide simultaneous protection against fouling and corrosion. This review study focuses on the potential applications of various nanomaterials, such as carbon-based nanostructures, nano-metal oxides, polymers, metal-organic frameworks, and nanoclays, in developing integrated multifunctional nano-based coatings. These emerging integrated multifunctional coating technologies recently developed and are currently in the first phases of development. The potential opportunities and challenges of incorporating nanomaterial-based composites into multifunctional coatings and their future prospects are discussed. This review aims to improve the reader's understanding of the integrated multifunctional nano-material composite coating design and encourage valuable contributions to its development.

Preventing biofouling in microalgal photobioreactors

Photobioreactors (PBRs) are used to grow the light-requiring microalgae in diverse commercial processes. Often, they are operated as continuous culture over months period. However, with time, biofouling layer develops on the inner surfaces of their walls. The fouling layer formation deteriorates the PBR performance as foulants reduce light penetration in it. Light is essential for photosynthetic cultures, and a deterioration in lighting adversely impacts algae growth and biomass productivity. Fouling requires a frequent shutdown to clean the PBR and add to the environmental impact of the operation by generating many wastewaters contaminated with the cleaning chemicals. Antibiofouling coatings could be used to modify the surfaces of existing and future PBRs. Therefore, transparent and non-toxic fouling-release coatings, produced using hydrogel technology, could transform the existing PBRs into efficient and enduring microalgae culture systems, requiring only the application of the coating to the inner walls, without additional investments in new PBRs.

Siloxane Containing Polyether Groups-Synthesis and Use as an Anti-Biocorrosion Coating

In the presented study, the effectiveness of a siloxane polyether (HOL7) coating on glass against microbiological colonization was assessed using microalgae as a key component of widespread aerial biofilms. The siloxane polyether was successfully synthesized by a hydrosilylation reaction in the presence of Karstedt's catalyst. The product structure was confirmed by NMR spectroscopy and GPC analysis. In addition, the thermal stability of HOL7 was studied by thermogravimetric measurement. Subsequently, the surfaces of glass plates were modified with the obtained organosilicon derivative. In the next step, a microalgal experiment was conducted. A mixture of four strains of algal taxa isolated from building materials was used for the experiment-Chlorodium saccharophilum PNK010, Klebsormidium flaccidum PNK013, Pseudostichococcus monallantoides PNK037, and Trebouxia aggregata PNK080. The choice of these algae followed from their wide occurrence in terrestrial environments. Application of an organofunctional siloxane compound on the glass reduced, more or less effectively, the photosynthetic activity of algal cells, depending on the concentration of the compound. Since the structure of the compound was not based on biocide-active agents, its effectiveness was associated with a reduction in water content in the cells.

Fouling-Resistant Behavior of Hydrophobic Surfaces Based on Poly(dimethylsiloxane) Modified by Green rGO@ZnO Nanocomposites

In line with global goals to solve marine biofouling challenges, this study proposes an approach to developing a green synthesis inspired by natural resources for fouling-resistant behavior. A hybrid antifouling/foul release (HAF) coating based on poly(dimethylsiloxane) containing a green synthesized nanocomposite was developed as an environmentally friendly strategy. The nanocomposites based on graphene oxide (GO) and using marine sources, leaves, and stems of mangroves (Avicennia marina), brown algae (Polycladia myrica), and zinc oxide were compared. The effectiveness of this strategy was checked first in the laboratory and then in natural seawater. The performance stability of the coatings after immersion in natural seawater was also evaluated. With the lowest antifouling (17.95 ± 0.7%) and the highest defouling (51.2 ± 0.9%), the best fouling-resistant performance was for the coatings containing graphene oxide reduced with A. marina stem/zinc oxide (PrGZS) and graphene oxide reduced with A. marina leaves/zinc oxide with 50% multiwall carbon nanotubes (PrGZHC50), respectively. Therefore, the HAF coatings can be considered as developed and eco-friendly HAF coatings for the maritime industry.

Assessment of the effectiveness of antifouling solutions for recreational boats in the context of marine bioinvasions

The recreational boating sector is a major vector for the introduction of non-indigenous species (NIS) via biofouling. Despite applying control measures to prevent the growth of fouling communities, most vessels are NIS carriers. This study assessed the effectiveness of different antifouling strategies in a manipulative experiment by testing two common coating typologies (biocide-based and foul-release coatings), accompanied with simulated maintenance practices. The experiment was carried out in the Gulf of La Spezia (Italy) and samples were collected at two different periods. Results showed significant differences among antifouling treatments regarding community structure, diversity, coverage and biovolume of the sessile component, alongside a significant decrease in the performance of biocide-based coating with time. Interestingly, peracarid NIS/native species ratio was higher for biocide-based treatments, suggesting potential biocide resistance. This study highlights the urgent need to develop common and feasible biofouling management plans and provides insights towards identification of best practices for recreational vessels.

Silicone-geranium essential oil blend for long-term antifouling coatings

This study explores the potential of geranium essential oil as a natural solution for combating marine biofouling, addressing the environmental concerns associated with commercial antifouling coatings. Compounds with bactericidal activities were identified by 13Carbon nuclear magnetic resonance (13C NMR). Thermogravimetric analysis (TGA) revealed minimal impact on film thermal stability, maintaining suitability for antifouling applications. The addition of essential oil induced changes in the morphology of the film and Fourier transform infrared spectroscopy (FTIR) analysis indicated that oil remained within the film. Optical microscopy showed an increase in coating porosity after immersion in a marine environment. A total of 18 bacterial colonies were isolated, with Psychrobacter adeliensis and Shewanella algidipiscicola being the predominant biofilm-forming species. The geranium essential oil-based coating demonstrated the ability to reduce the formation of Psychrobacter adeliensis biofilms and effectively inhibit macrofouling adhesion for a duration of 11 months.

Comparative Investigation of AquaSun Eco-Friendly Antifouling Coating via Rheological and Mechanical Characterization

Rheological and mechanical comparative tests of the new AquaSun antifouling sol-gel coating coated on shipbuilding steel compared to a commercial silyl acrylate antifouling top coat containing cuprous oxide and copper pyrithione show further evidence of the practical viability of this multifunctional coating for the protection of the immersed surfaces from biofouling. AquaSun is a less rigid or less viscous material than commercial top coat but more adherent to the steel substrate. These results support further investigation of this multifunctional sol-gel coating as an eco-friendly antifouling paint.

Antifouling Coatings from Glassy Polyelectrolyte Complex Films

Coatings that prevent or decrease fouling are sought for many applications, including those that inhibit the attachment of organisms in aquatic environments. To date, antifouling coatings have mostly followed design criteria assembled over decades: surfaces should be well/strongly hydrated, possess low net charge, and maintain a hydrophilic character when exposed to the location of use. Thus, polymers based on ethylene glycol or zwitterionic repeat units have been shown to be highly effective. Unfortunately, hydrated materials can be quite soft, limiting their use in some environments. In a major paradigm shift, this work describes glassy antifouling films made from certain complexes of positive and negative polyelectrolytes. The dense network of electrostatic interactions yields tough materials below the glass transition temperature, Tg, in normal use, while the highly ionic character of these polyelectrolyte complexes ensures strong hydration. The proximity of equal numbers of opposite charges within these complexes mimics zwitterionic structures. Films, assembled layer-by-layer from aqueous solutions, contained sulfonated poly(ether ether ketone), SPEEK, a rigid polyelectrolyte that binds strongly to a selection of quaternary ammonium polycations. Layer-by-layer buildup of SPEEK and polycations was linear, indicating strong complexes between polyelectrolytes. Calorimetry also showed that complex formation was exothermic. Surfaces coated with these films in the 100 nm thickness range completely resisted adhesion of the common flagellate green algae, Chlamydomonas reinhardtii, which were removed from surfaces at a minimum applied flow rate of 0.8 cm s-1. The total surface charge density of adsorbed cations, determined with a sensitive radioisotopic label, was very low, around 10% of a monolayer, which minimized adsorption driven by counterion release from the surface. The viscoelastic properties of the complexes, which were stable even in concentrated salt solutions, were explored using rheology of bulk samples. When fully hydrated, their Tg values were observed to be above 75 °C.

Systematic computational toxicity analysis of the ozonolytic degraded compounds of azo dyes: Quantitative structure-activity relationship (QSAR) and adverse outcome pathway (AOP) based approach

The present study identifies and analyses the degraded products of three azo dyes (Reactive Orange 16, Reactive Red 120, and Direct Red 80) and proffers their in silico toxicity predictions. In our previously published work, the synthetic dye effluents were degraded using an ozonolysis-based Advanced Oxidation Process. In the present study, the degraded products of the three dyes were analysed using GC-MS at endpoint strategy and further subjected to in silico toxicity analysis using Toxicity Estimation Software Tool (TEST), Prediction Of TOXicity of chemicals (ProTox-II), and Estimation Programs Interface Suite (EPI Suite). Several physiological toxicity endpoints, such as hepatotoxicity, carcinogenicity, mutagenicity, cellular and molecular interactions, were considered to assess the Quantitative Structure-Activity Relationships (QSAR) and adverse outcome pathways. The environmental fate of the by-products in terms of their biodegradability and possible bioaccumulation was also assessed. Results of ProTox-II suggested that the azo dye degradation products are carcinogenic, immunotoxic, and cytotoxic and displayed toxicity towards Androgen Receptor and Mitochondrial Membrane Potential. TEST results predicted LC50 and IGC50 values for three organisms Tetrahymena pyriformis, Daphnia magna, and Pimephales promelas. EPISUITE software via the BCFBAF module surmises that the degradation products' bioaccumulation (BAF) and bioconcentration factors (BCF) are high. The cumulative inference of the results suggests that most degradation by-products are toxic and need further remediation strategies. The study aims to complement existing tests to predict toxicity and prioritise the elimination/reduction of harmful degradation products of primary treatment procedures. The novelty of this study is that it streamlines in silico approaches to predict the nature of toxicity of degradation by-products of toxic industrial affluents like azo dyes. These approaches can assist the first phase of toxicology assessments for any pollutant for regulatory decision-making bodies to chalk out appropriate action plans for their remediation.

Marine biofouling and the role of biocidal coatings in balancing environmental impacts

Marine biofouling is a global problem affecting various industries, particularly the shipping industry due to long-distance voyages across various ecosystems. Therein fouled hulls cause increased fuel consumption, greenhouse gas emissions, and the spread of invasive aquatic species. To counteract these issues, biofouling management plans are employed using manual cleaning protocols and protective coatings. This review provides a comprehensive overview of adhesion strategies of marine organisms, and currently available mitigation methods. Further, recent developments and open challenges of antifouling (AF) and fouling release (FR) coatings are discussed with regards to the future regulatory environment. Finally, an overview of the environmental and economic impact of fouling is provided to point out why and when the use of biocidal solutions is beneficial in the overall perspective.

Surface change of microplastics in aquatic environment and the removal by froth flotation assisted with cationic and anionic surfactants

Microplastics (MPs) are increasingly released into the environment due to the widespread usage and improper management of plastics. Considerable research efforts have been devoted to the remediation of MPs. Froth flotation has been demonstrated as an effective method to remove MPs in water and sediment. However, there is a lack of knowledge on the regulation of the hydrophobicity/hydrophilicity of MPs surfaces. We found that exposure to the natural environment resulted in the increased hydrophilicity of MPs. The flotation efficiencies of polyvinyl chloride (PVC), polypropylene (PP), polystyrene (PS), and polyethylene glycol terephthalate (PET) MPs decreased to zero after six months of natural incubation in rivers. According to various characterizations, the hydrophilization mechanism is mainly correlated with surface oxidation and the deposition of clay minerals. Inspired by surface wettability conversion, we applied surfactants (collectors) to enhance MPs hydrophobicity and flotation efficiency. Anionic sodium oleate (NaOL) and cationic dodecyl trimethyl ammonium chloride (DTAC) were used to regulate surface hydrophobicity. The effects of collector concentration, pH, conditioning time, and metal ions on MPs flotation were thoroughly elucidated. Characterizations and adsorption experiments were performed to describe the heterogeneous adsorption of surfactants on MPs surfaces. The interaction between surfactants and MPs was explained through density functional theory (DFT) simulations. The dispersion energy between hydrophobic hydrocarbon chains attracts collectors on the MPs surface, and the collector molecules wrap and laminate to MPs surfaces. Flotation using NaOL exhibited a higher removal efficiency, and NaOL was environmentally friendly. Subsequently, we investigated the activation of Ca²⁺, Fe³⁺, and Al³⁺ to further improve the collecting efficiency of NaOL. Under the optimized conditions, MPs in natural rivers could be removed by froth flotation. This study shows the great promise of froth flotation for the application of MPs removal.