M.J. Smith

The early stages of marine biofouling and its effect on two types of optical sensors

This paper records the results of an investigation into the effects of biofouling on optical marine sensors and the organisms responsible for the deterioration in sensor accuracy. Two kinds of commercial sub-surface optical marine sensor, commonly used to measure water quality, were operated in a natural marine environment and allowed to foul while measurements of the actual conditions were made daily using clean instruments. A number of glass and acrylic coupons were placed in the same environment and were removed at intervals throughout the trial. These coupons were examined and the biological population quantified. Deterioration in the optical properties of the coupons was measured using image analysis and UV-visible spectroscopy. The results from the coupons were compared with the results from the commercial instruments. It was observed that the major deterioration in instrumental accuracy occurred when a bacterial population exceeding 105/mm2 was found on the coupons. The algal population had little effect on the instruments over this time period. The acrylic coupons supported a lower fouling population, apparently due to the increased solubility of acrylic in seawater. The two optical techniques returned similar patterns of results for the surface area fouled, although the numerical values returned by each technique were different. Neither of these two techniques returned values directly comparable with the deterioration in accuracy of the commercial instruments. The trial took place on the Isle of Cumbrae in the Firth of Clyde on the west coast of Scotland, U.K.

An alternative approach to antifouling based on analogues of natural processes

A number of marine organisms are able to resist fouling pressure and remain essentially free of fouling. Some organisms are totally devoid of even the first stages of biofilm formation involving bacteria and microalgae. A key feature in recent research has been the realisation that previous low adherence technology is an insufficient technical solution and that natural models, based on marine and other organisms, incorporate other passive techniques for fouling resistance. These characteristics may be incorporated into physical analogues of the natural processes. This paper describes ways of producing physical analogues of some such characteristics, the application of such techniques to surfaces in the marine environment and the environmental impact. The paper includes some results of recent trials and a cost comparison.

Study of PAH dissipation and phytoremediation in soils: Comparing freshly spiked with weathered soil from a former coking works

A comparison was made between the dissipation of polycyclic aromatic hydrocarbons (PAHs) in soil freshly spiked with pure PAHs, soil spiked with a coal tar mixture and a contaminated soil from a former coking works where the PAHs had been present for more than a century. The potential of five selected plant species for phytoremediation was investigated. The levels of all 7 PAHs in chemically amended soil, both planted and unplanted, fell significantly (>80% reduction) over the 12 weeks of the growing trial. In the coal tar treated soils all PAHs were significantly reduced. In both the planted and unplanted soils the 2-3 ringed compounds demonstrated much greater loss (>77%) than the 4-6 ringed (16-39%). The 3-4 ringed compounds demonstrated strong evidence of phytoremediation but not the 5-6 ringed. The coking soil showed limited reduction (7-24%) of all 12 PAHs present. There was little difference in dissipation between the PAHs and little evidence of a phytoremediation effect in coking soil. The results demonstrated that the form in which PAHs were added to soil influenced their susceptibility to dissipation. Therefore, predictions of PAH dissipation from laboratory amended soil do not reflect the true situation in the field.

The effect of benzalkonium chloride concentration on nine species of marine diatom

The effect of varying concentrations of benzalkonium chloride (BAK) on nine diatom species is measured, and related to the variation in tolerance levels of different species seen elsewhere in the literature. Different species showed different effective levels; however, all species were non-viable at 1×10−3% BAK. The technique being laboratory based and, therefore, immune from seasonal influences, is quick to perform and is easily adapted for bioassay work.

A novel technique to prevent bacterial fouling, using imposed surface potential

A. KERR, T. HODGKIESS, M.J. COWLING, C.M. BEVERIDGE, M.J. SMITH AND A.C.S. PARR. 1998. The effect of modest imposed surface potentials on the adhesion of marine bacteria to an electrically conducting layer deposited on silica glass is recorded. A positive shift increased bacterial settlement. However, a negative shift in potential was extremely beneficial in reducing numbers of adhered bacteria. An applied surface potential of − 66 mV SCE resulted in the bacterial population decreasing to approximately 12% of that on the uncharged reference sample. There was no further significant decrease in the adhered bacterial population when the magnitude of the negative potential was increased. The potential was maintained with very little current flow (less than 0·25 nA mm−2). The results were not due to any effect of the material used and therefore the technique could be useful for reducing bacterial fouling in many situations, including medical applications.

Method for the measurement of the diffusion coefficient of benzalkonium chloride

Biofilm formation on the optical ports of cameras and underwater sensors is the primary cause of their reduced useful deployment time. The use of a transparent hydrogel coating containing the cationic surfactant benzalkonium chloride has been shown to extend the deployment times for up to 12 weeks for these instruments. In order to predict the effective lifetime of these coatings it was necessary to obtain the diffusion coefficient of the benzalkonium chloride used in the coatings. Benzalkonium chloride can have different alkyl chain lengths ranging from C8H17 to C18H37 with chain length greatly affecting its chemical properties. The benzalkonium chloride materials investigated here were mixtures of C12H25 and C14H29 as well as C14H29 on its own. These materials were selected for their proven biofilm resistant qualities. The diaphragm diffusion cell technique was investigated for its applicability to the measurement of diffusion coefficients of molecules with surfactant properties and the ability to form micelles. The method was found to be satisfactory for the cationic surfactant benzalkonium chloride. The average value of the membrane cell integral diffusion coefficient D was 7.78 x 10(-6) cm2 s(-1) at 25 degrees C and there was no significant effect of alkyl chain length on the measured value of D.

Preparation of Magnetic Carboxymethylchitosan Nanoparticles for Adsorption of Heavy Metal Ions

The remediation of metal and heavy metal contaminants from water ecosystems is a long-standing problem in the field of water management. The development of efficient, cost effective, and environmentally friendly natural polymer-based adsorbents is reported here. Magnetic chitosan (CS) and carboxymethylchitosan (CMC) nanocomposites have been synthesized by a simple one-step chemical coprecipitation method. The nanoparticles were assessed for the removal of Pb2+, Cu2+, and Zn2+ ions from aqueous solution. Kinetic and thermodynamic models were used to describe and understand the adsorption process of the ions onto the nanomaterials. The interactions between the ions and the biopolymer-based composites are reversible, which means that the nanoparticles can be regenerated in weakly acidic or EDTA containing solution without losing their activity and stability for water cleanup applications.

The non-toxic effects of a novel antifouling material on oyster culture

The production traits (size, weight, mortality and condition) of Crassostrea gigas oysters were examined when cultured in cages coated with a novel antifouling material consisting of a polymer film based on a hydrogel which had been loaded with the active material (benzalkonium chloride—BCl), a mixture of alkyldimethylbenzylammonium chlorides. Production traits of adult oysters and growth rate of larvae obtained from BCl-exposed adults were equal to the controls. Toxicity of BCl, as assessed by the oyster embryo bioassay, was two orders of magnitude lower than TBT and one order of magnitude lower than copper, the active compounds presently used in antifouling paints.

Liquid infused porous surfaces for mineral fouling mitigation

Prevention of mineral fouling, known as scale, is a long-standing problem in a wide variety of industrial applications, such as oil production, water treatment, and many others. The build-up of inorganic scale such as calcium carbonate on surfaces and facilities is undesirable as it can result in safety risks and associated flow assurance issues. To date the overwhelming amount of research has mainly focused on chemical inhibition of scale bulk precipitation and little attention has been paid to deposition onto surfaces. The development of novel more environmentally-friendly strategies to control mineral fouling will most probably necessitate a multifunctional approach including surface engineering. In this study, we demonstrate that liquid infused porous surfaces provide an appealing strategy for surface modification to reduce mineral scale deposition. Microporous polypyrrole (PPy) coatings were fabricated onto stainless steel substrates by electrodeposition in potentiostatic mode. Subsequent infusion of low surface energy lubricants (fluorinated oil Fluorinert FC-70 and ionic liquid 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIm)) into the porous coatings results in liquid-repellent slippery surfaces. To assess their ability to reduce surface scaling the coatings were subjected to a calcium carbonate scaling environment and the scale on the surface was quantified using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES). PPy surfaces infused with BMIm (and Fluorinert to a lesser extent) exhibit remarkable antifouling properties with the calcium carbonate deposition reduced by 18 times in comparison to untreated stainless steel. These scaling tests suggest a correlation between the stability of the liquid infused surfaces in artificial brines and fouling reduction efficiency. The current work shows the great potential of such novel coatings for the management of mineral scale fouling.

Optimising optical port size on underwater marine instruments to maximise biofouling resistance

The limiting effects of biofouling have restrained the widespread deployment of optical marine sensors. This has necessitated the development of biofilm resistant coatings that are not detrimental to the quality of any measurement recorded. A comprehensive study has been carried out into the effect of changes in the diameter of optical ports. It was found that increasing the diameter of an optical port in the range 10-46 mm reduced the biofouling per unit area. Changes in the diameter did not affect the release of an antimicrobial agent from a hydrogel-based coating. The results show that the operational lifetime of optical ports is significantly improved for diameters over 30 mm and it is suggested that this should be considered a preferred design minimum for optical ports, regardless of the size of the underlying sensor.