Showing papers on "Fouling published in 1981"

Observations of fouling biofilm formation.

Abstract: Fouling biofilm development was monitored in a completely mixed tubular recycle reactor. A unique sampling system allowed direct (brightfield, epifluorescence, and scanning electron photomicroscopy...

Copper Immobilization in Fouling Diatoms

Abstract: Observations on the colonization of antifouling paints by diatoms have shown that a small number of tolerant species are usually involved. These species colonize as the toxin leaching rate declines following the initial peak values, and remain even after the onset of macrofouling. Colonization of toxic environments necessitates some form of resistance, whether intra or extracellular. In view of this, tolerant Amphora znaNavicula species colonizing cuprous oxide paints and exposed to increasing concentrations of CuCl2 were processed for transmission electron microscopy and analysed using an energy dispersive system. This enabled investigation of the ultrastructural effects coupled with intracellular copper localization. Ultrastructural examination revealed that copper had entered the cells and was located in either "polyphosphate" or "copper" bodies. The polyphosphate bodies, spherical in shape, and normally located within the cell vacuoles contained high concentrations of phosphorus in association with calcium, and in some, copper. The copper bodies, irregular in outline, and usually associated with membranes, contained high concentrations of sulphur with copper and calcium. The evidence suggests that these bodies are important structures in maintaining low concentrations of free copper within the cells and thus reducing its toxic effects.

Marine Algae and Fouling: A Review, with Particular Reference to Ship-Fouling

Abstract: The fouling of the submerged parts of ships, in particular by marine algae, is an age-old and costly economic problem, and conventional methods do not provide sufficient protection against the highly-resistant organisms involved. Research has been carried out over a number of years to provide new information on the biology of fouling algae, as a basis for improved methods of control, and this review summarises some of the more important findings which have been made, against a background of developing antifouling technology. Marine fouling is the result of settlement and growth of algae and invertebrate animals on the surfaces of sub· merged objects, and such fouling can create a number of important and costly economic problems. The fouling of the underwater areas of ships' hulls and harbour installations is well-known, but problems are also caused by colonization of other man-made structures. For example, fouling by marine organisms can markedly increase the loading forces caused by waves and currents on static offshore structures such as oil and gas platforms, and this could cause the design specification to be exceeded unless removed in time. In addition, marine growths severely hamper inspection and maintenance of such platforms, and may also accelerate localised corrosion (see paper by Terry and Edyvean in this volume). The patterns of colonization and abundance of species at different depths, the succession of communities which occurs and the growth rates, longevities and maximum sizes of the species involved therefore need to be determined and corordinated, from as many platforms and fields as possible. It would then be possible to determine whether loading forces are likely to exceed design specifications, and, in the longer term, such data may .provide the basis for some measure of biological control of the organisms concerned (Ralph and Goodman 1979; see also papers by Hardy; and Moss, Tovey and Court in this volume). Other structures where marine fouling accumulates include the effluents from power plants, and data by Thorhaug and Marcus (see paper in this volume) also suggests that extensive fouling by brown and red tropical macroalgae may occur in the new ocean thermal energy conversion machines (OTEC), which are planned for use in tropical marine waters as an alternative energy source. Fouling communities will occur on any substrates suspended in the sea, and where this affects economic efficiency, it is necessary to consider the development of a suitable long-term system for the protection of immersed surfaces against fouling. One of the most well-known effects of fouling is on the efficiency of movement of ships. Fouling can seriously increase the roughness of underwater parts of ships. This results in a considerable increase in the factional resistance to movement through the water, and thus an appreciable loss of speed, or, an increased use of fuel to maintain the normal operating speed. In the case of a large supertanker, where running costs are very high, an increase in costs of some 0.5% (£80,000 a year in 1972) would result from a loss of 0.1 knot on a service speed of 16 knots (Banfield 1972). Modern supertankers, because of their mode of operation (short stays in port, with rapid transition from temperate to tropical waters), are not on the whole subject to animal fouling, and seaweeds of different sorts are the principle fouling agents. The commonest of these is Enteroniorpha species (green, and often called "grass"), followed by Ectocarpus (brown), with other weeds e.g. Cladophora (green), Chaetomorpha (green), Ulothrix (green) and Polysiphonia or Ceramium (red) occurring in less significant quantities. The dominance ofEnteromorpha as a cosmopolitan fouling alga is the result of its ability to withstand wide fluctuations in environmental conditions such as temperature and salinity (Biebl 1962, Christie and Shaw 1968), coupled with a rapid and highly effective spore attachment mechanism (see later), in response to surface contact. In addition, the 0006-8055/81/0024-0167$02.00· · © by Walter de Gruyter & Co. · Berlin New York 168 Evans: Marine algae and fouling plant shows a considerable capacity for regeneration on tanker hulls, following mechanical underwater scrubbing techniques; basal parts of the thallus left behind after such cleaning, as well as detached pieces, were shown by Moss and Marsland (1976) to give rise to new thalli in the so-called "bottle-brush" formation, giving an increased amount of fouling following scrubbing. Various methods of reducing fouling on ships have been proposed and used down the ages, many based on the use of copper in one form or another. Originally used as metallic sheathing on wooden ships, the copper was later incorporated into paints known as antifouling compositions. Other toxic compounds are now used also, and re^ lease of these at a controlled rate results in the formation of a layer of high toxin concentration (the boundary layer) at the paint surface, and this poisons settling organisms. The thickness of the boundary layer depends on the leaching rate of the toxin, which in turn depends upon the temperature, pH and salinity of the seawater and on the water flow rate over the surface, being minimal under stationary conditions. As stated, for many years, copper compounds have been the main toxic components in antifouling compositions. The copper is used in the form of cuprous oxide (red), cuprous thiocyanate (white), copper acetoarsenite (green) or copper flake (copper bronze), and compounds of mercury, arsenic, tin, lead or zinc are sometimes included as boosters. Nowadays, these are largely excluded on the grounds of being health hazards, and organotin compounds are the main boosters used in copper based antifouling compositions. Marine organisms vary in their tolerance of copper: a leaching rate of 1-2 jug Cu cm" day" will prevent settlement of sensitive orgnisms such as mussels, whilst 10 Mg cm" day" is necessary to prevent settlement of barnacle larvae (Banfield 1980). Higher rates (approximately 20 jug cm" day") are reported to be required to prevent accumulation of diatoms and bacterial slimes, but such rates would mot be economic and the critical leaching rate for antifouling compositions based on copper used in practice is 10 jug cm" day" ^Banfield 1980). Until recent years, two types of antifouling composition were in widespread use, separated according to the mechanism by which toxins are released into the seawater. In the first, known as the soluble matrix type, (Fig. 1), the toxin particles are distributed in a binder, based on rosin, which is acidic and therefore slowly dissolves in the slightly alkaline seawater (pH 8.0—8.2), thus exposing the toxin particles which then dissolve. Merchant ships, drydocking every 12 months or so, commonly use this type of antifouling composition. The second type, the contact leaching type, has a higher copper content and the copper particles are closely packed (Fig. 2), so that as particles at the surface are dissolved so deeper ones become exposed. The matrix is largely insoluble and an intact skeleton is left, through which water penetrates. Contact leaching antifoulings are harder and thus better suited for faster vessels. Their active life is about

Influence of Fouling Biofilms on Heat Transfer

Abstract: In heat exchange equipment, fouling biofilm formation causes a significant energy loss by increasing heat transfer resistance. This paper describes experiments which quantify the influence of fouling biofilms on heat transfer resistance under controlled laboratory conditions. Experimental results compare well with a rather simple mathematical model employing friction factor, biofilm thickness, wall temperature, bulk temperature, and fluid properties as inputs. Limitations of the experimental apparatus and mathematical model are discussed

Effect of Manual Brush Cleaning on Biomass and Community Structure of Microfouling Film Formed on Aluminum and Titanium Surfaces Exposed to Rapidly Flowing Seawater

Abstract: Metals exposed to rapidly flowing seawater are fouled by microbes that increase heat transfer resistance. In this study, results of biochemical test methods quantitatively relating the biomass and community structure of the microfouling film on aluminum and titanium to heat transfer resistance across the metal surface during three cycles of free fouling and manual brushing showed that cleaning accelerates the rate of fouling measured as the loss of heat transfer efficiency and as microfouling film biomass. The results also showed that the rate of fouling, measured as an increase in heat transfer resistance, is faster on titanium than on aluminum but that the titanium surface is more readily cleaned. In three cycles of free fouling and cleaning with a stiff-bristle nylon brush, the free-fouling communities re-forming on aluminum became enriched in bacteria containing short-branched fatty acids as the cycling progressed. The free-fouling community on titanium revealed an increasingly diverse morphology under scanning electron microscopy that was enriched in a portion of the microeucaryotes. Brushing removed most of the biomass, but left a residual community that was relatively enriched in a portion of the bacterial assembly containing cyclopropane fatty acids on aluminum and in a more diverse community on the titanium surface. The residual communities left after cleaning of titanium revealed an increase in bacteria with short-branched fatty acids and in microeucaryotes as cleaning continued. No significant changes occurred in the residual microbial community structure left on aluminum with cleaning; it was, again, less diverse than that remaining on titanium. The residual communities secreted a twofold-larger amount of extracellular polymer, measured as the ratio of total organic carbon to lipid phosphate, than did the free-fouling community on both surfaces. Images

Fouling test apparatus

Abstract: A fouling test apparatus comprising a cylindrical pressure vessel, means for controlling the temperature of fluid contained in the vessel, cylindrical probe having a metallic surface concentric with the vessel walls and provided with a heater for such surface; stirrer in the form of a rotor open at at least one end and positioned between and concentric with the vessel walls and the probe, and sensor for measuring the temperature of the fluid contained in the vessel and the temperature of the probe surface. The probe simulates a heat exchanger surface exposed to a fouling liquid medium. Deposits accumulate on the heated surface in a similar fashion to an actual system and the parameters which affect fouling are all represented. The probe operates with a constant heat flux. As deposits accumulate, the surface temperature of the probe increases and is used as a measure of the deposit formation. The probe is maintained in a stationary position and the stirrer is not dependent on an electrical feed-through.

Cathodic electrochemical process for preventing or retarding microbial and calcareous fouling

Abstract: This invention relates to a method for preventing or retarding microbial or calcareous fouling of a conducting or semi-conducting surface in an aqueous environment. This method produces an effective concentration of hydrogen peroxide at or near the surface to be protected by applying a sufficient cathodic voltage and a sufficient cathodic current to electrochemically generate an effective concentration of hydrogen peroxide. This effective concentration is preferably produced at very low current densities, i.e., at densities of less than about 100 microamperes per square centimeter. This effective concentration is further preferably produced at cathodic voltages less than that required to generate hydrogen gas at the cathode.

Fouling on North Sea Platforms

Abstract: Fouling organisms were collected from a platform by divers whilst it was in position, and subsequently by the author after the platform had been removed and brought ashore. Techniques used included light and scanning electron microscopy and X-ray analysis (EDAX). Although relatively few species of algae were involved, results indicated that these might have significant effects.

Treatment of brackish water

Abstract: Brackish water resulting from steam extraction of heavy crude oils, including oil sands bitumen, is processed for reuse by removing hydrocarbon contamination and removing mineral contamination. The purified water can be boiled in conventional boilers without scaling or fouling occurring. Heat economy is used in carrying out the process.

A Biochemical Mechanism for Marine Biofouling

Abstract: Microbial communities form rapidly on all surfaces exposed to seawater. Microbial fouling is related to a number of problems in marine technology. Corrosion of metal structures in the ocean is affected by microbial films. In addition, microbial fouling induces the settlement of macrofouling organisms. We suggest in this paper a general model to describe the interactions among fouling organisms. This model is based on a study of the settlement and metamorphosis of a spirorbid polychaete. Our data indicate that carbohydrates produced by bacterial films induce larvae of invertebrates to foul a surface. This process appears to be mediated by the binding of the bacterial carbohydrates to proteins produced by the larvae. These carbohydrate-binding proteins are common in many plants and animals. Our model may explain at a biochemical level the controlling mechanism for fouling of surfaces immersed in the sea.

Process and apparatus for measuring corrosion rate of a heat transfer surface

Abstract: There is disclosed a novel fouling and corrosion test assembly including a metallic tube having a heating element embedded in a heat conductive material for controlled heat input and with a thermocouple to measure wall temperature of the tube, and a metallic sleeve disposed about a predetermined portion of the metallic tube whereby the fouling and corrosion test assembly is disposed within conduit and valve assemblies in fluid flow communication with a fluid to determine corrosion rate by weight loss of the metallic sleeve under controlled heat input, temperature conditions and fluid flow rates for a predetermined time period.

Condenser Biofouling Control With Ozone

Abstract: Tests to evaluate the effectiveness of ozone as an alternative to chlorine for condenser bioflouling control in a once–through cooling system were conducted at PSE's Bergen Generating Station. A pilot scale condenser system was used to simulate plant condenser operations. The minimum effective levels of ozone and chlorine were determined by daily measurements of the heat transfer coefficient across the model condenser tubes and/or the waterside pressure drop. Final evaluation was based on the mass of biofouling material evaluation was based on the mass of biofouling material collected from the tubewalls. The results, which are site–specific, suggest that although ozone is less effective than chlorine, on a weight basis, it can be used to control fouling at Bergen.

Control of marine biofouling in heat exchanger systems

Abstract: A critical review is provided of biofouling hazards associated with heat exchanger surfaces in contact with seawater; mechanisms of biofouling formation, environmental factors affecting fouling and control measures. Available antifoulants include elastomer or plastic-based toxic coatings, copper alloys, and the application of chemicals, principally chlorine. 29 refs.

OTEC biofouling, corrosion, and materials study from a moored platform at Punta Tuna, Puerto Rico - 1. - fouling resistance

Abstract: A biofouling test of 404 days was conducted on evaporator tubes of an ocean thermal energy conversion plant of the Center for Energy and Environmental Research. The fouling resistance (R/sub f/), total surface carbon and nitrogen content, ATP, and the wet film thickness (WFT) were determined throughout the test. Visual observations of the fouling film were made by light sectioning and scanning microscopy, and at the end of the test, a study was made of the macrofouling of the flow system. The results of these tests indicate that a base layer of bacteria and exudated polysaccharides enhance microbial adhesion and thereby create an environment conducive to rapid film growth. Fouling rates (dR/sub f//dt) for aluminum were generally higher than for titanium but they were linear for both materials and did not exceed 0.3(10/sup -4/)ft/sup 2/-hr-/degree/F/Btu-day for either material during the 13-month study. Excellent correlation was found to exist between R/sub f/ and WFT, which supports the hypothesis that it is the stagnant film of water entrapped by bacteria which is largely responsible for the insulating properties of the biofilm. The macrofouling study identified 61 species of benthic invertebrates representing ten phyla growing in those parts of the flow system, where more » flow was less than 3 fps but no macrofouling where the flow velocity significantly exceeded 3 fps. 24 refs. « less

In Situ Biofouling of Ocean Thermal Energy Conversion (OTEC) Evaporator Tubes

Abstract: The Puerto Rico Center for Energy and Environmental Research equipped a LCU facility in 1100 m of water near Punta Tuna, Puerto Rico to measure in situ biofouling of simulated Ocean Thermal Energy Conversion evaporator tubes. The system consisted of two 5052 aluminum alloy and two titanium tubes, through which a continuous flow of ocean water was maintained. The tubes were cleaned three times and the fouling resistance was measured, showing only slight differences between the tubes with respect to heat transfer loss resulting from biofouling. In all units, the average fouling rate after cleaning was greater than before cleaning, and only after the first cleaning did the aluminum units show greater fouling rates than did the titanium. The titanium units showed a progressive increase in the fouling rates with each cleaning. The subsequent average fouling rates for all units after eight months were between 4 and 4.6 x 0.000010 sq m-k/W-day.