Iodine-dispensing antifoulant implemented with dispensing shutter

Sensors, such as optical sensors and other sensors used in an aqueous environment are protected from biological contamination by applying a biocide behind a shutter. The shutter is capable of covering a subject portion of the sensor or surrounding mounting surface adjacent the sensor in at least a semi-sealing manner. A well or reservoir forms a chamber in the shutter that is capable of holding a biocide having a limited water solubility and a low environmental toxicity in the aqueous environment, for example, anhydrous iodine crystals. The reservoir is in communication with the portion of the sensor while positioned against the portion of the sensor or surrounding mounting surface adjacent the sensor.

BACKGROUND

The disclosed techniques relate to preventing or retarding biofouling of waterborne sensors such as optical lenses.

SUMMARY

Protection of a sensor in an aqueous environment is achieved by providing a shutter having a facing surface and a reservoir, the shutter being configured to cover a mating surface of the sensor or surrounding mounting surface in at least a semi-sealing manner. The reservoir is provided in the shutter and is capable of holding a biocide having a limited water solubility and a low environmental toxicity in the aqueous environment. The reservoir is in communication with the mating surface while positioned against the mating surface.

DETAILED DESCRIPTION

This disclosure describes providing a biocide delivery technique for preventing biofouling on marine sensors, with intermittent, long-term use. Such sensors include optical sensors and other sensors exposed to the aquatic environment.

Moored optical instruments in the ocean are highly susceptible to biofouling, a buildup of micro- and macro-organisms that cover the optical surface and limit the length of time an instrument is useful. As sensors are increasingly designed to be used for a year or more, it is crucial to find better methods of keeping the sensors clean from fouling, as these devices need substantially unobstructed light paths.

Visible biofouling usually consists of organisms such as barnacles, tubeworms, algae, etc. colonizing on the surface of the sensor; however, long before these organisms colonize a surface, two other layers must be established. On contact with sea water, a surface immediately acquires a protein layer, which in turn attracts a layer of marine bacteria. This bacteria layer provides an appropriate surface for the larvae of macroorganisms to settle.

Current methods of preventing biofouling of instruments include copper shutters, wipers/scrubbers, various biocides, anti-fouling paint, and UV LEDs. All have shown some benefit, but also have limitations for application to optical sensors and similar sensors which are intended to be exposed to the aquatic environment. In previous experiments, the use of copper shutters in an attempt to prevent biofouling resulted in a clear jelly-like precipitate between the shutter and sensor, which would inhibit light sensing. Wipers and scrubbers require large amounts of power to run regularly, which is difficult to achieve when leaving an instrument to run autonomously for long periods. Biocides have been shown to work in closed systems, but there is a lack of delivery method for systems where the sensor is exposed to the ocean environments. Anti-fouling paint has also been shown to be effective, but cannot be used on optical sensors and similar sensors which are intended to be exposed to the aquatic environment, as the surface must remain clear for light sensing. UV LEDs present an attractive option, as there are no moving parts and the application of UV effectively reduces fouling, but power requirements can again be prohibitive.

The technique may comprise the use of anhydrous iodine crystals and a plastic shutter to cover the sensor. The shutter includes a well to capture the iodine crystals. The iodine acts as the biocide, and the shutter acts as the delivery mechanism. Iodine is a known disinfectant, commonly used in low concentrations for water purification. When used in its crystalline form, the iodine dissolves to saturation in the presence of water, and the remainders of the crystals remain solid. The shutter may be perforated on its underside (the side adjacent to the sensor), allowing the crystals to remain captive, while water trapped in the space between the shutter and the sensor becomes saturated with the iodine.

The disclosed technique uses iodine as a biocide, and a shutter enclosing the sensor as a delivery system. Shutters have the advantage of shielding the sensor from both light (and thus photosynthesis) and a constant flow of salt water. However, this alone will not prevent fouling. The delivery of a biocide enhances the resistance to fouling, and the immediate and constant application inhibits the initial biofilm from forming, and therefore prevents the usual growth of micro- and macroorganisms.

FIGS. 1-3are diagrams of an example construction of a shutter111, implementing the disclosed techniques.FIG. 1is a top perspective view, showing the outside of a well or reservoir113, which serves as a chamber used for holding iodine crystals.FIG. 2is a bottom perspective view of shutter111, showing iodine crystals115in well113. The arrangement comprises shutter111with well113to hold iodine crystals115, and a screen or perforated surface117, shown inFIG. 3. The perforated surface117is used to keep the iodine crystals115captive while allowing water to enter and dissolve some of the iodine from the crystals115.

The shutter111is referred to as being mounted “semi-sealingly” in that the amount of fluid flow between the well or reservoir113and the sea or other aqueous environment is limited when the shutter111is closed, but such fluid flow is possible. The shutter111is mounted such that the volume encompassing the well or reservoir113and a sensor element119is not sealingly isolated from the ambient environment; rather, the small gap120between a facing surface121of shutter111and a surrounding mounting surface122(FIG. 1) of the sensor acts to limit the amount of flow of fluid occurring between the volume encompassing the reservoir113and the space in front of the sensor element119.

In the closed state, the shutter111engages the sensor element119in order to retain the iodine in solution in contact with the sensor element119. In order to do this, the shutter111engages a portion of the sensor element119or surrounding mounting surface122adjacent the sensor element119in order for the sensor element119to be protected in a semi-sealing manner. The portion of the sensor element119or surrounding mounting surface122adjacent the sensor thereby forms a mating surface for the shutter111.

The semi-sealing manner is intended to describe a circumstance in which the concentration of iodine in water held between the sensor element119and the shutter111is maintained sufficiently to substantially prevent the iodine from being dissolved from the crystals115by action of the water flushing out the solution when the shutter111is closed. It is presumed that a substantial portion of the solution will be lost during active operational periods of the sensor element119when the shutter111is not engaging the sensor element119, in which case, the iodine from the crystals115would again reach an equilibrium solution once the shutter111closes against the subject portion of the sensor element119or surrounding mounting surface122.

In that manner, the iodine from the crystals115is permitted to diffuse into the surrounding water, although most of this loss will occur at times when the shutter111is opened. While a semi-sealing relationship is described, it is expected that in some applications, a substantially sealed relationship will be effected between the shutter111and its mating surface on the sensor element119or surrounding mounting surface122adjacent the sensor element119. It is also expected that the shutter111may be configured to seal against a secondary mating surface (not shown) without covering the sensor element119when the shutter111is opened, thereby reducing iodine loss when the sensor element119is in operation. The secondary mating surface may be part of a housing for the sensor element119or may be a separate surface.

In one configuration, shown inFIG. 2, flat facing surface121is provided with a labyrinth seal123. Labyrinth seal123is used to maintain a semi-sealing relationship between the shutter111and a sensor's surrounding mounting surface (122,FIG. 1). In this manner, the shutter111can retain the iodine in an effective concentration against a subject portion of the sensor element119between active operational periods of the sensor.

In the configuration shown inFIG. 2, the shutter111and sensor's surrounding mounting surface122are constructed such that when the shutter111is closed, there is a labyrinth type seal which hydraulically couples and prevents the free exchange of biocide saturated fluid with the ambient fluid.

It is also possible to construct the shutter111without the use of a separate seal, using the flat surface121to achieve a semi-sealing engagement with its mating surface122. It is also expected that surface121may be formed to conform to the mating surface122which may not be flat. The flat surface121and the seal123may be made of a number of different materials, including metal, a polytetrafluoroethylene (PTFE) film, or any other suitable material. Alternatives include different shutter materials, considering characteristics such as strength, durability, and resistance to corrosion. Phenolic plastics have been considered and may be used, as they have good strength and toughness, and good resistance to solvents.

The technique is advantageous when used for long-term deployments, with intermittent data events. The shutter111is designed to cover a sensor element119with a small space120between the two. As described above, reservoir113containing iodine crystals115is covered with perforated surface117that faces the sensor element119. Perforated surface117is intended to keep the crystals115captive while allowing the iodine to saturate what should be a fairly static amount of water.

As the sensor element119is deployed, water will seep into the space between sensor element119and shutter111. During deployment, including at times when a biofilm would be likely to form, the water saturates with dissolved iodine, preventing the biofilm from forming in the first place. The minimal exchange of water through the space results in the constant presence of a saturated iodine solution, providing constant protection. Should some of the solution be flushed out and replaced with new water, the remaining iodine crystals115will dissolve until the solution reaches saturation.

During a data event, the shutter111opens briefly. Once the event is complete, the shutter111closes, containing a fresh volume of water at which point the saturation process begins again.

Crystallized iodine, which form crystals115, is well-suited for this use due to its low solubility. It takes very little dissolved iodine to saturate a volume of water; therefore the crystals115can last for a long-term deployment.

The low solubility of iodine and availability of the crystalline form makes iodine a suitable biocide for this system, as it takes only a small amount to saturate the water while the rest remains in its crystalline form. The capacity of iodine to last a long time allows for a long-term deployment.

Finally, iodine has the advantage of a lower environmental impact than other biocides in use, such as cuprous oxide, tributyltin (TBT) and Irgarol 1051. Iodine is a powerful oxidizer, toxic to living organisms in high doses but is also naturally-occurring in seawater in low concentrations. It does not bio-accumulate in the food chain like other biocides (e.g., lead, copper, mercury, TBT, Irgarol), and is actually an essential mineral for thyroid function in warm-blooded animals. Though it is toxic in large amounts, it is unlikely it will be released into the environment at harmful levels. Iodine is a naturally occurring element in seawater (about 0.0003 ppm), which is the primary source for commercial iodine production.

The biocide should dissolve rapidly enough for the biocide to become effective quickly enough to control microbial growth when the shutter is closed sufficiently. The biocide should also have longevity while in service, for example by reaching saturation as a solute when the shutter111is closed and dissolving slowly when the shutter111is opened.

One option in constructing the shutter111includes coating the outside of the shutter (the part not facing against or juxtaposed with the sensor element119) with a thin layer of copper. This would deter fouling in the vicinity of the sensor/shutter assembly and reduce the likelihood of malfunction of moving parts.

The configuration in which perforated surface117is flush with flat surface121is suitable for use with sensors which are recessed from their mounting surface. It is expected that the technique will be used with sensors which are not recessed, in which case, the shutter111should clear the sensor element119. In the configuration depicted inFIG. 4, a shutter411is constructed, so a facing surface421of the shutter is flat and may include a seal423. In the case of a flat sensor element119, the small space425forming a recess between sensor element119and shutter is built into the shutter by providing screen or perforated surface427as recessed from facing surface421. Perforated surface427forms a barricade between the solid iodine crystals (not shown) and the sensor element119in order to retain the crystals in the shutter411and is set back behind the plane of the facing surface421to define the recess425.

The mounting surface122onto which the shutter111is mounted is of course dependent on the sensor element119installation.FIG. 5is a diagram showing a non-limiting exemplary sensor element119mounting plate501having a curved outer mounting surface505. The sensor mounting plate501is provided with multiple sensor openings507supporting sensor elements119, two of which are depicted uncovered and two of which are depicted covered by shutters511. Shutters511can either be flat to seal against the mating sensor opening (507) or have mounting plates519which conform to curved surface505. In that manner, the facing surface (e.g., facing surface421,FIG. 4) conforms to mounting plate501and uses outer surface505as a mating surface.

If desired, mounting surface505may be faced (the surface mechanically prepared) with a desired finish. This permits the mounting surface505to conform to the shutters511as desired to achieve a sealing relationship with the shutters511or alternatively to achieve a semi-sealing relationship with the shutters511, achieved by a gap521between the shutters511and the mounting surface505.

The gap521between the sensor element119or the sensor's surrounding mounting surface505and the shutter511is in the range of 0.05 mm, with possible ranges varying greatly depending on the construction of the labyrinth seal123or423(FIGS. 2-4). Other ranges include 0.1 mm to 0.01 mm, or 0.5 mm to 0.002 mm. It is also possible to provide a substantially watertight seal, or a substantially watertight seal with a leakage passage accommodating variations in pressure.

In a test configuration, shutters511were mounted with fasteners531; however, it is expected that an automatic mechanism such as actuator or servo541will be used to control shutters511without the need for manual operation. It is also possible to couple the shutter511to a rotational arm532, which may be coupled to a servo (not shown) mounted beneath the mounting surface505.