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Baier, R. E., R. L. Forsberg, J. A. White, and A. E. Meyer, Ongoing. Mechanical Requirements for Spontaneous Release of Zebra Mussels from Nontoxic Coatings, SUNY at Buffalo, New York Sea Grant Institute -- Reprint from The 6th International Zebra Mussel Conference Proceedings, Dearborn Michigan, March 1996 Mechanical Requirements for Spontaneous Release of Zebra Mussels from Nontoxic CoatingsAfter four years of successful field trials at test sites in Western New York, it is apparent that some nonpolluting and nontoxic coatings can be maintained relatively free of troublesome zebra mussel accumulations by intermittent hydraulic cleanings at low water pressures that do not damage the coatings themselves. Light abrasion with brushes easily removes mussels and other macrofouling, with slightly greater pressures removing most microfouling from easy-release coatings without significant loss of coating thickness or compromise of initial fouling-resistant chemistries. Laboratory and field-deployed abrasion- testing apparatus has been constructed to quantify the mechanical detachment-strength requirements and coating losses or changes during intermittent cleaning cycles. Fouling or coating debris released from the panels and brush surfaces is collected and analyzed to identify basic mechanisms of release and to predict coating longevities. It has been noted in our field trials that zebra mussel clumps (druses) have typical wet weights of about 25 grams and are retained by fewer than 10 byssal thread/disk attachments when they "spontaneously" delaminate from the best nontoxic foul-release coatings, leaving no byssal disks or threads behind. The calculated mechanical strengths for simple tensile detachments of the byssus plaques from closely-packed methyl-group-dominated coatings (critical surface tensions between 22 and 24 mN/m) are in the neighborhood of 15 psi (0.1 MPa), but can be less when peeling shear forces (common in brushing and hydroblasting) are present. Conversely, nontoxic coatings having fouling-retentive properties (as indicated by critical surface tensions less than 20 mN/m, or greater than 30 mN/m) require significantly greater blasting or brushing pressures and always leave the byssal disk and thread apparatus behind as zebra mussel accumulations are detached by thread breakage. Examples of this have been fouling-retentive polyethylene and polyvinyl-coated trash racks, periodically inspected and hydroblast-cleaned during 3 years of zebra mussel fouling adjacent to methylsilicone-coated trashracks with excellent foul-release qualities maintained in the same environment. Thus, the quantitative mechanical requirements for nontoxic coatings to be designated as “foul-release" or “easy-release” is that they can be cleaned of hard macrofouling at pressures less than 20 psi without losing their initial surface chemical qualities for at least 20 cleaning cycles. These values are consistent with findings for coatings that easily release barnacles, tubeworms, encrusting bryozoa, and other hard biofouling deposits. Support for this research has been provided by Office of Naval Research, New York Sea Grant Institute, and Niagara Mohawk Power Corporation. Contact: R. E. Baier baier@ubvms.cc.buffalo.edu
at the University of Buffalo, 110 Parker Hall, Buffalo, NY 14214-3007 |