DETACHMENT STUDIES ON MICROFOULING IN NATURAL BIOFILMS ON SUBSTRATA WITH DIFFERENT SURFACE TENSIONS

Attachment strength of bacteria, diatoms, choanoflagellates and four g enera of ciliates (Corthunia, Vorticella, Zoothamnion, Ephelota) in na tural biofilms was studied on artificial substrata by exposing them to laminar flow in a radial flow chamber. Seven artificial materials (PT FE: polytetrafluorethylene, FEP: fluorethylenepropylene, PFA: olytetra fluorethylene/perfluorcompounds-copolymer, ETFE: ethylenetetrafluoreth ylene, HC: acetalpolymer, PC: polycarbonate, and glass) with surface t ensions between 19 and 64.5 mN m(-1) were used. Test panels were immer sed between 3 hours and 8 days in the sea to grow biofilms in a natura l environment. Attachment strength was studied by exposing the biofilm s to 4 different laminar flow pressure intervals (between 3.9 and 16.9 N m(-2)) in a radial flow chamber. The results showed that a minimum bioadhesive range between 20 and 25 m N m(-1) exists for bacteria and diatoms during early colonization periods (up to 2 days). However, bac teria and diatoms possess compensation mechanisms to overcome weaker a ttachment strength on these materials. Protozoa were studied after 5 a nd 8 days only. Their attachment strength did not improve during that interval. Significant differences between the materials were observed for Corthunia, Vorticella, and Ephelota. Highest detachment rates were usually recorded on materials between 20 and 25 mN m(-1). However, ev en after exposure to a flow pressure of 16.9 N m(-2) an average of mor e than 50% of the protozoans remained on each material. The present re sults indicate that although attachment strength of microfouling is af fected by surface tension to some extent, within a few days most inves tigated microfouling groups resisted considerably strong flow pressure on every material tested. Therefore, surface tension cannot be consid ered a powerful long-term device to prevent microfouling. (C) 1998 Els evier Science Ltd. All rights reserved.