Detachment studies on microfouling in natural biofilms on substrata with different surface tensions

Attachment strength of bacteria, diatoms, choanoflagellates and four genera of ciliates (Corthunia, Vorticella, Zoothamnion, Ephelota) in natural biofilms was studied on artificial substrata by exposing them to laminar flow in a radial flow chamber. Seven artificial materials (PTFE: polytetrafluorethylene, FEP: fluorethylenepropylene, PFA: polytetrafluorethylene/perfluorcompounds-copolymer, ETFE: ethylenetetrafluorethylene, HC: acetalpolymer, PC: polycarbonate, and glass) with surface tensions between 19 and 64.5 mN m−1 were used. Test panels were immersed between 3 hours and 8 days in the sea to grow biofilms in a natural environment. Attachment strength was studied by exposing the biofilms 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 mN m−1 exists for bacteria and diatoms during early colonization periods (up to 2 days). However, bacteria and diatoms possess compensation mechanisms to overcome weaker attachment strength on these materials. Protozoa were studied after 5 and 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, even after exposure to a flow pressure of 16.9 N m−2 an average of more than 50% of the protozoans remained on each material. The present results indicate that although attachment strength of microfouling is affected by surface tension to some extent, within a few days most investigated microfouling groups resisted considerably strong flow pressure on every material tested. Therefore, surface tension cannot be considered a powerful long-term device to prevent microfouling.